A pressure-controlled mechanical valve for controlling oil flow within a vacuum pumping system

Abstract

A vacuum pumping system comprises a vacuum pump, an oil supply line 106 to the vacuum pump, a valve 220 in the oil supply line, and a pressure-controlled valve actuator 109 to actuate the valve, prefe

Description

FIELD OF THE INVENTION The present invention relates to a vacuum system comprising a pressure-controlled or vacuum operated valve actuator for controlling flow of oil to a vacuum pump. BACKGROUND Many vacuum pumps receive, during operation, a supply of oil for lubrication and / or sealing purposes. By way of example, rotary piston pumps operate by using rotating pistons to create chambers within the pump housing that alternately expand and contract as the pistons rotate. This action draws in fluid at the pump inlet, compresses it, and then discharges it at a higher pressure at the pump outlet. Oil is typically supplied to a rotary piston pump during its operation, for example to provide lubrication, e.g. to pump bearings and the like, and to provide sealing between the pistons and the pump housing so as to prevent fluid from leaking out and ensuring efficient compression. SUMMARY OF INVENTION It tends to be desirable to supply oil to a rotary piston pump only when the pump is in operation, i.e. when the pump is pumping fluid or is “on”. Continuing to provide oil into the vacuum pump when the pump is not in operation, i.e. when the pump is not pumping fluid or is “off”, can cause hydraulic locking which may cause difficulties when restarting the vacuum pump. Conventionally, the supply of oil to a vacuum pump is coordinated by an electronically controlled valve disposed along the oil supply line, e.g. via a solenoid valve. However, the voltage and frequency of alternating current (AC) electricity used in vacuum pumping facilities varies from country to country throughout the world. Accordingly, different solenoid valve coils are required to be fitted to vacuum pumps in different geographical regions, presenting installation and supply issues. The present invention relates to use of a pressure-controlled or vacuum operated valve actuator to control a valve to selectively route oil to a vacuum pump, responsive to a pressure differential within the pressure-controlled valve actuator being above or below a threshold value. The pressure-controlled valve actuator is a mechanical valve actuator. The pressure-controlled valve actuator is self-actuated (i.e., requires no electrical input or manual operation by a user) by a pressure differential across a membrane within the valve actuator. Advantageously, such use of a pressure-controlled valve actuator avoids use of electronically controlled valves, such as solenoid valves, and the problems associated therewith. In an aspect, there is provided a vacuum pumping system, comprising: a vacuum pump; an oil supply line for supplying oil to the vacuum pump; a valve disposed along the oil supply line; and a pressure-controlled valve actuator configured to actuate the valve. The pressure-controlled valve actuator may be configured to actuate the valve depending on a pressure within the vacuum pump. The vacuum pumping system may further comprise a vacuum line coupled between the vacuum pump and the pressure-controlled valve actuator. The vacuum line may be coupled to a pumped fluid path within the vacuum pump at a point between an inlet of the vacuum pump and an outlet of the vacuum pump. The vacuum line may be coupled to the vacuum pump at a gas ballast port of the vacuum pump. The pressure-controlled valve actuator may comprise: a housing; a diaphragm assembly arranged within the housing and dividing the housing into a first chamber between the diaphragm assembly and a first end of the housing and a second chamber between the diaphragm assembly and a second end of the housing opposite to the first end; and a plunger extending from the housing and connected to the diaphragm assembly for being positioned by the diaphragm assembly in an actuating range as a function of a pressure differential across the diaphragm assembly. The plunger may be connected to the valve. The first chamber may be arranged to be in communication with a level of vacuum within the vacuum pump. The diaphragm assembly may be configured to position the plunger in the actuating range as a function of a level of vacuum communicated into the first chamber. The first chamber may be coupled to the vacuum line. The pressure-controlled valve actuator may be configured to, when the vacuum pump is in operation, open the valve thereby to allow oil to flow to the vacuum pump via the oil supply line. The pressure-controlled valve actuator may be configured to, when the vacuum pump is not in operation, close the valve thereby to prevent or oppose oil from flowing to the vacuum pump via the oil supply line. The pressure-controlled valve actuator and valve may be configured as a normally closed valve assembly. The vacuum pumping system may further comprise an oil reservoir arranged to supply oil under gravity to the oil supply line. The vacuum pump may be a rotary piston pump. In a further aspect, there is provided a method of operating a vacuum pumping system. The vacuum pumping system comprises a vacuum pump, an oil supply line for supplying oil to the vacuum pump, and a valve disposed along the oil supply line. The method comprises: controlling, by a pressure-controlled valve actuator, a position of the valve thereby to control a flow of oil into the vacuum pump via the oil supply line. The method may further comprise: communicating a level of vacuum within the vacuum pump to the pressure-controlled valve actuator; and controlling, by the pressure-controlled valve actuator, the position of the valve as a function of the communicated level of vacuum. The level of vacuum within a gas ballast port of the vacuum pump may be communicated to the pressure-controlled valve actuator. BRIEF DESCRIPTION OF DRAWINGS The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 depicts a vacuum pumping system; Figure 2 depicts a valve assembly and valve actuator of the vacuum pumping system; and Figure 3 is a process flow chart showing certain steps of a method for operating the vacuum pumping system. DETAILED DESCRIPTION Figure 1 is a schematic illustration (not to scale) of an embodiment of a vacuum pumping system 100. In this embodiment, the vacuum pumping system 100 comprises a vacuum pump 102, an oil reservoir 104, an oil supply line 106 for supplying oil to the vacuum pump 102 from the oil reservoir 104, a valve assembly 108 for controlling a flow of the oil along the oil supply line 106, and a valve actuator 109 for actuating the valve assembly 108. In this embodiment, the vacuum pump 102 is a rotary piston pump comprising a housing 110 defining a pumping chamber 112, and a piston 114 mounted within the pumping chamber 112 on a rotating shaft 116. The piston 114 is designed with a specific profile to create first and second chambers 118, 120 within the pumping chamber 112 between the piston 114 and walls of the pumping chamber 112. In operation, as the shaft 116 rotates, the piston 114 rotates (as indicated by arrows 122 in Figure 1) within the pumping chamber 112, expanding and contracting the first and second chambers 118, 120. The vacuum pump 102 comprises a fluid inlet 124 at which fluid to be pumped is introduced. As a chamber 118, 120 expands, a low-pressure volume is established therein, and fluid is drawn into that chamber 118, 120 from the fluid inlet 124 due to the pressure difference. Further rotation of the piston 114 causes the chamber 118,120 to contract. The fluid therein is thus compressed, and its pressure thereby increased. Further rotation of the piston 114 moves the chamber 118, 120 into fluid communication with a discharge port or fluid outlet 126 of the vacuum pump. As the chamber 118, 120 continues to rotate and expand again, the high-pressure fluid is expelled from the chamber 118, 120 through the fluid outlet 126. The piston 114 may be continually rotated to creating a continuous cycle of fluid intake, compression, and discharge. In this embodiment, the vacuum pumping system 100 is configured such that, while the vacuum pump 100 is in operation, i.e. is pumping fluid, oil is supplied to the vacuum pump 100 from the oil reservoir 104 via the oil supply line for the purposes of lubrication and sealing. In this embodiment, the oil reservoir 104 is positioned on top of the vacuum pump 100. The oil is supplied to the vacuum pump 100 from the oil reservoir 104 under gravity. The valve assembly 108 and the valve actuator 109 are configured to control the flow from the oil reservoir 104 to the vacuum pump 100. The valve assembly 108 will be described in more detail later below with reference to Figure 2. The valve assembly comprises a valve disposed along the oil supply line 106, for controlling the flow of the oil therethrough. The valve actuator 109 will be described in more detail later below with reference to Figure 2. The valve actuator 109 is configured to actuate the valve of the valve assembly. The valve actuator 109 is a pressure-controlled valve actuator. In this embodiment, the valve actuator 109 is coupled to a gas ballast port 128 of the vacuum pump 102 via a vacuum line 130. The gas ballast port 128 of the vacuum pump 102 is a port via which a gas ballast (such as air) may flow into the pumping chamber 112, at a certain part of the compression cycle, and allow vapours to be expelled, preferably without condensation or affecting the overall performance of the vacuum pump 100. Figure 2 is a schematic illustration (not to scale) showing further details of the valve assembly 108 and the valve actuator 109 coupled thereto. The valve assembly 108 comprises a valve assembly housing 200 through which a portion of the oil supply line 106 passes. The valve assembly housing 200 may be formed from any appropriate material, such as a metal or a plastic. Specially, the valve assembly housing 200 defines a portion of the oil supply line 106 between a valve assembly housing inlet 202 and a valve assembly housing outlet 204. The valve assembly 108 comprises a valve seat 206. The valve seat is defined along the oil supply line 106. The valve seat 206 is located between the valve assembly housing inlet 202 and the valve assembly housing outlet 204. The valve actuator 109 comprises a valve actuator housing 208, a diaphragm assembly 210, a plunger 212, a valve member 214, and a spring 215. The valve actuator housing 208 houses the diaphragm assembly 210 and a first end portion of the plunger 212. The valve actuator housing 208 is fixedly attached to the valve assembly housing 200, i.e. has fixed position relative to the valve assembly housing 200. The valve actuator housing 208 may be formed from any appropriate material, such as a metal or a plastic. The diaphragm assembly 210 is arranged within the valve actuator housing 208 to divide the valve actuator housing 208 into a first valve actuator chamber 216 and a second valve actuator chamber 218. The first valve actuator chamber 216 is defined between the diaphragm assembly 210 and a first end of the valve actuator housing 208. The first valve actuator chamber 216 is fluidly coupled to the vacuum line 130, and is thus in fluidic communication with the gas ballast port 128 of the vacuum pump 102. The second valve actuator chamber 218 is defined between the diaphragm assembly 210 and a second end of the valve actuator housing 208 opposite to the first end. The first and second valve actuator chambers 216, 218 may be substantially fluidly isolated from each other by the diaphragm assembly 210. The plunger 212 extends from the second end of the valve actuator housing 208. The plunger 212 is connected at one of its ends to the diaphragm assembly 210. The valve member 214 is attached to the other end of the plunger 212, i.e. at an opposite end to that attached to the diaphragm assembly 210. In this way, the plunger is connected to a valve 220, the valve 220 comprising the valve member 214 and the valve seat 206. The valve 220 is disposed along the oil supply line 106 between the valve assembly housing inlet 202 and the valve assembly housing outlet 204. In this embodiment, the spring 215 is disposed around the plunger 212, between the valve actuator housing 208 and the valve member 214. The spring acts to exert a biasing force against the valve actuator housing 208 and the valve member 214, to move the valve member 214 away from the valve actuator housing 208 and towards the valve seat 206. Accordingly, the valve 220 is a “normally closed valve”, that is closed when a pressure differential across the diaphragm assembly 210 (i.e., between the first and second valve actuator chambers 216, 218) is below a threshold value. In operation, when the vacuum pump 102 is pumping fluid, a pressure at the gas ballast port 128 of the vacuum pump 102 tends to be low, i.e. lower than atmospheric pressure. Thus, pressure within the first valve actuator chamber 216 is reduced, via the vacuum line 130, compared to the pressure within the second valve actuator chamber 218. Accordingly, a pressure differential is established across the diaphragm assembly 210 (i.e., between the first and second valve actuator chambers 216, 218). Once this pressure differential across the diaphragm assembly 210 exceeds the biasing force exerted on the valve member 214 by the spring 215 (i.e., the cracking pressure of the valve 216), the diaphragm assembly 210 deforms, pulling the plunger 212 further into the valve actuator housing 208 and moving the valve member 214 away from the valve seat 206. The valve 216 is thus opened, and oil is permitted to flow from the oil reservoir 104 to the vacuum pump, via the oil supply line 106. The oil travels through the valve assembly 108, between the valve assembly housing inlet 202 and the valve assembly housing outlet 204, passing through the open valve 220. In the event that the vacuum pump stops pumping fluid, a pressure at the gas ballast port 128 of the vacuum pump 102 tends to increase, e.g. approaching or becoming atmospheric pressure. Thus, pressure within the first valve actuator chamber 216 is increased, via the vacuum line 130. Accordingly, the pressure differential across the diaphragm assembly 210 is reduced. Once this pressure differential across the diaphragm assembly 210 becomes less than the biasing force exerted on the valve member 214 by the spring 215, the spring forces the valve member 214 onto the valve seat 206. The valve 220 is thus closed thereby preventing or opposing the flow of oil through the oil supply line 106. The supply of oil to the vacuum pump 102 is thus stopped. Thus, the above-described system and apparatus implements the pressure-controlled valve actuator 109 to control the valve 220 to selectively route oil to the vacuum pump 102, responsive to a pressure differential within the pressure-controlled valve actuator 109 being above or below a threshold value. The plunger 212 and valve member 214 are arranged to be positioned by the diaphragm assembly 210 in an actuating range of the valve actuator 109 as a function of a pressure differential across the diaphragm assembly 210. The first valve actuator chamber 216 is in fluidic communication with a level of vacuum within the vacuum pump 102 (via the vacuum line 130). The second valve actuator chamber 218 may be at approximately atmospheric pressure, e.g. may be communicated with atmospheric air. The diaphragm assembly 210 is configured to position the plunger 212 in the actuating range as a function of a level of vacuum communicated into the first valve actuator chamber 216. Figure 3 is a process flow chart showing certain steps of a method 300 of operating the vacuum pumping system 100. At step s302, the vacuum pump 102 is activated, i.e. is switched on. The vacuum pump 102 thus begins pumping fluid and a pressure differential within the pumping chamber 112 is thus established. Accordingly, a pressure at the gas ballast port 128 of the vacuum pump 102 is decreased below atmospheric pressure. At step s304, a level of vacuum within the vacuum pump 102 is communicated to the pressure-controlled valve actuator 109. More specifically, the level of vacuum at the gas ballast port 128 of the vacuum pump 102 is communicated to or established in the first valve actuator chamber 216, via the vacuum line 130. At step s306, the pressure-controlled valve actuator 109 controls the position of the valve 220 as a function of the communicated level of vacuum. In particular, when the level of vacuum within the first valve actuator chamber 216 is such that a pressure differential between the first valve actuator chamber 216 and the second valve actuator chamber 218 exceeds a threshold, the valve actuator 109 opens the valve 220. At step s308, the open valve 220 permits a flow of oil into the vacuum pump 102 via the oil supply line 106. At step s310, the vacuum pump 102 is deactivated, i.e. is switched off. The vacuum pump 102 stops pumping fluid and a pressure differential within the pumping chamber 112 decreases. Accordingly, a pressure at the gas ballast port 128 of the vacuum pump 102 increases towards atmospheric pressure. At step s312, a level of vacuum within the vacuum pump 102 is communicated to the pressure-controlled valve actuator 109. More specifically, the level of vacuum at the gas ballast port 128 of the vacuum pump 102 is communicated to or established in the first valve actuator chamber 216, via the vacuum line 130. At step s314, the pressure-controlled valve actuator 109 controls the position of the valve 220 as a function of the communicated level of vacuum. In particular, when the level of vacuum within the first valve actuator chamber 216 is such that a pressure differential between the first valve actuator chamber 216 and the second valve actuator chamber 218 is below the threshold, the valve actuator 109 closes the valve 220. At step s316, the closed valve 220 prevents or opposes a flow of oil into the vacuum pump 102 via the oil supply line 106. Thus, a method 300 of operating the vacuum pumping system 100 is provided. Advantageously, the above-described system and method tends to provide for simplified installation, improved reliability, reduced inventory for both manufacturing and repair / maintenance, and a reduction in cost. Advantageously, the valve actuator 109 is configured to actuate the valve 220 depending on a pressure within the vacuum pump 102 with no electrical input or manual operation by a user. The valve actuator 109 is a mechanical, selfactuated valve actuator. Advantageously, the above-described methods and apparatuses tend to eliminate a need for software-controlled valves, e.g., solenoid valves. The energy efficiency and reliability of vacuum pumping system which employ the above-described methods and apparatuses hence tends to be improved. Advantageously, the valve tends to require a reduced level of maintenance and / or servicing compared to, for example, solenoid valves. Advantageously, the valve actuator 109 is arranged such that, when the vacuum pump 102 is in operation, the valve actuator 109 automatically opens the valve 220 (caused by operation of the pump 102), thereby to allow oil to flow to the vacuum pump 102 via the oil supply line 106. Advantageously, the valve actuator 109 is arranged such that, when the vacuum pump 102 is not in operation, the valve actuator 109 automatically closes the valve 220 (caused by operation of the pump 102), thereby to prevent or oppose oil from flowing to the vacuum pump via the oil supply line. In the above embodiments, the valve actuator is in fluidic communication with the gas ballast port of the vacuum pump. Specifically, the first valve actuator chamber is arranged to be in communication with a level of vacuum at the gas ballast port via the vacuum line. Advantageously, the gas ballast port of the vacuum pump provides a convenient connection point to which to attach the valve actuator, thereby facilitating installation of the valve actuator. Moreover, during pump operation, the pressure at the gas ballast port tends to be at an intermediate level, between the relatively lower pressure level at the pump inlet and the relatively higher level at the pump outlet. This tends to provide for a balance between strength of vacuum for actuating the valve and actuator response times in the event of pump activation / deactivation. Nevertheless, in other embodiments, the vacuum line may couple the valve actuator to a different point along the pumped fluid path (i.e., different to the gas ballast port). Preferably, the vacuum line couples the valve actuator to a point within the vacuum pump swept volume between an inlet of the vacuum pump and an outlet of the vacuum pump. In some embodiments, a vacuum break may be implemented to improve actuator response times, for example in the event of pump deactivation. In the above embodiments, the vacuum pump is a rotary piston pump. However, in other embodiments, the vacuum pump is a different type of pump other than a rotary piston pump. In the above embodiments, the vacuum pump receives oil via a gravity feed. However, in other embodiments, the vacuum pump receive oil via a different mechanism, e.g. via pumping. In the above embodiments, the valve actuator comprises a spring for applying a biasing force to the valve member. However, in other embodiments, a different type of biasing means is implemented instead of or in addition to a spring. In the above embodiments, various characteristics of the valve may be selected based on known or predicted operating parameters of the vacuum pump to which oil is to be provided. Such characteristics may include, for example: plunger size; plunger weight; plunger shape; type of biasing means; the size of the biasing means; the shape and / or configuration of the biasing means; one or more elastic properties (e.g., a stiffness constant) of the biasing means; the material of the valve housing; the respective volumes of chambers within the housing; the type, shape, and / or configuration of diaphragm assembly, etc. In the description of the methods and apparatuses of the above embodiments, the terms “threshold”, “threshold value”, or “threshold pressure” is used to refer to the magnitude of the pressure differential between the first and second valve actuator chambers, which correspond to inlet pressure and ambient / atmospheric pressure respectively. However, as will be understood in context by the skilled addressee, the terms “threshold”, “threshold value”, or “threshold pressure” may also refer to the inlet pressure, i.e. the pressure in the first actuator chamber, at which the valve actuates, i.e. at which the plunger transitions the valve member between the open and closed positions. REFERENCE NUMERAL KEY 100 - vacuum pumping system 102 - vacuum pump 104 - oil reservoir 106 - oil supply line 108 - valve assembly 109 - valve actuator 110- housing 112- pumping chamber 114- piston 116- rotating shaft 118 - first chamber 120 - second chamber 122 - arrows indicating direction of movement 124-fluid inlet 126 - fluid outlet 128 - gas ballast port 130 - vacuum line 200 - valve assembly housing 202 - valve assembly housing inlet 204 - valve assembly housing outlet 206 - valve seat 208 - valve actuator housing 210 - diaphragm assembly 212 - plunger 214 - valve member 215 - spring 216 - first valve actuator chamber 218 - second valve actuator chamber 220 — valve 5 300 -method s302-s316- steps

Claims

1. A vacuum pumping system, comprising:a vacuum pump;an oil supply line for supplying oil to the vacuum pump;a valve disposed along the oil supply line; anda pressure-controlled valve actuator configured to actuate the valve.

2. The vacuum pumping system of claim 1, wherein the pressure-controlled valve actuator is configured to actuate the valve depending on a pressure within the vacuum pump.

3. The vacuum pumping system of claim 1 or 2, further comprising a vacuum line coupled between the vacuum pump and the pressure-controlled valve actuator.

4. The vacuum pumping system of claim 3, wherein the vacuum line is coupled to a pumped fluid path within the vacuum pump at a point between an inlet of the vacuum pump and an outlet of the vacuum pump.

5. The vacuum pumping system of claim 3 and 4, wherein the vacuum line is coupled to the vacuum pump at a gas ballast port of the vacuum pump.

6. The vacuum pumping system of any preceding claim, whereinthe pressure-controlled valve actuator comprises:a housing;a diaphragm assembly arranged within the housing and dividing the housing into a first chamber between the diaphragm assembly and a firstend of the housing and a second chamber between the diaphragm assembly and a second end of the housing opposite to the first end; anda plunger extending from the housing and connected to the diaphragm assembly for being positioned by the diaphragm assembly in an actuating range as a function of a pressure differential across the diaphragm assembly; andthe plunger is connected to the valve.

7. The vacuum pumping system of claim 6, wherein the first chamber isarranged to be in communication with a level of vacuum within the vacuum pump, and the diaphragm assembly is configured to position the plunger in the actuating range as a function of a level of vacuum communicated into the first chamber.

8. The vacuum pumping system of claim 6 or 7 when dependent on any of claims 3 to 5, wherein the first chamber is coupled to the vacuum line.

9. The vacuum pumping system of any preceding claim, wherein the pressure-controlled valve actuator is configured to:when the vacuum pump is in operation, open the valve thereby to allow oil to flow to the vacuum pump via the oil supply line; andwhen the vacuum pump is not in operation, close the valve thereby to prevent or oppose oil from flowing to the vacuum pump via the oil supply line.

10. The vacuum pumping system of any preceding claim, wherein the pressure-controlled valve actuator and valve are configured as a normally closed valve assembly.

11. The vacuum pumping system of any preceding claim, further comprising an oil reservoir arranged to supply oil under gravity to the oil supply line.

12. The vacuum pumping system of any preceding claim, wherein the vacuum pump is a rotary piston pump.

13. A method of operating a vacuum pumping system, the vacuum pumping system comprising a vacuum pump, an oil supply line for supplying oil to the vacuum pump, and a valve disposed along the oil supply line, the method comprising:controlling, by a pressure-controlled valve actuator, a position of the valve thereby to control a flow of oil into the vacuum pump via the oil supply line.

14. The method of claim 13, further comprising:communicating a level of vacuum within the vacuum pump to the pressure-controlled valve actuator; andcontrolling, by the pressure-controlled valve actuator, the position of the valve as a function of the communicated level of vacuum.

15. The method of claim 14, wherein the level of vacuum within a gas ballast port of the vacuum pump is communicated to the pressure-controlled valve actuator.

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