Method for degassing fuel in container with separating elastic shell and device for its implementation

Abstract

FIELD: fuel degassing.SUBSTANCE: method has been proposed for degassing fuel in a container with an elastic separation shell, which uses a container with an elastic separation shell comprising at least one neck, in the container the fuel cavity is separated from the gas cavity using an elastic separation shell, liquid fuel is filled into the fuel cavity through at least one neck so that in the gas cavity a certain amount of air remained, and the fuel placed in the fuel cavity was degassed using an elastic separation shell and a piping system, for this purpose, the volume of the gas cavity is increased by applying overpressure from the pneumatic supply source to the gas cavity, the pressure is measured when applying overpressure from the pneumatic supply source using a pressure measuring device, and the gas released from the fuel is forced out of the fuel cavity through at least one neck. The method is characterized by the use of a container and an elastic separation shell, in which an opening is made for connection to the pipeline system, while a gas cavity is formed in an elastic separation shell, which is located inside the fuel region, the pipeline system is designed to vacuum the gas cavity with a vacuum pump through an air sleeve connected to the gas cavity through a pressurization nozzle, configured to open and close it, the shape and dimensions of the holes in the tank and in the separating elastic shell are made corresponding to the connecting elements of the pipeline system, the gas released from the fuel under the action of vacuum is forced out of the fuel cavity through at least one neck, for which excess pressure is applied from the pneumatic supply source into the gas cavity through an air sleeve connected to the gas cavity through a pressurization nozzle, and when vacuuming with a vacuum pump and applying overpressure from a pneumatic supply source, the pressure is measured using a pressure measuring device.EFFECT: simplified degassing of fuel while maintaining the quality of its degassing.10 cl, 1 dwg

Description

[0001] Field of technology to which the invention relates

[0002] The invention relates to the field of degassing fuel placed in a fuel supply tank using a separating elastic shell, namely, refueling equipment and devices for removing gases from liquid fuel, and can be used in aviation, rocket and space technology, mechanical engineering, etc.

[0003] Technology Level

[0004] A prior art method for drying fuel or oil using a drying and degassing unit is known, according to patent RU 2690354 (published: 05 / 31 / 2019), in which fuel or oil is passed through a sprayer, producing a fine mist, heated, evaporated and dispersed water is removed using a vacuum pump, then the dried and degassed fuel or oil is pumped out using a pump through an opening made in the lower part of the tank.

[0005] The disadvantages of the drying and degassing method are the low technological effectiveness of the method due to the need to use additional equipment, limited conditions for using the method due to the high temperature of the liquid and high pressure at the inlet to the nozzle, as well as insufficient efficiency in removing dissolved air from the liquid.

[0006] Also known from the prior art is a method for degassing liquid fuel in a tank of a spacecraft propulsion system according to patent RU 2171907 (published: 10.08.2001), which is closest to the proposed invention and was chosen as a prototype.The method for degassing liquid fuel in a tank of a propulsion system of a spacecraft (hereinafter referred to as SC) consists in the fact that for degassing liquid fuel in a tank of a propulsion system of a SC, including imparting acceleration to the fuel, a time delay for separating gas bubbles and discharging the separated gas outside the SC, the overload that occurs during descent at the beginning of aerodynamic braking of the SC in the atmosphere of a planet is used, wherein the SC is oriented so that the direction of the main vector of the aerodynamic force acting on the SC coincides with the direction from the liquid cavity of the tank to the intake along the axis of the intake, and the discharge of gas is carried out through the control engines of the same propulsion system, creating identical moments in mutually opposite directions, during the specified orientation during the period of time determined as the ratio of the mass of gas in the liquid cavity of the tank to the total gas flow through the control engines being activated.

[0007] The disadvantages of the method of degassing liquid fuel in the tank of the spacecraft propulsion system are the need to impart acceleration to the fuel, a time delay for the separation of gas bubbles and the discharge of the separated gas outside the spacecraft, as well as the need to use the overload that occurs during descent at the beginning of aerodynamic braking of the spacecraft in the atmosphere of the planet, which is applicable only to the spacecraft and cannot be used for degassing fuel in other containers using a separating elastic shell, including in ground conditions.

[0008] A device for drying fuel or oil using a drying and degassing unit according to patent RU 2690354 (published: 05 / 31 / 2019) is known from the prior art, comprising a vacuum tank, a nozzle with a sprayer located in the vacuum tank, a feed hydraulic pump connected via a pipeline to the nozzle, a pumping hydraulic pump connected via a pipeline to the tank, and a vacuum pump connected via a pipeline to the tank.

[0009] The disadvantage of a fuel or oil drying device using a drying and degassing unit is the complexity of the design, the need for additional equipment, and limited operating conditions of the device due to the need to create a high liquid temperature and high pressure at the inlet to the injector.

[0010] Also known from the prior art is a device for degassing liquid fuel in a spacecraft propulsion system tank, according to patent RU 2171907 (published: 10.08.2001), which is closest to the proposed invention and was selected as a prototype. The device for degassing liquid fuel in a spacecraft propulsion system tank comprises a pressurization gas cylinder, starting valves, a pressure reducer, a fuel tank, a separating elastic shell, gas and liquid cavities of the tank, an intake, a pressure sensor, and control motors.

[0011] The disadvantages of the liquid fuel degassing device in the spacecraft propulsion system tank are the complexity of the design, the need to impart acceleration to the fuel, a time delay for separating gas bubbles and discharging the separated gas outside the spacecraft, as well as the need to use the overload that occurs during descent at the beginning of aerodynamic braking of the spacecraft in the planet's atmosphere, which is applicable only to the spacecraft and cannot be used for degassing fuel in other containers using a separating elastic shell, including in ground conditions.

[0012] Disclosure of the essence of the invention

[0013] The technical problem that the claimed invention is aimed at solving is the creation of a simplified method and device for degassing fuel in a container using a separating elastic shell after filling such a container with fuel, including in ground conditions.

[0014] The technical problem is solved by a method for degassing fuel in a container with a separating elastic shell. This method utilizes a container with a separating elastic shell containing at least one neck. The container and separating elastic shell each contain an opening for connection to the piping system for vacuuming the gas cavity and supplying excess pressure to the gas cavity. The shape and size of the openings in the container and separating elastic shell correspond to the connecting elements of the piping system.

[0015] In the container, the fuel cavity is separated from the gas cavity using a separating elastic shell, while the gas cavity is formed in the separating elastic shell, which is located inside the fuel cavity.

[0016] Fill the liquid fuel into the fuel cavity through at least one neck so that a certain volume of air remains in the gas cavity.

[0017] The fuel located in the fuel chamber is degassed using a separating elastic shell and a piping system. This is accomplished by increasing the volume of the gas chamber by applying excess pressure from a pneumatic supply source to the gas chamber. The piping system is designed to allow the gas chamber to be evacuated using a vacuum pump through an air hose connected to the gas chamber via a booster nozzle, which is installed with the ability to be opened and closed.

[0018] Measure the pressure during evacuation by a vacuum pump and supply of excess pressure from a pneumatic power source using a pressure measuring instrument.

[0019] Gas released from the fuel under the action of a vacuum is forced out of the fuel cavity through at least one neck, for which purpose excess pressure is supplied from a pneumatic supply source to the gas cavity through an air hose connected to the gas cavity through a booster nipple.

[0020] In a particular case of implementing the method, the technical problem is solved due to the fact that the booster nipple is installed with the possibility of opening and closing it using a booster nipple plug.

[0021] In another particular case of implementing the method, the technical problem is solved due to the fact that the booster nozzle is installed by means of a detachable connection in the hole of the separating elastic shell.

[0022] In the third particular case of implementing the method, the technical problem is solved due to the fact that the pressurization nozzle is installed by means of a detachable connection on the outer surface of the container or outside the outer surface of the container, while one end of the pressurization nozzle is connected with the possibility of disconnecting through a pipeline with an opening of the separating elastic shell, and the other end of the pressurization nozzle is connected with the possibility of disconnecting with the air hose.

[0023] In the fourth particular case of the method implementation, the technical problem is solved due to the fact that during vacuuming with a vacuum pump and supplying excess pressure from a pneumatic power source, the pressure is measured using a pressure-vacuum gauge.

[0024] The technical problem is also solved due to the fact that the device for degassing fuel in a container with a separating elastic shell contains a container with at least one neck, configured to open and close each of the at least one neck, a fuel cavity and a gas cavity separated from each other, a separating elastic shell, which is a closed fuel-impermeable soft shell located inside the fuel cavity, separating the fuel cavity from the gas cavity, as well as a system of pipelines for vacuuming the gas cavity and supplying excess pressure to the gas cavity, connecting a pneumatic power source for displacing the gas released from the fuel using at least one neck, shut-off valves, and a pressure measuring means.

[0025] At the same time, an opening is made in the container and in the separating elastic shell for connection to the gas cavity vacuum pipeline system and supplying excess pressure to the gas cavity through an opening for installing a pressurization nozzle.

[0026] The piping system is designed to evacuate the gas cavity using a vacuum pump through an air hose connected to the gas cavity via a pressurization nozzle, which can be opened and closed. The shape and size of the openings in the tank and in the separating elastic shell correspond to the connecting elements of the piping system.

[0027] The pressure measuring device is installed with the ability to measure pressure during vacuuming with a vacuum pump and supplying excess pressure from a pneumatic power source.

[0028] In a particular case of the device implementation, the technical problem is solved due to the fact that the booster nipple is installed with the possibility of opening and closing it using the booster nipple plug.

[0029] In another particular case of the device implementation, the technical problem is solved due to the fact that the booster nozzle is installed by means of a detachable connection in the hole of the separating elastic shell.

[0030] In the third particular case of the device implementation, the technical problem is solved due to the fact that the pressurization nozzle is installed by means of a detachable connection on the outer surface of the container or outside the outer surface of the container, while one end of the pressurization nozzle is connected with the possibility of disconnection through a pipeline with an opening of the separating elastic shell, and the other end of the pressurization nozzle is connected with the possibility of disconnection to the air hose.

[0031] In the fourth particular case of the device implementation, the technical problem is solved due to the fact that the measuring instrument, installed with the ability to measure the pressure during evacuation by a vacuum pump and supply of excess pressure from a pneumatic power source, is made in the form of a pressure-vacuum gauge.

[0032] The technical result consists in the fact that the method and device for degassing fuel in a container with a separating elastic shell make it possible to significantly simplify the degassing of fuel filled into the container, while maintaining the quality of its degassing, and also to ensure the possibility of degassing fuel in a container with a separating elastic shell after filling such a container with fuel, including in ground conditions.

[0033] Brief description of drawings

[0034] The essence of the claimed invention is explained in the drawing. Fig. 1 shows a diagram of the device implemented in a separating container with an elastic shell. The following positions are indicated in Fig. 1:

[0035] 1 - capacity;

[0036] 2 - fuel cavity;

[0037] 3 - neck;

[0038] 4 - gas cavity;

[0039] 5 - separating elastic shell;

[0040] 6 - boost nipple;

[0041] 7 - air sleeve;

[0042] 8 - connecting nipple;

[0043] 9 - vacuum tap;

[0044] 10 - vacuum pump;

[0045] 11 - pneumatic power source;

[0046] 12 - excess pressure supply hose;

[0047] 13 - excess pressure supply nipple;

[0048] 14 - excess pressure supply valve;

[0049] 15 - pressure change means;

[0050] 16 - vacuum pump on / off switch;

[0051] 17 - power indicator;

[0052] 18 - connector for connecting the power cable;

[0053] 19 - Power supply cable.

[0054] Implementation of the invention

[0055] The method of degassing fuel in a container with a separating elastic shell is as follows.

[0056] To implement the method, a container 1 with a separating elastic shell 5 is used, containing at least one neck 3.

[0057] In this case, in the container 1 and in the separating elastic shell 5, an opening is made for connecting to the pipeline system for vacuuming the gas cavity 4 and supplying excess pressure to the gas cavity 4 through an opening for installing the pressurization nozzle 6. The shape and dimensions of the openings in the container 1 and in the separating elastic shell 5 are made to correspond to the connecting elements of the pipeline system.

[0058] The booster nipple 6 is installed in the opening of the separating elastic shell 5 by means of a detachable connection, for example, a threaded one, with the possibility of opening and closing it, for example, using a plug (not shown in the figure).

[0059] If necessary, the booster nipple 6 is installed by means of a detachable connection, for example, a threaded one, on the outer surface of the tank 1 or outside the outer surface of the tank 1.

[0060] In this case, one end of the pressurization nipple 6 is releasably connected through a pipeline to the opening of the separating elastic shell 5, and the other end of the pressurization nipple 6 is releasably connected to the air hose 7.

[0061] In container 1, fuel cavity 2 is separated from gas cavity 4 using separating elastic shell 5, wherein gas cavity 4 is formed in separating elastic shell 5, which is located inside fuel cavity 2.

[0062] Liquid fuel is poured into the fuel cavity 2 through at least one neck 3 in such a way that a certain volume of air remains in the gas cavity 4, intended to compensate for the thermal expansion of the fuel during operation of the container 1.

[0063] The fuel placed in the fuel cavity 2 is degassed using the separating elastic shell 5 and the pipeline system, for which purpose the volume of the gas cavity 4 is increased by supplying excess pressure from the pneumatic supply source 11 to the gas cavity 4.

[0064] In this case, the pipeline system is designed with the possibility of vacuuming the gas cavity 4 with a vacuum pump 11 through an air hose 7 connected to the gas cavity 4 through a pressurization nozzle 6 installed with the possibility of opening and closing it.

[0065] To degas the fuel placed in the fuel cavity 2, the gas cavity 4 is evacuated through the open vacuum valve 9 to an absolute pressure of no more than 10 kPa (0.1 kgf / cm 2) using a vacuum pump 10 for a specified period of time, for example, 10 minutes. During this process, a vacuum is created in the gas cavity 4 under the effect of reduced pressure, and a "fuel boiling" effect is created in the fuel cavity 2, causing dissolved gaseous substances, such as nitrogen and oxygen, to be released from the fuel. Thus, a certain volume of gas released from the fuel, the presence of which is unacceptable, forms in the fuel cavity 2.

[0066] To remove gas from the fuel cavity 2, turn off the vacuum pump 10, close the vacuum valve 9, connect the pneumatic power source 11 through the excess pressure supply hose 12 connected to the excess pressure supply nipple 13, open at least one of the necks 3 of the tank 1. Supply the gas cavity 4 through the open excess pressure supply valve 14, the air hose 7 and the booster nipple 6 with an excess pressure of no more than 50 kPa (0.5 kgf / cm 2) from the pneumatic supply source 11 through the excess pressure supply hose 12, connected to the excess pressure supply nipple 13. In this way, the separating elastic shell 5 unfolds and displaces the volume of gas released from the fuel through at least one of the necks 3, and when fuel appears in at least one of the necks 3, it and the excess pressure supply valve 14 are closed and the supply of excess pressure from the pneumatic supply source 11 is stopped.

[0067] When evacuating with a vacuum pump 10 and supplying excess pressure from a pneumatic power source 11, the pressure is measured using a pressure measuring device 15, for example, a pressure-vacuum gauge.

[0068] To ensure fuel degassing, the “vacuuming - gas removal” cycle is repeated.

[0069] The device for degassing fuel in a container with a separating elastic shell contains a container 1 with at least one neck 3, made with the possibility of opening and closing each of the at least one neck 3, for example, by turning a valve or installing a plug (not shown in the figure).

[0070] The separating elastic shell 5, which is a closed fuel-impermeable soft shell located inside the fuel cavity, separates the fuel cavity 2 from the gas cavity 4.

[0071] The separating elastic shell 5 can be made, for example, from a thermoplastic polyurethane film of the Vitur brand.

[0072] At the same time, in the container 1 and in the separating elastic shell 5, an opening is made for connecting to the pipeline system for vacuuming the gas cavity 4 and supplying excess pressure to the gas cavity 4 through an opening for installing the pressurization nozzle 6. The shape and dimensions of the openings in the container 1 and in the separating elastic shell 5 are made to correspond to the connecting elements of the pipeline system.

[0073] The device also contains a pipeline system for evacuating the gas cavity 4 with a vacuum pump 10 and supplying excess pressure from a pneumatic power source 11 to the gas cavity 4, which is a pipeline system connecting the vacuum pump 10, the evacuation valve 9, the pneumatic power source 11, the excess pressure supply valve 14 from the pneumatic power source 11, the connecting nipple 8 and the excess pressure supply nipple 13, as well as a pressure measuring device 15.

[0074] The pipeline system is designed with the possibility of vacuuming the gas cavity 4 with a vacuum pump 10 through an air hose 7 connected to the gas cavity 4 through a booster nipple 6.

[0075] The vacuum pump 10 is installed with the possibility of vacuuming the gas cavity 4 using a system of vacuum pipelines and a vacuum tap 9 through an air hose 7 connected to the gas cavity 4 through a booster nipple 6.

[0076] The booster nipple 6 is installed in the opening of the separating elastic shell 5 by means of a detachable connection, for example, a threaded one, with the possibility of opening and closing it, for example, using a plug (not shown in the figure).

[0077] The pressurization nipple 6 can be installed by means of a detachable connection, for example, a threaded one, on the outer surface of the tank 1 or outside the outer surface of the tank 1. In this case, one end of the pressurization nipple 6 is detachably connected through a pipeline with the opening of the separating elastic shell 5, and the other end of the pressurization nipple 6 is detachably connected to the air hose 7.

[0078] The excess pressure supply nipple 13 allows the use of any pneumatic supply source, such as a gas cylinder.

[0079] The means for measuring the pressure 15 in the fuel system can be made in the form of a pressure-vacuum gauge installed in the system of vacuum and nitrogen supply pipelines with the possibility of measuring the pressure in the fuel system during the process of vacuuming the gas cavity 4 by the vacuum pump 10 and supplying excess pressure from the pneumatic supply source 11 to the gas cavity 4.

[0080] The device also includes a vacuum pump on / off switch 16, a power indicator 17, a power cable connector 18, and a power supply cable 19.

[0081] The fuel degassing device in the tank 1 with the separating elastic shell 5 operates as follows.

[0082] Before degassing the fuel in tank 1 with the separating elastic shell 5, all valves are closed. At least one of the necks 3 is opened and liquid fuel is poured into fuel cavity 2 of tank 1 so that a certain volume of air remains in gas cavity 4 to compensate for the thermal expansion of the fuel.

[0083] To degas the fuel placed in the fuel cavity 2, the gas cavity 4 is evacuated through the open vacuum valve 9 to an absolute pressure of no more than 10 kPa (0.1 kgf / cm 2) using a vacuum pump 10 for a specified period of time, for example, 10 minutes. During this process, a vacuum is created in the gas cavity 4 under the effect of reduced pressure, and a "fuel boiling" effect is created in the fuel cavity 2, causing dissolved gaseous substances, such as nitrogen and oxygen, to be released from the fuel. Thus, a certain volume of gas released from the fuel, the presence of which is unacceptable, forms in the fuel cavity 2.

[0084] To remove gas from the fuel cavity 2, turn off the vacuum pump 10, close the vacuum valve 9, connect the pneumatic power source 11 through the excess pressure supply hose 12 connected to the excess pressure supply nipple 13, open at least one of the necks 3 of the tank 1. Supply the gas cavity 4 through the open excess pressure supply valve 14, the air hose 7 and the booster nipple 6 with an excess pressure of no more than 50 kPa (0.5 kgf / cm 2) from the pneumatic supply source 11 through the excess pressure supply hose 12, connected to the excess pressure supply nipple 13. In this way, the separating elastic shell 5 unfolds and displaces the volume of gas released from the fuel through at least one of the necks 3, and when fuel appears in at least one of the necks 3, it and the excess pressure supply valve 14 are closed and the supply of excess pressure from the pneumatic supply source 11 is stopped.

[0085] When evacuating with a vacuum pump 10 and supplying excess pressure from a pneumatic power source 11, the pressure is measured using a pressure measuring device 15, for example, a pressure-vacuum gauge.

[0086] Repeat the “vacuuming - gas removal” cycle to ensure fuel degassing.

[0087] It has been experimentally established that the method for degassing fuel in a container 1 with a separating elastic shell 5 according to the proposed invention, by repeating the "evacuation - gas removal" cycle twice, ensures the absence of dissolved gas in the fuel, and the vacuuming within each cycle takes 10 minutes. Moreover, in comparison with patent RU 2171907, selected as a prototype, the fuel degassing does not require a complex design, the need to impart acceleration to the fuel, a time delay for separating gas bubbles and discharging the separated gas outside the spacecraft, and the need to use the overload that occurs during descent at the beginning of aerodynamic braking of the spacecraft in the planet's atmosphere, which is applicable only to the spacecraft.

[0088] The method for degassing fuel in a container with a separating elastic shell and the device for implementing it can find wide application in the field of degassing fuel placed in fuel supply containers using a separating elastic shell and can significantly simplify the degassing of fuel, while maintaining the quality of its degassing, and also ensure the possibility of degassing fuel in a container with a separating elastic shell after filling such a container with fuel, including in ground conditions.

Claims

1. A method for degassing fuel in a container with a separating elastic shell, which involves using a container with a separating elastic shell containing at least one neck, separating a fuel cavity from a gas cavity in the container using a separating elastic shell, filling the fuel cavity with liquid fuel through at least one neck in such a way that a certain volume of air remains in the gas cavity, degassing the fuel placed in the fuel cavity using a separating elastic shell and a pipeline system, for which purpose the volume of the gas cavity is increased by supplying excess pressure from a pneumatic supply source to the gas cavity, measuring the pressure when supplying excess pressure from a pneumatic supply source using a pressure measuring device, displacing gas released from the fuel from the fuel cavity through at least one neck, characterized in that a container and a separating elastic shell are used,in which an opening is made for connection to the pipeline system, wherein the gas cavity is formed in a separating elastic shell, which is located inside the fuel region, the pipeline system is designed with the possibility of evacuating the gas cavity with a vacuum pump through an air hose connected to the gas cavity through a pressurization nozzle installed with the possibility of opening and closing it, the shape and dimensions of the openings in the tank and in the separating elastic shell are made corresponding to the connecting elements of the pipeline system, gas released from the fuel under the action of a vacuum is displaced from the fuel cavity through at least one neck, for which excess pressure is supplied from a pneumatic power source to the gas cavity through an air hose connected to the gas cavity through a pressurization nozzle,and when evacuating with a vacuum pump and supplying excess pressure from a pneumatic power source, the pressure is measured using a pressure measuring device.

2. The method according to paragraph 1, characterized in that a booster nozzle is installed with the possibility of opening and closing it using a booster nozzle plug.

3. The method according to paragraph 1, characterized in that the pressurization nozzle is installed by means of a detachable connection into the opening of the separating elastic shell.

4. The method according to paragraph 1, characterized in that the pressurization nozzle is installed by means of a detachable connection on the outer surface of the container or outside the outer surface of the container, while one end of the pressurization nozzle is releasably connected through a pipeline with an opening in the separating elastic shell, and the other end of the pressurization nozzle is releasably connected to the air hose.

5. The method according to paragraph 1, characterized in that during vacuuming with a vacuum pump and supplying excess pressure from a pneumatic power source, the pressure is measured using a pressure-vacuum gauge.

6. A device for degassing fuel in a container with a separating elastic shell, comprising a container with at least one neck configured to open and close each of the at least one neck, a fuel cavity and a gas cavity separated from each other, a separating elastic shell that is a closed fuel-impermeable soft shell, a pipeline system connecting a pneumatic power source for displacing gas released from the fuel using at least one neck, shut-off valves, a pressure measuring means, characterized in that in the container and in the separating elastic shell located inside the fuel cavity, separating the fuel region from the gas region, an opening is made for connection to the pipeline system through an opening for installing a pressurization nozzle, the pipeline system is configured to evacuate the gas cavity with a vacuum pump through an air hose,connected to the gas cavity through a pressurization nozzle installed with the possibility of opening and closing it, the shape and dimensions of the openings in the container and in the separating elastic shell are made to correspond to the connecting elements of the pipeline system, and the pressure measuring device is installed with the possibility of measuring the pressure during evacuation by a vacuum pump and supplying excess pressure from a pneumatic power source.

7. The device according to paragraph 6, characterized in that the booster nozzle is installed with the possibility of opening and closing it using a booster nozzle plug.

8. The device according to paragraph 6, characterized in that the pressurization nozzle is installed by means of a detachable connection in the opening of the separating elastic shell.

9. The device according to paragraph 6, characterized in that the pressurization nozzle is installed by means of a detachable connection on the outer surface of the container or outside the outer surface of the container, wherein one end of the pressurization nozzle is detachably connected through a pipeline to the opening of the separating elastic shell, and the other end of the pressurization nozzle is detachably connected to the air hose.

10. The device according to paragraph 6, characterized in that the measuring device, installed with the possibility of measuring the pressure during evacuation by a vacuum pump and supplying excess pressure from a pneumatic power source, is made in the form of a pressure-vacuum gauge.

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