Off-on control for an inflation aspirator

In an aspirator (10) for pumping air into an inflatable (16), initial delivery of an aspirating fluid extends a piston (68) and the piston (68) extends an aspirator tube (24) to open an ambient air inlet (30) and render the aspirator (10) operable. Aspirating fluid pressure acts on a valve plug (112) and moves it into a first position in which the aspirating fluid pressure is connected to the linear fluid motor (66) for extending the piston (68). When inflation is substantially completed, back pressure from the inflatable (16) acts on a movable wall (74) which is connected to the valve plug (112) to produce a force which overrides the force of the aspirating fluid pressure acting on the valve plug (112). The overriding force moves the valve plug (112) into a second position in which flow of aspirating fluid into the linear motor (66) is blocked and the piston (68) is vented. A spring (48) then retracts the aspirator tube (24 ) closing the ambient air inlet (30), and disabling the aspirator (10).

TECHNICAL FIELD 
The present invention relates to aspirators for use in the inflation of gas 
confining inflatables, such as aircraft escape slides, inflatable life 
rafts, and the like. More particularly, it relates to the provision of an 
aspirator which opens and becomes operative in response to the delivery of 
a pressurized pumping or aspirating fluid to the aspirator and closes and 
becomes inoperative in response to the ratio of aspirating gas pressure to 
back pressure in the inflatable reaching a condition short of a "stall" 
condition. 
BACKGROUND ART 
A rapid inflation rate is a requirement of many inflatable devices, 
particularly those used in an emergency, such as aircraft escape slides 
and inflatable rafts. In a typical inflation system a pressurized 
aspirating or pumping fluid is introduced as a high velocity stream or 
streams into a venturi nozzle adapted to discharge into the inflatable. 
The upstream end of the nozzle is open to the surrounding air during 
inflation and the high velocity gas stream, or streams, creates a suction 
to draw or aspirate ambient air into the stream or streams for increasing 
its or their volume. When the inflatable is substantially inflated, it is 
common practice to shut off or disable the aspirator and complete the 
inflation by use of the aspirating fluid alone. 
A known aspirator includes an aspirator tube which is movable in and out 
relative to a housing that is fixed to the inflatable and mounts a group 
of jet tubes which convert the pressurized pumping fluid into high 
velocity jet streams. At the start of inflation the tube is extended into 
the inflatable to open an ambient air inlet at its outer end. Near the 
completion of inflation the aspirator tube is retracted out from the 
inflatable and its outer end functions as a closure for the ambient air 
inlet. Inflation is completed by the pressurized fluid alone. Such a prior 
art aspirator is shown by FIGS. 1 and 2. This type of aspirator includes a 
linear fluid motor that is connected to the aspirator tube by a connector 
rod. At the start of inflation some of the aspirating fluid pressure is 
directed into the linear fluid motor for moving the rod to extend the 
aspirator tube. A normally opened spool valve is provided in a passageway 
for delivering aspirating fluid pressure into the linear fluid motor. This 
valve is normally biased into an open position by a compression spring 
which is on one side of a movable wall. The opposite side of the movable 
wall is in communication with back pressure from the inflatable. When back 
pressure is developed this back pressure is imposed on the movable wall to 
produce a force in opposition the spring force. Near the completion of 
inflation the back pressure acting on the movable wall creates a force 
sufficient to overcome the force of the spring. When this happens the 
movable wall moves and repositions the valve spool to block flow of 
aspirating fluid into the linear fluid motor and at the same time vent the 
linear fluid motor. In response, a spring acts to retract the aspirator 
tube and close the ambient air inlet. A major disadvantage of this type of 
system is that the aspirator can only be set for a single pressure value, 
viz. a pressure sufficient to overcome the force of the biasing spring 
acting on the valve spool. An aspirator is required to operate over a 
large range of environmental conditions which have a direct effect on both 
pressure of the aspirating fluid at the inlet and back pressure in the 
inflatable. An aspirator set to close the ambient air inlet at a single 
pressure value is simply inadequate. 
U.S. Pat. No. RE 27,860, granted Jan. 1, 1974, to Ronald H. Day, discloses 
an aspirator which operates in essentially the same way as the "prior art" 
aspirator shown by FIGS. 1 and 2 of the drawing. The aspirator tube 
retracts to close the ambient air inlet when the back pressure reaches a 
predetermined value and produces a force sufficient to overcome a spring 
force which biases the control valve into a first position. 
U.S. Pat. No. 4,566,862, granted Jan. 28, 1986, to Richard A. Halavais, 
discloses an inflation system comprising a container of pressurized gas, a 
regulator for regulating the pressure of the gas as it leaves the 
container, a controller and an aspirator or ejector. The controller 
monitors the dynamic pressure within the aspirator and the static pressure 
within the inflatable to provide a feed back to the regulator. The 
objective is to provide a constant total mass flow through the aspirator 
at all times throughout the inflation cycle. 
Other known inflation aspirators existing in the patent literature are 
shown by U.S. Pat. No. 3,460,746, granted Aug. 12, 1969, to Charles J. 
Green et al, by U.S. Pat. No. 3,460,747, granted Aug. 12, 1969, to 
Charles. J. Green et al, by U.S. Pat. No. 3,640,645, granted Feb. 8, 1972 
to Alan K. Forsythe, and by U.S. Pat. No. 3,684,404 granted Aug. 15, 1972 
to Lyle D. Galbraith. 
A principal object of the present invention is to provide an improved 
inflation aspirator of the type having an aspirator tube which is 
retracted to close the ambient air inlet of the aspirator to, disable the 
aspirator, characterized by an improved control mechanism which causes 
such retraction to occur when the ratio of aspirating fluid pressure to 
back pressure approaches but has not yet reached a stall condition. 
DESCRIPTION OF THE INVENTION 
Aspirators embodying the present invention are basically characterized by a 
valve plug in the delivery path of aspirating fluid to the linear fluid 
motor which extends the aspirator tube. Upon the delivery of aspirating 
fluid to the aspirator, to start inflation, the pressure of this fluid 
acts on the valve plug and moves it into a position communicating such 
fluid pressure with the linear fluid motor. The fluid motor responds by 
extending the aspirator tube, to open the ambient air inlet of the 
aspirator. According to the invention, a connector rod extends from the 
valve plug to and through an end wall of a chamber in which the valve plug 
is situated and moves. The end of the connector rod opposite the valve 
plug is connectable to a movable wall. The rod side the movable wall is in 
communication with the interior of the inflatable so that the back 
pressure is exerted on this side of the movable wall. The opposite side of 
the movable wall is vented to atmospheric pressure. In preferred form, the 
pressure of the aspirating fluid acting on the valve plug produces a force 
on the valve plug in opposition to a biasing spring. This force overrides 
the spring force and moves the valve plug into a position communicating 
the aspirating fluid pressure with the base of the piston in the linear 
fluid motor. The biasing spring and back pressure acting on the movable 
wall together produce a force acting on the valve plug in the opposite 
direction. The spring force and the area relationship of the valve plug to 
the movable wall are chosen such that the combined force of the biasing 
spring and the force created by the back pressure acting on the movable 
wall will, in response to the back pressure in the inflatable reaching a 
predetermined level below a stall condition, shift the valve plug in 
position to block delivery of aspirating fluid pressure with the base of 
the piston and at the same time communicate the base of the piston with a 
vent passageway. The venting of the base end of the piston permits 
retraction of the piston, and hence a retraction of the aspirator tube to 
close the ambient air inlet of the aspirator, to in that manner disable 
the aspirator. Typically, a spring is used for retracting the aspirator 
tube.

DESCRIPTION OF THE BEST MODE 
FIG. 1 illustrates an embodiment of the invention. This embodiment is like 
a prior art aspirator except for the mechanism which controls the delivery 
of fluid pressure to and from the linear fluid motor which extends the 
aspirator tube. FIGS. 2 and 3 show a prior art control mechanism in the 
same aspirator. FIGS. 4-7 show embodiments of the invention. 
Referring first to FIG. 1, the aspirator 10 comprises an outboard housing 
12 which is attached to a wall portion 14 of an inflatable 16, at the 
inlet for the inflatable 16. Housing 12 includes a base portion 18 which 
is positioned on the outside on the wall 14. It is secured to an annular 
collar 20 which is positioned on the inside of wall 14, such as by the use 
of screw fasteners, as disclosed by the aforementioned U.S. Pat. Nos. 
3,684,404 and RE 27860. 
Base 18 includes a tubular portion 22 for guiding an elongated tube 24 
which will herein be referred to as the "aspirator tube." Housing 12 also 
concludes a head portion 26 which is spaced outwardly from the base 
portion 18. A circular array of spacer bars or members 28 extend between 
and interconnect the head and base portions 16, 18. A circular array of 
inlet openings are defined by and between the connector members 28. This 
construction is as clearly shown by FIG. 1 of the aforementioned U.S. Pat. 
3,684,404. These openings together define an ambient air inlet 30 which is 
annular except where it is interrupted by the connectors 28. 
Head portion 26 includes a high pressure fluid chamber or manifold 32. A 
source 34 of high pressure fluid is connected to an inlet passageway 36 
which leads to a valve chamber 38. A passageway 40 connects the valve 
chamber 38 with manifold 32. A plurality of jet nozzles 42 extend from 
chamber 32 axially of the aspirator tube 24. The end wall 44 of head 
portion 26 is somewhat conical in form and is of concave curvature in the 
axial direction. Surface 44 functions to redirect the ambient air which 
enters inlet 30 from a substantially radial flow into an axial flow 
through the aspirator tube 24. 
The outer end of aspirator tube 24 may include an annular seal ring 46 
constructed from an elastomeric material, as illustrated. Or, the outer 
end of aspirator tube 24 may be in the form of an annular flange which 
contacts an elastomeric seal ring carried by head portion 26, in the 
matter disclosed by the aforementioned U.S. Pat. No. RE 27,860. 
FIG. 1 shows aspirator tube 24 in a retracted position with its outer end 
in sealing engagement with a confronting surface portion of head member 
26. In the same matter as shown the aforementioned U.S. Pat. No. RE 
27,868, an accordian-like spring member 48 may be secured at one end 50 to 
an inner end portion of aspirator tube 24 and at its opposite end 52 to 
base portion 18. This spring 48 normally biases the aspirator tube 24 into 
a retracted position in which the outer end portion of tube 24 closes the 
ambient air inlet 30. This position is shown in solid line in FIG. 1. The 
extended position of the outer end of aspirator tube 24 is shown in broken 
line in FIG. 1. When aspirator tube 24 is extended ambient air may enter 
into the inlet 30, between the spacer members 28, and between guide wall 
44 and the outer end surface of member 46. 
A poppet valve member 54 is located within the valve chamber 38. It 
includes a valve plug 56 and a stem 58. One end of a compression spring 60 
abuts against the valve plug 56, about its connection to the stem 58. The 
opposite end of spring 60 is received in a passageway 62 which is in axial 
alignment with inlet passageway 36. The spring 60 normally biases the 
valve plug 56 into a closed position. 
In operation of the aspirator, to the extent that it has so far been 
described, a pressurized aspirating or pumping fluid is delivered from the 
source 34 into the inlet passageway 36. The fluid pressure acts against 
valve plug 56 and moves the valve plug axially in opposition to the force 
of spring 60. Most of the fluid then flows through passageway 40 into 
manifold 32 and from manifold 32 into and through the nozzles 42. The 
nozzles 42 convert the pressure fluid into high velocity jets and it is 
these jets which pump or aspirate ambient air into the ambient air inlet 
30 and then through the aspirator tube 24 into the inflatable 16. The 
spring 48, or a substituted equivalent structure, biases the aspirator 
tube 24 into a retracted position in which it closes the ambient air inlet 
30. 
In a manner to be hereinafter described, some of the pressure fluid 
delivered into the inlet passageway 36 is directed into a piston chamber 
64 of a linear fluid motor 66, at the base end of a piston 68. This fluid 
pressure is exerted against the piston 68, causing it to move axially 
through the piston chamber 64. A connector rod 70 is connected at its 
outer end to piston 68 and at its inner end to a spider 72 which is 
connected to an inner end portion of the aspirator tube 24. Thus, 
extension of the piston 68 causes an extension of both the connector rod 
70 and the aspirator tube 24. So long as pressure fluid is within the 
piston chamber 64, at the base of the piston 68, the aspirator tube 24 is 
fully extended and the ambient air inlet 30 is open. 
As previously mentioned, FIGS. 1 and 4-7 disclose control mechanism of the 
present invention for controlling fluid pressure into and out from the 
piston chamber 64. This mechanism will hereinafter be described, but first 
a prior art control mechanism will be described, with reference to FIGS. 2 
and 3 of the drawing. 
As will be apparent, the basic aspirator structure shown in FIGS. 2 and 3 
is the same as disclosed in FIG. 1. For that reason, only the head portion 
of the aspirator housing 12 is illustrated in FIGS. 2 and 3. In other 
words, the portion of the aspirator that is not illustrated in FIGS. 2 and 
3 is identical to what is disclosed if FIG. 1. As previously stated, this 
structure is essentially prior art structure. 
Referring to FIGS. 2 and 3, the prior art control comprises a valve spool 
74 which is connected at its outer end to a movable wall 74. Movable wall 
74 is in the nature of a diaphragm having a peripheral edge portion 76 
which is clamped between head portion 26 of body 12 and end cap 78. A 
compression spring 80 is positioned on the side of wall 74 opposite the 
valve spool 78. Spring 80 normally biases the valve spool into the 
position shown by FIG. 2. The end of spring 80 opposite wall 74 is 
contained within a socket 82 formed in a cup 84. Cup 84 includes threads 
which engage threads in a central opening in the cap 78 to form a threaded 
connection 86. 
Valve spool 72 includes an annular passageway 88 formed between a pair of 
spaced apart lands 90, 92. When the valve spool 72 is in the position 
shown by FIG. 2, and poppet valve 56 is open, allowing fluid pressure into 
valve chamber 38, this fluid pressure is delivered to region 94 of piston 
chamber 64 by way of a first port 96 in a wall of the valve plug chamber, 
the annular passageway 88, a second port 98 in the wall of the valve plug 
chamber, and a passageway 100. The fluid pressure acts on the piston 68, 
moving it lengthwise of the piston chamber 64. This extends the connector 
rod 70 and in turn the aspirator tube 24 to which the connector rod 70 is 
connected, to in that manner open the ambient air inlet 30. The continuous 
introduction of pressure fluid into inlet passageway 36 maintains the 
poppet valve 56 open and results in such pressure fluid first entering the 
manifold 32 and then flowing out of the manifold 32 through the jet tubes 
42. The jets of pressurized fluid flowing out from the tubes 42, axially 
of the aspirator tube 24, "pumps" a substantial quantity of ambient air 
into the ambient air inlet 30 and through the aspirator tube 24 into the 
inflatable 16. 
The prior art system shown by FIGS. 2 and 3 includes a tubular connector 
28' which provides a back pressure passageway 102 which communicates the 
interior inflatable 16 with a back pressure chamber 104. As illustrated, 
back pressure chamber 104 is bounded at its outer end by the movable wall 
74. The side of wall 74 opposite the back pressure chamber 104 is vented 
to the atmosphere, by way of a vent passageway 106 in the end wall of cap 
84. Owing to this construction, the only force acting to extend valve plug 
92 is the force produced by the spring 80. At times an opposing force is 
applied to valve spool 72 in the opposite direction. This force is the 
product of the fluid pressure in back pressure chamber 104 and the area of 
movable wall 74. 
In operation of the prior art device shown by FIGS. 2 and 3, the poppet 
valve 56 is normally open and the valve spool 72 is normally in an open 
position, as shown by FIG. 2. When it is desired to inflate the inflatable 
16, a pressurized fluid from a source 34 is introduced into the inlet 
passageway 36. This fluid first acts on valve plug 56, moving it endwise 
in opposition to the spring 60 into an open position. Following opening of 
valve plug 56, some of the pressurized fluid flows through port 96, 
passageway 88, port 98 and passageway 90 into region 94 of piston chamber 
64. This pressure acts on piston 68, extending it, the connector rod 70 
and the aspirator tube 24, to move the aspirator tube 24 into an operative 
position and at the same time open the ambient air inlet 30. The remainder 
of the pressurized fluid flows through passageway 40 into manifold 32 and 
from manifold 32 out through the jet tubes 42. The fluid issues from the 
tubes 42 as high velocity jet streams. These streams entrain or pump 
ambient air into the inlet 30 and then into and through the aspirator tube 
24 into the inflatable 16. 
As the inflatable 16 fills, a back pressure is developed. This back 
pressure is communicated by the passageway 102 to the back pressure 
chamber 104. Near the end of inflation the back pressure in back pressure 
chamber 104 acting on movable wall 74 will produce a sufficient force in 
opposition to the force of spring 80 to override the spring 80 and move 
the valve plug 72 endwise from the position shown by FIG. 2 into the 
position shown by FIG. 3. When this happens, the land 72 moves into a 
position above port 98. This communicates piston chamber region 94 with 
the back pressure chamber 104 via passageway 100, port 98, end region 108 
of the valve plug chamber, and a port 110. The pressure in back pressure 
chamber 104 is substantially lower than the pressure in region 94 of 
piston chamber 64. As a result, the pressure in region 94 is vented into 
the back pressure chamber 104 releasing pressure from piston 68. This 
release of pressure from piston 68 allows the spring 48 to retract the 
aspirator tube 24 and close the ambient air inlet 30. Inflation of the 
inflatable 16 is then completed by continuing the introduction of the 
pressurized fluid into the inflatable 16 through the nozzles 42. 
The prior art system shown by FIG. 2 can only be set to close in response 
to a single back pressure value. The force of spring 80 is a fixed value 
and the area of movable wall 74 is a fixed value. The spring force is over 
come when the back pressure within chamber 104 reaches a fixed value. An 
aspirator is required to operate within a substantial range of 
environmental conditions which have a direct effect on both inlet and back 
pressures. For this reason, a control valve which closes in response to a 
single back pressure value is not suitable for all operating conditions. 
Testing has shown that choosing one closing pressure either closes the 
aspirator prematurely, which decreases the efficiency of the unit, or 
closes the aspirator late which results in reversed flow and reduced 
inflatable pressure. Also, it may be possible that under some conditions 
the back pressure required for closing the valve is never developed. In 
such a case, the unit would stay open until the aspirating fluid pressure 
can no longer maintain the aspirator in the open position. 
The aspirator control of the present invention will now be described with 
reference first to FIGS. 4 and 5. As previously mentioned, and as shown by 
FIG. 1, the portion of the aspirator 10 that is not shown by FIGS. 4 and 5 
is identical to the prior art aspirator. 
Referring to FIGS. 4 and 5, in illustrated embodiment, the valve spool 72 
in the prior art aspirator is replaced by a valve plug 112, a connector 
rod 114, a chamber end wall 116 including an opening through which the rod 
114 extends, and a seal 118 sealing between such opening and the rod 114, 
so that pressure fluid will not leak out between the rod and the opening. 
As shown, one end of the rod 114 is connected to the valve plug 112 and 
the opposite end of rod 114 is connected to the movable wall 74. The 
biasing spring 80 that was in the prior art device has been omitted, and 
the at rest position of the movable wall 74 is now up against an outer 
stop 120 whereas the at-rest position of movable wall 74 in the prior art 
device was down against a lower stop 122. As shown by FIG. 4, the at rest 
position of valve plug 112 places it axially between the side wall ports 
96 and 98. 
In operation, pressurized fluid from a suitable source is introduced into 
the inlet passageway 36, as in the prior art aspirator. This pressure 
fluid opens the poppet valve 56. As in the prior art device, some of the 
pressure fluid flows to and through the port 96. However, this time it 
exerts a force on the rod end of the valve plug 112. The force is a 
product of the fluid pressure and the area of the valve plug 112 in the 
annular region surrounding rod 114. At this time the pressure within back 
pressure chamber 104 is low and so no counter force is developed by back 
pressure acting on area 74 in opposition to the delivered pressure acting 
on valve 112. As a result, the delivered pressure acting on valve plug 112 
moves the valve plug from the position shown by FIG. 4 into the position 
shown by FIG. 5. In this new position the valve plug 112 is positioned 
below port 98, allowing the pressure fluid to flow from the valve plug 
chamber 124 through the port 98 and into the region 94 of piston chamber 
64. Within chamber 94 the pressure fluid acts on the piston 68, moving it 
endwise of the chamber 64 and extending the connector rod 70 and the 
aspirator tube 24, as in the prior art aspirator. Thus, the ambient air 
inlet 30 is open and the aspirator 10 is made operable, in essentially the 
same manner as in the prior art aspirator. 
The pressure fluid continues to flow into inlet passageway 36, into the 
manifold 32 (FIG. 1), and from manifold 32 into and through the jet 
forming nozzles 44 (FIG. 1). The jet streams pump in ambient air and move 
it into the inflatable 16. The back pressure developed in the inflatable 
16 is communicated via a passageway 102 into the back pressure chamber 
104. This pressure is relatively small in comparison to the aspirating 
fluid pressure being delivered into the aspirator inlet passageway 36. 
However, it acts on movable wall 74 which is substantially larger in area 
than the area of valve plug 112. The working area of valve plug 112 and 
the area of movable wall 74 are chosen so that the force developed by the 
back pressure acting on wall 74 will override the force produced by the 
aspirating fluid pressure acting on valve plug 112 at a time when the 
system is approaching but has not yet reached a "stall" condition. In 
response, the overriding force acts on valve closure 112 by way of the 
connector rod 114. The movable wall 74 is moved from the position shown by 
FIG. 5 into the position shown by FIG. 4 and the valve plug 112 is once 
again positioned above the port 98. This movement of valve plug 112 causes 
the region 94 of piston chamber 64 to be vented to the back pressure 104 
by way of passageway 98, chamber region 108 and port 110. The fluid 
pressure acting on the base of piston 68 is thus vented into the back 
pressure chamber 104, allowing the spring 48 to move the aspirator tube 
into a retracted position. As in the prior art aspirator, this movement of 
the aspirator tube 24 closes the ambient air inlet 30. The delivery of 
fluid into the inlets 36 and manifold 32 is continued and such fluid flows 
through the nozzles 42 and by itself completes the inflation of the 
inflatable 16. 
FIGS. 6 and 7 show two different modified embodiments of the invention. The 
embodiment of FIG. 6 is identical to the embodiment of FIGS. 4 and 5, 
except that a biasing spring 126 is positioned within chamber region 108. 
Spring 126 normally biases valve plug 112 and rod 114 upwardly and movable 
wall 74 into a position against stop 120. The force created by the 
aspirating fluid pressure acting on the rod end of valve plug 12 is 
sufficient to overcome the force of spring 126 at the start of and during 
most of the inflation process. When a back pressure is being felt in back 
pressure chamber 104, the spring force and the force produced by the back 
pressure acting on the area of movable wall 74 together oppose the force 
of the aspirating fluid acting on the rod side of the closure member 112. 
In this embodiment, the working surface area of valve plug 112 and the 
area of movable wall 74 are chosen such that the force produced by the 
back pressure acting on movable wall 74, in combination with the spring 
force produced by spring 126, will together override the force produced by 
the aspirating fluid pressure acting on the rod side of the valve plug 112 
at a time when the system is approaching but has not yet reached a "stall" 
condition. 
The embodiment of FIG. 7 is like the embodiment shown by FIGS. 4 and 5 and 
also like the embodiment shown by FIG. 6, except that a conical biasing 
spring 128 is employed and it is positioned between a spring abutment 130 
and the movable wall 74. The spring abutment 130 may be in the form of an 
annular shoulder formed in the structure which defines stop 124 and 
together with insert 116 also defines the outer end of the valve plug 
chamber. The shoulder 130 defines a reduced diameter boss which is sized 
to fit into the small end of the spring 128. The opposite larger end of 
the spring 128 preferably engages the movable wall 74 adjacent the 
periphery of the wall 74. FIG. 7 shows the spring 128 functioning to urge 
the movable wall 74 against the stop 120. 
As will be apparent from FIG. 7, when aspirating fluid pressure is acting 
of the valve plug member 112, the force of spring 128 will be overcome and 
the movable wall 74 will be moved into the position by FIG. 5. The spring 
128 will compress sufficiently to allow movable wall 74 to move down into 
contact with the stop 122. The embodiment of FIG. 7 functions like the 
embodiment of FIG. 6, but with the biasing spring 128 performing the 
function of biasing spring 126. The embodiment of FIG. 7 is the preferred 
embodiment and hence is the best mode of the invention known at this time. 
In each embodiment of the invention, the movable wall 74 is shown in the 
form of a diaphragm that is secured at its outer periphery, in a known 
manner, between two housing members. In other embodiments, the movable 
wall may take the form of a piston. Also, as in the prior art device, a 
sleeve may be fitted into a bore to form the valve plug chamber and the 
ports 96, 98, 110 may be formed in side wall portions of the sleeve Also, 
member 116 may be an end portion of the sleeve, or may be a separate 
member or collar sized to fit into the outer end portion of the sleeve. 
FIG. 8 is a plot of aspirating fluid pressure versus back pressure over a 
wide range of operating conditions. The "stall line" divides the graph 
into an upper region in which the aspirating fluid pressure is sufficient 
to aspirate ambient air into the inflatable. The region below the "stall 
line" is the region in which the back pressure overrides the aspirating 
fluid pressure and stalls the aspirator, resulting in fluid flow out from 
the inflatable through the aspirator to the atmosphere. According to the 
invention, working the area of the valve plug and the area of the movable 
wall are chosen such that the force of the back pressure acting on the 
movable wall, either alone or in combination with a biasing spring force, 
will exceed the force of the aspirating fluid pressure acting on the valve 
plug member when the aspirator operation is approaching but has not yet 
reached a stall condition. The two areas and the spring force, if a 
biasing spring is used, can be chosen so as to cause the aspirator to 
close on a "close line" above the "stall line", as shown in FIG. 8. 
It is to be understood that the illustrated embodiments are presented 
merely by way of example. The scope of protection is not to be limited by 
these embodiments, but only by the appended claims, interpreted in 
accordance with established rules of patent claim interpretation, 
including use of the doctrine of equivalents.