Impeding vapour condensation with mechanical vacuum pumps

Abstract

A controller or method for a mechanical vacuum pump configured, in response to receipt of an instruction to shut-down the pump D5, to activate a shutdown mode. The shut-down mode comprises monitoring

Description

FIELD OF THE INVENTION The field of the invention relates to mechanical vacuum pumps and to impeding the condensation of vapour in such vacuum pumps during shutdown and start up. BACKGROUND Vacuum pumps may corrode internally where they are used to pump vapour and are then switched off immediately after pumping leading to the risk of residual vapour condensing inside the pump. This may cause components to rust and may also damage lubricants and impair the pump’s ability to reach ultimate pressure in subsequent pumping operations. There may also be issues of condensation at startup if the pump is not warmed up properly prior to starting pumping vapour. Although vacuum pumps may be supplied with instructions indicating that they should be warmed up prior to pumping vapour, that they should run with gas ballast throughout and be cleaned up again prior to shutting down, this advice may be onerous for a user to follow, may not be followed correctly and / or may be ignored. It would be desirable if such processes could be more accurately and automatically managed. SUMMARY A first aspect provides a controller for a mechanical vacuum pump comprising: control circuitry configured, in response to receipt of an instruction to shutdown said vacuum pump, to activate a shutdown mode, whereby said shutdown mode comprises: monitoring an operational property associated with said vacuum pump while continuing to drive a pumping mechanism of said vacuum pump, said operational property being indicative of an amount of vapour within said pump; and in response to said monitoring indicating residual vapour within said pump being reduced to below a predetermined amount, shutting down said vacuum pump. It was recognised that problems can arise when vacuum pumps are shutdown in that as the pressure rises and the temperature falls within the vacuum pump, any vapour within the pump will condense and this condensation will sit within the non-operational pump and may cause corrosion. Many mechanical pumps which operate at lower vacuums, where this may be a particular problem such as Roots pumps, scroll pumps, screw pumps, claw pumps, diaphragm pumps or rotary vane pumps are manually operated, such that any control is performed by a user. Although such pumps may be supplied with instructions to perform the shutdown of the pump in a certain way to mitigate for such condensation, these instructions may not always be followed correctly. It was also recognised that the amount of vapour within the pump affects its operation, and that there are certain operational properties of the pump that when measured provide an indication of the amount of vapour currently present within the pump. In light of this a controller is provided that monitors at least one of these properties and controls a shutdown mode in dependence upon the property. Thus, by monitoring this operational property, the controller determines when the residual amount of vapour within the pump is deemed to have dropped to an acceptable level and only when this point is reached is the pump stopped and in this way the risk of corrosion mitigated. Although the operational property may be any property indicative of an amount of vapour, in some embodiments, said operational property comprises a property indicative of at least one of: power consumption of a motor driving said pumping mechanism, pressure within said vacuum pump or within a chamber being evacuated, or difference in pressures measured by two different types of pressure sensor. Various operational properties may be measured to determine an amount of vapour. For example, the pressure within the pump or within a vacuum chamber being evacuated may be measured and this may provide a relatively accurate indication of an amount of vapour, however it does require a pressure sensor which the pump or vacuum chamber may not have. A further more accurate measurement may be provided by comparing readings from two different types of pressure sensors, one being gas type dependent and the other gas type relatively independent. In this case the sensors provide different readings when vapour such as water vapour is present, but these readings converge as vapour is removed. Thus, monitoring the difference between the two readings may provide a particularly accurate indication of the presence of vapour. However, two different types of pressure sensors are required for this. The power consumption of a motor by contrast is also an indication of the amount of vapour present and although this may not be as accurate an indication as pressure measurements may be such a measurement may be more readily available for use by the controller and may still provide acceptable control. In some embodiments, said monitoring comprises at least one of: comparing said operational property with a predetermined value; and comparing a rate of change of said monitored operational property with a predetermined rate of change. The comparing of the property with a predetermined value may take various forms depending on the property being measured. It may be the value of the monitored property falling below a predetermined value as the vapour is removed from the chamber that is the determining factor and / or it may be the rate of change of these values that is used in the comparison to determine if the motor can be stopped. In some embodiments, said property comprises power consumption of a motor driving said pumping mechanism. Where power consumption of the motor is the property monitored and compared with a predetermined value, then in cases where ballast gas is used the predetermined value may be a value indicative of the pump pumping predominantly gas ballast. Alternatively, and / or additionally said operational property comprises pressure within said vacuum pump or within a chamber being evacuated by said vacuum pump. Where the property comprises pressure then the predetermined value may be a pressure approaching base ultimate, with or without gas ballast. Alternatively, it may be a rate of change of pressure that is determined and compared with a predetermined rate of change value. Pressure may be a more accurate measure than motor power is, as to whether there is a certain amount of vapour in the pump or not. In some cases there may be a pressure sensor associated with the vacuum pump and the controller may receive measurements from this. Alternatively and / or additionally the vacuum pump controller may comprise a port for receiving a signal from a remote pressure sensor associated with a system being evacuated. Alternatively and / or additionally said operational property comprises a difference in pressure readings measured by two different types of pressure sensor associated with said vacuum pump. The different types of pressure sensor operate using different principles, one (such as a strain gauge, diaphragm gauge or capacitance manometer) providing a substantially gas type independent pressure measurement and the other (such as a Pirani gauge) providing a measurement that is more dependent on gas type. Owing to these differences, when there is vapour present the readings from the two sensors will differ, and as vapour is removed the readings from the two different sensors will converge. Thus, the property indicating residual vapour within the pump has been reduced to below a predetermined amount may be a difference in the two measurements falling below a predetermined value. In some embodiments, said vacuum pump further comprises a controllable gas ballast valve, said controller being configured to control said gas ballast valve to remain open during at least a portion of said shutdown mode. In many cases mechanical vacuum pumps may have a gas ballast valve which allows gas ballast to be used when pumping. Where such gas ballast is available, then it may be that during the shut down mode the controller controls the gas ballast valve to be open for at least some of the time, in many cases for all of the time of the shut down mode. The gas ballast helps remove any vapor from the pump and ensure that no or very little vapour remains in the pump when it is shut down. In some embodiments, said control circuitry is configured in response to receipt of an immediate shutdown instruction not to activate said shutdown mode and to shutdown said pump. The controller may be provided with an immediate shutdown operational mode which may be activated for example by the user pushing the shutdown button twice in quick succession. This will enable the pump to be shut down immediately where this may be desirable. It may be that a vacuum pump is required to be shut down at a certain time and providing an immediate shut down operation allows this to happen. It may be applicable where the pump is to be used again shortly such that the problem of vapour within the pump causing corrosion does not arise, or when an emergency stop is required to avoid injury or damage. In some embodiments, said control circuitry is further configured in response to receipt of an instruction to start said vacuum pump, to activate a warm up mode to raise a temperature of said vacuum pump prior to indicating said vacuum pump is available for pumping operations, whereby said warm up mode comprises: driving said pumping mechanism without initiating operation of a cooling fan; determining a temperature of said pump; and in response to determining said temperature of said pump has reached a predetermined temperature; indicating to a user that said pump is available for pumping. As well as potential problems of condensation arising at shut down, these problems may also arise during start up where a vacuum pump is cold when it starts pumping a gas that contains vapours, such that the vapours will condense within the pump and may remain there and cause corrosion. Embodiments provide for an automatic warm up procedure to inhibit this occurring, during which the cooling fans of the pump are not activated until the temperature of the pump has reached a predetermined temperature. During this procedure use of the pump for pumping a gas is inhibited. In some embodiments, said predetermined temperature is higher than a usual operating temperature. Although the predetermined temperature may be the normal operating temperature of a vacuum pump, in some embodiments it is a higher temperature. This higher temperature may be effective at inhibiting any initial condensation of vapour and will increase the capacity of vapour the pump can handle without condensation. It should not be too much higher as the operation / reliability of the vacuum pump may be affected. A temperature increase of between 5 and 30 degrees C, preferably 5 and 20 degrees C may be acceptable. In some embodiments, the vacuum pump controller is operable to initiate operation of said cooling fan in response to determining said temperature has reached said predetermined temperature. ln some embodiments, said vacuum pump further comprises a controllable gas ballast valve, said controller being configured to control said gas ballast valve to remain open during at least a portion of said warm up mode. Where the vacuum pump has an automatically controllable gas ballast valve then during at least a portion of the warm up mode, in some cases during the entire warm up mode, this may be controlled to be open. A further aspect provides a mechanical vacuum pump comprising: a pumping mechanism for pumping a gas from an inlet to an outlet; a motor for driving said pumping mechanism; and a vacuum controller according to an aspect. In some embodiments, said mechanical vacuum pump further comprises a controllable gas ballast valve. In some embodiments, said vacuum pump further comprises a pressure sensor. In some embodiments, said vacuum pump further comprises two pressure sensors configured to operate according to different principles. A yet further aspect provides a method of shutting down a mechanical vacuum pump comprising: receiving a shutdown instruction from a user; in response to said shutdown instruction, activating a shutdown mode, the shutdown mode comprising: monitoring an operational property associated with said vacuum pump while continuing to drive a pumping mechanism of said vacuum pump, said operational property being indicative of an amount of vapour within said vacuum pump; and comparing said monitored operational property with a predetermined value, and in response to said comparison indicating residual vapour within said pump being reduced to less than a predetermined amount, shutting down said vacuum pump. ln some embodiments, the method further comprises keeping a gas ballast valve open during said shutdown mode. A yet further aspect provides a vacuum pump controller configured in response to receipt of an instruction to start said vacuum pump, to activate a warm up mode to raise a temperature of said vacuum pump prior to indicating said vacuum pump is available for pumping operations, whereby said warm up mode comprises: driving said pumping mechanism without initiating operation of a cooling fan; determining a temperature of said pump; and in response to determining said temperature of said pump has reached a predetermined temperature; indicating to a user that said pump is available for pumping. A still further aspect provides a method performed by a vacuum pump comprising: in response to receiving an instruction to start, activating a warm up mode to raise a temperature of said vacuum pump prior to indicating said vacuum pump is available for pumping operations, said warm up mode comprising: driving said pumping mechanism without initiating operation of a cooling fan; determining a temperature of said pump; and in response to determining said temperature of said pump has reached a predetermined temperature; indicating to a user that said pump is available for pumping. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1 schematically shows a vacuum pump and vacuum pump controller according to an embodiment; Figure 2 schematically shows a flow diagram illustrating steps in a method of shutting down a vacuum pump according to an embodiment; and Figure 3 schematically shows a flow diagram illustrating steps in a method of warming up a vacuum pump according to an embodiment DESCRIPTION OF THE EMBODIMENTS Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments, recognise that some pumps, such as smart pumps, may comprise sophisticated pump controllers and sensors associated with the pumps and that these capabilities may be used to enable at least one of: automatic warm up prior to pumping vapour and automatic clean at shutting down. Figure 1 shows a vacuum pump 10 evacuating a vacuum chamber 20. Vacuum pump 10 is a vacuum pump according to an embodiment and comprises a motor 12 for driving a pumping mechanism 33. Vacuum pump 10 comprises a pump controller 14 for controlling the operation of the vacuum pump. The pump controller 14 has a port 16 for receiving signals from sensors associated with the vacuum chamber 20. In this embodiment, the vacuum pump 10 has a sensor 18 for measuring pressure and a sensor 15 for measuring temperature. In this embodiment the pressure sensor 18 is a Pirani gauge. In other embodiments, the vacuum chamber may have a pressure sensor and signals from the pressure sensor may be input at port 16. In still other embodiments the sensor 18 may be two pressure sensors, a Pirani gauge and a diaphragm gauge, the pump controller being responsive to differences between the readings of these two gauges. There is also a gas ballast valve 17 for controlling the ingress of gas ballast to the vacuum pump. There is also a fan 19 for providing cooling to the vacuum pump and motor 12. Pump controller 14 is configured to control operation of the vacuum pump and in particular to control the motor 12, the fan 19 and the gas ballast valve 17. Pump controller 14 is configured with a start up mode and a shut down mode of control. In the shut down mode of control, the pump controller 14 responds to an operator indicating that the vacuum pump is to shut down by continuing to operate the motor 12 and keep the gas ballast valve 17 open, until either a reading from pressure sensor 18, or where there are two pressure sensors, differences between the readings from the two sensors, have dropped below a predetermined value indicative of vapour within the pump, having reached a value deemed acceptable to inhibit corrosion. At this point the pump controller 14 may shut the vacuum pump down, by stopping the motor and closing the gas ballast valve. Where the pump controller 12 is configured with a start up mode of operation then in response to a user indicating that the pump should start the motor will start operation but the pump controller will not start operation of fan 19 until temperature sensor 15 indicates that the temperature of the pump has reached a predetermined value. At this point the fan 19 will be controlled to start operating and the user may receive an indication via indicator 11 that the pump can start evacuating the vacuum chamber. The indicator 11 may be a light that is illuminated, or some other means of conveying information. In some embodiments, the pump may start evacuating the vacuum chamber automatically and may not indicate this to the user. Vacuum pump 10 also comprises a control panel 30 for a user to interact with the controller and the control panel 30 includes a start and a stop button. In some embodiments, the pump controller is configured to respond to an operator activating the stop button twice in quick succession to stop operation of the vacuum pump immediately by switching the motor off without performing a shut down mode to remove vapour from the pump. Figure 2 shows steps in a method performed by a pump controller controlling a vacuum pump according to an embodiment. In an initial step at S10 the pump is operated to evacuate the chamber and a gas ballast valve is open. It is then determined at D5 whether a shut down instruction has been received. If it has it is determined at D15 if it is an immediate shutdown instruction. If it is then where the gas ballast valve is a controllable valve it is closed and the motor of the pump is turned off and the pump stops operation at step S40. If it is not an immediate shutdown then step S20 is performed and the pump continues to operate. At step S30 an operational property of the pump is monitored. This operational property is indicative of an amount of vapour within the pump and may be the power of the motor or the pressure within the pump or within the chamber. At step D25 it is determined if the operational property has fallen below a predetermined value and when it is determined that it has then step S40 is performed and the gas ballast valve is closed and the motor is turned off and the pump shuts down. Figure 3 shows steps in a method performed by a pump controller during a warm up mode of the pump. At step S100 an instruction is received to start the pump. At step S120 the pump controller activates a warm up mode for the pump. This comprises at step S130 driving the pumping mechanism, opening the gas ballast valve but not operating the cooling fan. At step D115 it is determined if a predetermined temperature has been obtained. If it has then the cooling fan is activated and an indicator 16 is illuminated to indicate to a user that the pump is available for pumping at step S150. In summary embodiments may provide one or more of the following: • Automatic warm-up mode where the pump lets you know when it has reached a desired operating temperature, or starts pumping automatically at this point • End point for warm up could be based on temperature sensor already built into the pump • The above can be enhanced where a solenoid operated gas ballast GB valve is fitted to warm the pump through faster, the pumping of additional gas ballast making the pump work harder and increases the temperature of the pump more quickly • The controller also delays operation of the cooling fan so the pump runs hotter • Automatic shutdown mode is provided to allow the pump to clean itself up before turning off • End point for clean-up is based on a detected property of the pump indicative that vapour has been removed. For example, drive power (power would reduce as vapour is removed) or pressure where a gauge is connected (recovery to base ultimate) • Shutdown can be enhanced where a solenoid operated gas ballast valve is fitted, if one is not fitted then a user may manually open, or leave open the valve during shutdown mode. Embodiments may be implemented with a vapour mode, which could have the following use cases Basic vapour mode - no additional accessories • When the start button is pressed the pump enters a warm-up mode, fan operation is delayed to warm the pump up faster. Pump may also reach a higher temperature than normal mode to enable more vapour to be pumped. • When the pump reaches operating temperature it lets the user know via an LED on the pump and / or via message over the comms bus. • When the stop button is pressed the pump goes into shutdown mode, the pump continues to run until a monitored predetermined property reaches a desired value (instructions that are supplied with the pump may indicate gas ballast should remain on throughout). • Pressing the stop button twice turns the pump off immediately. Enhanced vapour mode - solenoid gas ballast valve fitted • When the start button is pressed the pump enters a warm-up mode, fan operation is delayed and gas ballast is opened to warm the pump up faster. Pump also reaches a higher temperature than normal mode to enable more vapour to be pumped. 5 • When the pump reaches operating temperature it lets the user know via an LED on the pump and / or via message over the comms bus. • Gas ballast remains open whilst the pump is running. • When the stop button is pressed the pump goes into shutdown mode, the pump continues to run with gas ballast open either until the power is restored or a 10 predetermined pressure is reached. • Pressing the stop button twice turns the pump off immediately. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the 15 invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents. REFERENCE SIGNS 10 vacuum pump 11 indicator 12 motor 5 14 pump controller 15 temperature sensor 16 input port 17 gas ballast valve 18 pressure sensor io 19 cooling fan 20 vacuum chamber 30 control panel 33 pumping mechanism

Claims

1. A controller for a mechanical vacuum pump comprising:control circuitry configured, in response to receipt of an instruction to shutdown said vacuum pump, to activate a shutdown mode, whereby said shutdown mode comprises:monitoring an operational property associated with said vacuum pump while continuing to drive a pumping mechanism of said vacuum pump, said operational property being indicative of an amount of vapour within said pump; andin response to said monitoring indicating residual vapour within said pump being reduced to below a predetermined amount, shutting down said vacuum pump.

2. A vacuum pump controller according to claim 1, wherein said monitoring comprises at least one of:comparing said operational property with a predetermined value; and comparing a rate of change of said operational property with a predetermined rate of change.

3. A vacuum pump controller according to any preceding claim, wherein said operational property comprises power consumption of a motor driving said pumping mechanism.

4. A vacuum pump controller according to any preceding claim, wherein said operational property comprises pressure within said vacuum pump or within a chamber being evacuated by said vacuum pump.

5. A vacuum pump according to any preceding claim, wherein said operational property comprises a difference in pressure readings measured by two different types of pressure sensor associated with said vacuum pump.

6. A vacuum pump controller according to any preceding claim, wherein said vacuum pump further comprises a controllable gas ballast valve, said controller being configured to control said gas ballast valve to remain open during at least a portion of said shutdown mode.

7. A vacuum pump controller according to any preceding claim, wherein said control circuitry is configured in response to receipt of an immediate shutdown instruction not to activate said shutdown mode and to shutdown said pump.

8. A vacuum pump controller according to any preceding claim, said control circuitry being further configured in response to receipt of an instruction to start said vacuum pump, to activate a warm up mode to raise a temperature of said vacuum pump prior to indicating said vacuum pump is available for pumping operations, whereby said warm up mode comprises:driving said pumping mechanism without initiating operation of a cooling fan;determining a temperature of said pump; andin response to determining said temperature of said pump has reached a predetermined temperature;indicating to a user that said pump is available for pumping.

9. A vacuum pump controller according to claim 8, wherein said predetermined temperature is higher than a usual operating temperature.

10. A vacuum pump controller according to any one of claims 8 or 9, said control circuitry being further configured to initiate operation of a cooling fan in response to determining said temperature has reached said predetermined temperature.

11. A vacuum pump controller according to any one of claims 8 to 10, wherein said vacuum pump further comprises a controllable gas ballast valve, saidcontroller being configured to control said gas ballast valve to remain open during at least a portion of said warm up mode.

12. A mechanical vacuum pump comprisinga pumping mechanism for pumping a gas from an inlet to an outlet;a motor for driving said pumping mechanism; anda vacuum controller according to any one of claims 1 to 5 and 7 to 10.

13. A mechanical vacuum pump according to claim 12, said mechanical vacuum pump further comprising a controllable gas ballast valve and a vacuum controller according to any one of claims 6 or 11.

14. A method of shutting down a mechanical vacuum pump comprising: receiving a shutdown instruction from a user;in response to said shutdown instruction, activating a shutdown mode, the shutdown mode comprising:monitoring an operational property associated with said vacuum pump while continuing to drive a pumping mechanism of said vacuum pump, said operational property being indicative of an amount of vapour within said vacuum pump; andcomparing said monitored operational property with a predetermined value, and in response to said comparison indicating residual vapour within said pump being reduced to less than a predetermined amount, shutting down said vacuum pump.

15. A method according to claim 14, further comprising keeping a gas ballast valve open during said shutdown mode.

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