Test method for testing a cable for leaks and leak testing device for carrying out the method

Description

[0001] The present invention relates to a test method for testing a cable for leaks and a device for carrying out the test method.

[0002] The term "cable" is understood here as a strand of several wires, which can often have a common sheath or cable jacket, but do not necessarily have to. A "wire" refers to the separately insulated cores of a cable, so that a group of parallel wires can also constitute a cable. A "core" is a wire or strand made of electrically conductive material. A "cable connection" represents the connection of the wires (or cores) of a first cable to wires of a second or other cable and / or to each other and / or to contacts of another component.

[0003] To connect multiple cables or wires of a cable with other wires of the same or another cable, or with connecting elements such as plugs or sockets, the wires, particularly their free ends, are stripped of the surrounding or enclosing insulation and electrically connected to similarly exposed sections of other wires or to a connecting contact. The remaining free, unconnected wire ends at the other end of the cable are used to connect electrical consumers, energy sources, or transmitters or receivers of electrical signals.

[0004] Particularly in the automotive industry, but also in other industrial sectors, so-called "cable harnesses" are known. These consist of a plurality of cables, wires and connections between them and are pre-assembled with specific connectors or connectors and certain, different lengths.

[0005] All cable connections between the aforementioned elements are fundamentally exposed to the risk of a change in their contact resistance and thus a reduction in their functionality if the insulation of the wires has been removed to create the connection, meaning that the electrical contact points are exposed to the environment, particularly oxygen in the atmosphere or liquids such as water or aggressive media. Therefore, in many applications where failure or deterioration of the electrical contact must be prevented as permanently as possible, the contact points are encased in plastic, e.g., shrink tubing or other insulating material, and thus permanently sealed from the environment, effectively preventing the ingress of air and surrounding media.

[0006] The quality of this connection, or rather the seal between a cable end and an element connected to the cable, e.g., a connector, a cable lug, a grommet, or the like, must be tested for functionality and leak-tightness as part of the material testing before installation. Therefore, such cables with an element connected to the cable are also referred to as end cables.

[0007] The present invention relates to a device for testing the tightness of such cables or lines, in particular by means of an enclosing shrink tube for sealing the element connected to the cable end, i.e. an end cable. State of the art

[0008] Probably the oldest and most well-known leak testing method is the so-called "bubble test," in which a test specimen to be tested for leaks, such as a cable wrapped in heat-shrink tubing, is immersed in a water container, then pressurized, and visually inspected by a worker for the escape of air bubbles. This bubble test is very precise and is therefore still widely used.

[0009] The German utility model DE 20 2016 104 484 U1 discloses a device for carrying out a leak test with a pressure chamber formed by a base and a cover for receiving the line to be tested, which is pressurised and in which test gas contained or escaping outside the pressure chamber is then detected by a leak sniffer.

[0010] From the German utility model DE 203 08 615 U1, a leak measuring computer for pressure ranges between -1 bar negative pressure and 100 bar positive pressure is also known, which has devices for recording the filling pressure and the filling time.

[0011] DE 10 2016 107 216 A1 discloses a device for testing the leak tightness of a component of a wiring harness. The device comprises an evacuable test container that can be closed via a lid-like test adapter and is configured for connecting or threading components through such that the component is fluidically connected to the interior of the test container, or a first part is arranged inside the test container and a second part is arranged on an exterior of the test container. In this solution, the cable end with the connector to be tested for leak tightness is inserted into the test container and tested. This device is therefore relatively large.

[0012] US Pat. No. 4,811,252 discloses a differential pressure method in which a test vessel to be tested is pressurized with a test volume and a reference vessel is pressurized with a reference volume of the same size as the test volume. A differential pressure sensor arranged between the test vessel and the reference vessel detects the pressure difference between the test vessel and the reference vessel.

[0013] Further devices that work with a differential pressure method are known from CN 107884143 A, JP 05215588 A, US 8,201,438 B1.

[0014] A measuring method and a measuring device of a different type are known from DE 20 2016 104 484 U1. Disadvantages of the state of the art

[0015] The bubble test, or the device used to conduct it, is complex because it requires water, which is often undesirable in the production process. Furthermore, the test is dependent on the tester, who must detect even the smallest bubbles.

[0016] Known measuring devices detect a leak in a component via a pressure loss in a container subjected to a test pressure relative to the external pressure, to which the test specimen is connected. The test specimen itself can also represent the container. To detect the smallest possible leak rate, the volume must be as small as possible.

[0017] The differential pressure method is relatively accurate. It measures the pressure difference between a test volume and a reference volume using a differential pressure gauge. Since the pressure difference is relatively small, a gauge with a narrow measuring range can be used, keeping measurement errors relatively small. A disadvantage of the differential pressure method is the relatively complex measurement setup, including a reference volume and the associated control valves. A further disadvantage is that it cannot provide any information about the magnitude of the leak rate.

[0018] The pressure difference method (relative pressure, pressure increase, pressure drop) is somewhat less accurate and does not require a reference volume. This method measures the pressure loss over a specific period of time, which requires the use of a measuring device with a larger measuring range. This means that the resolution is lower and the measurement error of the system is greater. The advantage of the pressure difference method is its relatively simple design. However, in order to make a statement about the leak rate, the volume of the measuring body must be known. This is not the case in most cases. Previous measuring methods only consider the pressure difference relative to a specified period of time (test period) or record incoming gases.These known methods follow the following measurement procedure: evacuating a test chamber, calming the test chamber, measuring the pressure, waiting, measuring the pressure again and calculating the difference between the first and second pressure measurements.

[0019] Furthermore, a measurement can be performed using a differential pressure test according to DIN EN 1779, in which the test specimen is connected to a reference specimen via a type of siphon. The fluid in the siphon then deflects toward the leaking side, similar to a scale. Task / Technical Problem

[0020] Based on this prior art, the invention is based on the object of at least partially avoiding these disadvantages and, in particular, of providing a simply constructed, robust and easy-to-operate leak testing device and leak testing method.

[0021] In particular, the invention is intended to provide a measuring method and a device for carrying it out, which enables the test pressure to be generated in a simple manner while simultaneously calculating the test volume, because this is the basis for a subsequent determination of a leak rate by means of a pressure difference method. invention

[0022] This problem is solved by the features of the independent claims; preferred, but not mandatory, further developments are recited in the subclaims. The subject matter of the invention is defined by the claims.

[0023] The invention thus makes use of the knowledge gained during development that absolute tightness does not actually exist in the practical sense and that this is not required for all practical applications. Rather, for normal use, compliance with an acceptable, defined leak rate is necessary; in motor vehicles, this is an essentially water- or vapor-tight design, i.e. the avoidance of drips, which corresponds to a leakage of 1 cm3< gas loss in 100 seconds at a pressure difference of 1000 mbar. For other pressure differences, the leak rate can be related to / converted accordingly. In some circumstances, a vapor-tight design is also appropriate, which corresponds to a gas loss of 1 cm3< in 15 minutes.

[0024] For the purposes of the invention, the term "test specimen" refers to a cable that is open at the front and has the cable connection to be tested at the rear end. The open front end of the test specimen is referred to simply as the "plug-in end," and the rear end to be tested for leaks is referred to as the "test end."

[0025] The test method is particularly characterized in that an open and possibly stripped front end of the test body, i.e. cable, is inserted into an adapter, that the adapter with the test body accommodated therein is sealed against the environment, that the volume inside the measuring cell thus formed is first determined automatically.

[0026] The measuring cell comprises the space inside the test specimen and the adapter with the connected pressure sensor up to the valve.

[0027] Since the volume of the adapter, the pressure sensor, and the line up to the valve are constant, the reference volume within the test specimen is easily determined. This reference volume can thus be determined from the volume extracted from the measuring cell and, for the first time, provides a reference value to which a subsequent pressure difference test can refer to in order to determine the extent of the leak.

[0028] During the determination of the reference volume, a test pressure in the form of a negative or positive pressure is then applied to the test specimen or the cable over a certain test time and a leakage rate is determined by detecting the volume flowing into the cable or the cable connection by measuring the pressure change.

[0029] According to the invention, every leak in the test specimen is detected.

[0030] The invention is based on the following findings: The volume of the main piston V 1 of the pneumatic cylinder or the pressure generating unit up to the valve can be determined via the known geometry and the position sensor or the movement of a servo motor.

[0031] The "volume of the test specimen" refers only to the inner, gas-filled area of the test specimen.

[0032] The test specimen can be inserted into the adapter to different depths, so that the free volume of the adapter results from the insertion depth of the test specimen.

[0033] The reference volume V 2 includes the free volume of the adapter and the gas-filled area within the test specimen, i.e. V 2 = V Adapter + V Prüfkörper

[0034] This reference volume V 2 can be determined, assuming a constant temperature, by varying the pressure at the actuating piston p 1 , which can be measured using the pressure sensor on the adapter ps, using the ideal gas equation (p*V = const): p S , 1 * V 1 , 1 + V 2 = p S , 2 * V 1,2 + V 2 .

[0035] They are: Ps,x = pressure at the sensor at time x V 1 , x = Volumen des Hauptkolbens zum Zeitpunkt x

[0036] At time 1, external pressure is applied and the cylinder is in its initial position. At time 2, the cylinder is actuated and has generated working pressure.

[0037] The invention thus allows for inferring a possible leak in the test specimen from a volume difference relative to the reference volume without a surrounding, larger reference body, namely by measuring a pressure difference with the pressure sensor. The volume difference is thus calculated indirectly via the pressure difference and the standardized reference volume.

[0038] After determining the reference volume V 2 , the valve is closed and the leakage Q is calculated from Q = p S , , 4 − p S , 3 ∗ V 2 t 4 − t 3 Tx = time x.

[0039] In contrast to the state of the art, no reference volume is required outside the test specimen. This reduces the installation space of the test device and enables rapid testing.

[0040] The invention thus creates its own reference system with the reference volume in the measuring cell at the beginning of the test. Unlike prior art differential pressure testing methods, which measure a pressure difference between predetermined containers, the invention does not require such a reference container.

[0041] Furthermore, the state-of-the-art methods only check whether a seal is good or bad, but do not provide a numerical value for the quality of a leak.

[0042] The invention thus provides a leak rate as a numerical value with little effort, which provides information about the quality of the test specimen.

[0043] The leak rate is therefore the volume flowing in or out over a given time unit, the test time, for which the following formula applies:

[0044] The invention is therefore based on the realization that tight within the meaning of the invention is not to be understood as absolutely tight, but can rather be defined differently depending on the application and product in terms of an accepted leak rate. In this respect, it is strictly speaking a method for determining a permissible leak rate in a test specimen as well as a leak tightness or leak rate testing device. In contrast to existing measuring methods, the test method according to the invention uses this accepted leak rate to test the volume flowing into the test specimen during the test time. In this respect, classification within certain specifications is possible for the first time, so that the leak rate that is still acceptable can be determined depending on the application or product to be tested.

[0045] The following table shows accepted leak rates for various applications, which can represent the accepted leak rates (Q): Hole diameter Leak rate in mbar xl / s general leak rate description (Δ p = 10 5 < Pa) Gas leakage description (Δ p = 10 5 < Pa) ≈ 1 mm 10 2< Water leaks out ≈ 300 µm 10 1< ≈ 100 µm 10 0< Dripping faucet ≈ 1 cm 3< gas loss / sec. ≈ 30 µm 10 -1< ≈ 1 cm 3< gas loss / 10 sec. ≈ 10 µm 10 -2< waterproof (does not drip) ≈ 1 cm 3< gas loss / 100 sec. ≈ 3 µm 10 -3< vapor-tight (sweating) ≈ 1 cm 3< gas loss / 15 min. 1 gas bubble / sec. ≈ 1 µm 10 -4< bacteria-proof ≈ 1 cm 3< gas loss / 3 hours ≈ 300 nm 10 -5< petrol and oil-tight ≈ 1 cm 3< gas loss / day ≈ 100 nm 10 -6< virus-proof ≈ 1 cm 3< gas loss 10 days ≈ 30 nm 10 -7< gas-tight ≈ 1 cm 3< gas loss / 100 days ≈ 10 nm 10 -8< virus-proof (secured) ≈ 1 cm 3< gas loss / 3 years ≈ 3 nm 10 -9< gas-tight (secured) ≈ 1 cm 3< gas loss / 30 years ≈ 1 nm 10 -10< absolutely tight (technically) ≈ 1 cm 3< gas loss / 300 years ≈ 0.3 nm 10 -11< ≈ 1 cm 3< gas loss / 3000 years Relationship between hole size and associated leak rate (estimate)

[0046] According to the invention, an overpressure and a negative pressure can be applied as test pressure.

[0047] The testing method may, although not laid down in the claims, comprise the following steps: Clamping the test specimen to be tested for leaks, in particular a terminal cable, with the open test end into an adapter of a measuring cell of the leak testing unit, applying a test pressure to the test system comprising the adapter, the interior of the test specimen and the connecting line from the adapter to the pressure generation unit, in particular designed as a piston vacuum pump and thus the test specimen, first calming, determining the reference volume with 2 measured values and calculation using the ideal gas equation; can already include several termination criteria: shutting off the measuring cell from the pressure generator using a valve, second calming of the system and pressure measurement of the test specimen until the expiry of a defined termination time or a defined pressure difference.

[0048] The volume in the test specimen is measured by determining the pressure change, in particular by means of a pressure sensor and calculating the volume using the ideal gas equation.

[0049] In the preferred embodiment, which is not part of the claims, the volume of the reference volume is determined by first generating a test pressure by a pressure generating unit.

[0050] This pressure generation unit preferably comprises a piston vacuum pump with a main piston that is moved by two actuating pistons arranged laterally next to it, and whose displacement is measured, e.g., via a displacement recorder. Since the volume of the pneumatic cylinder is at least 1.5 times, preferably 2.5 times, the volume to be evacuated from the test specimen, whereby this is fundamentally dependent on the resolution (fineness) of the measuring instrument, the generated test pressure continues to be present in the test system, in particular the test specimen, even after the measuring cell containing the test specimen has been separated from the pressure generation unit.

[0051] A more adjustable development involves an electric motor, particularly a stepper motor, to actuate the main piston of the piston vacuum pump. This motor helps prevent the slip-stick effect that sometimes occurs and can cause measurement inaccuracies. Furthermore, the main piston of the working cylinder can be adjusted much more precisely using the motor, particularly the stepper motor.

[0052] In a particularly space-optimized design, the main piston of the piston vacuum pump is split, i.e., it comprises two or more sub-pistons that are interconnected to form a total piston volume. When using a motor to actuate the individual sub-pistons, this motor can be arranged between two sub-pistons and actuate several sub-pistons simultaneously. With this design, the overall height or length of the pistons can be adjusted as desired; when a main piston is split into two sub-pistons, it can be reduced by half, so that the pressure generation unit can be better accommodated in the single housing. The use of a stepper motor has the further advantage that no displacement recorder is required.

[0053] After applying the test pressure to the system with the measuring cell and the test specimen contained therein, the volume in the pneumatic cylinder is determined, e.g., using a displacement recorder, which records every piston movement of the pneumatic cylinder's main piston, including any possible changes after the initial application of the test pressure. Since the geometric parameters of the pneumatic cylinder's main piston are known, the displacement travel can be used to accurately calculate the evacuated and / or inflowing volumes, taking the individual pressure into account.

[0054] To improve the measurement results, the volume of the test specimen is determined at least twice.

[0055] The volume determination of the test specimen is followed by the determination of the permissible leakage rate of the test specimen using the pressure difference test.

[0056] To improve measurement accuracy, it has proven useful to provide at least one, preferably several, settling periods within which the system can settle and thus equilibrate. These settling periods serve in particular to compensate for changes in air temperature (during evacuation, the temperature drops dramatically), ambient pressure, and humidity, allowing the air to creep or flow at the outermost end of the line. Preferably, a first settling period is provided before the volume determination, and a second settling period or rest phase is provided before the actual measurement operation to determine the leak rate.

[0057] A settling period preferably occurs after the measuring cell is sealed. The duration of the settling period(s) can be adjustable.

[0058] Embodiments not forming part of the present claims include the possibility of adjusting any or all of the various test and / or settling times.

[0059] Preferably, the settling times are about 10 to 240 seconds.

[0060] Furthermore, the leak rate to be tested or accepted can be adjusted for the respective application or the product to be tested.

[0061] When calculating the leak rate, one or more of the following groups of influencing factors can also be taken into account or recorded: Temperature; ambient pressure; changes in ambient pressure before and during the test; pressure difference; volume of the test specimen; the time course of the evacuated volume and possibly also the air humidity.

[0062] The test procedure, which is not part of the claims, can be initiated by pressing the "Start" button, so that the subsequent process sequence runs fully automatically: 1. Sealing the test specimen from the environment using an adapter designed to accommodate the open insertion end of the test specimen. 2. Applying test pressure (overpressure or underpressure) to the adapter using a pressure generation unit. 3. Initial settling, T1, preferably 10 to 180 seconds. 4. Recording two different pressure values with an intervening settling time T2 and determining the reference volume V2; 5. Disconnecting the pressure generation unit from the measuring cell (from V3 = switching point) so that the applied test pressure is present in the test specimen; particularly preferably, the vacuum or underpressure is approximately 500-700 mbar. 6. Further settling time, preferably 10 seconds. 7. Starting the measurement cycle, preferably also recording the ambient pressure. 8. Continuous recording ("writing away") of the relevant pressures, in particular the ambient and line pressure, during the measurement cycle. 9.The measuring cycle is completed when the adjustable value T4 has elapsed, which is preferably 180 seconds, or a specific pressure difference is recorded, e.g., 5 mbar. 10. Determine the leak rate as the pressure difference in conjunction with the volume in the measuring cell and thus the test specimen. 11. Convert the leak rate to a leak rate of approximately 1000 mbar, i.e., close to ambient pressure (the "standard leak rate"). 12. Classify the test specimen as leaky or tight based on specified, product-specific parameters in accordance with the respective specified requirements.

[0063] According to the method, the respective ambient pressure is taken into account each time a volume (V2, V3) is determined, preferably by a central ambient pressure sensor.

[0064] From step 3 onwards, a pre-selection of a defective test specimen can be carried out if, for example, a vacuum cannot be generated due to leaks.

[0065] If a leak occurs in the test specimen, ambient air flows in during the evacuation period and can thus falsify the determined volume measurement result. During the development of the invention, it became apparent that, by retrospectively examining the volume, starting from the point at which the volume increases linearly relative to a time interval, a nearly real or true volume (reference volume without leakage) can be calculated. In other words: If the determined curve of pressure and volume relative to the constant time interval results in a linear gradient, this inflection point can be used to calculate the true volume (reference volume without leakage).

[0066] In the preferred embodiment, which is not part of the claims, the pressure generating unit comprises at least one pneumatic cylinder with at least one main piston for generating pressure or negative pressure, which is driven by at least one, preferably two, actuating pistons.

[0067] Not all process steps necessarily have to be completed. The measurement cycle can also be terminated prematurely using suitable termination criteria, for example, if a previously defined pressure difference is exceeded. Standard leaks can be used for calibration, which provide information about the quality of the measurement.

[0068] It is therefore essential that the method according to the invention and the leak testing device used to implement it automatically determine the reference volume at the beginning of the test cycle, which allows conclusions to be drawn about the line cross-section and line length, preferably by mapping them in a table with empirical values in the leak testing device or software. These conclusions are important for the temporal test sequence and for the precision of the measured volume.

[0069] This testing and measuring method has numerous advantages. Since no water is required, the measuring method can be easily and effectively integrated into a production process. Furthermore, the measuring method is very fast, taking 180 to 480 seconds depending on the pipe cross-section of the test specimen, and 240 seconds in particular, although a termination criterion can also be considered here.

[0070] The test time can be reduced by providing several measuring cells, so that a parallel test of several test specimens can be carried out.

[0071] The testing procedure thus enables absolute fault tolerance at a reasonable cost, in the sense that 100 percent product testing is feasible. This not only means that every product can be tested, but also that even an otherwise faultless product, but due to a defect or incorrect operation of the measuring device, such as a leak in the adapter, will be identified by the system as defective, thus reliably ruling out a defective product in any case. In cases of doubt, a so-called "pseudo-reject" is generated, meaning that an otherwise faulty product is declared defective, which could be validated by a second test.

[0072] In the simplest embodiment, the leak tightness or leak rate testing device comprises at least one adapter which is open on one side and has a receiving end designed to sealingly receive a plug-in end of a cable or test body which is open on the front and therefore accessible on the inside, in particular a line to be tested for leaks with an element connected at a rear end via a cable connection, e.g. a plug, a grommet or the like, at least one pressure generating unit, in particular designed as a vacuum piston pump, for generating a negative or positive pressure in the adapter and an evaluation unit for recording a leak rate of the test body in a test period.

[0073] The leak testing device essentially comprises the following components: at least one measuring cell with adapter, valve and pressure sensor), at least one pressure generation unit (vacuum generator / overpressure generator) with a displacement measuring device, preferably designed as a piston vacuum pump, a pressure sensor, also for detecting the ambient pressure, and the evaluation software.

[0074] The leak testing device consists almost exclusively of "commercially available" components, i.e. a pneumatic cylinder, a pressure sensor, a valve, preferably an electromechanical pneumatic valve, in particular a 3 / 2-way valve, and the corresponding lines, so that no special components are required.

[0075] The only special feature is the adapter designed according to the invention, which is designed to accommodate the test specimen. Otherwise, standardized, commercially available components are used, which reduces costs and significantly improves the maintenance of the system by purchasing spare parts.

[0076] Furthermore, a valve is provided associated with the adapter, which separates or switches off the adapter from the pressure generation unit.

[0077] The adapter is therefore designed to seal off the test specimen or cable from the environment or to receive it in a sealed manner. The adapter preferably has an adapter housing extending along an adapter longitudinal axis and having an insertion opening formed at a front end of the adapter and preferably extending along the adapter longitudinal axis. Sealing rings, preferably toroidal or annular, are received in the adapter housing with their central through-openings collinear with the adapter longitudinal axis and can be compressed in the adapter housing via a piston or pressure plate that is received in the adapter housing in a relatively movable manner. The piston is preferably pneumatically actuated via a control line. When the sealing rings are compressed via the piston in the adapter longitudinal direction, these sealing rings are compressed and expand towards the central insertion opening.The test specimen inserted into the insertion opening is thus radially sealed circumferentially via the sealing rings.

[0078] In a preferred further development, the adapter comprises a return spring to simplify the opening or release of the test specimen, even with larger test specimens, e.g., after reducing the pressure on the control line to close the adapter. This return spring is preferably arranged between the outer adapter housing and the piston, which is accommodated in this adapter housing in a relatively movable manner. In a particularly preferred embodiment, this compression spring bears with a rear end against a collar or a plate of the piston and sits with a front end in an annular space or a spring seat on the adapter housing.

[0079] The cable, especially a terminal cable, i.e., the test specimen, is inserted with a possibly stripped and thus open front end (the "plug-in end") into at least one insertion opening of an adapter of the leak test device. The plug-in end inserted into the adapter should be free of damage and dirt, and it should also not be a deformed cable end.

[0080] The adapter preferably comprises a plurality of sealing rings, preferably arranged one behind the other in the longitudinal direction of the adapter, preferably two sealing rings. The use of sealing rings made of chloroprene rubber and neoprene has proven particularly advantageous.

[0081] Particularly uniform compression and thus extended service life of the sealing rings is achieved when the sealing rings are surrounded on the outside by preferably circular thrust washers. Preferably, such a thrust washer is also arranged between adjacent sealing rings. This design creates uniform surface pressure on the sealing rings, simplifies or improves compression, and thus extends their service life.

[0082] For measuring different cable cross-sections and adapting to different batches, only adapters of different sizes need to be provided, which are therefore preferably designed to be interchangeable.

[0083] The adapter can be constructed in multiple parts, preferably two parts, with an outer part and an insert part that can be inserted into the outer part and preferably detachably connected to the outer part. The insert part can include insertion openings and sealing rings of various sizes for adaptation or easy adaptation to different cable cross-sections. This design offers several advantages. Firstly, no enclosed and sealed receiving space is required for the cable or line to be tested for leaks.

[0084] The previously described valve, which is preferably designed as a slide valve or 3 / 2-way valve, can sometimes distort the volume in the measuring cell when switching. Clamping the open plug end into the adapter can also sometimes cause an undesirable pressure buildup in the measuring cell, which can distort the measured values. Furthermore, the measured values can be distorted by thermal influences caused by the solenoid valve.

[0085] To avoid these problems, the valve for shutting off the adapter is designed in a preferred further development as a vacuum control block, which in particular comprises three pneumatically controlled 2 / 2-way valves, of which - seen from the adapter - the first and the second valve are connected in series and the third valve is connected in parallel to the first two valves.

[0086] Preferably, each of these valves comprises two valve pistons which abut against one another with valve surfaces in the closed position. Of these valve pistons, a first valve piston is stationary and a second valve piston can be pressed by control pressure applied via a control line against a spring arranged between the valve pistons in the longitudinal axis of the valve, which spring presses the valve pistons outwards against the housing of the vacuum control block. A sealing ring arranged between the valve surfaces of the valve pistons which project towards one another closes the central passage between the valve pistons in the closed state when they are pressed against one another by pressure from the control line assigned to each valve. The valves are therefore open in the rest position (without pressure on the control line) and release the passage. By applying valve pressure to a control line assigned to each valve, the valves can be opened and closed as desired.

[0087] The valve pistons are designed in such a way that the negative pressure applied to the valve housing by means of a connecting line from the pressure generating unit enters the movable valve piston of the third valve from the side.

[0088] Each movable valve piston has a piston passage opening extending through the valve piston transversely to the piston longitudinal axis, which extends along the spring arranged between the valve pistons.

[0089] The valve pistons are preferably arranged in these receiving openings or bores with piston walls enclosing the valve pistons. The piston walls between adjacent pistons can have a wall opening through which the prevailing pressure can flow from one piston chamber into the adjacent piston chamber. If this wall opening is arranged at the level of the piston through-openings between two adjacent valves, the pressure can flow through the adjacent valves even when they are closed. If, on the other hand, the wall opening in a partition is formed at the level of the valve surfaces of two adjacent valves, the pressure can only flow from one piston to the adjacent piston when the adjacent valves are also open.

[0090] According to the invention, the wall opening is formed in the outer piston wall between the second and the third valve at the level of the piston passage opening in the movable piston and in the inner piston wall at the level of the valve surfaces between the first and the second valve.

[0091] Through the wall opening in the outer piston wall, the pressure applied to the outside of the vacuum control block can flow through the outer piston wall formed between the third and second valve at the level of the piston passage opening into the second, middle valve, even when the third valve is closed.

[0092] If the second valve is closed, nothing else happens. If the second valve is open, however, the negative pressure flows longitudinally along the second valve and then laterally across the open valve surface through the wall opening in the inner piston wall between the first and second valves, and thus into the pressure sensor and adapter.

[0093] If the first valve closest to the adapter is closed, the adapter is sealed.

[0094] For better sealing of the sealing surfaces of the valve pistons which are in contact with each other in the closed position, an additional seal can be provided, in particular a ring seal.

[0095] The flow direction in the valves is therefore as follows: The applied pressure flows through the lateral valve opening in the movable valve piston and then, deflected by 90° in the longitudinal direction of the valve, along the spring to the sealing surface between the valve pistons. If this is open, the pressure flows out through the open sealing surface and through the wall opening into the adjacent open valve. If the valve is closed, the pressure flows only through the valve opening in the movable valve piston and, if a wall opening is provided in the wall between the adjacent valves, into the valve opening of the adjacent movable valve piston.

[0096] The vacuum control block according to the invention is very compact, simple in design, and has little dead space. The valve pistons only need to move a few millimeters to open and close, allowing them to be actuated quickly. Since the vacuum control block is connected almost directly to the adapter, no lines are required. Since the valves are controlled pneumatically, not electrically, no heat is generated that could distort the measured values, thus improving measurement accuracy.

[0097] The three 2 / 2-way valves in the vacuum control block therefore have the following functions: Valve 1 (closest to the adapter): shuts off the adapter for calibration of the pressure generating device (main piston) and self-testing; Valve 2 (middle valve): shuts off vacuum generation. Only the adapter and the test piece are connected. This enables particularly precise measurements; Valve 3 (farthest from the adapter): vents the measuring cell.

[0098] When testing a test specimen, these three valves within the vacuum control block operate as follows: 1. Insert test specimen; all three valves are open; 2. Clamp the test specimen; 3. Close vent valve 3; 4. Apply vacuum to the measuring cell via open valves 1 and 2; 5. The actuating piston of the pressure generation unit is regulated so that the test pressure is constant, e.g. a constant 600 mbar; 6. Determine the reference volume in the measuring cell. 7. Middle valve 2 closes and regulates pressure generation. The pressure sensor is therefore only connected to the adapter and the test specimen contained therein. We wait to see whether the pressure drops and thus the leakage is calculated. 9. Vent via valve three: adapter opens and piston moves to the basic position.

[0099] Although the invention is preferably used for testing cable seals at cable ends, i.e. end cables, it will be understood by those skilled in the art that it can just as well be used for testing the tightness of a connection or seal of a test specimen of any type, e.g. a pipe without a cable with an element connected at one end, e.g. a container, a housing or the like.

[0100] In the following detailed description, reference is made to the accompanying drawings, which form a part of this specification, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top," "bottom," "front," "back," "fore," "rear," etc., will be used with reference to the orientations of the described figure(s). Since components of embodiments can be positioned in a number of different orientations, the directional terminology is for the purpose of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description is not to be taken in a limiting sense.

[0101] Throughout this description, the terms "connected," "attached," and "integrated" are used to describe both direct and indirect connections, direct or indirect connections, and direct or indirect integration. In the figures, identical or similar elements are designated by identical reference numerals where appropriate.

[0102] Reference lines are lines that connect the reference symbol to the part in question. An arrow that doesn't touch any part, however, refers to the entire unit to which it is directed. The figures are not necessarily to scale. To illustrate details, certain areas may be exaggerated. Furthermore, the drawings may be simplified and not include every detail that might be present in practice. The terms "top" and "bottom" refer to the representation in the figures.

[0103] They show: Figure 1 shows an isometric front view of the vacuum leak testing device comprising a total of eight adapters; Figure 2 shows an isometric rear view of the vacuum leak testing device according to Figure 1with partially assembled outer housing; Figure 3 an isometric view of a measuring cell comprising an adapter, a pressure sensor and a valve; Figure 4 a section of the measuring cell according to Figure 3 ; Figure 5 a cross section through the leak testing unit according to Figure 1 ; Figure 6: an enlarged longitudinal section of an adapter; and Figure 7: a graphic representation of a typical test procedure; Figure 8: a graphic representation of the pressures and volumes recorded during the test procedure in a defective (detectable leakage) and a faultless (no leakage detectable) test specimen over time, which shows a precise sub-process of Figure 7from the beginning to the end of time T2; Figure 9: a cross-section of an alternatively designed measuring cell with an adapter with a spring and a vacuum control block instead of a 3 / 2-way valve; Figure 10: a pneumatic plan of a measuring cell; and Figure 11: an isometric side view of an alternative test unit with the side panel removed.

[0104] Figure 1 shows an isometric front view of a leak testing device according to the invention, in this case comprising eight measuring cells.

[0105] Accordingly, the leak testing device has a circumferentially enclosing, box-like housing 2, which defines an interior in which several measuring cells and the other equipment are arranged.

[0106] Each measuring cell comprises a substantially hollow-cylindrical adapter 4, which, in the installed position, protrudes with its forwardly open insertion opening 4a from a corresponding opening in the housing 2, so that a test specimen or test item with an open test end can be inserted into this insertion opening 4a. Each adapter 4 is connected to a valve 8 via a line section 6 arranged at the rear end of the adapter 4. Furthermore, a pressure sensor 10 is connected to the line section 6, which measures the line pressure as well as the system pressure in the line and the test specimen. Finally, the valve is connected via a line to a piston vacuum pump 12. Each adapter 4 comprises a supply line for supplying compressed air, which is used to actuate the adapter.

[0107] The Figures 3 and 4show an enlarged isometric view of the adapter 4 with its front insertion opening 4a, the line section 6 extending at the rear along the longitudinal direction of the adapter 4, the pressure sensor 10 branching off diagonally from the line section and the valve 8 provided at the rear end of the line section 6.

[0108] Figure 2 shows piston vacuum pumps 12 arranged side by side in the housing 2, each of which interacts with a measuring cell. Each piston vacuum pump 12 comprises a central piston cylinder in which a main piston 12a is relatively movable, namely by means of two actuating pistons 12c, 12d arranged laterally next to the main piston 12a, which drive an actuating plate 12b with their working ends, which is connected to the push rod of the main piston 12a. In addition, each piston vacuum pump 12 comprises a displacement recorder 12e, with which the displacement of the main piston can be precisely recorded.

[0109] By activating the respective piston vacuum pump 12, i.e., raising the main piston 12a relative to the stationary outer cylinder, the main piston 12a travels a precisely measurable distance, which can be used to accurately calculate the evacuated or inflowing volume. The displacement recorder 12e thus initially provides a precise statement about the volume evacuated from the system until the specified test pressure of preferably 600 mbar is reached, and then about the volume evacuated from the test specimen to determine its volume.

[0110] The Figure 6shows an enlarged longitudinal section of an adapter 4 according to the invention. This comprises a substantially hollow cylindrical adapter housing which, approximately in the middle, forms a shoulder and transitions from a front, hollow cylindrical seal housing 4b with a first outer diameter into a rear, likewise hollow cylindrical outer housing 4c with a second outer diameter which is wider than the seal housing 4b.

[0111] The front seal housing 4b comprises a front insertion opening 4a, which extends along the adapter's longitudinal axis along the overall rotationally symmetrical adapter housing and is designed to receive the test end of the test specimen. Slightly offset inward from this insertion opening 4a, it transitions into a slightly widened receiving space, forming an inner shoulder, in which two rubber sealing rings 4d, 4e with corresponding outer diameters are arranged, arranged longitudinally one behind the other. Pressure washers are also arranged outside of and between the sealing rings 4d, 4e.

[0112] A piston is mounted for relative movement in the rear outer housing 4c of the adapter housing, which has an inner diameter approximately twice the inner diameter of the receiving space of the seal housing 4b. This piston comprises a hollow cylindrical inner body 4f that is collinear with the adapter's longitudinal axis and encloses it with its outer surface. A disk 4g extends radially outward from the outer surface of the inner body 4f. The front end of the hollow cylindrical inner body 4f acts on the sealing rings 4d, 4e with the interposition of a spacer plate. Via a supply line 4h in the outer housing part 4c, the pressure plate 4g can be pressurized with a fluid, preferably compressed air, and is thus displaced axially in the stationary adapter housing to compress the stationary sealing rings 4d, 4e.During this compression, the sealing rings 4d, 4e can only expand radially inwards and thus completely and tightly seal a test specimen inserted into the insertion opening 4a against the environment.

[0113] The sealing rings 4d, 4e are axially enclosed on the outside by thrust washers 4i, 4k, i.e., circular disks that reduce the surface pressure on the sealing rings 4d, 4e and thus ensure a more uniform force distribution of the inner body 4f during relative movement with respect to the stationary adapter housing. Preferably, a thrust washer 4j is also arranged between the two adjacent sealing rings 4e, 4d. The thrust washers preferably comprise metal disks.

[0114] In the Figure 7The graph of pressure over time shown describes a typical sequence of a test method according to the invention on a cable for the automotive industry using the leak testing device according to the invention, which in this example operates at a typical ambient pressure of approximately 1000 mbar. After the test specimen has been inserted into the insertion opening 4a of the adapter 4, the test specimen is first sealed from the environment by applying pressure to the pressure plate 4g via the supply line 4h, the inner body 4f is displaced axially forward in the adapter housing and thus compresses the sealing rings 4d, 4e, which in turn circumferentially seal the test specimen from the environment.

[0115] The principle sketch in Figure 7 explains in principle test methods which are not part of the present claims, using a representation of the pressure over time. 1. Applying test pressure (T0): First, the piston vacuum pump 12 is activated and thus generates the test pressure of preferably -600 mbar in the system during the period T0, which in this case is 1 second. 2. First settling period (T1) : During the first settling time T1, which in this case is approximately 10 to 180 seconds, the pressure drops and approaches the working pressure of preferably -600, and the system settles. 3. Volume measurement of the test specimen (T2): At the beginning of the time interval, a first volume determination V2 is made, and at the end of the time interval T2, a second volume determination V3 is made. The difference between V2 and V3 allows for a rough preliminary estimate of the leak rate, which can be used to correct the volume determination. 4. Valve shutdown: Then, at the end of time T2, the valve switches off the pressure generator, thus disconnecting the pneumatic cylinder 12 from the measuring unit. 5. Second settling period (T3):A second settling time T3, which in this case is approximately 10 seconds, then follows the switchover to give the system another opportunity to settle and equilibrate before the actual measurement begins. The length of this second settling time T3 generally depends on the material properties of the test specimen, and the leak testing device or its software preferably specifies a permissible pressure increase. 6. Measure leak rate (T4):Since the volume of the test specimen has been determined, the pressure difference from the beginning to the end of time t4 is now only measured via the pressure sensor in the measuring cell. When determining the leak rate, a constant comparison of two consecutively measured pressure values (P4 and P5) is also carried out. If the pressure difference is greater than a certain value, e.g. 5 mbar, the measurement can be terminated before the end of T4, which is approximately 180 seconds. From the volume V3 determined in step 3 and the pressures P4 and P5, in conjunction with the time T4, the slope of the straight line in the period T4 is then determined, and thus the leak rate is determined.

[0116] The measurement can therefore be terminated if a pressure difference greater than 5 mbar is measured within the time T4 or if the time T4 expires.

[0117] The length of the time periods T0 to T4 is adapted to the material properties and the conductor cross-section of the test specimen. The thinner and longer the test specimen, the longer the respective time periods.

[0118] Figure 8 shows the pressure curve within the measuring cell P1 and the evacuation progress in the test specimen P2 over time. Also shown is the curve of the currently calculated reference volume within a test specimen with and without detectable leakage.

[0119] It can be seen that the pressure P1 inside the measuring cell and the pressure P2 inside the test specimen, i.e. the line measurement, approach the pressure P1 inside the test chamber and are almost the same from about 180 seconds.

[0120] The calculated line test volume of the measuring cell without a detectable leak initially increases continuously but with a decreasing gradient, and then remains constant for the selected test specimen from approximately 180 seconds onwards, thus extending in a straight line. The calculated line test volume of the measuring cell with a detectable leak initially increases similarly to the measuring cell with an undetectable leak, but more sharply than the latter. Crucially, after the initial volume determination—in the selected case, at 180 seconds—the calculated line test volume appears to continue increasing with a significant gradient. This is therefore an "apparent volume" because, due to a leak, a volume is calculated that does not correspond to reality.

[0121] From these observations, it was concluded that the actual measurement must only begin after a certain time, which depends on the conductivity properties of the test specimen. After this waiting period, pressure measurements and volume determinations are performed twice. If the volume increases from the first volume determination to the second volume determination, this is an indication of a leak within the test specimen. For the test specimen in question, the first volume and pressure determination takes place after 180 seconds, and the second volume and pressure determination takes place after approximately 240 seconds.

[0122] Figure 9 shows an enlarged cross-section of an alternatively designed measuring cell, also without a connecting line to the pressure generating device. This differs from the Figure 4illustrated embodiment, on the one hand by the compression spring 4i acting between the front seal housing 4b and the inner body 4f or the disc 4g, which sits with the rear end adjacent to the disc 4g on a spring sleeve and sits with the front end in a spring groove 4j or a spring seat on a spring seat at the rear end of the seal housing 4b.

[0123] Otherwise, the adapter 4 is constructed like the one in Figure 6 illustrated first embodiment.

[0124] To reduce measurement inaccuracies, the line section 14 between the rear end of the adapter 4 and the valve 16 is significantly shortened and the pressure sensor 10 is integrated into the housing of the valve 16 on the left.

[0125] In this embodiment, the valve is designed as a vacuum control block 16, which comprises a total of three 2 / 2-way valves arranged one behind the other in the housing, each of which can be controlled individually via a compressed air cylinder. The first valve 16a is the valve closest to the adapter 4, the second valve 16b is the middle valve, and the third valve 16c is the valve furthest from the adapter 4.

[0126] Each valve 16a, 16b, 16c comprises two valve pistons extending transversely to the longitudinal direction of the vacuum control block 16 and between each of which a spring is arranged, which presses the valve pistons outwards against the housing of the vacuum control block 16. Of the valve pistons, one valve piston is stationary and a movable valve piston, which is located closer to a corresponding control line, is movable against the spring force by pressure applied to the control line 16a, 16b, 16c. Thus, the valves 16a, 16b, 16c can be actuated by applying pressure through the control line assigned to each valve 16a, 16b, 16c. <v1> , <v2> , <v3>can be opened and closed optionally.

[0127] Each movable valve piston has a piston passage opening 16f, 16g, 16h extending transversely to the piston longitudinal axis through the valve piston.

[0128] Between the adjacent pistons, a separating piston wall 16d, 16e is formed, which seals off and encloses the pistons from each other, namely an outer piston wall 16d between the third valve 16c and the second valve 16b and an inner piston wall 16d between the second cylinder 16b and the first cylinder 16a.

[0129] Each piston wall has a wall opening 16i, 16j through which the pressure can pass.

[0130] According to the invention, the wall opening 16i is formed in the outer piston wall 16d between the third 16c and second valve 16b at the level of the piston passage opening 16f, 16g in the movable piston.

[0131] In the inner piston wall 16e, however, this wall opening 16j is formed at the level of the valve surfaces between the first valve 16a and the second valve 16b.

[0132] Figure 10 shows a simplified pneumatic diagram of the adapter, the vacuum control block, and the vacuum generator (pressure generation unit). The vacuum control block 16 comprises three adjacently arranged 2 / 2-way valves 16a, 16b, and 16c. Valves 16a and 16b are connected in series, and the third valve 16c is connected in parallel to the first two valves 16a, 16b.

[0133] The first valve 16a, controlled via the control line V1, opens and closes the adapter.

[0134] The pressure sensor 10 is arranged between the first valve 16a and the second valve 16b.

[0135] The second valve 16b, which is controlled via the control line V2, blocks the compressed air or the negative pressure from the pressure generating unit.

[0136] And the third valve 16c, which is controlled via the control line V3, allows venting in the open position.

[0137] To improve the sealing of the sealing surfaces of the valve pistons which are in contact with one another in the closed position, a sealing ring or an additional seal can be provided, in particular a ring seal.

[0138] The pressure generating unit, which is also designed as a piston vacuum pump, is used in the Figures 10 and 11 The illustrated embodiments are designed with two equally sized partial pistons 18a, 18b, which are arranged parallel and adjacent to one another, and whose working pistons can be adjusted via a stepper motor 18c arranged between the partial pistons 18a, 18b. The partial pistons 18a, 18b are connected to one another via a connecting line 18d to generate a total volume. This design has the advantage that the overall height is reduced by half and the pressure generation unit or the vacuum generator can be integrated horizontally into the housing 4, which reduces the overall height. Furthermore, the servo motor can be adjusted more precisely in both directions.

[0139] Figure 11 shows several of these piston vacuum pumps with two partial pistons 18a, 18b installed horizontally in the housing 2. The vacuum control blocks 16 of each measuring cell 16 are arranged above the respective partial pistons 18a, 18b, each with a vacuum control block 16 and a pressure sensor 10. The adapters 4 with the plug-in openings are in turn arranged on the front side of the housing. A total of 8 of these measuring cells are arranged in the housing 2 and can be operated independently of one another. The subject matter of the present invention arises not only from the subject matter of the individual patent claims, but also from the combination of the individual patent claims with one another. All information and features disclosed in the documents - including the abstract - in particular the spatial configuration shown in the drawings are claimed as essential to the invention, insofar as they are new compared to the prior art, individually or in combination. List of reference symbols

[0140] 2 Housing 4 Adapter 4a Insertion opening 4b Seal housing 4c Outer housing part 4d, 4e Sealing ring 4f Inner body 4g Disc 4h Supply line 4i Compression spring 4j Spring groove 4i, 4j, 4k Pressure washer 6 Line section 8 Valve 10 Pressure sensor 12 Piston vacuum pump 12a Main piston 12b Actuating plate 12c, d Actuating piston 12e Position transducer 14 Line section 16 Vacuum control block 16a First valve 16b Second valve 16c Third valve 16d Outer piston wall 16e Inner piston wall 16f, g, h Piston through-hole 16i, j Wall opening 16k Sealing ring <v1>Control line for first valve <v2>Control line for second valve <v3> Control line for third valve 18Piston vacuum pump 18a, 18bPartial piston 18cStepper motor 18dConnecting line 20Connecting line< / v3> < / v2> < / v1>

Claims

1. Test procedure for testing a test specimen comprising a cable which is formed open at a front end so that an inside of the cable is accessible, and which is provided at a rear end of the cable with a sealed cable connection for connection to an element, and wherein a test pressure is generated in the test specimen by means of a pressure generating unit for carrying out a pressure difference measurement by means of a pressure sensor (10), CHARACTERIZED IN THAT the front, possibly stripped, end of the cable is introduced into an adapter (4), that the test pressure is applied by the pressure generating unit and a reference volume (V2) is automatically determined in the interior of a measuring cell which comprises the space within the test specimen and the adapter with the connected pressure sensor up to a valve, THAT the measuring cell is uncoupled from the pressure generating unit by means of the valve (8, 16) and that a leakage rate of the test body in the measuring cell is determined with the aid of a pressure difference method.

2. Test procedure according to claim 1, wherein the reference volume (V2) comprises the volume within the adapter (4) and the volume within the test body.

3. Test procedure according to claim 1 or 2, wherein the measuring cell comprises the volumes within the test body, the closed adapter (4) receiving the test body, the pressure sensor (10) and lines connecting these components up to the valve (8, 16), if necessary.

4. Leak testing device for automatically carrying out the test method according to one or more of the preceding method claims, with a pressure generating unit designed to generate a negative or positive pressure and a measuring cell designed to receive a test body to be tested for leaks, comprising a cable with an open front end and an element connected to a rear end of the test body by means of a sealed connection, CHARACTERIZED IN THAT the measuring cell comprises at least one adapter (4) which is open on one side and has an insertion opening (4a) designed to receive the front end of the test body in an insertion manner, that the pressure generating unit is designed to first evacuate air contained within the measuring cell and then to apply a test pressure to the test body over a certain test time, that the adapter (4) comprises an adapter housing extending along a longitudinal axis of the adapter and at least two sealing rings (4d, 4e) located on behind the other in the adapter housing, in that a piston acting on the sealing rings (4d, 4e) is arranged so as to move relative to the adapter housing, in that the sealing rings (4d, 4e) can be compressed by actuating the piston, and in that a return spring (4i) is arranged between the adapter housing and the piston.

5. Leak testing device according to claim 4, wherein the sealing rings (4d, 4e) are surrounded by pressure letters (4i, 4i, 4k).

6. Leak testing device according to claim 4 or 5, wherein the piston comprises an inner body (4f) and a disk (4g) widened relative to the inner body (4f).

7. Leak testing device according to any one of claims 4 to 6, wherein the pressure generating device comprises a piston vacuum pump with several, in particular two interconnected partial pistons (18a, 18b).

8. Leak testing device according to claim 7, wherein the stepper motor (18c) is arranged between the interconnected partial pistons (18a, 18b)9. Valve for carrying out a test method according to one of the method claims 1 to 8 with a leak test device according to one of the device claims 4 to 12, wherein the valve is designed as a vacuum control block (16), which comprises three 2 / 2-way valves (16a, 16b, 16c) controlled via corresponding control lines <V1>, <V2>, <V3>, of which a first valve (16a) is located closest to the adapter (4), a second valve (16b) is spaced apart from the adapter (4) via the first valve (16a) and a third valve (16c) is spaced apart from the adapter (4) via the first (16a) and the second valve (16b).

10. Valve according to claim 9, wherein the first valve (16a) and the second valve (16b) are connected in series and the third valve (16c) is connected in parallel with the first two valves (16a, 16b).

11. Valve according to claim 9 or 10, wherein each valve (16a, 16b, 16) comprises two valve pistons which, in the closed position of the valve, bear sealingly against one another with valve surfaces, in that the valve pistons can be pressed by a control pressure, which is applied via a control line, against a spring which is arranged between the valve pistons in a valve longitudinal axis and which presses the valve pistons against one another outwards against a housing of the vacuum control block (16) into an open position.

12. Valve according to claim 11, wherein a first, stationary valve piston is stationary and a second, movable valve piston is movably arranged in the housing.

13. Valve according to claim 12, wherein the movable valve piston is located closer to the corresponding control line <V1>, <V2>, <V3>.

14. Valve according to claim 13, wherein the movable valve piston comprises a piston passage opening (16f, 16g, 16h) extending transversely to a longitudinal piston axis through the valve piston.

15. Valve according to one of claims 9 to 14, wherein the valve pistons are arranged in openings or bores with piston walls (16d, 16e) enclosing them in the housing of the vacuum control block (16), and that the piston walls (16d, 16e) comprise wall openings (16i, 16j) for the passage of a pressure applied to the valve, which are arranged either at the level of the piston passage openings (16f, 16g, 16h) of the movable valve pistons or at the level of the valve surfaces between two adjacent valves (16a, 16b, 16c).