Fluid operated hydraulic pump including noise reduction means

A fluid operated hydraulic pump of the type using air pressure to produce high pressure hydraulic fluid wherein an air pressure driven motor and a hydraulic pump are positioned in adjacent axially aligned relationship and the air motor includes a reciprocating piston which drives the hydraulic pump. The air motor includes an exhaust passage having an expansion chamber therein for receiving exhaust air flow and including a plurality of baffles therein, the expansion chamber and the baffles functioning in combination to reduce the noise generated by the air motor without the use of other muffling material thereby avoiding undue back pressure in the air motor and increasing the speed and efficiency and operation of the air motor and the pump.

BACKGROUND OF THE INVENTION 
The present invention relates generally to improvements in fluid driven 
hydraulic pumps and more particularly to improvements in fluid driven 
motors used in such hydraulic pumps to drive the hydraulic pumps. 
Fluid actuated hydraulic fluid pressure producing units are shown, for 
example, in U.S. Pat. No. 3,041,975, issued July 3, 1962 to Atherton et 
al. and in U.S. Pat. No. 3,463,053, issued Aug. 26, 1969 to Leibundgut, 
both of these patents being assigned to the assignee in common with that 
of the present invention. 
Fluid actuated hydraulic power units of the type referred to in the above 
patents are generally intended to use a source of air pressure, such as 
that commonly available in garages or in industrial applications, and 
which produce air pressure on the order of 100 psi, to supply high 
pressure hydraulic fluid at pressures on the order of 10,000 psi to 
operate hydraulic fluid motors or other hydraulic tools. Such hydraulic 
power units include a reciprocating piston air motor wherein the piston is 
driven by the compressed air supplied to the air motor and wherein the 
piston is functional to reciprocate a piston of a hydraulic pump to 
thereby drive the hydraulic pump and supply high pressure hydraulic fluid 
through an output passage to a hydraulic tool or the like. 
During the operation of such power units, air flows through the air motors 
at relatively high velocities and as a result, unrestricted air flow 
through such power units generates a substantial amount of noise. The 
prior art apparatus has included muffling devices such as muffling 
materials placed in the exhaust passages of the power units in order to 
reduce the noise generated by the fluid motors. However, use of muffling 
materials generates back pressure in the fluid motor thereby decreasing 
its efficiency of operation and also functioning to reduce the speed of 
the fluid motor. 
SUMMARY OF THE INVENTION 
The present invention provides an improved fluid motor for use in a fluid 
driven hydraulic pump unit which includes an improved means for reducing 
the noise generated by the fluid motor without reducing the efficiency of 
operation of the fluid motor and without decreasing the speed of the fluid 
motor. 
The fluid motor of the present invention includes an exhaust passage 
extending between the motor chamber and the ambient atmosphere, the 
exhaust passage including an expansion chamber which facilitates expansion 
of the fluid being exhausted from the motor chamber whereby the velocity 
of this fluid is reduced and the noise level produced thereby consequently 
diminished. The expansion chamber also includes a plurality of baffles 
comprising planar vanes which extend into the expansion chamber to control 
the flow of fluid through the expansion chamber and further reducing the 
noise generated by the exhaust flow. The air motor also includes a 
substantial number of narrow passages extending between the expansion 
chamber and the ambient atmosphere to provide for fluid communication 
therebetween, the plurality of narrow passages functioning to prevent high 
velocity fluid flow from the air motor thereby cutting down the operating 
noise level of the fluid motor. 
Further advantages of the present invention will be apparent from the 
following description of a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, the power unit shown therein as embodying the 
invention comprises, in general, a unitary body 10 supported by a base 12 
and having an actuating lever or treadle 14 pivoted thereon. The body 10 
includes a fluid or air motor portion 16 closed at one end by an air motor 
valve block 18 and having a hydraulic reservoir housing 20 extending from 
its opposite end and a hydraulic pump valve block 22 interposed between 
the air motor 16 and the hydraulic reservoir housing 20. The body 10 is of 
generally cylindrical shape, and the air motor portion 16, air motor valve 
block 18, hydraulic reservoir housing 20, and hydraulic pump valve block 
22 are in axial alignment. The air motor 16 and the air motor valve block 
18 are shown as being comprised from plastic and can be advantageously 
formed by injection molding, however, a plurality of other materials such 
as die cast aluminum could be used. The air motor 16 is secured to the 
hydraulic pump valve block 22 by a restraining band 24 which can be 
received around an end portion 17 of air motor 16 whereby that end of the 
plastic air motor can be clamped against a projecting annular end 26 of 
the hydraulic valve block 22 by means of a tightening screw 28. The 
hydraulic reservoir housing 20 is comprised in part of a cylindrical 
sleeve 21 which includes an open end which is received around an end 27 of 
the hydraulic valve block 22 and secured thereto by screws 30. 
Live air or other pressurized fluid from a suitable source 32 (FIG. 3) is 
admitted through a conduit 33 to the air motor valve block 18 by means of 
an air inlet coupling 34, which is threadably received within a bore 35 in 
the valve block 18, and high pressure hydraulic fluid is discharged from 
the hydraulic pump valve block 22 through a high pressure pump outlet 
swivel coupling 36. 
Air Motor 
Referring to the air motor 16 and air motor valve block 18 shown in FIGS. 
3-7, air from the supply source 32 is intended to pass through the air 
inlet coupling 34 and through an air filter 38 threadably journalled 
therein and within the bore 35. The flow of air through the air inlet 
coupling 34 is governed by a check valve poppet 40 which includes a flange 
42 at one end receivable against a valve seat 44 (FIG. 4) to prevent fluid 
flow into the air motor. The check valve poppet 40 is axially slideably 
supported in an axial bore 46 in the air motor valve block 18 and is 
co-axial with the longitudinal axis of the air motor 16, hydraulic 
reservoir housing 20, and hydraulic valve block 22, and the axial position 
of the check valve poppet 40 is governed by a spring biased shuttle valve 
48 as will be described hereinafter. When the check valve poppet 40 is in 
a position to permit air flow into the bore 46 (FIG. 3), the air will then 
flow through a supply passage 50 (FIG. 5) in the air valve block 18 to a 
cylindrical bore 52 housing an actuating throttle valve assembly 54. The 
actuating throttle valve assembly 54 is slideably received in the bore 52 
and fluid-tight relationship is maintained by resilient O-ring seals 56. 
The actuating throttle valve assembly 54 includes a generally cylindrical 
valve body 55 and a slideable throttle valve poppet 57 which is axially 
movable within a bore 58 in the valve body 55 and which includes a flange 
60 at one end normally seated against a valve seat 62 of the valve body 55 
and biased toward a fluid flow restricting position by air pressure in the 
supply passage 50. The valve body 55 also includes a port 64 therethrough 
in open communication with the axial bore 58 in the valve body 55 and 
intended to facilitate air flow through an axial supply passage 66 in the 
air valve block 18 and air motor 16 whereby air can be supplied to the air 
motor displacement chamber 68. 
The air motor portion 16 also includes an axially aligned stepped 
cylindrical valve chamber 70 adjacent its end wall 71, the valve chamber 
70 being defined in part by a cylindrical bore in an axial projection 72 
of the air motor portion 16 and which is receivable in fluid tight 
relationship within the air motor valve block 18. The valve chamber 70 
slideably houses the shuttle valve poppet 48 which is in turn functional 
to permit exhaust from the chamber 68 into the valve chamber 70. 
An exhaust passage from the chamber 68 to the ambient atmosphere is defined 
in part by an exhaust port 85 which extends through the wall of the axial 
projection 72 from valve chamber 70 to a generally annular expansion 
chamber 87. The annular expansion chamber 87 is defined by a generally 
cylindrical cavity in the air motor valve block 18 defined by a 
cylindrical wall 87a and an end wall 87b, the cylindrical cavity also 
being bounded by the end wall 71 of the air motor 16 and surrounding the 
axial projection 72. As best shown in FIG. 7, the expansion chamber 87 
includes therein a plurality of opposed circumferentially spaced apart 
baffles 89 and 92 (FIGS. 4 and 5) which comprise generally planar vanes 
integrally attached to the cylindrical wall 87a and the end wall 87b of 
the air motor valve block 18 and opposed circumferentially spaced apart 
planar baffles 91 integrally attached to the end wall 71 and the axial 
projection 72 of the air motor 16, the baffles 89, 92 and 91 each lying in 
planes extending radially outwardly from the longitudinal axis of the air 
motor and project into the annular expansion chamber 87. The baffles 91 
are shown in FIGS. 7-10 as being positioned so as to be receiveable 
between the baffles 89 and 92 and in spaced apart relationship from them 
such that the baffles are arranged in the expansion chamber 87 in such a 
manner as to disrupt the direction of fluid flow through the expansion 
chamber but permit free flow of exhaust air from the exhaust port 85, 
through the expansion chamber 87 and to the atmosphere through a plurality 
of small exhaust ports 74 in the end wall of the air motor valve block 18. 
The arrangement of baffles shown in the drawings merely illustrates a 
preferred embodiment and other arrangements including baffles which may 
have shapes other than those shown could also be used. 
As hereinbefore explained, air or gas driven motor 16 comprises a gas 
displacement chamber 68; a motor piston 90 in chamber 68 reciprocably 
movable between two positions, i.e., such as the end of its intake and 
exhaust strokes; a gas inlet or supply passage 66 in the motor for 
admitting pressurized gas into chamber 68 to move the piston from one 
position (end of exhaust stroke) to another (end of intake stroke); a gas 
exhaust port 85a in the motor for allowing exhaust gas to be expelled from 
chamber 68; and a muffler on the motor and connected to gas exhaust port 
85a for exhausting gas to a region of pressure relief, such as atmosphere, 
and for reducing noise generated by such exhaustion. As FIGS. 7, 8, 9, and 
10 best show, the muffler comprises annular expansion chamber 87. The 
first or exhaust port 85 is connected to gas exhaust port 85a on the motor 
16 for directing pressurized gas into one portion of said annular 
expansion chamber 87. A plurality of second or small exhaust ports 74 
exhaust gas from another portion of the annular expansion chamber to the 
region of pressure relief outside the muffler. The baffle means located in 
the annular expansion chamber 87 on opposite sides of first port 85 and 
between the first port 85 and the second ports 74 are for the purpose of 
controlling gas flow between the first port 85 and the second ports 74. As 
hereinbefore explained, passage 94a is provided which, when piston 90 
moves near the end of its intake stroke, connects gas chamber 68 of motor 
16 to a point in annular expansion chamber 87 between the baffle means and 
the second ports 74. The annular expansion chamber 87 is defined by the 
pair of spaced apart end walls 87b and 71, the circumferential side wall 
87a extending between the end walls, and the axial projection 72 extending 
between the end walls. Port 85 is located in annular expansion chamber 87 
on one side of projection 72. The plurality of second ports 74 are located 
in annular expansion chamber 84 on another side of projection 72 in end 
wall 87b. The baffle means comprise a pair of spaced apart first baffles 
89 disposed on opposite sides of first port 85, each first baffle 89 
extending between the end walls 87b and 71 and circumferential side wall 
87a and extending toward but spaced from projection 72, each first baffle 
89 defining a first passage 89a near projection 72. A pair of spaced apart 
second baffles 91 are disposed on opposite sides of and spaced from the 
pair of first baffles 89, each second baffle 91 extending between 
projection 72 and circumferential side wall 87a and end wall 71 and 
extending toward but spaced from the other of end wall 87b, each second 
baffle 91 defining a second passage 91a near end wall 87b. A pair of 
spaced apart third baffles 92 are disposed on opposite sides of and spaced 
from second baffles 91, each third baffle 92 extending between projection 
72 and circumferential side wall 87a and end wall 87b and extending toward 
but spaced from the other end wall 71, each third baffle 92 defining a 
third passage 92a near end wall 71. The passages cause gas entering port 
85 to be directed by the baffle means through the first, second, and third 
passages and out through the second ports 74. 
The shuttle valve poppet 48 and the check valve poppet 40 are secured 
together in axially aligned relationship by a screw 83 extending axially 
through the shuttle valve poppet 48 and into a threaded bore 40b in the 
check valve poppet 40. Movement of the shuttle valve poppet 48 is thus 
functional to control axial movement of the check valve poppet 40. The 
shuttle valve poppet 48 also includes a molded resilient piston portion 75 
at one of its ends, the piston portion 75 being axially slideable within 
the valve chamber 70, and a coil spring 76 is positioned between an 
annular inwardly projecting flange 78 of the air motor 16 and the piston 
portion 75. A circular disc-like resilient seal 82 is secured by means of 
a backup member 82a and the screw 83 to the end of the shuttle valve 
poppet 48 opposite the piston 75 and is normally received against a seat 
84 of the annular flange around opening 85a to prevent exhaust of air from 
the chamber 68 through the valve chamber 70. The air motor 16 also 
includes a cylinder 86 which defines the air motor displacement chamber 68 
and which receives an axially movable piston 90 therein. A fluid tight 
seal is maintained between the cylinder walls of the cylinder 86 and the 
periphery of the piston 90 by a seal 108. 
In order to facilitate reciprocation of the piston 90 in the displacement 
chamber 68, fluid communication between the ambient atmosphere and that 
portion of the chamber 68 between the piston 90 and the hydraulic valve 
block 22 is provided by means of an air passage, shown in FIG. 3, and 
defined by a port 92a through the wall of cylinder 86, and a 
longitudinally extending passage 94a which communicates with the expansion 
chamber 87. The piston 90 also includes an annular groove 110 surrounding 
its circumference and a plurality of ports 112 to provide communication 
between the displacement chamber 68 and the groove 110 and to permit air 
flow through the port 92a as the piston 90 reaches the end of its forward 
stroke. 
The displacement chamber 68 is vented through a port 92 which is remote 
from the air motor valve block 18 and in communication with the bore 70 
through a cylindrical cavity 94, surrounding the cylinder 86, and through 
a passage 96 in the air motor valve block 18. The port 92 is positioned 
such that it is adapted to be uncovered by the air motor piston 90 only 
when the piston 90 reaches the end of its forward stroke. 
Seated against the front face of the air motor piston 90 is a small 
diameter hydraulic fluid pump piston 98 slideably receivable in a cylinder 
99 and operable to pump hydraulic fluid through passages in the hydraulic 
block 22 as will hereinafter more fully appear. The rear of the hydraulic 
pump piston 98 extends into the air motor displacement chamber 68 and is 
formed with an enlarged head 100 having a rounded or spherical bearing 
surface 101 urged against a complementary rounded surface 102 in the face 
of the piston 90 by a spring 104 compressed between and seated against the 
rear of the hydraulic valve block 22 and an annular disc 106 supported by 
the pump piston 98 and adjacent to its head end 100. 
The air motor 16 and the air motor valve block 22 of the embodiment of the 
invention shown in the drawings are each comprised of injection molded 
plastic. A particular advantage of constructing these components in such a 
manner is that the bores and passages formed therein as well as the 
baffles 89, 91 and 92 can be conveniently formed during the molding 
process avoiding subsequent manufacturing steps. 
Air Motor Operation 
In operation and assuming that the piston 90 begins its reciprocal movement 
in the position shown in FIG. 3, wherein the force of the spring 104 urges 
the piston 90 against the shuttle valve poppet 48 thereby causing the 
check valve poppet 40, secured in abutting relationship thereto by the 
screw 83, to move axially in bore 46 and the flange 42 thereof to be moved 
away from the valve seat 44 whereby air can pass through the bore 46 into 
the passageway 50 (FIG. 4). Movement of the flange 42 away from the valve 
seat 44 is accompanied by simultaneous engagement of the resilient seal 82 
against the seat 84 to close off exhaust flow from chamber 68 to the valve 
chamber 70. To cause actuation of the air motor, the operator depresses 
treadle 14 such that the tab 120 (FIG. 6) at the end of the treadle 14 
engages the upwardly projecting end 59 of the actuating throttle valve 
poppet 57 thereby moving the flange 60 away from the valve seat 62 and 
permitting compressed air to flow from supply passage 50 through passages 
64 and 66 into the cylinder cavity 68. The resulting air pressure in 
cavity 68 will force air piston 90 and the hydraulic fluid piston 98 to 
the position shown in FIG. 4 thereby providing a hydraulic fluid pumping 
effect. Such movement of the piston 90 to the end of its stroke will 
uncover the port 92 thereby permitting compressed air in the displacement 
chamber 68 to communicate through passages 94 and 96 with the valve 
chamber 70. The compressed air flowing through passages 94 and 96 into the 
chamber 70 will cause the piston portion 75 of the shuttle valve poppet 48 
to move to the left to the position shown in FIG. 4 against the force of 
the spring 76, and whereby the check valve poppet 40 is also moved to the 
left and the flange 42 of the check valve poppet 40 is received against 
the seat 44 thereby restricting further flow of air through the passage 50 
into the air motor 16. 
When the shuttle valve piston 75 moves to the position shown in FIG. 4, the 
disc 82 moves away from the seal 84 thereby permitting the compressed air 
within the displacement chamber 68 to exhaust through the valve chamber 70 
and to flow into the exhaust port 85. The exhaust air then flows through 
the exhaust port 85 and into the expansion chamber 87, and finally through 
the plurality of small exhaust passages 74. When the air flows into the 
expansion chamber 87, the air expands whereby the velocity of the air from 
the exhaust port 85 is reduced and whereby the noise level produced by the 
exhaust air is substantially reduced. The spaced apart baffles 89, 92 and 
91 in the expansion chamber 87 function to further reduce this noise level 
by disrupting the direction of air flow through the expansion chamber. 
As the compressed air is thus exhausted from the displacement chamber 68, 
the spring 104 forces the piston 90 to return toward its original position 
as shown in FIG. 3. As shown in FIG. 5, the piston 90 nears its original 
position, the piston 90 contacts the screw 83 and backup washer 82a 
thereby causing the shuttle valve poppet 48 and the check valve poppet 40 
to be forced to the right whereby the flange 42 of the check valve poppet 
40 moves away from the seat 44 to permit air flow from the supply source 
32 into the passage 50. Furthermore, it will be appreciated that before 
the piston 90 reaches the end of its return stroke, the flange 42 of the 
check valve poppet 40 is forced away from the seat 44 sufficiently that 
air flow through the passage 50 and into the displacement chamber 68 will 
effect damping of the return stroke of the piston 90. As long as the 
treadle 14 is depressed and the actuating throttle valve 57 is open, 
whereby passage 50 and the passages 64 and 66 are in communication, the 
air motor will continue to pump in a similar fashion as that described 
above until hydraulic fluid pressure in the cylinder 99 reaches a desired 
level. 
Hydraulic Fluid Pump 
In this manner, the hydraulic pump piston 98 is thus caused to reciprocate 
within the hydraulic pump cylinder 99 by the combined action of the air 
motor piston 90 and the return spring 104. While the hydraulic pump 
cylinder 99 may be formed directly in the hydraulic pump valve block 22, 
it is preferably formed as shown in a readily removable and replaceable 
cartridge 124 which is threadably received within a bore 125 in the 
hydraulic valve block 22. Fluid-tight relationship between the hydraulic 
piston 98 and cylinder 99 is maintained by a seal 126 secured within the 
cartridge 124 by a backup ring 128 and a snap ring 130. The hydraulic 
circuitry of the hydraulic pump is encased within the hydraulic valve 
block 22 (FIG. 3) and comprises in part a suction or supply passage 131 
extending from the hydraulic reservoir 132 within the hydraulic reservoir 
housing 20 past a spring biased ball check valve 134 to the hydraulic 
pressure chamber 135. The ball check valve 134 includes a ball 136 being 
seated against a removable seat 138 to close the passage 131 during the 
forward stroke of the piston 98 and being unseated to open the passage 131 
during the return or suction stroke of the piston 98. The ball 136 is 
biased against the seat 138 by a spring 139 supported by the end of the 
replaceable cartridge 124. The passage 131 extends through a generally 
hollow cylindrical hydraulic fluid filter 137 which is threadably secured 
within a bore 137a in the hydraulic valve block 22 and which extends into 
the reservoir 132. The fluid filter 137 is constructed from a material 
which permits hydraulic fluid to flow through it but which prevents 
impurities from entering the pumping chamber 135. 
The hydraulic valve block 22 also includes a high pressure discharge or 
outlet passageway 141 past a one-way ball check valve 142. The ball check 
valve 142 is comprised of a valve seat 143 threadably and removably 
secured within a bore 144 in the hydraulic valve block 22 and a check ball 
146 biased against the valve seat 143 by a spring 147. The outlet passage 
141 is defined by an axially extending bore 140 through the valve seat 143 
and by a longitudinal bore through a cylindrical sleeve 183 which has one 
end threadably secured within the bore 144 of the valve block 22 and 
another end supporting a freely rotatable coupling member 148 of the 
swivel coupling 36. The coupling member 148 includes a stepped central 
bore 149 in communication with the passage 141, the central bore 149 
including a threaded end 149a for threadably receiving a hydraulic hose or 
the like. A fluid-tight seal is maintained between the coupling member 148 
and the cylindrical sleeve 183 by a resilient O-ring 150 and relative 
rotation of the coupling member 148 around the end of the sleeve 183 is 
facilitated by a pair of retaining pins 152 extending through the coupling 
member 148 and receivable in a circumferential groove 152a in the sleeve 
183. 
Also formed in the valve block 22 is a relief valve assembly 150 comprising 
a generally cylindrical valve housing 151 threadably secured within a bore 
152 in the valve block 22, the relief valve assembly 150 intended to 
provide communication of hydraulic fluid between the hydraulic pressure 
chamber 135 and the reservoir 132 in the event the fluid pressure in the 
pressure chamber 135 becomes too great. A port 154 in the valve block 22 
extends from the hydraulic pressure chamber 135 into the bore 152 and a 
similar but transverse bore 156 extends from the bore 152 into the 
hydraulic reservoir 132. The cylindrical valve housing includes a central 
chamber 153 in communication with the port 154 through a bore 155 and 
similarly in communication with transverse bore 156 through a bore 159, 
however, fluid flow therethrough is prevented by means of a spring biased 
check valve 157 in the valve housing 151, the check valve 157 being 
comprised of a ball 158 received against a seat 160 and biased 
thereagainst by a spring 162 and a ball support member 164. The biasing 
force of the spring 162 can be adjusted by an accessible screw 166. 
The oil in the reservoir 132 is confined within a container formed by a 
flexible membrane or bladder 168 having a generally cylindrical shape and 
having one end reversed inwardly and received in fluid-tight relationship 
in a circumferential groove 167 around a cylindrical plug housing 169 
threadably received in a bore 171 in the end of the hydraulic reservoir 
housing 20. The other end of the container 168 is secured between the wall 
of the hydraulic reservoir housing 20 and the circumferential periphery of 
the valve block 22 and includes a circumferential bead 170 received within 
a circumferential groove 172 around the hydraulic valve block 22. The 
chamber 173 of the hydraulic reservoir housing 20 supporting the flexible 
membrane 168 is vented to the atmosphere by means of a vent hole 174. To 
permit access to the interior of the flexible membrane 168 for re-filling 
and like purposes, a suitable passageway 176 is provided within the plug 
housing 169 and is closed by a threaded plug 178. 
As previously indicated, the throttle valve 57 is actuated by downward 
movement of the treadle 14. While the design of the treadle 14 may, of 
course, be varied, it is preferable that the treadle 14 be pivotably 
mounted or supported at a point intermediate the ends of the hydraulic 
pump. Treadle 14 is shown in FIGS. 1 and 2 as including a pair of 
downwardly extending lobes 180 and 182 at its opposite sides, these lobes 
including bores therein and being respectively pivotably supported by a 
cylindrical shaft portion 181 of the cylindrical valve housing 151 and by 
the cylindrical shaft portion of the cylindrical sleeve 183 whereby the 
treadle 14 is supported for pivotal movement about a horizontal axis. In 
its preferred form, the treadle 14 is of integral one-piece construction 
and has a longitudinally rearwardly extending treadle portion 184 in turn 
having an end 120 positionable above the upwardly projecting end 59 of the 
throttle valve 57 to permit actuation of the throttle valve 57 upon 
downward application of pressure upon treadle portion 184. The treadle 14 
also includes a pair of forwardly and upwardly directed side arms 186 and 
188 joined at their upper or forward end by a cross piece 190. 
Hydraulic Pressure Release Mechanism 
To release the pressure developed in the high pressure hydraulic output 
passage 141 upon completion of the desired work, a release valve assembly 
200 is provided, operable for providing fluid communication between the 
output passage 141 and the hydraulic reservoir 132. A threaded bushing 192 
is threadably removably secured within a threaded bore 194 in the 
hydraulic valve block 22 and the bushing 192 includes a central concentric 
stepped bore 196 therein communicating with the output passage 141 through 
a plurality of passages 197 (FIG. 3) 198, and 199 (FIG. 6). The bore 196 
houses a reciprocal plunger 204 and a spring biased check ball 206 which 
is receivable against a removable valve seat 208 and biased there against 
by a spring 210. The reciprocal plunger 204 is biased away from the ball 
206 by a spring 215 in turn supported against valve seat 208. The fluid 
passage 199 which is in communication with the output passage 141 by means 
of passages 197 and 198 is also in communication with an annular chamber 
212 of the stepped bore 196. Due to the high hydraulic fluid pressures 
created within the output passage 141 and consequently within the chamber 
212, the check ball 206 is forced against the seat 208 with substantial 
force. It is desireable, however, that the plunger 204 be easily movable 
to unseat the ball 206 in order to release fluid pressure in the output 
passage 141, i.e., to permit fluid flow from the chamber 212 through the 
bore 214 in the seat 208 and consequently through the passage 216 and 
through a passage 218 into the reservoir 132. To thus facilitate 
reciprocation of the plunger 204 and movement of the ball 206 away from 
valve seat 208, a passage 220 is provided connecting the chamber 212 with 
an annular chamber 222 in the stepped bore 196. Furthermore, the plunger 
204 is provided with a stepped configuration and an annular flange 224 
adjacent the annular chamber 222. The differences between the cross 
sectional areas between the upper end 226 and the flange 224 is only 
slightly less than the effective cross sectional area of the bore 214 and 
the fluid pressure upon the flange 224 and the upper end 226 will be equal 
to the fluid pressure upon the ball 206. Thus, the forces on the ball 206 
and the plunger 204 will be substantially balanced and the necessary 
downward force on the plunger 204, which is necessary to force the ball 
206 away from the seat 208 to permit fluid flow through the passage 214, 
will be relatively small. In order to further provide means for easy 
manipulation of the plunger 204, the upper end of the plunger supports a 
roller 228 receivable against a curved cam surface 230 comprising an 
integral configuration of the lower portion of the treadle 14. The curved 
cam surface 230 is particularly provided with a configuration such that 
the wedge angle between the cam surface and the roller 228 is very slight 
when the cam surface 230 and plunger 204 are in the position shown in FIG. 
6. Pivotal movement of the treadle 14 in the counterclockwise direction as 
seen in FIG. 6 will generate a downward force on the plunger 204 whereby 
the check ball 206 can be biased away from the seat 208 and hydraulic 
fluid caused to return to the reservoir 132. The cam surface has the 
particular configuration that as the treadle 14 is further depressed and 
cam surface 230 moves relative to the plunger 204 the wedge angle 
increases. This construction facilitates substantial reciprocal travel of 
the valve plunger 204 once the ball 206 has been unseated thereby 
facilitating increased fluid flow back to the reservoir once the ball 206 
has been unseated. 
RESUME 
The fluid motor of the present invention provides an improved means for 
substantially reducing the noise generated by exhaust fluid flowing from 
the fluid motor and avoids the use of muffling materials thereby avoiding 
the back pressure in the fluid motor normally caused by use of muffling 
materials and increasing the efficiency of operation of the motor. The use 
of muffling materials is avoided since the fluid motor exhaust passage 
includes an expansion chamber wherein fluid flowing from the motor chamber 
is allowed to expand thereby reducing the velocity of air exhausted into 
the atmosphere. The expansion chamber is also provided with baffles 
disposed therein to disrupt the direction of flow of exhaust fluid and to 
function to decrease the kinetic energy of the exhaust fluid. In order to 
further control the noise resulting from the exhaust fluid, the exhaust is 
conveyed from the expansion chamber to the atmosphere through a plurality 
of passageways thereby avoiding constriction of the exhaust fluid through 
a single passage. 
A further advantage of the invention described is that the air motor is 
comprised of molded plastic components, the construction of the fluid 
motor and fluid motor valve block being such that the expansion chamber 
can be readily formed and the baffles molded integrally with the fluid 
motor components.