FR2863322A3 - PUMPING DEVICE COMPRISING MEANS FOR CONTROLLING THE STATUS OF THE SEAL SEALS OF THE ASPIRE VOLUME - Google Patents

Abstract

Pumping device in which a duct supplies a flow of gas to a sealed chamber surrounding the volume drawn from a pump. The conduit includes a flow restrictor to limit the flow of gas to the sealed chamber. Signals sent by pressure transducers present on either side of the flow restrictor are used to detect gas leakage from the sealed chamber to the pump suction volume, thus indicating the condition of the seal. sealing surrounding the aspirated volume.

Description

PUMPING DEVICE

  The present invention relates to pumping devices. BACKGROUND OF THE INVENTION The present invention relates to pumping devices.

  Vacuum pumps are known which are oil-free in their vacuum chambers and are therefore useful in clean environments such as those existing in the semiconductor manufacturing industry. In this type of environment, if lubricant materials were present in the vacuum chamber, these materials could potentially retro-migrate into the semiconductor processing chamber and, in doing so, could cause contamination of the product being processed. Manufacturing. These "dry" vacuum pumps are often multi-stage volumetric pumps using rotors meshing in the vacuum chamber of each stage of the pump. The rotors can have the same type of profile in each chamber, or the profile can change from one chamber to another.

  Whether in a Roots, Screw or Northey ("Claw") type device, each chamber is typically defined by two separately machined pump stator elements, with the pump rotor elements located in the cavity defined between the stator elements. It is necessary to provide a seal between the stator elements so as both to prevent leakage of the process gas ("process" gas) sucked from the cavity and to prevent ambient air from entering the chamber. cavity. An O-ring seal is typically provided for accomplishing this sealing function. This type of seal is, in a typical manner, made of fluoroelastic material, such as for example Viton.

  Dry vacuum pumps are frequently used in applications where they are required to pump large quantities of corrosive fluids, especially halogenated gases and solvents. These materials attack the O-rings, resulting in these seals becoming excessively plastic or brittle, which can seriously affect the integrity of the seal between the stator members.

  The intensity of the attack on the seal depends on several variables, among which, for example, the nature of the pumped fluid, the material in which the O-ring is made, and the temperature of the pump. In view of this, it is very difficult to predict the appropriate interval to replace the seals and thus maintain the integrity of the pump. External inspection of joints is rarely practical.

  These problems are particularly acute when pumping reactive gases, such as fluorine, from semiconductor production equipment, where the gaseous compositions are modified by reactions in the equipment. In this case, even a precise knowledge of the gaseous flows admitted into the manufacturing chamber allows only very poor predictions on the quantity or the nature of the reactive gas entering the pump and therefore on the expected service life for the seal. Maintenance recommendations often include frequent leak checks at the joint, but this is expensive, inconvenient and therefore these recommendations are often ignored.

  In the principles, other types of sensors could be used to try to measure the integrated exposure level of the joints and, therefore, the state of the joints. For example, a spectroscopic or chemical technique could be used to measure the composition of the gas. However, these techniques would require complex calibration procedures and would be expensive to implement.

  In at least its preferred embodiment, the present invention seeks to solve these and other problems.

  The present invention provides a pumping device comprising a pump suction volume, a hermetic chamber surrounding the aspirated volume, a conduit for supplying a fluid to the chamber, the conduit including a flow restrictor to limit the flow of fluid to the chamber. the chamber, and means for determining a pressure difference across the flow choke.

  Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front view of a stator member showing a seal assembly; sealing; Figure 2 is a side view of the seal assembly of Figure 1; Figure 3 illustrates a device for monitoring the integrity of the seal assembly; and Figure 4 is a graph showing the variation over time of the pressure of a gas in the seal assembly.

  Figure 1 illustrates the surface 3 of a stator element 1 of an exhaust stage of a dry pump. A surface of a second stator element (not shown) is brought into contact with the corresponding surface 3 of the stator element 1 and a cavity 2 is formed between the adjacent stator elements. This cavity 2 is provided to receive the rotor element (not shown) of the pump when the pump is assembled, and is generally called the suction volume of the pump. A dry pump typically comprises a plurality of these cavities, each cavity 2 communicating with an adjacent cavity through an orifice 4.

  A first sealing O-ring 5 is placed around the periphery of the cavity 2. The O-ring 5 is preferably formed from a fluoelastomer material, such as Viton, and provides fluid sealing between adjacent stator members, such that when the pump is used, the process or cleaning gases pumped through the cavity 2 can not escape from the cavity 2, and the However, as discussed above, these gases can be particularly aggressive and can easily damage many parts of the pump. Typically, the O-ring seal 5 is the first component to be damaged in such circumstances. In consideration of this, a second O-ring 6, similar to the first O-ring 5, is placed between the first O-ring 5 and the periphery of the recess 2. O-rings 5, 6 are separated by a groove or shallow channel 7 formed between grooves 8, 8a used to position the sealing o-rings 5, 6 between the adjacent stator members, these grooves being shown in FIG. channel 7 allows a small amount of fluid, for example a gas such as nitrogen, to be trapped between the two adjacent stator members and the O-rings 5, 6, which together define a hermetic chamber for the gas . The gas enters the channel 7 through the orifice 7a of a gas tank, as indicated at 16 in FIG. 3, via a duct 9.

  As shown in Figure 3, the conduit 9 includes a flow restrictor 10 and a check valve 11. Two pressure transducers 12, 13 are placed in fluid communication with the respective ends of the flow restrictor.

  The flow restrictor may be made of a slightly porous sintered material which blocks a flow of gas so that when the flow restrictor is placed in the conduit 9, it acts in the manner of a dam, allowing only an infiltration of gas to cross it. The flow choke could alternatively be in the form of a fine metering valve, or creating a fine capillary hole through a solid material.

  The check valve 11 prevents contamination of the supply tank in the event that the pressure in the pump rises above that of the gas supply. The valve 11 also serves to minimize the pressure fluctuations in the conduit 9 downstream of the valve 11 in the event that the gas supply is temporarily interrupted or otherwise affected.

  The pressure transducers 12, 13 respectively measure the pressure P2 and P 1 in the duct 9, on either side of the flow restrictor 10, and send signals indicating the measured pressure to a controller 14.

  The supply of gas to the duct 9 is controlled by a gas module 15. In this assembly, the gas module 15 is an active manifold which regulates the supply of gas from the tank into the duct 9. The gas module 15 is configured to send a signal to the controller 14 to give an indication of one or more characteristics, such as flow rate and pressure, of the gas supplying the conduit 9. This type of gas module may be used to dispense gas at different locations in the pump, for example if the gas is to be used as a purge gas to drive off impurities from the pump.

  In use, the pressurized gas (typically about 6 psi) is fed into the conduit 9, passes through the flow restrictor, and enters the channel 7 until a pressure balance is reached. is established between the gas upstream of the flow restrictor and the gas downstream of the flow restrictor. Due to the presence of pressurized gas in the channel 7 downstream of the flow restrictor, during the use of the pump a significant pressure difference will be experienced from side to side of the O-ring. 6, because the gas pumped into the cavity 2 (the volume drawn from the pump) will be sub-atmospheric (typically 800 mbar) when the pump is under normal operating conditions in steady state. In this situation, when the second O-ring 6 is new and has no faults, the signals emitted from the pressure transducers 12, 13 will be approximately equal and non-fluctuating. However, in the event that the second O-ring 6 is damaged by the pumped gas to the point that the physical integrity of the second O-ring 6 is adversely affected, pressurized gas may begin to escape. from the channel 7 to the cavity 2 due to the presence of a gas under relatively high pressure in the channel 7 and a gas under relatively low pressure in the cavity 2, this leak attempting to equalize these pressures. Due to the presence of the flow restrictor in the conduit 9, the pressure P2 measured by the pressure transducer 12 will begin to fall, as shown in FIG. 4, while the pressure P1 measured by the pressure transducer will stay at the supply pressure. The difference between the pressures P 1 and P2 is therefore an indication of a gas leak in the cavity 2, and is therefore indicative of a failure of the second O-ring seal 6. This may allow the controller 14, which receives the signals sent by the pressure transducers 12, 13, to emit an alarm, for example by means of a screen, indicating the failure of the second O-ring 6 if the pressure difference exceeds a predetermined value.

  The device described above can thus provide a reliable indication of the state of the essential seals within a pump. This indication can increase the intervals for maintenance and reduce operating costs without intrusive intervention. As the predictability of the deterioration of these critical components can be improved, the probability of potentially hazardous leakage is therefore decreased.

  In summary, a conduit supplies a flow of gas to an airtight chamber surrounding the suction volume of a pump. The conduit includes a flow restrictor to limit the flow of gas to the sealed chamber. Signals sent by pressure transducers present on either side of the flow restrictor are used to detect gas leakage from the sealed chamber to the pump suction volume, thereby indicating the state of the gasket. sealing around the aspirated volume.

Claims (12)

  A pumping device, comprising an aspirated pump volume (2), an airtight chamber (7) surrounding the aspirated volume (2), a conduit (9) for supplying fluid to the chamber, the conduit including a choke (10). ) to restrict the flow of fluid to the chamber, and means (12, 13, 14) for determining a pressure difference across the flow restrictor.   A pumping device as claimed in Claim 1, wherein the choke (10) is provided with a narrowing within the conduit.   A pumping device as claimed in Claim 1 or Claim 2, wherein the flow of fluid on either side of the choke (10) is such that fluctuations in fluid pressure on one side of the choke (10) are not rapidly transmitted to the fluid on the other side of the choke (10).   A pumping device according to any one of the preceding claims, wherein the choke (10) is a member selected from the group consisting of a porous sintered material, a capillary formed in a non-porous locking member, and a valve .   The pumping device according to any one of the preceding claims, wherein the means for determining the pressure difference comprises at least one pressure transducer (12, 13).   A pumping device according to Claim 5, wherein said at least one pressure transducer (12,13) comprises a first pressure transducer (13) configured to output a signal indicative of a fluid pressure in the upstream conduit. a choke (10) and a second pressure transducer (12) configured to output a signal indicative of a fluid pressure in the conduit downstream of the choke (10).   A pumping device as claimed in Claim 6, comprising a controller (14) for receiving signals from the first pressure transducer (13) and the second pressure transducer (12) and generating a difference alert. between the fluid pressures indicated by the signals.   The pumping device according to Claim 7, wherein the alert is generated when the pressure difference across the choke (10) exceeds a predetermined value.   A pumping device according to any one of the preceding claims, wherein the conduit (9) is connected to a reservoir for a fluid supply.   The pumping device of claim 9, wherein the reservoir is configured to supply a purge gas to a pump on the pumping device.   A pumping device according to any one of the preceding claims, wherein the hermetic chamber is defined in part by two O-rings (5, 6).   The pumping device according to Claim 11, wherein the sealing O-rings (5, 6) are made of an elastomeric material.