Dual pressure gas motor, and method of operation

A cylindrical shell with a double acting piston, having a high pressure area and a low pressure area on each side thereof, is provided with a valve for alternately injecting high pressure gas to each small area to provide an initial piston drive, and valving for injecting gas under the pressure, opposite from the first high pressure end to the opposite larger area providing a secondary piston drive using expansion of the high pressure expanded gas from the opposite end of the piston. In reversing the piston, the opposite end becomes the drive end in the same manner. In one form, a two position slide valve, initially actuated by piston movement and completed by gas pressure movement, provides a transfer means for gas streams internally of the motor and for exhaust of the secondary expanded gas. The valve is arranged for an initial mechanical movement from one position toward the other position by contact with the end wall of the low pressure cylinder and then completely moved to other position by gas pressure. This arrangement permits a very slow piston reciprocation without stalling.

The present invention relates to gas driven reciprocating motors, 
particularly for driving liquid pumps, however, such motors may be used 
for driving other types of devices from its reciprocating piston rod. 
The invention may be classified as a free valve, gas operated motor, and 
may be considered as a compound, two-stage-gas-drive reciprocating motor, 
and hereafter the invention may sometimes be referred to simply as motor. 
High pressure air or gas has been used to operate various types of motors, 
pumps or machinery, and it is known to be desirable to take advantage of 
the expansion of the gas from its initial high pressure to a low pressure 
and thereby use some of the pressure energy in the gas. In the use of gas 
operated motors, it is sometimes necessary to use more than one stage in 
the motor to take a further economical advantage of the two stage 
expansion of the high pressure gas. Commonly, dual acting pistons have 
been used for two stage motors, and for more sophisticated motors two or 
more pistons have been used, with each piston driving a reciprocable pump. 
High pressure, natural gas is commonly used for operating a motor for 
pumping glycol in a well-head dehydrator installation, wherein gas is 
separated from the water and the hydrates in the gas. The operation 
involves pumping glycol as a dehydrator for the gas, and the glycol is 
circulated between a gas contact chamber under high pressure to a 
regenerator-drier where the water is removed from the glycol from a lower 
pressure. Gas power motors and glycol pumps have heretofore been used for 
this purpose. The depletion of cheap natural gas, however, has required a 
change in this procedure, and has created a substantial need for a more 
efficient gas powered motor. More importantly, the gas source for the 
wellhead pumps, which were in past years at comparatively high pressure, 
such as a thousand pounds per square inch or more, are generally now at 
much reduced pressures. Thus, few problems were previously encountered in 
using gas powered motors for glycol pumps in wellhead treaters, but at the 
present, many of the established gas sources, now at the lower pressures, 
render the conventional gas powered motors for the glycol pumps unsuitable 
and inefficient for purposes at hand. 
PRIOR ART 
The compound steam or gas engine shown in U.S. Pat. No. 1,627,427 has a two 
stage piston, which is a double acting piston for both the high pressure 
and the low pressure stages. The major concept of the invention is to 
mechanically control the action of the valve which controls the movement 
of the piston. This engine uses a steam chest with a reciprocable sleeve 
which acts as a valve, that is mechanically positioned by a controlled rod 
to determine the operation of the engine as (1) a compound high and low 
pressure engine, (2) as a high pressure engine of reduced power, or (3) as 
a high engine of maximum power. The actual operation of the piston 
controls the movement of the engine slide valve by mechanical movement of 
a push-pull rod connected to the slide valve. The patentee states that the 
entire internal valve is reciprocated lengthwise by means of the push-pull 
rod, which in turn is reciprocated by an eccentric mounted on piston rod. 
In U.S. Pat. No. 3,846,049, a pilot valve is mechanically shifted by a 
push-pull rod from a single stage hydraulic motor to change the flow of 
hydraulic fluid to one side or the other of piston of the hydraulic motor. 
The pilot valve acts to shift a spring loaded slide valve which 
alternately introduces hydraulic pressure into one chamber of the piston 
motor while releasing hydraulic fluid from the other chamber of the piston 
motor. Neither the pilot valve nor the spring loaded slide valve is free. 
U.S. Pat. No. 134,212 shows a tappet rod for reciprocating the distributing 
slide valve of a piston motor. Carr et al U.S. Pat. No. 186,539 
reciprocates a slide valve to a piston, reciprocating motor by a rocker 
actuated push-pull rod. The rocker is actuated by the piston of the motor. 
Thomson U.S. Pat. No. 683,523 shows a compound, single acting, high 
pressure one side and single acting low pressure other side piston motor. 
The slide valve of the motor is moved by a push-pull rod bearing against 
an eccentric fitted on the motor shaft. 
The hydraulic tandem piston pump of Shaddock U.S. Pat. No. 3,700,360 uses 
solenoids to actuate a pilot valve for moving a spring centered spool 
valve. Staats U.S. Pat. No. 2,862,478 uses a spring powered valve rod to 
shift hydraulic fluid from one side to the other side of a single stage 
double acting piston motor. The outlets from each cylinder end are open to 
a common outlet manifold which exhausts out a common outlet line. Due to 
the open outlet ports this motor would probably not be operatable without 
check valves or the like in the outlet ports. 
Other gas motor disclosures show various types of units, for example, 
French Pat. No. 1,143,694 using a compound, two separate pistons, gas 
motor, with each piston having its own slide valve shows one type. Moeller 
U.S. Pat. No. 3,019,735 shows a two piston, each single acting, motor-pump 
combination requiring 3 separate slide valves for operating the single 
pistons transferring gas from chamber to chamber of the piston motors. 
This is accomplished by the piston, with an attached eccentric actuating 
the push-pull rod of the valve, exemplified by railroad steam engines. The 
second type gas or hydraulic motors which do not have an external means 
(usually a push-pull rod) to actuate the slide valves must operate at a 
high speed, and these have complicated valving arrangements, and are not 
automatic operating motors suitable for remote unattended use. 
OBJECTS AND ADVANTAGES OF THE INVENTION 
Included among the objects and advantages of the present invention is to 
provide a compound, two stage drive piston motor, of a reciprocating 
piston type, which is arranged in a manner that produces an automatic, 
slow speed continuous pumping action, using gas at two pressure levels for 
expansion to drive a gas motor, for operating piston pumps, and other 
types of machinery from a reciprocating piston rod. 
Another object of the invention is to provide a two stage gas driven, 
reciprocating piston motor of simple design, which may be easily 
manufactured, and simply and easily maintained. 
Still another object of the invention is to provide a compound, two stage, 
reciprocating piston motor, which is especially suited for operating at 
low speed, for actuating piston type fluid pumps, particularly pumping 
glycol or other fluid. 
Yet another object of the invention is to provide a novel, improved gas 
operated, reciprocating piston motor which may operate through the 
expansion of the driving gas, and which is easily adapted to operate 
automatically at a wide range of different available gas pressures. 
An additional object of the invention is to provide an improved gas 
operated motor which will provide maximum expansion of the driving gas to 
minimize the quantity of gas required for the operation of the motor, and 
includes a slide valve design permitting slow speed reciprocation of the 
piston without stalling. 
Other objects of the invention are to provide an improved compound two 
stage gas operated motor which is rugged and durable, reliable and capable 
of operating for long periods of time without maintenance, and which may 
be readily and easily controlled as to speed of reciprocation of the 
piston under various pressure conditions. 
These and other objects and advantages of the invention may be readily 
ascertained by referring to the following description and appended 
illustrations:

DETAILED DESCRIPTION OF THE ILLUSTRATION 
In accordance with the invention, a cylindrical piston is mounted for 
reciprocation in a cylinder housing with a piston rod extending from one 
end of the housing to provide activation of a driven unit. The drawings 
are illustrated with a combined motor and a liquid pump. This is one 
method of the use of the motor of the invention. Other types of driven 
units may be driven from the piston rod. 
The slide valve configuration with the gas passages is critical to slow 
speed operation of the motor without stalling. In a cycle, where the 
piston assembly is moving in one direction under the influence of gas on 
the piston, it is important to mechanically move the slide valve (by 
contact with a cylinder wall) for the initial phase where exhausting gas 
from the chamber is stopped and expanding gas is admitted while the piston 
is still reciprocating in the one direction, so that the slide valve is 
fully actuated the opposite direction by gas pressure, while the piston 
continues in the one direction to the end of its stroke. Unless the double 
actuation occurs during the oneway movement of the piston, the motor will 
stall. 
In the device illustrated in FIG. 1, a shell housing 10 for a gas motor, 
provides a primary cylinder section 12 in which a cylindrical double 
acting piston assembly 14 reciprocates. A centrally disposed, 
circumferential section 16 of the housing provides means for the 
reciprocation of an integral, second stage, double acting secondary, 
piston assembly 14a mounted centrally on the piston 14. A pump housing 20 
is integrally mounted with the housing 10 joining the left side of section 
12, and this housing provides for the reciprocation of a piston 21 of the 
pump connected, by means of a piston rod 22, to one end 40 of the motor 
piston 14. Thus, the piston 21 reciprocates jointly with the reciprocation 
with the piston 14. The pistons are cylindrical, reciprocating in 
cylindrical cylinders and the pistons are free to rotate in the housing. 
The motor is provided with a gas inlet 30 and a gas outlet 32. The inlet 30 
communicates at all times, by means of an internal inlet passage 31, 
through the housing into annular passage 33 in the left end of the piston. 
The arrangement provides inlet gas completely around the circumference of 
the piston. The annular passage 33 is connected by means of an interior 
passage 34, through the piston, to a circular passage reciprocably housing 
a slide valve 35, illustrated in large detail in FIG. 3. The inlet passage 
34 is in continuous communication with an annular groove 36 around the 
center portion of the valve 35 and defined by lands 35a and 35b. The inlet 
gas passage is arranged to be in communication with the annular groove at 
all times, to provide a continuous supply of incoming high pressure gas 
into the groove 36. A passage 37 in the piston 14 routes from a point 
adjacent the port or outlet of passage of 34 to left end 39 of the piston 
14, providing a passage for gas into and from a chamber LP at the left end 
of the piston. A primary chamber LP is formed by a cylinder head 12L at 
the end of the housing enclosing the left end of the cylinder 12 and the 
piston end 39. In a similar manner, a passage 38 starting adjacent the 
port or outlet of passage 34, extends thru the piston 14 to an outlet in 
right end 40 of the piston 14 into the right primary chamber RP formed by 
the end of the piston 40 and cylinder head 12R closing the chamber RP. 
While the slide valve 35 is arranged so that passage 34 is always in 
contact with the circumferential groove 36, the passages 37 and then 38 
will alternately be in contact with the groove 36, to alternately provide 
high pressure (incoming) gas into the primary chambers at either end of 
the piston 14. The secondary, integral piston 14a is provided with an end 
area 42 at the left end and an end area 43 at the right end, which provide 
secondary chambers SL and SR, respectively with the cylinder closures or 
heads 16L and 16R, at each end of the secondary housing 16. The secondary 
piston 14a provides the chamber SL, defined by the left end 42, annular 
cylinder 16 and ring shaped head 16L. On the opposite side of the 
secondary stage of the motor, chamber SR is defined by the piston end 43, 
cylinder 16 and the ring shaped head 16R. 
On either side of the annular groove 36 on the slide valve is an adjacent 
small annular groove. These are a groove 46 at the right side and a groove 
47 at the left side. Bore 48 in the groove 46 is an inlet to passage 48 
providing a passage from the groove to the valve end 35R. In a similar 
manner, a bore 49, starting at the bottom of the groove 47, extends 
through the slide valve to the end 35L. A snap ring retainer 50 is mounted 
in a groove adjacent the right end of the valve, and a snap ring retainer 
51 is mounted in a groove adjacent the left end of the valve, to limit 
motion of the reciprocating valve in its circular passage in the secondary 
piston 14A. 
An outer annular groove 55 is located in th peripheral, circumferential 
surface of the secondary piston 14A, and it communicates by means of 
passage 56 at the right side and passage 57 at the left side with the 
slide valve bore. The passages 56 and 57 communicate with annular grooves 
46 and 47 when aligned therewith. The piston 14 is sealed in the cylinder 
12 by means of outer seal rings 60 and 61 (on opposite sides of groove 33) 
at the left end, and a seal ring 62 adjacent end 40 at the piston's 
opposite end. In a similar manner the secondary piston is sealed by seal 
ring 64, at one side, and seal ring 65 at the opposite side. 
The piston of the pump 21 reciprocates in the chamber of the cylinder 20, 
and the outer end of the cylinder 20 is sealed by an end wall or head 20R. 
The piston is sealed in the cylinder by means of a seal ring 70. The pump 
piston is a double acting piston, and is provided with inlets 71R and 71L 
respectively to right and left pump chambers. Each inlet is provided with 
a check valve 72 in a line connected to a common liquid inlet or feed line 
73. The pump is, also, provided with an outlet for each chamber in the 
form of passages 74R and 74L, which pass through check valves 75 to a 
common outlet 76, variously closable by throttle valve 78, all in 
conventional manner. 
The general operation of the motor is as follows: 
High pressure gas enters thru inlet 30 into the passage 31 and then into 
the annular groove 33. This provides gas at inlet gas pressure into line 
34 and the groove 36 in the valve, for passage into either the passage 38 
or 37. In the position of the valve of FIG. 1, the annular groove 36 is 
arranged to direct high pressure gas through the passage 37 into the 
chamber LP at the left end of the piston. Gas from the previous stroke or 
cycle in chamber RP passes through the passage 38, which is in contact 
with the groove 47, so that the gas passes through the slide valve passage 
49 into the chamber SL. 
The surface area of primary piston end 39 or 40 is substantially less than 
the area of either side 42 and 43 of the secondary piston. For example, 
the area of the piston end 39 is substantially less than the area of 
piston end 42 of the secondary piston, and the area of the end of 
secondary piston 43 is larger than the area of the piston end 40. Thus, as 
high pressure gas enters the chamber LP, at a constant, approximate inlet 
pressure Ps, it initiates movement of the piston to the right as indicated 
by the arrow. This continues until slide valve 35 is mechanically, and by 
gas pressure, moved to the left before the end of the piston stroke, 
cutting off the incoming gas. The piston, by one or the other primary 
chambers, is subject to full pressure of the incoming gas for a 
substantial portion of its stroke. Any gas in the chamber RP (from the 
previous stroke) passes through passage 38 into the passage 49 and expands 
into the chamber SL, where expansion of the gas against the larger piston 
area aids in forcing the piston to the right. At the same time the outlet 
56 is in communication with the groove 46 and gas in chamber SR passes 
through the passage 48 and out to the passage 56 into the groove 55 and 
thru the outlet 32. Thus, as high pressure gas is introduced at an inlet 
pressure into the chamber LP, the secondary chamber SR is exhausting gas 
through the outlet, while gas in chamber RP is passing into chamber SL for 
expansion and a secondary power force on the piston. The piston on its 
travel to the right causes the valve 35 to contact the wall 16R and the 
slide valve is pushed to the left changing the communication of the 
passages of the valve, as shown in FIG. 2. With the valve 35 shifted to 
the left, the high pressure gas is now introduced into chamber RP through 
the passage 34 into the groove 36 and through the passage 38 into the 
chamber RP. In the meantime gas in chamber SL has exhausted through the 
outlet 32 via passage 49, groove 47 and groove 55, while the gas in 
chamber LP passes through the passage 37 into the chamber SR to provide 
additional power for the stroke. There is, therefore, a net increase in 
the force acting on the two stage piston. The forces which combine are the 
incoming gas pressure acting on the ends of the primary piston 14, and the 
gas exhausting from the ends of the primary piston 14 to expand against 
the areas of the secondary piston 14A, thus providing additional work but 
at a lower pressure than the initial pressure entering the inlet through 
30. Detailed valve action in a cycle is given below. 
The proper automatic and efficient operation of the pump, particularly at 
very low operating speeds, is dependant on the configuration of the 
completely free slide valve, and the proper shifting cannot be done 
totally by mechanical action (wall contact and piston movement) mainly the 
movement of the motor piston. A pressure force must be used to complete 
the valve shifting action after an initial mechanical movement, making the 
motor an internally actuated, automatic piston motor. 
The design of the valve is critical for the slow, automatic functioning of 
the motor. The sequence of operation is shown in FIGS. 5-8. At one point 
in a cycle, shown in FIG. 5, the piston is moving to the left, indicated 
by the arrow, wherein the right primary chamber RP is being charged with 
high pressure gas from passage 34 passing the valve through annular 
passage 36, formed by lands 35a and 35b, into passage 38. The left primary 
chamber LP is communicating through passage 37 into passage 48 of the 
valve and into the right secondary chamber SR. The left secondary chamber 
SL is exhausting through passage 49 in the valve to annular passage 47. 
From passage 47 the exhausting gas goes out passage 57 to annular passage 
55 then out the outlet 32. In FIG. 6, the first valving sequence of the 
cycle occurs after initial contact of the valve end 35L with the left head 
wall 16L. The valve shifts slightly to the right (as the piston continues 
left) until the edge 47a (one side of the annular passage 47) exactly 
closes the port to the exhaust passage 57. The gas remaining in SL chamber 
is now trapped and is compressed slightly as the piston moves left to its 
limit of movement. As the piston continues to move left, the valve is 
pushed to the right to the condition of FIG. 7. In this condition land 35a 
completely closes passage 38, while gas from the left primary continues to 
pass from passage 37 into chamber SR. The edge 47b is at zero lap with the 
port of passage 38 completely shutting passage 38. The primary chamber RP 
is no longer receiving high pressure gas from the passage 38, while the 
gas in chamber SL is still trapped and still undergoing slight 
compression. The final phase of the valve shift is shown in FIG. 8. The 
edge 47b of land 35a opens slightly to passage 38, permitting high 
pressure gas from primary chamber PR into secondary chamber SL. The 
pressure in opposite secondary chamber SR is only a fraction of the higher 
pressure gas entering chamber SL, so that the pressure differential 
between the two secondary increases, and the greater pressure in chamber 
SL causes the valve to move suddenly to the right against the lower 
pressure in chamber SR. Because of the unbalanced force the valve moves 
completely to its far right position. The piston continues to move to the 
left after the valve has moved to the right, and the piston reverses at 
the end of the left movement because of high pressure, incoming gas in 
chamber LP, and the primary expanded gas from chamber RP going into 
secondary chamber SL. The end of the cycle is on the reversal of the 
piston, and a second cycle commences, as described above, except the 
action is to the left. 
The design of the valve configuration in conjunction with the ports of the 
passages, cause the initial valve movement as a mechanical movement of the 
valve by impingement or stepping on the chamber wall while the piston is 
moving toward the wall. The pressure differential between the two upper 
secondary chambers causes the sudden pressure shift of the valve in the 
same direction. The mechanical movement is necessary for the initial 
changing of the ports, and to change gas pressure differentials in the 
secondary chambers causing the gas the pressure movement of the valve. 
This is critical to the slow operation of the motor, especially in the 
speed range below about 50 cycles per minute, and particularly in the very 
low speed ranges of 5-15 cycles per minute. 
It is preferable to have the passages in the motor of sufficient size to 
provide a low pressure drop of the gas passing through the passages. 
Particularly it is preferable to have the openings to the outlet sized so 
that the gas pressure is almost immediately reduced in the chambers SR and 
SL when connected to the outlet. 
In the action of the pump, when the piston 21 is traveling to the right 
side, the inlet check valve is closed and the liquid under pressure is 
forced off through the outlet passage and 74R check valve into the common 
outlet 76. On the opposite side of the piston there is an intake stroke 
wherein the outlet check valve is closed, the inlet check valve is open, 
and liquid is pulled into the chamber. As the piston reverses, the action 
is reversed so that liquid is forced out of the chamber on the left side 
and liquid is drawn into the chamber on the right side, as is conventional 
with reciprocating piston pumps. 
By the use of a throttle valve 78 on outlet line, the pressure of the 
outlet liquid may be controlled to control the speed of the pump. By 
restricting the outlet line, the speed of the pump (and motor) is reduced. 
The pump may pump liquid or gas, depending on the unit. Also, the piston 
rod may be used to drive other types of machinery using a reciprocating 
motion for the drive. 
The speed of the pump may also be controlled by throttling the inlet gas 
supply using a conventional throttle valve (not shown).