US3406897A

US3406897A - Mechanical vacuum pump

Info

Publication number: US3406897A
Application number: US565885A
Authority: US
Inventors: Diels Karl Gustav Kurt
Original assignee: Leybold Holding AG
Current assignee: Leybold Holding AG
Priority date: 1966-07-18
Filing date: 1966-07-18
Publication date: 1968-10-22
Anticipated expiration: 1985-10-22

Description

Oct. 22, 1968 K. c. K. DIELS MECHANICAL VACUUM PUMP Filed July 18. 1966 INVENTOR:

16/! Qatar Zfzrz .Dz'ds United States Patent ABSTRACT OF THE DISCLOSURE A valve for closing the inlet passage of the vacuum pump includes a piston-like closure member which extends into the inlet passage to engage an annular valve seat, The closure end of the piston member is exposed to the pressure at the outboard side of the valve seat; and the opposite end of piston member is exposed to the pressure in a control chamber. The control chamber communicates with atmosphere through a vent passage; and the clearance space between the piston-like member and its bore defines a restricted flow path communicating the control chamber and the inlet passage at the inboard side of the valve seat. A valve member for closing the vent passage is biased to the open position and is closed by an electromagnetic actuator. The electric drive motor for the pump and the electromagnetic actuator are energized and deenergized simultaneously. When the pump motor is deenergized, differential pressure across the inlet valve effects closing of the valve and the pump chamber'is vented to atmosphere.

This invention relates generally to mechanical vacuum pumps and more particularly to a mechanical vacuum pump having an intake passage which is automatically closed in response to deenergization of the pumps rotor assembly.

Isolating valves are frequently connected between a vacuum pump and the vacuum system which it is evacuating. =During operation of the pump the valve is in an open position permitting gas communication between the vacuum system and the vacuum pump but upon deactivation of the vacuum pump, the valve is closed to isolate the vacuum system from the pump. Because of this isolation, vacuum pressure can be retained in the system despite the pressure rise which occurs within the pump itself after deactivation. The isolating valve also provides the useful function of preventing oil contamination of the systemchamber during the inactive period of the pump. This contamination can result from either the flow of oil vapor between the pump chamber and the system chamber or by actual oil creepage along the inner surfaces of the vacuum lines connecting these parts.

- Frequently, however,-a mechanical vacuum pump will become inadvertently deactivated because of, for example, power failure, bearing failure, etc. In such cases a manually operated isolating valve may not be closed and the above described contamination of the vacuum system will occur. To alleviate this problem various types of automatic isolating valves have been proposed. These include, for example, bellows controlled valves which oper ate directly in response to the pressure within the pump chamber, mechanically actuated valves indirectly responsive to the pressure within the pump chamber, flotation valves responsive to a rising oil level, etc.

All of the known automatic isolating valves, in addition to being somewhat unreliable, have suffered two major disadvantages. Because they are designed for connect-ion between the vacuum system and the pumps intake port, they are inherently space consuming, costly to build and install, and relatively complicated to control, Furthermore, prior automatic isolating valves have failed to eliminate one of the more serious problems associated with either inadvertent or controlledvacuum pump deactivation. This problem arises becauses upon deactivation of the pump rotor a reduced pressure will exist in the pumping chamber and in the pumps intake passage while an atmospheric pressure normally exists above the oil in the pumps oil reservoir. Because of the pressure differential, an undesirable migration of oil can occur from the oil reservoir, through the clearances between the pumps rotor and stator parts and into the pumping chamber and intake passage.

The object of this invention, therefore, is to provide a mechanical vacuum pump which will be automatically and effectively isolated from a connected vacuum system upon either inadvertent or regulated deactivation of the pump.

One feature of this invention is the provision of a mechanical vacuum pump having a solid pump body which defines a pump chamber, an intake passage and a discharge passsage; and an isolating valve positioned in the pumps intake passage and adapted to automatically close the intake passage in response to deenergization of the pumps rotor assembly and to open the intake passage in response to energization thereof.

Another feature of this invention is the provision of a mechanical vacuum pump of the above feature type wherein the pumps intake passage is bifurcated to form axially aligned branch passages, one of which accommodates the stem of the isolating valve and the other of which accommodates the isolating valve seat and communicates with the pumps intake port.

Another feature of this invention is the provision of a mechanical vacuum pump of the above featured types wherein the dimensions of the valve stem and accommodating branch passage are such as to provide a slide fit therebetween thereby permitting the attainment of transient differential pressures on opposite ends of the valve stem.

Another feature of this invention is the provision of a mechanical vacuum pump of the above featured types including a vent passage which provides gas communication between atmosphere and the end of the valve stem which is opposite the point of intake passage bifurcation.

Another feature of this invention is the provision of a mechanical vacuum pump of the above featured types including a control valve adapted to close the vent passage in response to energization of the pumps rotor assembly and to open the vent passage in response to deenergization thereof.

Another feature of this invention is the provision of a vacuum pump of the above featured types wherein a gas communication path is provided between the vent passage and the pump chamber so as to induce venting thereof upon opening of the control valve.

Another feature of this invention is the provision of a vacuum pump of the above featured types wherein the control valve comprises an electromagnetic actuator which is connected so as to be energized and deenergized simultaneously with the electric motor which drives the pumps rotor assembly.

These and other objects and features of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawing which is a cross-sectional view of a preferred embodiment of the-invention.

Referring now to the drawing there is shown the rotary mechanical vacuum pump 11 supported by the pump stand 12. The pump includes the oil reservoir housing straddled by the pump body 15 and the electric drive motor 14. A central bore 16 through the pump body 15 serves as a pumping chamber which communicates with the intake passage bore 17 and the discharge passage bore which extends into the oil reservoir housing 13. The intake passage 17 is bifurcated into the axially aligned valve branch passage 19 and the intake branch passage 21 which terminates at the intake port 22. Positioned Within the pump chamber 16 is the conventional rotor assembly 23 including the spring loaded vanes 24 which project into contact with the inner surface of the pump chamber. The rotor assembly 23 is attached for rotation with the drive shaft 25 which extends through the reservoir housing 13 and is connected to the electric drive motor 14.

Located in the intake passage 17 is an isolating valve including the annular valve seat 26 mounted in the intake branch passage 21 and the cylindrical valve stem 27 positioned in the cylindrical valve branch passage 19. A small annular clearance 28 is provided between the outer surface of the valve stem 27 and the inner surface of the valve branch passage 19. The clearance 28 permits reciprocal movement of the valve stem 27 within the valve passage 19, in addition to providing a gas communication path, the purpose of which is described below. It is important, however, for reasons also described below, that the clearance 28 be small enough to permit at least transient pressure differentials on opposite sides of the valve stem 27.

Movement of the valve stem 27 is produced by the valve actuator 31 having the electromagnetic actuator 32 and the armature 33. The armature 33 functions as a control valve having the recess 30 which seats against the end of the cylindrical plug 34 to cover an axial passage 35 therein. The tension springs 36, bias the armature 33 away from the plug 34 and into contact with the electromagnet 32. Extending between the outer surface of the pump body and one end of the valve passage 19 is the vent passage bore 37. The plug 34 projects into and seals the vent passage 37 from atmosphere except for the gas communication path provided by the axial passage 35. Energization for the electromagnet 32 is provided by the electrical leads 38 connected in parallel with the electrical windings (not shown) of the drive motor 14.

After energization of the electric drive motor 14, the rotor assembly 23 will be actuated and the parallel connected electromagnet 32 energized. The magnetic field produced by the electromagnet 32 is adapted to repel the armature 33 against the biasing force of the springs 36. This movement causes the end of the plug 34 to extend into the recess 30 and seat against armature 33 thereby sealing the axial passage 35. At the same time, the rotational movement of the rotor assembly will produce the familiar pumping action wherein gas from the inlet passage 17 is compressed within the pump chamber 16 and discharged through the discharge passage 18 into the oil reservoir housing 13 for ultimate discharge into the atmosphere via the discharge port 39. This pumping action will reduce the pressure in the intake passage 17 and thereafter in the lower portion of the valve passage 19 because of the limited conductance path provided by the clearance 28. When the pressure in the lower portion of the valve passage 19 is reduced to a value below that in the intake branch passage 21 the valve stem 27 will be forced downwardly out of contact with the valve seat 26 and providing gas communication between the pump chamber 16 and the inlet port 22. Continued operation of the rotor assembly 25 will remove gases in the conventional manner from a vacuum chamber (not shown) connected to the inlet port 22.

Upon interruption of power to the electric motor 14 because of, for example, manual opening of the energizing switch, automatic opening of an over-load responsive breaker, interruption of power from the mains, etc., the rotor assembly 25 will be deactivated and the parallel connected electromagnetic 32 deenergized. The resultant elimination of the magnetic field provided by the electromagnet 32 causes the armature 33 under the biasing force of the springs 36 to move out of contactwith the plug 34 thereby exposing the axial passage 35 to the atmosphere. This produces an atmospheric pressure in both the vent passage 37 and the lower portion of the valve passage 19 and a transiently lower pressure in the intake passage 17 above the valve stem 27 because of the limited conductance exhibited by the clearance 28. Accordingly, the valve stem 27 will be forced upwardly into seating engagement with the valve seat 26 to thereby seal off the inlet port 22. In this way the interior of the vacuum chamber (not shown) connected to the inlet port 22 will beisolated from the pump chamber 16.

In addition, the leakage which occurs through the clearance 28 eventually produces atmospheric pressure Within both the intake passage 17 and the pump chamber 16. Thus, any differential pressure between the pump chamber 16 and the atmospheric pressure above the oil in the oil reservoir 13 is eliminated and creepage of oil through the clearances between the vanes 24 and the pump body 15 into the pump chamber 16 and intake passage 17 is reduced. Upon subsequent reenergization of the electric motor 14, the electromagnet 32 will again be energized to close the axial passage 35 and the valve stem 27 will move downwardly to open the intake branch passage 21, as described above.

Thus, the present invention provides a mechanical vacuum pump which includes as an intregal part thereof a valve which automatically isolates a connected vacuum chamber in response to deactivation of the pump. This is accomplished without connection of any additional accessories between the pump and the connected vacuum chamber. In addition, the invention provides for automatic venting of the intake passage and pump chamber in response to pump deactivation. 6

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A mechanical vacuum pump comprising:

a housing defining a pump chamber, inlet and discharge passages communicating with said pump chamber, and a control chamber, the outboard end of said inlet passage being adapted for communication with a chamber to be evacuated; a pump rotor in said pump chamber adapted to be coupled to a suitable drive motor;

an inlet passage closure for selectively opening and closing said inlet passage between its outboard end and said pump chamber; a reciprocable, pressure actuated control member for actuating said inlet valve closure; said control member having a first pressure surface exposed to the pressure in said inlet passage on the outboard side of said inlet valve closure, and having a second opposing pressure surface exposed to the pressure in said control chamber;

vent passage means for venting said control chamber to atmosphere; restricted flow passage means communicating said control chamber and said inlet passage on the pump chamber side of said inlet passage closure, said restricted flow passage means permitting transient pressure differences between said control chamber and said inlet passage;

valve means for selectively opening and closing said control chamber vent passage means; and means for closing said vent valve means in response to rotation of the pump rotor, and for opening said vent valve means in response to cessation of rotation of the rotor.

2. A mechanical vacuum pump as set forth in claim 1:

said means for closing said vent valve means comprising an electromagnetic actuator which is energized in response to rotation of the pump rotor to close said valve means and which is deenergized in response to cessation of rotation of the rotor to effect opening of said valve means.

3. A mechanical vacuum pump as set forth in claim 2:

an electric drive motor for driving the pump rotor; and means for energizing and deenergizing said electric drive motor and said electromagnetic actuator simultaneously.

4. A mechanical vacuum pump as set forth in claim 1:

said control member comprising a piston-like member disposed for reciprocating sliding movement in a housing bore providing a small clearance between said piston-like member and said bore; said bore opening at one end to said inlet passage and at the other end to said control chamber; and said pistonlike member including said inlet valve closure.

5. A mechanical vacuum pump as set forth in claim 4:

said inlet passage defining an annular valve seat; said inlet valve closure being engaged with said valve seat to close said inlet passage; and said valve closure, in the seated position, presenting a pressure surface exposed to the pressure in said inlet passage on the outboard side of said inlet valve seat.

6. A mechanical vacuum pump as set forth in claim 4-:

said clearance between said piston-like member and said blower defining said restricted flow passage between said control chamber and said inlet passage.

7. A mechanical vacuum pump as set forth in claim 1: said vent passage means and said restricted flow pas- References (Iited UNITED STATES PATENTS 2,043,058 6/1936 Ploeger 230-138 X 2,044,867 6/1936 Woodard 230-138 2,062,052 11/1936 Horlacher 230138 X 2,722,395 11/1955 Boyce 23023 X 2,977,039 3/1961 Green et al. 230138 X 3,122,308 2/1964 Andersson et a1. 230-438 FOREIGN PATENTS 496,351 11/1938 Great Britain.

531,444 1/1941 Great Britain.

407,167 12/ 1944 Italy.

FRED C. MATTERN, JR., Primary Examiner. W. J. KRAUSS, Assistant Examiner.