Oil lubricated vacuum pump with improved oil seal

Abstract

An oil lubricated vacuum pump with an improved oil seal is provided. A vacuum pumping system (100) includes an oil-lubricated rotary vacuum pump (20), an electric motor (30) driving the pump, and a gas ballast device supplying gas to the pump (20) and fluidly coupled with the motor (30) to draw back oil leaking from the pump (20) into the motor (30) into the pump (20). The fluid coupling is effected by a leaked oil recovery unit (50) housed in the region of the inner cavity of the motor (30) in which ballast gas and leaked oil are present, and which establishes communication between the region of the inner cavity of the motor and the pumping chamber.

Description

Technical Field

[0001] The present invention relates to vacuum pumping systems, and more particularly, to a vacuum pumping system of an oil-lubricated rotary vacuum pump having an improved oil seal. Background Art

[0002] A vacuum pump is used to achieve a vacuum state, i.e. to evacuate a chamber (the so-called "vacuum chamber") and to establish a subatmospheric pressure state in said chamber. Many different types of vacuum pumps are known, having different structures and operating principles, and the specific vacuum pump is selected each time depending on the requirements of the specific application, i.e. on the vacuum degree to be achieved in the respective vacuum chamber.

[0003] Typically, a vacuum pump comprises a pump housing, in which one or more pump inlets and one or more pump outlets are provided, and a pumping element arranged in the pump housing and configured to pump gas from the pump inlet to the pump outlet: by connecting the pump inlet to a vacuum chamber, the vacuum pump allows the gas in the vacuum chamber to be evacuated, thereby creating a vacuum condition in the chamber.

[0004] In a vacuum pump, the pumping element comprises a stator defining a pumping chamber and a rotor rotatable in the pumping chamber and cooperating with the stator to pump gas from a pump inlet to a pump outlet. In such a vacuum pump, the rotor is typically mounted to a rotating shaft driven by an electric motor.

[0005] Such pumps are usually connected to an oil tank, whereby oil can be delivered from the tank to the vacuum pump, in particular to the pumping chamber, for acting as a coolant and lubricating fluid and for sealing the chamber, and for protecting the pump components from possible corrosive effects of the gas being pumped. Among such systems, those using a rotary vane vacuum pump may be mentioned, and the following description will relate to such a system.

[0006] A conventional vacuum pumping system using an oil lubricated rotary vane vacuum pump is shown in FIG. 1 and generally indicated at 10 .

[0007] The pumping system 10 mainly comprises the actual vacuum pump 20 and an electric motor 30 for driving the pump 20. For the sake of simplicity, only the part of the pump 20 adjacent to the motor 30 is shown.

[0008] The pump 20 comprises a pump housing 21 in which one or more pump inlets and one or more pump outlets (not shown in the figure) are defined. The pump housing 21, which also serves as a pump stator, internally defines a pumping chamber in which a pump rotor 23 rotates eccentrically. The rotor 23 is fastened to or integral with a pump shaft 24 driven in rotation by a motor 30 and is provided with one or more radially sliding blades 25 (only one is visible in the figure) which move in contact with the inner wall of the pumping chamber during the rotation of the rotor. As is known, in pumps of this type, oil is introduced into the pumping chamber to lubricate and cool the pump and to separate areas at different pressures.

[0009] In case the pump is provided with a gas ballast arrangement, a further inlet (also not shown in the figures) is defined in the pump housing 21 for introducing ballast gas (typically air) into the pumping chamber.

[0010] The motor 30 in turn comprises a housing 31 which is fastened to the pump housing 21 and which encloses a motor stator 32 and a motor rotor 33. The motor stator 32 and the motor rotor 33 cooperate with each other so as to drive the pump rotor 23 in rotation via a drive shaft 34 associated with the motor rotor 33. The drive shaft 34 may be coupled to the pump shaft 24, or it may be made as an integral unit with the pump shaft 24 and the pump rotor 23, as shown. End walls 35, 36 close the chamber accommodating the motor rotor 33 and rotatably support the ends of the shaft 34 in association with suitable rolling bearings.

[0011] In order to prevent oil and possibly toxic gases present in the pumping chamber from entering the motor 30 and escaping to the environment through the motor housing 31, a dynamic radial seal 40, typically a lip seal, is provided around the shaft 34 between the motor housing 31 and the pump housing 21. The dynamic seal is also intended to prevent dust from entering the pumping chamber.

[0012] In the case of rotary vane vacuum pumps, dynamic seals are the main cause of oil leakage during pump operation. Oil leakage is obviously undesirable, since the resulting reduction in the amount of oil in the pumping chamber may impair the effectiveness of the oil action. In addition, as mentioned above, the oil may contain toxic gases, which may become a source of pollution and danger if they escape into the environment through the motor housing 31.

[0013] EP 1249648 B1 discloses an improved radial lip seal for a rotating shaft, the surface profile of which is configured to allow leaked fluid to be transported back to the space to be sealed when the shaft rotates. The improved seal disclosed in this prior art document has a complex structure, making it quite expensive. In addition, there is no provision for handling the fluid that is not transported back to the space to be sealed.

[0014] EP 714482 B1 discloses an oil-lubricated rotary vane vacuum pump with gas ballast, in which oil collected from an oil separator arranged downstream of the pump outlet is returned to the pump through a gas ballast inlet. The pump has a sealing ring that seals the pump shaft relative to the bearing member, but it has no provisions for dealing with possible oil leakage from the pumping chamber, so it cannot ensure that the pumping module is completely sealed. Summary of the invention

[0015] An object of the present invention is to provide a vacuum pumping system that solves the above-mentioned problems of the prior art.

[0016] Another object of the present invention is to provide a vacuum pumping system with an oil-lubricated rotary vacuum pump equipped with means for dealing with oil leakage from the pumping chamber in a simple and effective manner.

[0017] More specifically, the present invention provides a vacuum pumping system comprising an oil-lubricated rotary vacuum pump, an electric motor driving the pump, and a gas ballast device supplying gas to the pump, wherein the gas ballast device is fluidly coupled to the motor to draw oil leaking from the pump into the motor back into the pump.

[0018] The gas ballast device is configured to provide permanent gas ballast.

[0019] Advantageously, the gas ballast device is fluidically coupled to the motor via a leakage oil recovery unit, the leakage oil recovery unit being housed in the region of the inner cavity of the motor in which gas and leakage oil from the gas ballast device are present, and the leakage oil recovery unit being arranged to establish communication between said region of the inner cavity of the motor and the pumping chamber. This region also faces a dynamic radial seal which prevents the oil present in the pumping chamber from passing to the motor.

[0020] In a preferred embodiment of the present invention, the leakage oil recovery unit comprises a pipe having a first end adjacent to the seal and a second end cooperating with a non-return valve, the non-return valve being interposed between said second end of the pipe and the pumping chamber and being configured to allow the oil collected by the pipe to pass to the pumping chamber together with the ballast gas when the pump is turned on and to prevent the oil from leaking towards the motor when the pump is turned off.

[0021] Advantageously, the non-return valve is a ball-spring valve.

[0022] According to another advantageous feature of the invention, the non-return valve is received in a seat, a section of which is formed with a calibrated orifice regulating the flow of ballast gas directed to the pumping chamber and serving as a gas inlet for the pumping chamber.

[0023] In an embodiment of the invention, a non-return valve is associated with said second end of the conduit and a section of the valve seat having a calibrated orifice is formed between the valve and the pumping chamber and opens directly into the pumping chamber.

[0024] In an alternative embodiment, a section of the valve seat having the calibrated orifice is formed between the second end of the conduit and the check valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Preferred embodiments of the invention given by way of non-limiting examples will be described below with reference to the accompanying drawings, in which:

[0026] FIG1 is a longitudinal sectional view of a portion of a prior art pumping system;

[0027] Figure 2 is a perspective view of a pump used in a pumping system according to the present invention, wherein a leakage oil recovery unit is assembled in its operating position;

[0028] Figure 3 is with Figure 2 a similar view with the spill oil recovery unit disassembled; and

[0029] Figure 4 and Figure 5 Enlarged cross-sectional views of the leakage oil recovery unit with the pump on and off, respectively.

[0030] exist Figure 2-Figure 5 1 , the same reference numerals as in FIG. 1 are used to denote identical or functionally equivalent elements. DETAILED DESCRIPTION

[0031] Reference now Figure 2-Figure 5 The present invention is applicable to vacuum pumping system 100 equipped with gas ballast device, especially device providing permanent gas ballast, for reasons explained below. According to the present invention, gas ballast device is fluidly coupled with motor 30 to suck oil leaking from pump 20 into motor 30 back into pump 20.

[0032] The gas ballast arrangement is completely conventional and is therefore not shown in these figures. Furthermore, the motor structure is not affected by the present invention and therefore, for simplicity, only the drive shaft 34 with the seal 40 is shown in the figures.

[0033] Fluid coupling is achieved by a leakage oil recovery unit 50 located in the region of the inner cavity of the motor 30 housing the rotor, facing the seal 40 and receiving oil that may leak from the pumping chamber. In addition, gas, typically air, supplied by a gas ballast device is also present in this region.

[0034] The unit 50 comprises a duct 51 establishing communication between the area and the pumping chamber. One end of the duct 51 is arranged adjacent to the seal 40 and the other end is connected to a non-return valve 52 mounted in a support 53 received in a seat 54 formed with a calibrated orifice 55 for regulating the air flow directed to the pumping chamber and serving as an inlet for directing such air into the pumping chamber. In the embodiment shown, the section of the valve seat 54 with the orifice 55 is located between the valve 52 and the pumping chamber, and the orifice 55 opens directly into the pumping chamber.

[0035] like Figure 4 and Figure 5 As shown, the check valve 52 is advantageously of the ball-spring type and is configured to close when the pump 20 is opened ( Figure 4 ) allows the air and oil collected by the pipe 51 to pass to the pumping chamber and when the pump 20 is closed ( Figure 5 ) prevents oil from leaking toward the motor 30. The path of the combined flow of air and oil through the unit 50 to the pumping chamber is as follows Figure 4 As shown by the arrow X in FIG.

[0036] A valve seat 54 with a calibrated orifice 55 is mounted or machined directly in a wall 56 separating the pumping chamber from the region of the interior cavity of the motor 30 .

[0037] By the disclosed arrangement, when and only when the dynamic seal 40 starts to lose oil, the conduit 51 drives the leaking oil together with the ballast air, first through the check valve 52 , then through the calibrated orifice 55 , and finally directly into the vacuum pump 20 .

[0038] This occurs automatically, taking advantage of the vacuum obtained in the pump 20, which creates a pressure difference that causes the leaking oil to be sucked back. This suction is achieved by a continuous flow of ballast air, which is absolutely necessary for the operation of the unit 50, since the pressure in the area of ​​the oil leak is not sufficient to guarantee a pressure difference that allows the oil to be sucked back. The oil is thus collected in a collecting bowl 57 connected to the end of the pipe 51 adjacent to the seal 40, and it can then be sucked back into the pumping chamber through a ballast channel that is appropriately designed to open a zone in which the pressure obtained in the pump is able to allow the process of the invention.

[0039] The invention thus provides a simple and therefore cost-effective means for ensuring complete sealing of the pumping chamber to prevent oil leaks. No special work is required to arrange the oil recovery unit 50 in the pumping system 100, since the existing inlet for the ballast gas is used to reintroduce the recovered oil into the pumping chamber. Making the existing ballast gas inlet also used to reintroduce the recovered oil into the pumping chamber, in addition to contributing to cost-effectiveness, has the advantage of being particularly suitable for retrofitting.

[0040] Of course, while remaining unchanged the principle of the invention, the structural details may vary widely with respect to what has been described and illustrated purely by way of non-limiting example, without departing from the scope of the invention as defined in the following claims.

[0041] For example, the positions of the check valve 52 and the calibrated orifice 55 may be reversed relative to the positions shown in the drawings. Regardless of the arrangement, ballast air can pass through the valve 52 to the pumping chamber when a certain pressure differential is established by the pump 20, which causes compression of the spring of the valve 52 and displacement of the ball, thereby opening the passage for air to pass.

[0042] The invention has been described with reference to preferred embodiments. However, it will be appreciated that variations and modifications may be effected by those skilled in the art without departing from the scope of the invention.

Claims

1. A vacuum pumping system (100) comprising an oil-lubricated rotary vacuum pump (20), an electric motor (30) for driving the pump (20) and a gas ballast device for supplying gas to the pump (20), characterized in that: The gas ballast device is fluidly coupled to the motor (30) to draw oil leaking from the pump (20) into the motor (30) back into the pump (20).

2. The vacuum pumping system (100) according to claim 1, wherein: The gas ballast device provides permanent gas ballast.

3. The vacuum pumping system (100) according to claim 1 or 2, wherein: The gas ballast device is fluidically coupled to the motor (30) via a leakage oil recovery unit (50), the leakage oil recovery unit (50) being accommodated in an area of ​​an inner cavity of the motor (30), gas and leakage oil from the gas ballast device being present in the area of ​​the inner cavity of the motor, and the leakage oil recovery unit (50) being arranged to establish communication between the area of ​​the inner cavity of the motor and a pumping chamber of the pump (20).

4. The vacuum pumping system (100) according to claim 3, wherein: The area of ​​the inner cavity of the motor (30) faces a dynamic radial seal (40) intended to prevent the passage of oil from the pump (20) to the motor (30).

5. The vacuum pumping system (100) according to claim 3 or 4, wherein: The leakage oil recovery unit (50) comprises a pipe (51) having a first end adjacent to the seal (40) and a second end cooperating with a check valve (52), the check valve being interposed between the second end of the pipe (51) and the pumping chamber and being configured to allow air and oil collected by the pipe (51) to pass to the pumping chamber when the pump (20) is turned on and to prevent oil from leaking toward the motor (30) when the pump (20) is turned off.

6. The vacuum pumping system (100) according to claim 5, wherein: The check valve (52) is a ball-spring valve (52).

7. The vacuum pumping system (100) according to claim 5 or 6, wherein: The check valve (52) is received in a valve seat (54), a section of which is formed with a calibrated orifice (55) which regulates the flow of ballast gas directed to the pumping chamber and acts as a gas inlet for the pumping chamber.

8. The vacuum pumping system (100) according to claim 7, wherein: The non-return valve (52) is associated with the second end of the conduit (51), and the section of the valve seat (54) is formed between the valve (52) and the pumping chamber and opens directly into the pumping chamber.

9. The vacuum pumping system (100) according to claim 7, wherein: The section of the valve seat (54) is formed between the second end of the pipe (51) and the valve (52).

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