Method and apparatus for flow diversion in a high pressure fluid delivery system

A method and apparatus for the diversion of fluid flow at reduced pressure out of a high pressure fluid delivery system when the discharge of the system is closed. A bypass valve having a movable piston oriented transverse to the flow direction and a slidable seal oriented parallel to the flow direction is located between the system pump and discharge. The movable piston has two working surfaces of different areas which define planes parallel to the flow direction so that the working surfaces and therewith the piston are generally responsive only to static fluid pressure. The slidable seal is responsive to dynamic fluid pressure so that when the discharge is closed and the dynamic fluid pressure thereby reduced, the seal moves to interrupt fluid communication between the two working surfaces of the piston. Interruption of fluid communication between the two working surfaces allows for a static fluid pressure differential on the two working surfaces which moves the piston and opens the bypass valve so that the flow of fluid is diverted out of the system at a substantially reduced pressure.

BACKGROUND OF THE INVENTION 
This invention relates to a pressurized fluid delivery system in which 
fluid is pumped under relatively high pressure from a supply to a 
discharge, and more specifically to a method and apparatus for diverting 
the flow of fluid from the delivery system at a substantially reduced 
pressure when the discharge is closed. 
In conventional pressurized fluid delivery systems, a fluid, e.g. water, is 
pumped from a supply, such as a tank, at a generally constant volumetric 
flow rate. The pressurized fluid is transported through a conduit to a 
discharge having a small opening where it exits at a relatively high 
velocity. A typical fluid delivery system of this type is in use in 
commercial car washes. In such fluid delivery systems, the pump operates 
generally at a constant velocity and thus pumps fluid from the supply at a 
generally constant volumetric flow rate. It is thus necessary to divert 
the flow of fluid when the discharge is closed in order to prevent adverse 
pressure build up within the system. 
Conventional devices for diverting the flow when the discharge is closed 
are pressure-sensitive devices which are activated by the sudden pressure 
rise caused by the closing of the discharge. These conventional bypass 
valves utilize the pressure rise to move a movable check valve, such as a 
ball or piston, to thereby open a bypass port and allow the flow to be 
diverted to a drain, e.g. a conduit connected back to the fluid supply. In 
some versions of these bypass valves, the pressure rise moves an 
intermediate member, such as a diaphragm or plunger, which in turn moves 
the check valve to open the bypass port. When the flow is thus diverted, 
since the opening of the bypass port is generally substantially larger 
than the small opening of the discharge, the pressure flowing from the 
pump through the bypass valve, out the bypass port and back to the drain 
or supply is flowing at a substantially reduced pressure than would 
otherwise exist if the flow were through the discharge. 
The conventional bypass valves have several inherent disadvantages. The 
primary disadvantage is that the movable check valve does not move until 
the pressure within the system reaches an extremely high value, for 
example several times the pressure for which the system is designed to 
operate. This high pressure produces adverse stresses both on seals within 
the system and on the pump. A second disadvantage in some types of 
conventional bypass valves is that a high pressure is required not only to 
activate the check valve but also to keep the check valve open so that 
fluid may be diverted to the bypass port. Thus it is necessary that there 
be a perfect seal around both the check valve and the discharge so that a 
high pressure is maintained within the bypass valve. Otherwise, any 
leaking of fluid out the discharge or past the check valve will decrease 
the pressure and cause the check valve to reseat, thereby closing the 
bypass port and redirecting the flow out the discharge. 
SUMMARY OF THE INVENTION 
The present invention provides a method and apparatus for diverting the 
flow of fluid in a pressurized fluid delivery system whereby flow is 
diverted at reduced pressure merely in response to the cessation of flow 
out the discharge and regardless of the pressure within the system. 
A typical high pressure fluid delivery system involves a supply, such as a 
tank, a means for introducing the fluid from the supply into the system at 
a relatively high pressure, e.g. a pump, a conduit system, and a nozzle 
for discharging the pressurized fluid at a relatively high velocity. The 
present invention provides a flow diversion means located between the pump 
and the discharge for diverting the flowing fluid out of the system at a 
substantially reduced pressure when the discharge is closed. 
The means for diverting the flow is a bypass valve which comprises 
generally a housing having an inlet, an outlet, and a bypass port between 
the inlet and outlet. Located within the housing and movable generally 
transverse to the direction of flow from the inlet to the outlet is a 
piston for blocking the bypass port. The piston has at least two working 
surfaces of different areas which define planes generally parallel to the 
direction of flow of the fluid from the inlet to the outlet. Because the 
working surfaces are generally parallel to the direction of flow when the 
discharge is open, the working surfaces and therewith the piston are 
responsive generally only to the static pressure of the flowing fluid, and 
not to dynamic pressure. Accordingly, when the discharge is open and fluid 
is flowing from the pump to the inlet side of the bypass valve, past the 
piston, through the outlet side of the valve, and out the discharge, the 
static fluid pressure on each of the working surfaces is generally equal. 
However, since one of the working surfaces has an area greater than the 
other, the force acting on the larger working surface exceeds the force 
acting on the smaller working surface thereby forcing the piston to block 
the bypass port. Fluid is therefore directed out the discharge and is 
prevented from passing through the bypass port. 
Also located within the bypass valve is a channel which provides fluid 
communication between the two working surfaces. The larger working surface 
and a portion of the housing define a chamber which is in fluid 
communication by means of the channel with the smaller working surface and 
the flowing fluid. Located within the housing proximate the outlet are 
means for obstructing the channel and thus interrupting fluid 
communication between the working surfaces. This interrupting means 
comprises generally a slidable seal responsive to the dynamic pressure of 
the flowing fluid and resilient means, e.g. a spring, for urging the seal 
to obstruct the channel when the discharge is closed. Thus, with the 
discharge open, the dynamic pressure of the fluid flowing through the 
outlet forces the slidable seal away from the channel and thereby 
compresses the spring. The fluid flows around the slidable seal, out the 
bypass valve outlet and out the discharge. When the discharge is closed, 
the flow of fluid ceases and the dynamic pressure drops essentially to 
zero, thereby presenting equal fluid pressure on both sides of the 
slidable seal. However, because the compressed spring is now acting on one 
side of the slidable seal, that spring forces the slidable seal against 
the channel thereby interrupting fluid communication between the two 
working surfaces of the piston. 
It should be apparent that with the discharge closed, fluid communication 
between the two working surfaces obstructed, and the pump continuing to 
pump fluid from the supply through the system under pressure, the fluid 
pressure acting on the smaller working surface slowly begins to increase. 
Additionally the fluid within the chamber is passed out of the system and 
thus the fluid pressure on the larger working surface decreases. 
Accordingly, the force acting on the smaller working surface of the piston 
exceeds the force acting on the larger working surface and the piston is 
moved away from the bypass port to permit the flow of fluid out of the 
fluid delivery system at a substantially reduced pressure. 
Means are provided for adjusting the maximum travel of the movable piston 
and thus for varying the area of the opening of the bypass port. The 
pressure of the fluid flowing out the bypass port is directly related to 
the area of the opening and thus the piston travel adjusting means allows 
preselection of the fluid pressure of the diverted flow. The present 
invention thus does not rely on a sudden pressure rise caused by closing 
the discharge to force open a diaphragm or plunger and there is no 
requirement that the pressure remain high in order to maintain the bypass 
port open. Rather, it is the cessation of flow and the decrease in dynamic 
pressure which activates the slidable seal to obstruct the channel and 
thereby permit the piston to move away from the bypass port. 
When the closed discharge is opened, fluid again flows through the outlet 
of the bypass valve and the dynamic pressure of the flowing fluid forces 
the slidable seal to compress the spring to thereby again provide fluid 
communication between the working surfaces of the piston. Thus again the 
larger working surface of the piston has applied to it a greater force 
than the smaller working surface and the piston will move in the opposite 
direction to close the bypass port and stop the diversion of fluid out of 
the system. 
Means are also provided with the present invention for sensing the position 
of the movable piston to thereby indicate whether the fluid is flowing 
through the discharge or through the bypass port. By sensing the position 
of the piston, for example with a micro-switch mechanically coupled to the 
piston, it is thus possible to generate an electrical signal which 
activates a fluid heater, such as a water heater, a warning light, or any 
other control device, such as a chemical injection system. Thus, if hot 
water is being delivered through the system, the micro-switch turns off 
the hot water heater when the water is being diverted. Or, if a chemical 
is being injected into the fluid, the micro-switch turns off the injection 
system when the flow is being diverted. 
The present invention also provides means for permitting use of the flow 
diversion device in fluid delivery systems in which the fluid pressure is 
regulated. Applicant is co-inventor of a pressure regulator, disclosed in 
U.S. Pat. No. 3,856,043, which maintains fluid pressure within 
predetermined limits in high pressure fluid delivery systems employing 
closable discharges. The present invention, which is adaptable for use 
with such a pressure regulator, permits fluid pressure to be regulated 
when the discharge is open and the bypass port is blocked, and also 
permits the flow to be diverted through the bypass port and pressure 
regulator when the bypass port is open and the pressure regulator is not 
functioning. 
The novel features which are believed to be characteristic of the 
invention, together with objects and advantages thereof, will be better 
understood from the following description considered in connection with 
the accompanying drawings in which preferred embodiments of the invention 
are illustrated by the way of example. It is to be expressly understood, 
however, that the drawings are for the purpose of illustration and 
description only and are not intended as a definition of the limits of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, the present invention provides a method and 
apparatus for operating a fluid delivery system of the type having a fluid 
supply 2, a pump 4 for introducing fluid from the supply 2 under pressure, 
a closable discharge 6, such as a hand-held gun having an outlet nozzle 8, 
and conduit 10 interconnecting the supply 2, pump 4 and discharge 6. In 
such a system, fluid is introduced from the supply 2 under pressure into 
the conduit 10 and out the nozzle 8. The pump 4 pumps fluid at a generally 
constant volumetric flow rate, and may be any type of conventional pump, 
such as a piston, vane, or centrifugal type pump. 
In the operation of such a fluid delivery system, it is necessary to divert 
the flow out of the system, e.g. through a drain back to the supply 2, 
when the discharge 6 is closed, so as to prevent adverse pressure build up 
within the system. It is desirable to divert the flow at a pressure 
substantially less than the pressure within the system when the discharge 
6 is open, since by so doing the pump 4 operates under less load and 
thereby requires less energy. 
In conventional fluid delivery systems of this type, it is also common to 
regulate the pressure within the system when the flow is out the discharge 
6 to prevent pressure pulsations within the system caused by piston-type 
pumps. One such type of pressure regulator, of which applicant is 
co-inventor, is disclosed in U.S. Pat. No. 3,856,043. This pressure 
regulator 12 operates to relieve transient pressure rises within the 
system by directing a portion of the fluid within the system out of the 
system through the pressure regulator 12 and out a drain, e.g. a conduit 
21 connected back to the supply 2. Thus in operation, this type of 
pressure regulator 12 effectively removes a small amount of fluid each 
time it senses a pressure rise within the system. 
The present invention provides a method and apparatus for operating a fluid 
delivery system of the above-described type, and specifically a method and 
apparatus for diverting the flow out of the system at substantially 
reduced pressure when the discharge 6 is closed. Referring to FIGS. 2 and 
3, the invention is a bypass valve 11 which comprises generally a housing 
14, a movable piston 16, a channel 18 within the housing 14, and a 
slidable seal 20. 
The bypass valve 11 is one component of the fluid delivery system shown in 
FIG. 1. The housing 14 of the bypass valve 11 has a central cavity 13, an 
inlet 22 which is connected to the pump 4 by conduit 10, and an outlet 24 
which is connected to the discharge 6 by conduit 10. A bypass port 26 
preferably opens directly into the center of the pressure regulator 12, or 
if there is no pressure regulator located proximate the bypass valve 11, 
the bypass port 26 is connected directly to a drain, e.g. conduit 21 which 
leads back to the supply 2. 
Located within the housing 14 are a movable bypass port blocking means, 
e.g. a piston 16, and a slidable seal 20. The movable piston 16 has a 
central cylindrical portion 23 which has a diameter sufficiently less that 
the diameter of the wall 19 of the central cavity 13 so that fluid may 
freely pass the piston 16 from the inlet 22 to the outlet 24. The slidable 
seal 20 is designed so that fluid may flow around it and through a 
plurality of apertures 25 within it to the outlet 24. Thus neither the 
piston 16 nor the slidable seal 20 hinders the flow of pressurized fluid 
from the pump 4 to the discharge 6. 
The piston 16 is a shaft-like structure having an enlarged diameter portion 
27 at one end, a central cylindrical portion 23, and a conically shaped 
sealing means 28 at the other end. The conical sealing means 28 seals off 
bypass port 26 when it is seated within the complementarily shaped piston 
seat 46 located proximate the bypass port 26. The enlarged diameter 
portion 27 is bounded by two working surfaces 30 and 32. The working 
surface 30 has a larger effective area than the working surface 32. The 
two working surfaces 30 and 32 are separated from one another and 
generally permanently sealed from one another by "O" rings 34 and 36. The 
"O" rings 34 and 36 are between the outer walls 38 and 39 of the enlarged 
portion 27 of piston 16 and the wall 19 of the central cavity 13. A 
channel 18 within the housing 14 provides fluid communication between the 
two working surfaces 30 and 32. 
The working surfaces 30 and 32 and therewith the piston 16 are responsive 
to fluid pressure within the fluid delivery system generally and within 
the bypass valve 11 specifically. The larger working surface 30 has an 
effective area generally equal to the circular area of the end of the 
piston. The smaller working surface 32 has an area generally equal to the 
area of the annular surface defined by an outer wall 38 of enlarged 
diameter portion 27 and the outer wall 33 of the cylindrical portion 23. 
The piston 16 is positioned within the central cavity 13 of housing 14 and 
is movable therein only in a direction generally transverse to the 
direction of flow from the inlet 22 to the outlet 24. Because the piston 
16 is restrained from motion in other directions, only the fluid pressure 
within the bypass valve 11 which acts on the working surfaces 30 and 32 is 
effective to move the piston in either direction. Within the center of the 
piston 16 is an opening or passage 44 which provides fluid communication 
between the larger working surface 30 and the bypass port 26. Also located 
within the housing is piston travel adjustor 48 for varying the distance 
which the piston 16 may travel. Thus the limits of piston travel or motion 
are generally defined by the distance which the seat 46 and the adjustor 
48 are separated. A portion of the central cavity 13 generally defines a 
chamber 52 which is in fluid communication, by means of channel 18, with 
another portion of the central cavity 13 and with smaller working surface 
32 when the discharge 6 is open. 
The slidable seal 20 is located within the outlet 24 of the housing 14 and 
is movable therein. The slidable seal is oriented axially generally in the 
direction of flow through the bypass valve 11 from the inlet 22 through 
the outlet 24. The slidable seal 20 has a plurality of apertures 25 for 
permitting the passage of fluid around the slidable seal 20 and out the 
outlet 24 towards the discharge 6. The slidable seal 20 is acted upon by 
resilient means, e.g. spring 56, which moves it in the direction opposite 
to the direction of fluid flow from the inlet 22 towards the outlet 24. 
The slidable seal 20 has a conically shaped end 58 on which are located 
"O" rings 60 and 62. The slidable seal 20 is limited in its movement 
within the bypass valve 11 by the housing interior wall 64. The two "O" 
rings 60 and 62 are spaced on the conically shaped end 58 of the slidable 
seal 20 so that when the slidable seal 20 is at its innermost position so 
as to contact the interior wall 64 of the housing 14, the two "O" rings 60 
and 62 are on opposite sides of the channel 18. 
The pressure regulator 12, which is fully disclosed in U.S. Pat. No. 
3,856,043, comprises generally a movable plate 68 having a central orifice 
70. The movable plate 68 is restrained by springs (not shown) and is 
sensitive to fluid pressure within the fluid delivery system. When the 
pressure exceeds a predetermined level, the plate 68 moves away from 
surface 69 and bypass port 26 so as to permit the passage of a small 
amount of fluid between plate 68 and surface 69, through the orifice 70, 
and back through conduit 21 to the supply 2. Thus when the discharge 6 is 
open and the fluid pressure is being continually regulated by the 
regulator 12, fluid is intermittently passing through the orifice 70 in 
response to transient pressure rises such as those caused by the piston 
action of the pump 4. When the discharge 6 is open and bypass port 26 
blocked, the housing 14 permits fluid communication between the bypass 
valve 11 and the pressure regulator 12 by means of a plurality of openings 
72. 
The invention as thus described can be better understood by considering the 
function of the component parts in operation. Referring first to FIG. 2, 
which illustrates the position of the component parts of both the bypass 
valve 11 and the pressure regulator 12 when the discharge 6 is open, the 
sealing means 28 of the piston 16 is seated within the piston seat 46 
proximate the bypass port 26 so that the bypass port 26 is blocked. Thus 
with the discharge 6 open fluid passes into the inlet 22 of the housing 
14, is in fluid communication with plate 68 of the pressure regulator 12 
by means of the plurality of openings 72, and passes out the outlet 24 to 
the discharge 6. While fluid is flowing in such a manner with the 
discharge 6 open, the fluid pressure within the system is continually 
regulated by means of the pressure regulator 12 and small amounts of fluid 
are intermittently passing through openings 72, between plate 68 and 
surface 69 and out orifice 70 in response to transient pressure rises. 
When fluid is flowing through the bypass valve 11 and out the discharge 6, 
the slidable seal 20 is forced away from the channel 18 by the dynamic 
pressure of the flowing fluid and compresses the spring 56. Because the 
discharge 6 is open and the dynamic pressure of the flowing fluid forces 
the slidable seal 20 away from the channel 18 in such a manner, there is 
continual fluid communication by means of channel 18 between the two 
working surfaces 30 and 32. Because of such fluid communication and 
because the working surface 32 defines a plane generally parallel to the 
direction of flow of fluid so that the working surface 32 is thus 
responsive only to the static pressure of the flowing fluid, the fluid 
pressure on both working surfaces 30 and 32 is generally equal. However, 
working surface 30 has a greater effective area than working surface 32 
and thus the component fluid force acting on working surface 30 
substantially exceeds the oppositely acting force on the working surface 
32. Accordingly, the piston 16 is thus forced in position so that the 
sealing means 28 is seated within the piston seat 46 thereby blocking 
bypass port 26 and preventing any bypass of fluid through bypass port 26. 
Even though bypass port 26 is blocked by the sealing means 28, the 
plurality of openings 72 located proximate the bypass port 26 permit fluid 
communication between the bypass valve 11 and the regulator 12 so that 
fluid may pass between plate 68 and surface 69 and out through the orifice 
70 of the regulator 12 as the fluid pressure is continually regulated 
within the system. Even though the discharge 6 is open and bypass port 26 
is blocked, an extremely minute flow of fluid is passing from chamber 52 
through passage 44 in piston 16 and out the bypass port 26. 
Referring now to FIG. 3, the operation of the bypass valve 11 to divert the 
flow at a substantially reduced pressure can be better understood. When 
the discharge 6 is closed the flow of fluid through the bypass valve 11 is 
effectively stopped and thus the dynamic pressure acting on the slidable 
seal 20 is substantially reduced, essentially to zero. Thus the only 
forces acting on the slidable seal 20 when the discharge 6 is closed are 
the force caused by static fluid pressure and the spring force. Since 
fluid can pass freely on either side of the slidable seal 20 because of 
the apertures 25, the forces caused by the static pressure of the fluid 
are generally equal on both sides of the slidable seal 20. Thus the spring 
force is the determining force acting on the slidable seal 20. Because the 
spring 56 was compressed when the slidable seal 20 was biased away from 
the channel 18 by the dynamic pressure of the flowing fluid, this 
compressed spring force acts to now urge the slidable seal 20 against the 
interior wall 64 of the housing to thereby interrupt fluid communication 
between the two working surfaces 30 and 32 provided by the channel 18. 
With the channel 18 thus obstructed by the slidable seal 20, fluid 
communication between the two working surfaces 30 and 32 is interrupted 
and the fluid pressure acting on the two working surfaces 30 and 32 is now 
not necessarily equal. Bearing in mind that the pump 4 is continuing to 
introduce fluid under pressure into the system despite the fact that the 
discharge 6 is closed, the fluid pressure within the bypass valve 11 
begins to increase. At the instant the discharge 6 is closed, the sudden 
pressure rise within the bypass valve 11 causes the plate 68 of regulator 
12 to move away from surface 69 to thereby allow flow of fluid out orifice 
70. Also, the pressure on smaller working surface 32 begins to increase. 
Since the channel 18 is obstructed and since the fluid within the chamber 
52 is under pressure, the fluid within the chamber 52 passes out the 
passage 44 and out the bypass port 26. Thus when discharge 6 is closed, 
not only does the pressure on the smaller working surface 32 increase, but 
the pressure on the larger working surface 30 decreases. The effect is 
that even though the two working surfaces 30 and 32 have substantially 
different effective areas upon which the fluid pressure acts, the fluid 
pressure is substantially greater upon the smaller working surface 32 than 
upon the larger working surface 30 and thus the resultant force pushes the 
piston away from the piston seat 46 and the bypass port 26 to thereby open 
bypass port 26. When the piston is in such a position, as shown in FIG. 3, 
fluid now passes from the inlet 22 past the sealing means 28, out the 
bypass port 26, through the regulator 12 and back to the supply 2. Because 
the area of the opening of the bypass port 26 is significantly greater 
than the area of the opening of the nozzle 8, the fluid which is thereby 
diverted out the bypass port 26 flows at a substantially reduced pressure, 
thereby allowing the pump 4 to operate under less of a load with less 
demand for energy. 
The fluid pressure of the diverted flow may be altered by varying the 
adjustor 48 which varies the travel of the piston 16 and thus the 
effective area of the opening between sealing means 28 and piston seat 46. 
When the discharge 6 is closed and the piston 16 is in position as shown 
in FIG. 3, the pressure regulator 12 is essentially non-functional since 
all of the fluid from the pump is now directed through the bypass port 26 
at substantially reduced pressure. The plate 68 rests on surface 69 and 
none of the fluid passes through the plurality of openings 72 within the 
housing 14. 
Means are provided with the present invention for sensing the position of 
the piston 16 within the housing 14. Located within the housing 14 and 
projecting through the adjustor 48 is a plunger 74 which is movable within 
the adjustor 48. The lower tip 76 of the plunger 74 contacts a 
micro-switch 78. The end of the piston contacts the base 80 of the plunger 
74. A spring 73 maintains the plunger 74 in contact with the base of the 
piston 16 regardless of the position of the piston 16. Such an arrangement 
of a piston position sensing means thus permits the micro-switch 78 to 
activate any of numerous types of devices. For example, the micro-switch 
78 may be electrically coupled through a heater 82 in FIG. 1, so that when 
the piston 16 is not blocking the bypass port 26 and fluid is being 
diverted back to the supply 2, the heater 82 which heats the fluid within 
the supply 2 is turned off. The combination of the piston position sensing 
device with the heater 82 thereby saves energy since fluid which is 
diverted need not be reheated. Additionally, the micro-switch 78 may be 
electrically coupled to a chemical injection system 84 for introducing a 
second fluid into the system. For example, if it is desired to inject a 
chemical substance into the fluid, and further if the concentration of the 
chemical substance within the fluid must be maintained within specific 
limits, the injector 84 may be turned off when the bypass port 26 is open 
and fluid is being diverted back to the supply 2. 
It should be apparent that the present invention as thus described allows 
for the diversion of fluid out of a pressurized fluid delivery system at a 
substantially reduced pressure when the discharge 6 is closed, and further 
that the flow diversion means does not rely upon sudden pressure rises or 
the maintenance of a high pressure within the system to keep the bypass 
valve 11 open. Rather, it is the slidable seal 20 which is responsive not 
to sudden pressure rises but only to the cessation of flow and thus to the 
absence of dynamic fluid pressure, which effectively interrupts fluid 
communication between two working surfaces 30 and 32 of a movable piston 
16 so that static fluid pressure moves the piston 16 away from a bypass 
port 26 to thereby divert the fluid out of the delivery system at a 
reduced pressure. 
Because the bypass valve 11 is responsive to flow, and specifically to the 
cessation of flow, it is capable of functioning in fluid delivery systems 
which have multiple discharges. Thus the closing of one of the discharges 
does not activate the bypass valve 11 to divert the flow since fluid 
flowing out the remaining open discharges forces the slidable seal 20 away 
from channel 18. In certain conventional pressure-responsive bypass valves 
the closing of one discharge creates a pressure rise within the system 
which often inadvertently opens a check valve to prematurely divert the 
flow. 
It should also be apparent that while the specific embodiment discussed 
herein has related to the use of a liquid as the pressurized fluid, the 
present invention is fully operable if the fluid is a gas. The bypass 
valve will function equally as well if the fluid is a gas since the 
slidable seal 20 is responsive only to the dynamic pressure of the moving 
gas and since the two working surfaces 30 and 32 of the piston 16 are 
generally responsive only to the static pressure of the gas. 
While the preferred embodiments of the present invention have been 
illustrated in detail, it should be apparent that modifications and 
adaptations of those embodiments will occur to those skilled in the art. 
However, it is to be expressly understood that such modifications and 
adaptations are within the sphere and scope of the present invention as 
set forth in the following claims.