Vacuum pump with lubricant control system to interrupt lubricant flow upon loss of pump pressure

A vacuum pump, having a pumping chamber with intake and exhaust ports communicating therewith, is provided with an arrangement to insert a liquid lubricant into the pumping chamber. A sensing device is utilized to detect the pressure at the exhaust port, the sensing device permitting operation of a deactivating unit when the pressure at the exhaust port falls below a predetermined value, pressure below the predetermined value being indicative of improper pumping action in the pump. The deactivating unit acts to render inoperative the lubricant introducing arrangement when the sensing device detects a pressure at the exhaust port below the predetermined value, thus precluding the insertion of lubricant into the pumping chamber upon the occurrence of defective pumping action in the vacuum pump.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a vacuum pump having a system for 
controlling the introduction of liquid lubricant into the pumping chamber 
of the vacuum pump, and more specifically, this invention relates to a 
control system for precluding the insertion of lubricant into the pumping 
chamber of a vacuum pump in response to the pressure at the exhaust port 
of the pump falling below a predetermined level indicative of improper 
pumping action. 
2. Description of the Prior Art 
Although the vacuum pumps toward which this invention is directed may be 
occasionally used as pressure pumps or compressors, their primary 
usefulness is in the evacuation of vessels, chambers, cavities, etc., in 
which a very low pressure (high vacuum) is required. In such vacuum pumps, 
a liquid lubricant, such as oil, is inserted into the pumping chamber. One 
type of such liquid lubricant insertion arrangement employs a bath of the 
lubricant in which the stator assembly of the pump is partially immersed, 
with a lubricant introducing conduit running from the bath to the pumping 
chamber. Another type of lubricant inserting arrangement employs an oil 
pump, driven by the same motor shaft that drives the rotor of the vacuum 
pump, to insert oil into the pumping chamber. 
During operation of the pump, the small amount of lubricant inserted into 
the pumping chamber is exhausted with the gases being expelled through the 
exhaust port, as a result of the pumping action of the rotor in the 
pumping chamber, which results in a pressure being developed at the 
exhaust port. If, for some reason, the pumping action in the pumping 
chamber is deficient, the pressure at the exhaust port will decrease. 
Therefore, as a result of the decreased efficiency of the pumping action, 
the oil being introduced into the pumping chamber will tend to accumulate, 
since it is not being properly expelled. Similarly, at least in the case 
where an oil bath is employed, merely stopping operation of the pump will 
result in an accumulation of lubricant in the pumping chamber. Although 
various disconnect arrangements are frequently employed between the vacuum 
pump and the chamber being evacuated, these disconnect devices frequently 
do not suffice to prevent the accumulated lubricant from being sucked back 
into the cavity being evacuated, thus contaminating the cavity. Therefore, 
there exists a real need for a control arrangement that precludes the 
accumulation of lubricant in the pumping chamber. 
As a result of being driven by the motor shaft that drives the rotor of the 
vacuum pump, an oil insertion pump has a built-in control of lubricant 
insertion upon deactivation of the motor. However, there may still be some 
accumulation of oil in the pumping chamber during the period when the 
rotation of the motor shaft is slowing down, since there will still be 
some pumping of lubricant into the pumping chamber, but the pumping action 
may not be sufficiently vigorous to expel all of the lubricant. Further, 
in other types of pump failure when the motor shaft continues to rotate, 
at least for a time, after a decrease in the pumping action, oil will 
accumulate in the pumping chamber of a vacuum pump having an oil insertion 
pump, with the attendant contamination of the cavity being evacuated. 
SUMMARY OF THE INVENTION 
With the present invention, the problems of oil contamination of the cavity 
being evacuated that occur with prior art devices may be obviated. This is 
accomplished by utilizing a pressure sensitive device to determine the 
pressure at the exhaust port and preclude the insertion of lubricant when 
that pressure falls below a predetermined value indicative of improper 
pumping action. 
A vacuum pump has a pumping chamber in a stator assembly, the stator 
assembly including a conventional stator and appropriate end plates. 
Intake and exhaust ports open into the pumping chamber, and a rotor is 
rotated in the pumping chamber to provide the desired pumping action. In 
the preferred embodiment of the invention disclosed herein, the exhaust 
port is located in one of the end plates, which is termed the exhaust end 
plate for ease of reference. The exhaust port includes a conventional 
check valve, and the exhaust end plate may be either a single member or, 
as in the preferred embodiment disclosed herein, a double member. 
A lubricant inserting arrangement, such as a conduit extending through the 
exhaust end plate from an oil bath to the pumping chamber, is utilized to 
insert a liquid lubricant, such as oil, into the pumping chamber. During 
rotation of the rotor, the resulting pumping action draws gases into the 
pumping chamber through the intake port and expels gases and lubricant 
through the exhaust port to produce a pressure at the exhaust port which 
may be detected by an appropriate pressure sensing device, such as a 
flexible or elastomeric diaphragm. A deactivating unit, such as a bias 
spring acting on a reciprocable plunger, the bias spring producing a force 
on the plunger in opposition to the force on the plunger produced by the 
diaphragm in response to the pressure at the exhaust port, may be utilized 
to render the lubricant inserting arrangement inoperative when the 
pressure at the exhaust port falls below a predetermined value, thus 
indicating improper pumping action. The plunger is used to deactivate the 
oil insertion arrangement when the force of the bias spring overcomes the 
force of the sensing diaphragm. By the combined action of the diaphragm 
and the deactivating unit, the input of lubricant to the pumping chamber 
is prevented in the event of improper or inadequate pumping action, while 
yet permitting lubricant insertion if the pumping action is proper. 
The remainder of the deactivating arrangement includes an elastomeric 
sealing member, such as an O-ring, positioned at the end of a stem. 
Actuation of the plunger by the bias spring causes a cam portion at one 
end of the plunger to bear against the sealing member to preclude the 
insertion of lubricant into the pumping chamber. The stem may be a screw 
or bolt having a head at one end, which positions the sealing member, and 
a nut at the other end, the bias spring engaging the nut to hold the stem 
in position. The stem is located in the oil insertion conduit with a space 
between the stem and the plunger and between the sealing member and the 
wall of the conduit, so that the lubricant can flow along the stem, over 
the sealing member and into the pumping chamber, unless the cam portion of 
the plunger is brought into engagement with the sealing member to close 
the lubricant inserting conduit. 
With this arrangement, the elastomeric sensing diaphragm will hold the 
plunger away from the sealing member against the force of the bias spring, 
so long as the pressure at the exhaust port exceeds a predetermined value. 
When the pressure of the exhaust port falls below this predetermined 
value, the bias spring will actuate the plunger to engage the sealing 
member and preclude the insertion of lubricant into the pumping chamber of 
the vacuum pump, thus preventing contamination of the cavity being 
evacuated when the pumping action is deficient for any reason whatsoever. 
These and other objects, advantages and features of this invention will 
hereinafter appear, and for purposes of illustrated, but not of 
limitation, an exemplary embodiment of the subject invention is shown in 
the appended drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
While the present invention may be employed with any vacuum pump in which 
oil is introduced into a pumping chamber, the invention will be explained 
with particular reference to the vacuum pump 10 illustrated in FIGS. 1-4. 
Vacuum pump 10 includes a drive motor 11, a mounting plate 12 and a pump 
housing 13. A carrying handle 14 is connected to the mounting plate 12, 
and rubber feet or bumpers 15 are affixed to a frame 16 for supporting the 
vacuum pump when it is set down for operation or storage. 
Motor 11 is in a conventional drive motor for a vacuum pump. A motor drive 
shaft 17 extends from motor 11 in order to drive the rotor of vacuum pump 
10. 
Mounting plate 12 has an inlet fitting 18, which communicates with an inlet 
conduit 19. Conduit 19 communicates with another conduit 20 (FIG. 3), 
which, in turn, leads to an intake port 21 (FIGS. 3 and 4). Gas ballasting 
is achieved by means of the knurled nut 22, which is connected to a 
threaded rod, and interconnecting conduits 23 and 24. 
A pumping module 25 has a stator assembly including a stator 26 and end 
plates 27 and 28. The module 25 is connected to the mounting plate 12 by 
bolts 29 and 30, which extend through openings 31 and 32 in module 25 and 
are screwed into appropriate threaded openings 33 and 34 in mounting plate 
12. 
With reference to the exploded view of FIG. 3, the details of the pumping 
module 25 may be seen in greater detail. The stator assembly of stator 26 
and end plates 27 and 28 encloses a pumping chamber 35, in which is 
located a rotor 36. Rotor 36 has vane slots 37, in which spring biased 
vanes 38 (FIG. 4) are located. As may be seen from FIG. 4, rotor 36 is 
eccentrically mounted in the pumping chamber 37, so that upon rotation of 
the rotor 36 an appropriate pumping action is achieved. Rotor 36 is 
connected to a rotor shaft 39, which is mounted on a bearing 40 in end 
plate 27 and provided with a rotational seal 41 in mounting plate 12. 
Rotor shaft 39 is connected to motor shaft 17 by an elastomeric cross 
piece 42, which fits in cruciform slots 43 on the rotor shaft 39 and 
corresponding slots 44 in a connecting member 45, connecting member 45 
being rigidly affixed to motor shaft 17. Bolts 46, 47, 48 and 49 connect 
stator 26 and end plates 27 and 28 together to form the pumping module 25. 
Bolts 29 and 30 then affix this module 25 to the mounting plate 12. 
An exhaust port 50 communicates with the pumping chamber 35 and an exhaust 
conduit 51. An appropriate check valve of a conventional type is located 
in the exhaust conduit 51. 
Housing 13 is a fluid tight enclosure in which a bath of liquid lubricant, 
such as oil, is located to partially immerse or surround the stator 
assembly formed by stator 26 and end plates 27 and 28. An oil level sight 
glass 52 is located in housing 13, while an oil drain tap 53 is formed 
near the lower portion of the housing to permit drainage of the oil in the 
housing. A pump discharge vent 54 is located at the top of the housing 13 
to discharge pressure to the atmosphere. Housing 13 is affixed to mounting 
plate 12 by a plurality of bolts 55. 
In operation, rotation of rotor 36 causes gas to be pulled or sucked from a 
cavity to be evacuated, which is connected to fitting 18, through the 
intake port 21. This gas, as well as any lubricating oil that has been 
inserted into the pumping chamber, is then expelled through exhaust port 
50 and exhaust conduit 51 to the interior of housing 13. The expelled oil 
is then returned to the oil bath in housing 13, while the gas is vented to 
the atmosphere through the pump discharge vent 54. For a more complete 
description of pump 10, reference may be made to the copending application 
of Vytautas Andriulis entitled "MODULAR PUMP APATUS AND ASSEMBLY," U.S. 
Pat. application Ser. No. 394,092, filed on Sept. 4, 1973 and assigned to 
the same assignee as the present application. 
With reference now to FIG. 5, a pumping module 25' modified in accordance 
with the present invention is illustrated. The stator assembly includes a 
stator 26' and end plates 27' and 28'. However, end plate 28', in this 
preferred embodiment, has two sections 60 and 62. In should be recognized, 
however, that the end plate 28' coulld be a single member. Further, the 
end plate 28' has been characterized as the exhaust end plate for purposes 
of distinguishing it from end plate 27', and in view of the fact that the 
exhaust function is being carried out through this end plate in the 
preferred embodiment disclosed herein. However, it should be recognized 
that this preferred embodiment is not the only form that the invention 
could take. 
In the cross sectional view of FIG. 6, the details of the preferred 
embodiment of this invention are depicted. An exhaust port 50' is in 
communication with the pumping chamber. Expulsion of gases and lubricant 
from the pumping chamber is achieved through the exhaust port 50' and the 
exhaust conduit 51'. A check valve is located in the exhaust conduit 51', 
as represented by the spring 64 and ball seal 66. A leaf spring 68 also 
provides a type of check valve, as it moves to the open position shown in 
dotted lines when the pressure at the exhaust port 50' is sufficiently 
great to flex the leaf spring. However, the purpose of this leaf spring 68 
is to prevent oil in portion 70 of conduit 51' from flowing back into the 
pumping chamber, since the pumping action of the vaned rotor produces a 
pulsating condition at exhaust port 50'. The pressure in portion 70 of 
exhaust conduit 51' is communicated to a chamber 72 via an opening 74. The 
pressure in chamber 72, in which the pressure at exhaust port 50', is 
applied to a flexible sensing diaphragm 76. 
Diaphragm 76 is formed of an elastomeric material, such as rubber, and has 
the outer portion 78 thereof firmly stationed between a portion 80 of the 
end plate and a shoulder 82 on the section 62. Opening 74 is formed 
through the portion 80. Portion 80 has and end 83 thereof carried by a 
shoulder 84 in section 60 and the other end 86 thereof in engagement with 
a sleeve or bushing 88, which is also mounted on section 60. 
An inner diameter portion 90 of flexible diaphragm 76 is firmly affixed 
between flanges 92 and 94 of a plunger 96. Plunger 96 is mounted for 
reciprocable motion in oil inserting conduit 98, which leads from the oil 
bath in housing 13 to the pumping chamber 35. For illustrative purposes, 
the oil inserting conduit 98 is shown as communicating with pumping 
chamber 35 at opening 100, although in actual practice this portion of the 
conduit would probably take the shape shown in dotted lines at 102. 
Since the plunger 96 is in sliding contact with the sleeve 88, in the 
preferred embodiment shown herein, sleeve 88 is formed of bronze, although 
it could be formed of any other suitable material, such as the steel of 
the end plate. 
A biasing arrangement, such as a suitable bias spring 104, engages the 
upturned ends 106 of flange 92 to urge the plunger 96 toward the left in 
the orientation of FIG. 6. As a result of this bias, it may be noted that 
the flange 92 need not be integral with the plunger 96, but may be 
separate therefrom, as it will be held in unitary juxtaposition with the 
other portions of plunger 96 by the force of spring 104. 
The pressure in chamber 72 causes the flexible diaphragm 76 to exert a 
force against plunger 96 that opposes the force of the bias spring 104. 
Hence, so long as the pump is producing an appropriate pumping action, 
with the corresponding pressure at exhaust port 50', the plunger 96 will 
remain in the position shown in FIG. 6. However, if the pressure at 
exhaust port 50' falls below a predetermined value that is established by 
the force of the spring 104, the force exerted by the diaphragm 76 will 
not be sufficient to offset the spring force and plunger 96 will be moved 
to the left in the orientation of FIG. 6. As plunger 96 is moved to the 
left, a cam portion or end 108 thereof will engage a sealing member 110. 
Sealing member 110 is formed of an elastomeric material, and in this 
preferred embodiment may be a rubber O-ring. When cam portion 108 is 
brought into engagement with sealing member 110, the oil insertion conduit 
98 is closed to prevent the insertion of lubricant into the pumping 
chamber. 
Sealing member 110 is mounted adjacent one end of a stem 112, which is 
located in the lubricant inserting conduit 98. In this preferred 
embodiment, stem 112 may be a bolt or screw having a head 114 and a 
threaded portion 116. A nut 118 is threaded on portion 116 of stem 112. 
Bias spring 104 engages the nut 118 to hold the bolt or stem 112 in the 
position illustrated. Sealing member 110 is located on the head 114 of the 
bolt 112 and is spaced from the wall 120 of the lubricant inserting 
conduit 98, so that the oil may flow therebetween. Similarly, the stem 112 
is spaced from the internal diameter of plunger 96, so that the oil may 
flow about spring 104, past stem 112 and around the sealing member 110, 
when the pump is pumping properly. As previously indicated, when the 
pumping action is insufficient, spring 104 and plunger 96 serve as a 
deactivation arrangement to render the oil insertion conduit 98 
inoperative as a result of the sealing action achieved by cam portion 108 
engaging the sealing member 110. 
With the structure described herein, a system has been provided to preclude 
the insertion of lubricant into the pumping chamber of a vacuum pump when 
the pumping action has become deficient. This is achieved by sensing the 
pressure at the exhaust port, and deactivating the oil insertion 
arrangement when this pressure falls below a predetermined value 
indicative of proper pumping action. 
It should be understood that various modifications, changes and variations 
may be made in the arrangements, operations and details of constructions 
of the elements disclosed herein without departing from the spirit and 
scope of this invention.