US3815481A

US3815481A - Power cylinder with piston return by own vacuum force

Info

Publication number: US3815481A
Application number: US00244019A
Authority: US
Inventors: R Pauliukonis
Original assignee: Individual
Current assignee: PAULIUKONIS GRAZINA I
Priority date: 1972-04-14
Filing date: 1972-04-14
Publication date: 1974-06-11
Anticipated expiration: 1991-06-11

Abstract

A power cylinder converting pressure energy into linear motion and more particularly to a power cylinder having cylinder and piston of differential diameters and designed so as to create vacuum force by the piston forward motion inside a cylinder subjected to pressurized fluid to extend a piston rod attached thereto and to perform work, said vacuum force large enough to return piston and rod assembly back into the original first retracted position without the use of springs and capable of operating as a double acting cylinder controlled by a simple 3way valve of solenoid or manual type.

Description

United States Patent [1 1 Pauliukonis June 11, 1974 [76] Inventor: Richard S. Pauliukonis, 6660 Greenbriar Dr., Cleveland, Ohio 44130 221 Filed: Apr. 14, 1972 1211 Appl. NO; 244,019

[521 US. Cl 92/86, 92/130, 92/132, 92/170, 92/248 [51] Int. Cl. FOlb 31/00, Fl6j H00 [58] Field of Search 92/86, 107, 130, 132, 152, 92/170, 248, 249; 91/469 2,982,257 5/1961 Fagge 92/152 X 3,040,712 6/1962 Harrah 92/248 X 3,063,423 11/1962 Riordan l l 92/86 X 3,376,795 4/1968 Allen 92/132 X Primary Examinerlrwin C. Cohen [57] ABSTRACT A power cylinder converting pressure energy into linear motion and more particularly to a power cylinder having cylinder and piston of differential diameters and designed so as to create vacuum force by the pisston forward motion inside a cylinder subjected to pressurized fluid to extend a piston rod attached thereto and to perform work, said vacuum force large enough to return piston and rod assembly back into the original first retracted position without the use of springs and capable of operating as a double acting cylinder controlled by a simple 3-way valve of solenoid or manual type.

7 Claims, 2 Drawing Figures POWER CYLINDER WITH PISTON RETURN BY OWN VACUUM FORCE The present invention relates to the fluid power equipment, and more particularly to an actuating power cylinder applicable alike to single acting or double acting actuators energized either hydraulically or pneumatically in a-given power system, although in its preferred specific embodiment, it is most efficient in single acting cylinders.

The inherent defects and shortcomings of existing power cylinders of the double acting type necessitating the use of 4-way valves for their operation, result in premature cylinder deterioration when subjected to unidirectional load service because of the physical abuse the cylinder experiences upon return with full force of the working fluid affecting the piston and cylinder end with resultant energy waste and product deterioration prematurely, in particular if employed with pressure reducers in a conduit less loaded because of reducer inefficiency in the ultimate analysis, plus extra cost, extra spacerequirements and system reliability reduction, all passed over to the user of conventional systems at the expense of ignorance and lack of better components.

In single acting-spring return cylinders thatnormally require theme of a 3-way directional valve for their operation, the return of the piston from the extended position to that of the retracted position is done by a spring assembled thereto, with the spring resistance representing a sizeable energy loss during the spring compression cycle. In addition, the use of a spring requires an extra length of cylinder body for spring accommodation with more waste. Standard diameter piston rods presently used with conventional cylinders are limited as to the side loads they tolerate.

Prior art cylinders normally made of metallic cylindrical bodies within'which are located all metallicpiston rod assemblies and metallic end caps, including appropriate elastomer seals, and consisting of a piston to which an actuating rod is secured permanently either by soldering or simply by bolting together, can beconsidered obsolete in view of the proposed improvements this invention offers. it is obviously desirable to provide cylinders of simplified design with improved quality, performance and operating capabilities. It is also desirable to provide a cylinder which can be mass produced utilizing a process and equipment known to reduce cylinder manufacturing costs. The present invention provides a cylinder which incorporates completely new features in cylinder design, with differential diameter piston capable of being mass produced at reduced manufacturing cost. This cylinder even when produced by conventional means provides design simplification and improved service, because of a built in facility to perform as a double acting cylinder, while actuated by a simple 3-way directional valve as a result of a vacuum force, such design further enabling cylinder operation as either a single acting or as a double acting cylinder.

Further, when operating as a double acting cylinder the piston rodassembly retracts automatically by its own vacuum force created by the differential diameter piston inside differential diametercylinder thereby dispensing of a costly 4-way valve conventional double acting cylinders necessitate. When operating as a single acting cylinder actuated by a 3-way valve, the automatic re-traction of piston rod assembly permits dispensing of springs conventional single acting cylinders necessitate. This invention also enables the fabrication of an all-plastic power cylinder with one-piece piston rod assembly at a drastic cost reduction. It further provides a means of molding a differential diameter piston with a rod of metal, is desired, or for integrally molding at least one end cap with the differential diameter cylinder body from any material, metal or plastics.

The present invention provides cylinders of this general type which are simple in design because of reduced cylinder complexity, and hence competitive in cost. It should be noted that the cylinder according to the present invention is particularly suitable for miniaturization and automation, but is by no means limited to it.

These and other objects and advantages of the invention will become more fully apparent from the following description of the embodiment of the invention. taken together with the accompanying drawings.

IN THE DRAWINGS.

FIG. 1 is a cross-sectional view of a typical power cylinder of differential diameter design with piston rod retracted, and a piston rod assembly fabricated.

FIG. 2 identifying functionally identical cylinder to that of FIG. 1 except for position of piston, shows the details of an all plastic cylinder of differential diameter design which are typical to injection molded products. with piston rod extended depicting evacuated annulus more conspicuously.

Shown in FIG. 1 is an all-metal one piece cylinder housing 1, having a tubular body 2 of differential internal diameters with a small internal diameter 3 closed by a blind end 4 which in the illustrated case is integral with cylinder 3 but in practice may be a detachable cylinder blind end. e

The small diameter cylinder 3 continues longitudinally inwardly toward the opposite cylinder open receiver end 5 midway initiating with a coaxial larger cylindrical portion 6 which starts at shoulder 24 dividing the differential diameter tubular body into one smaller diameter cylinder 3 provided with a blind end wall 4 and another larger diameter coaxial cylinder 6 with an open receiver end 5. A fluid entrance port 7 is provided in the cylinder blind end 4 to serve as supply and exhaust port means for pressurized working fluid when provided with a 3-way operating valve( not shown An all-metal coaxial piston and rod assembly 28 holds an elongated differential diameter piston 8 at one 4 end and a tubular piston rod 9 at the other end. Midway thereof is situated a larger diameter short piston 17 with rod 9 secured thereto centrally by means of threads 10 entering face 21 of piston 17 while the smaller diameter piston 11 of elongated configuration terminates at piston end 14 facing cylinder blind end wall 4 when slidably inserted into the differential diameter body 2. The diameter of piston 11 is made to be slightly less than that of the internal diameter 3 to facilitate close sliding fit of the elongated piston 11 which is slightly shorter than the portion of the cylinder 3 inside tubular body 2 allowing piston 17 to bottom first and to rest on the shoulder 24 when piston is assembled, with diameter of piston 17 approaching that of the larger cylindrical portion6. Grooves l2 and 13

housing seals

15 and 16 respectively are located at the piston end 14 of the small diameter piston 11 facing cylinder blind end wall 4. A seal 18 permanently secured inside larger diameter piston 17 insures that the space between

seals

16 and 18 is never exposed to the working fluid under pressure entering the fluid entrance port 7 in blind end wall 4, and is not open to the atmosphere during the cycling of the piston-rod assembly in operation irrespective of the position of the piston inside the cylinder. This is so because seal 16 never disengages small diameter cylinder 3 even if piston-rod assembly is; in the extended position as that shown in FIG. 2,and the seal 18 inside piston 17 never leaves larger diameter cylindrical portion 6 when the cylinder is operated with piston-rod assembly moving axially from piston rod retracted first position shown in FIG. I to that of piston-rod extended second position shown in FIG. 2. I

Between the seal grooves 12 and 13 there is a small hole 19 radially entering piston end 14 to lead toward a blind axial bore 20 beginning at the center of large piston face 2l'partially threaded inwardly as shown by 22 to receive tubular piston rod 9 provided with mating threads 10, and exhausting to the atmosphere, should seal 15 exposed to the working fluid pressure leak, and to insure that no air lock between

seals

15 and 16 hinders cylinder operation, as well as to permit air venting during'the initial piston assembly with smaller cylinder while changing position is doing work and simultaneously creating a new annulus at vacuum between 3 while forcing large piston to expel all air from the space it accupies' when bottomed initially against the shoulder 24 and to displace such air between

seals

16 and 18 when piston 11' is positioned in the cylinder as shown in FIG. 1. Experiments with, different se'alconfigurations in piston grooves-identified a need for differentte chniques to force'piston against the shoulder 24-initially'in order to insure a complete air displacement from the space to be filled by the differential diameter piston 8 when pistonrod is in the first retracted position, and ,to' render completely evacuated annulus between piston 11 and cylindrical portion 6 when piston rod is'in the second extended position. It was found howeverfthat after initialpiston assembly with the differential diameter cylinder, the operation of the cylinder is not dependent on seal configuration at all although the use ofU -cups has facilitated considerably easier cylinder assembly initially and could be used succesfully in lieu of O-rings for cylinder sealing during cylinder operation in service. In the illustrated case of FIG. 1, the large di'ameter piston 17 against shoulder 24 identifies piston rod position after initial assembly of the cylinder. -A rod end closure 26 provided with central opening 27 for the passage of rod.9 during the position change of the piston-rod assembly in service, is slipped over'the piston rod 9 and subsequently secured in the receiver open end 5 permanently serving as a stop that defines'the' cylinder stroke length, to complete cylinder assembly. The central opening 27 slidably receiving piston rod 9 provides atmospheric rod clearance 27-a around the piston rod 9 to serve as a bearing means in service, resulting in improved capability for power cylinder to sustain side loads. Opening 27 also provides atmospheric environment for the face 21 of short piston with rod 9. When port 7 is connected to the pressurized working fluid controlled by a 3-way valve, the small cylinder end 29 may be energized. The working fluid entering port 7 pushes against piston end 14 resulting in a position change of the piston-rod assembly and rod extension at the opposite cylinder end with annulus 2S exhausting via clearance 27-a to the atmosphere. The piston rod assembly under pressure larger diameter cylindrical portion 6, shoulder 24, piston 17 and the elongated small piston diameter 11 between

seals

16 and 18 of the'small and large piston ends respectively until large piston face 21 becomes stopped at the end of piston stroke by inside face 30 of the rod end closure 26 constituting the piston-rod assembly in extended position(shown if FIG. 2) and creating-an evacuated annular space between

seals

16 and 18 as well as shoulder 24 and piston 17 facing it. Subsequent rod retraction and return of the piston to the original position shown in FIG. 1 is accomplished automatically by the vacuum force described and in conjuction with atmospheric pressure force over piston [7 face 21. A simple but effective means of piston rod retraction by its own vacuum'force in accordance with invention objectives is hereby provide. Tests with prototypes proved this out.

It should be noted that even with the rod extended there is considerably more engagement of piston and rod in this cylinder than in conventional cylinders. This is due to the elongated piston 8 inside tubular body 2 having reaction points at pistonsll and 17 wide spread and offering a considerably wider bearing span for supporting side loads and thereby increasing usefulness of such cylinders manyfold. In particular that in the design of FIG. 1 there is no need for rod seal inside rod end closure 26, and thus there is no practical limit to the size dimensionally chosen for the piston rod, a factor limiting the design flexibility of theconventional cylin-, drs which require rod seals inside the rod end closure.

The net vacuum force together with atmospheric pressure force shall be proportioned so as to enable the return of the piston to the original position automatically, and the large piston diameter has to-be sized so as to result in such net vacuum force as needed for proper cylinder operation in service be it single acting or double actingcylinder with piston rod return to the original position by its ownvacuum force.

FIG. 2 identifies a cylinder which functionally is identical to that shown in FIG. 1 except for modifications in both materials of construction and means ofsealing during the piston axial motion within the tubular body while performing work as a double acting or as single acting cylinder with capability to retract by its own vacuum force. Because of experimental findings cited, identifying clearly that the use of U-cups in lieu of 0- rings not only simplifies such assembly but also eliminates the need to control piston air lock and the use of double seals in-many applications, in particular in such applications that can tolerate their use, U-cups were chosen. Specifically, the U-cups are considered low pressure seals, and therefore their use may be associated with power cylinders serving such pressu-re ranges. However some designs of U-cups can be used for high pressures as well.

Shown in FIG. 2 is an all-plastic one piece molded cylinder housing 40 having a tubular body 60 of differential internal diameters with open receiver end 44 of enlarged cylindrical diameter 55 at one cylinder end and a closed opposite end 32 with integrally molded blind end wall 54 at the end of a smaller coaxial cylindrical portion 34, initiating midway with shoulder 38 acting as a stop for larger diameter piston in service.

A fluid entrance port 37 is provided in the cylinder blind end wall 54 to serve as fluid supply and exhaust port means when provided with a 3-way directional operating valve (not shown).

An all-plastic one piece molded piston and rod assembly 56 with an elongated differential diameter piston 52 at one end and a solid piston rod 49 at the other opposite end has a short larger diameter piston 43 situated midway and terminating with a raiser 43 having coaxially attached by molding piston rod 49, and a shoulder 36 on the piston inside. I

With the cylinder receiver end 44 open, the piston and rod assembly 56 is slidably inserted into cylinder 60 by having elongated piston 52 to enter smaller cylindrical portion 34 and larger short piston 43 to enter enlarged cylindrical portion 55 until shoulder 36 of piston 43 bottoms shoulder 38 of cylinder 60 displacing air therefrom when assembly is completed and comprising the first piston rod retracted position in cylinder operation before the working fluid entering via port 37 begins to act over the piston rod end 51. The diameters of

pistons

52 and 43 are made to be slightly less than their respective cylindrical portions to facilitate close sliding fit of piston and rod assembly 56 inside tubular body 60. A rod end closure 47 provided with central opening 48 for the passage of piston rod 49 is slipped over and securedin the receiver open end by way of threads 46 permanently serving as a stop against the inside face 50 defining stroke to completethis assembly. The central opening 48 with piston rod 49 slidably assembled therethrough serves also as the bearing means for improved capability of this cylinder tosustain side loads in operation. An annular space-63 of the piston rod 49 inside opening 48 permits air venting during the piston forward motion axially within its stroke limitation from the first initially assembled position with piston resting onshoulder of the cylinder as shown in FIG. 1 to that-of piston rod extended position as shown in FIG. 2 after the cylinder was energized by the working A fluid entering port 37 to act against piston end 51 creating such forward motion and forming void 39 in the cylinder end as shown in FIG. 2. Piston forward motion from the original assembly position creates also evacuated annulus 31 between the elongated smaller diameterpiston 52 and cylinder 55, as well as shoulder 36 of large diameter piston 43 and cylinder shoulder 38 separated by seals and 45 in their

respective grooves

33 and 62. The annulus 31 under vacuum provides means forpiston return to the original assembly position together with atmospheric pressure action over larger diameter piston side with face raiser 53 always exposed to the atmospheric air by way of annulus 63 shown, fa-

cilitating piston rod return from the second extended to first retracted position by its own vacuum force as soon as the cylinder void 39 becomes open to exhaust. And in turn, as soon as the cylinder void becomes reenergized, the position changes to that shown in FIG. 2 clearly indentifying advantages of U-cup seal with mouth facing piston end 51 which together with seal never leaves cylindrical piston 34 during the operation of cylinder, and U-cup lip 61 resisting pressure leakage into evacuated annulus 31 with pressure increase which also increases sealing abilities ofthe lip 61 against the wall of the smaller diameter cylinder 34. Creation of vacuum when pressure enters cylinder end void 39 is hereby insured, although the cylinder operation and piston return by its own vacuum force is attainable even without pressurization, as experienced during the prototype tests after assemblying the piston rod with U-cups inside the differential diameter cylinder of this design positively displacing all air by flowing it across the seals with ease from within the annulus 31 initially, and operating thereafter mannually when pulled by protruding rod'extension with automatic return from the second piston extended to the first piston retracted position in accordance with invention objectives disclosed.

For prevention of undesired dimensional changes of masses not properly proportioned, in order to facilitate ability of cylinder manufacture by molding, the cylinder components of FIG. 2 were modified in accordance with molding requirements. Including in FIG. 2 is a recess 41 entering radially cylinder blind end wall 54 to enable removal of cylinder core without undesirable radius and to insure cylinder manufacture with straight tubular sections without undue stress raisers that in service will effect cylinder integrity. Also shown is an elongated blind cavity 42 entering piston end 51 in-' wardly to terminate in the vicinity of the short larger diameter piston of this coaxial piston of differential diameters.

Thus it has been demonstrated that the differential diameter power cylinder with piston return by its own vacuum force as described above accomplishes all stated objectives and provides drastically new'product of this type. y

Although a preferred embodiment of this invention is disclosed, it is to be understood that various modifications and rearrangements of parts may be resorted to without 'departingfrom the scope of thisinvention disclosed and claimed herein.

What is claimed is: 1. A hydraulic/pneumatic power cylinder for use with pressurized working fluid comprising: I an elongated cylinder of tubular configuration, internally having a portion of smaller diameter with an end wall at one cylinder end forming one cylinder end blind, a shoulder approximately midway leading to another coaxial portion of larger diameter with an open end forming an opposite cylinder receiver end open and adaptable to be closed by a rod end closure, a fluid supplyv and exhaust port means in said cylinder. blind end, a rod end closure including a central opening and mounted on said open end a coaxial piston and rod assembly with a differential diameter piston having a small diameter elongated piston at one end and a piston rod at the other end with a larger diameter short piston approximately midway thereof, said small elongated piston being in close sliding fit with said smaller diameter cylinder, said larger diameter short piston being in close sliding fit said larger cylinder, said piston rod'being permanently secured to the face of said larger diameter piston centrally comprising a coaxial piston and rod assembly, said piston being slidably received in said elongated cylinder with the small diameter elongated piston entering the small diameter cylinder and the larger diameter short piston entering the larger diameter cylinder until it abuts and bottoms at said shoulder, seals on said small piston exposed to said cylinder blind end and on said larger diameter short piston, said piston rod protruding said cylinder open end when said larger diameter short piston is bottomed at said shoulder, said rod closure slidably accommodating said pis-ton rod, fastening means for securing said rod end closure within said cylinder open receiver end to close said cylinder and to serve as a piston stop when the piston is urged to axially move from a first piston rod retracted position toa se-cond piston rod extended position, venting means for admitting atmospheric pressure to the space between said larger piston and said rod end closure, said small and larger piston, said seals, said cylinder, and said shoulder defining an isolated and evacuated annulus when said piston rod is moved to extend axially therein to assume said second piston rod extended position, whereby a vacuum'force is generated which force together with atmospheric pressure acting over the surface of larger piston and rod exposed thereto develops a sufficiently large combined force for piston rod return by its own vacuum force from the second piston rod extended position to the first piston rod retracted position, and whereby when said piston is in said piston rod extended position, said small piston end with said seal is engaged in said smaller diameter cylinder portion. r

2. A hydraulic/pneumatic power cylinder for use with pressurized working fluid comprising:

an elongated cylinder of tubular configuration internally having a portion of smaller diameter with an end wall at one cylinder end forming one cylinder end blind, a shoulder approximately midway leading to another coaxial portion of larger diameter with anopen end forming an opposiee cylinder receiver end open and adaptable to be closed by a rod end closure,

a fluid. supply and exhaust port means in said cylinder blind end,

a coaxial piston and rod assembly with small and large diameter pistons incorporated therein having .a small diameter elongated piston at one end and a piston rod at the other end with a larger diameter short piston approximately midway thereof, said small elongated piston being in close sliding fit with said small diameter cylinder, and said larger diameter short piston being in close sliding fit with said larger cylinder,

saidpiston rod permanently secured to the face of said larger diameter piston and located centrally to provide said coaxial piston and rod assembly, seals on said small and large pistons, said piston slidably received in said cylinder with the small diameter elongated piston entering the small diameter cylinder and the larger short diameter piston entering larger diameter cylinder for operating between a first piston rod'retracted position and a second piston rod extended position, whereby when said piston is in the first retracted position, said larger diameter short piston abuts and bottoms said shoul der while said elongated small piston fully engages the small diameter cylinder portion thereby displacing all air from the space occupied by said piston, and when said piston is in the second extended position, an isolated and evacuated annulus is created between said smaller and larger pistons, said seals, said cylinder, and said shoulder when said larger piston moves axially away from said shoulder upon cylinder actuation by pressurized fluid entering fluid supply port means in said cylinder blind end, said evacuated annulus providing a vacuum force for piston return to the original first piston rod retracted position automatically when said pressurized fluid is allowed to escape from said cylinder blind end via said fluid exhaust port means,

rod receiving end closure secured in said cylinder open end including venting means for the space between the larger piston and the end end closure whereby when said short piston is moved from said first piston rod retracted position to said second piston rod extended position atmospheric air is displaced therefrom to facilitate proper operation of the cylinder and whereby when the cylinder blind end is allowed to exhaust, said atmospheric air returns thereto to act upon said larger diameter short piston and together with said vacuum force in said annulus to return said piston automatically to the original first piston rod retracted position, said second piston rod extended position being determined by the position of said rod end closure,

3. A cylinder as in claim 2 wherein said seals on said pistons are of U-cup configuration.

4. A cylinder as in claim 1 wherein said small piston end includes dual seals with seal venting means therebetween for exhaust to the atmosphere, said seal venting means includinga passage initiating between said seals of said elongated smalll piston end by entering thereto radially to meet an axial passage provided therein communication with a passage in said piston rod leading to the atmosphere.

5. A cylinder as in claim 2 wherein all components are non-metallic.

6. A power cylinder with piston return by its own vacuum force comprising: a cylinder having shoulder defined between differential diameter portions, a piston having a shoulder defined between differential diame- Q I ter portions, said piston in its retracted position being positioned within said cylinder with said respective differential diameter portions of said piston and cylinder being in close sliding fit and with the respective shoulders of said piston and cylinder abutting and bottoming on one another, seals on the differential diameter portions of said piston, a piston rod attached to the face of the larger diameter portion of saidipiston and protruding at one cylinder open end, a cylinder closure at another cylinder end adjacent said small dianieter comprising a cylinder blind end, port means opening into a said cylinder at said blind end for supply and exhaust of the pressurized working fluid and adaptable for connecting a 3-way operating valve thereto to control the directional flow to and from the cylinder blind end during the cylinder operation, said cylinder operation including piston axial movement from a first piston rod retracted position to a second piston rod extended position in response to the directional flow of pressurized fluid whereby when said fluid is allowed to enter said cylinder blind end via said port provided therein, said piston is moved to assume said second piston rod extended position, and when said fluid is allowed to exhaust therefrom via said port, said piston is moved to assume said first piston rod retracted position, said piston motion from said first to said second positions developing an isolated and evacuated annulus between said piston and cylinder, said seals. and said shoulders to produce a vacuum force large enough to return said 3 ,8 1 5,481 9 10 piston from said second to said first positions when said ing fit, and end face of the larger piston abutting cylinder blind end is open to exhaust. and bottoming on said shoulder, and the larger pis- 7. A power cylinder with piston re by O n ton entering the larger diameter cylinder postion in force p close sliding fit for axial movement within the cylan elongated cylinder means having one cylinder end blind defined by an end wall and another cylinder end open, a rod end closure including a central opening connected by securement means to said open end, said cylinder means including internal diameter tubular portions of different coaxial diinder limited by said rod end closure at one piston rod extended position and said cylinder shoulder seals on said smaller and larger diameter piston portions, said rod end closure opening receives said piston rod, fluid supply and exhaust means at said irl nd,heb 'ct' n ameters separated by a shoulder substantially mid- Cy! b md er y f by pressurized working fluid entering said fluld supply way thereof with the larger diameter portion mitld h t t m n id t m n ating at the cylinder open end while the smaller diaus por d if S i 5 mo.ves ameter portion continues inwardly from said shoultowar S an exten e posmon eve g an def until it meets Said blind end wall, 15 lated and evacuated annulus between said shoulaplastic differential diameter piston means including Plston and cylmder pQrtlonsr and 531d a coaxial piston rod attached thereto, said piston seals {p t herem wherfiby p?" means having an elongated smaller diameter piston exhaustmg Pressurlzed worklng fl through 51nd at one end and a short diameter larger piston with pp y and eXhaUSI f d piston eans IS resaid rod at the other end slidably received inside turned to retracted. PO t y e fOrCe of he said cylinder means with the small piston entering vacuum. the smaller diameter cylinder portion in close slid-

Claims

1. A hydraulic/pneumatic power cylinder for use with pressurized working fluid comprising: an elongated cylinder of tubular configuration, internally having a portion of smaller diameter with an end wall at one cylinder end forming one cylinder end blind, a shoulder approximately midway leading to another coaxial portion of larger diameter with an open end forming an opposite cylinder receiver end open and adaptable to be closed by a rod end closure, a fluid supply and exhaust port means in said cylinder blind end, a rod end closure including a central opening and mounted on said open end a coaxial piston and rod assembly with a differential diameter piston having a small diameter elongated piston at one end and a piston rod at the other end with a larger diameter short piston approximately midway thereof, said small elongated piston being in close sliding fit with said smaller diameter cylinder, said larger diameter short piston being in close sliding fit said larger cylinder, said piston rod being permanently secured to the face of said larger diameter piston centrally comprising a coaxial piston and rod assembly, said piston being slidably received in said elongated cylinder with the small diameter elongated piston entering the small diameter cylinder and the larger diameter short piston entering the larger diameter cylinder until it abuts and bottoms at said shoulder, seals on said small piston exposed to said cylinder blind end and on said larger diameter short piston, said piston rod protruding said cylinder open end when said larger diameter short piston is bottomed at said shoulder, said rod closure slidably accommodating said pis-ton rod, fastening means for securing said rod end closure within said cylinder open receiver end to close said cylinder and to serve as a piston stop when the piston is urged to axially move from a first piston rod retracted position to a se-cond piston rod extended position, venting means for admitting atmospheric pressure to the space between said larger piston and said rod end closure, said small and larger piston, said seals, said cylinder, and said shoulder defining an isolated and evacuated annulus when said piston rod is moved to extend axially therein to assume said second piston rod extended position, whereby a vacuum force is generated which force together with atmospheric pressure acting over the surface of larger piston and rod exposed thereto develops a sufficiently large combined force for piston rod return by its own vacuum force from the second piston rod extended position to the first piston rod retracted position, and whereby when said piston is in said piston rod extended position, said small piston end with said seal is engaged in said smaller diameter cylinder portion.

2. A hydraulic/pneumatic power cylinder for use with pressurized working fluid comprising: an elongated cylinder of tubular configuration internally having a portion of smaller diameter with an end wall at one cylinder end forming one cylinder end blind, a shoulder approximately midway leading to another coaxial portion of larger diameter with an open end forming an opposiee cylinder receiver end open and adaptable to be closed by a rod end closure, a fluid supply and exhaust port means in said cylinder blind end, a coaxial piston and rod assembly with small and large diameter pistons incorporated therein having a small diameter elongated piston at one end and a piston rod at the other end with a larger diameter short piston approximately midway thereof, said small elongated piston being in close sliding fit with said small diameter cylinder, and said larger diameter short piston being in close sliding fit with said larger cylinder, said piston rod permanently secured to the face of said larger diameter piston and located centrally to provide said coaxial piston and rod assembly, seals on said small and large pistons, said piston slidably received in said cylinder with the small diameter elongated piston entering the small diameter cylinder and the larger short diameter piston entering larger diameter cylinder for operating between a first piston rod retracted position and a second piston rod extended position, whereby when said piston is in the first retracted position, said larger diameter short piston abuts and bottoms said shoulder while said elongated small piston fully engages the small diameter cylinder portion thereby displacing all air from the space occupied by said piston, and when said piston is in the second extended position, an isolated and evacuated annulus is created between said smaller and larger pistons, said seals, said cylinder, and said shoulder when said larger piston moves axially away from said shoulder upon cylinder actuation by pressurized fluid entering fluid supply port means in said cylinder blind end, said evacuated annulus providing a vacuum force for piston return to the original first piston rod retracted position automatically when said pressurized fluid is allowed to escape from said cylinder blind end via said fluid exhaust port means, a rod receiving end closure secured in said cylinder open end including venting means for the space between the larger piston and the end end closure whereby when said short piston is moved from said first piston rod retracted position to said second piston rod extended position atmospheric air is displaced therefrom to facilitate proper operation of the cylinder and whereby when the cylinder blind end is allowed to exhaust, said atmospheric air returns thereto to act upon said larger diameter short piston and together with said vacuum force in said annulus to return said piston automatically to the original first piston rod retracted position, said second piston rod extended position being determined by the position of said rod end closure.

4. A cylinder as in claim 1 wherein said small piston end includes dual seals with seal venting means therebetween for exhaust to the atmosphere, said seal venting means including a passage initiating between said seals of said elongated smalll piston end by entering thereto radially to meet an axial passage provided therein communication with a passage in said piston rod leading to the atmosphere.

5. A cylinder as in claim 2 wherein all components are non-metallic.

6. A power cylinder with piston return by its own vacuum force comprising: a cylinder having shoulder defined between differential diameter portions, a piston having a shoulder defined between differential diameter portions, said piston in its retracted position being positioned within said cylinder with said respective differential diameter portions of said piston and cylinder being in close sliding fit and with the respective shoulders of said piston and cylinder abutting and bottoming on one another, seals on the differential diameter portions of said piston, a piston rod attached to the face of the larger diameter portion of said piston and protruding at one cylinder open end, a cylinder closure at another cylinder end adjacent said small diameter comprising a cylinder blind end, port means opening into a said cylinder at said blind end for supply and exhaust of the pressurized working fluid and adaptable for connecting a 3-way operating valve thereto to control the directional flow to and from the cylinder blind end during the cylinder operation, said cylinder operation including piston axial movement from a first piston rod retracted position to a second piston rod extended Position in response to the directional flow of pressurized fluid whereby when said fluid is allowed to enter said cylinder blind end via said port provided therein, said piston is moved to assume said second piston rod extended position, and when said fluid is allowed to exhaust therefrom via said port, said piston is moved to assume said first piston rod retracted position, said piston motion from said first to said second positions developing an isolated and evacuated annulus between said piston and cylinder, said seals, and said shoulders to produce a vacuum force large enough to return said piston from said second to said first positions when said cylinder blind end is open to exhaust.

7. A power cylinder with piston return by own vacuum force comprising: an elongated cylinder means having one cylinder end blind defined by an end wall and another cylinder end open, a rod end closure including a central opening connected by securement means to said open end, said cylinder means including internal diameter tubular portions of different coaxial diameters separated by a shoulder substantially midway thereof with the larger diameter portion initiating at the cylinder open end while the smaller diameter portion continues inwardly from said shoulder until it meets said blind end wall, a plastic differential diameter piston means including a coaxial piston rod attached thereto, said piston means having an elongated smaller diameter piston at one end and a short diameter larger piston with said rod at the other end slidably received inside said cylinder means with the small piston entering the smaller diameter cylinder portion in close sliding fit, and end face of the larger piston abutting and bottoming on said shoulder, and the larger piston entering the larger diameter cylinder postion in close sliding fit for axial movement within the cylinder limited by said rod end closure at one piston rod extended position and said cylinder shoulder seals on said smaller and larger diameter piston portions, said rod end closure opening receives said piston rod, fluid supply and exhaust means at said cylinder blind end, whereby upon actuation by pressurized working fluid entering said fluid supply and exhaust port means said piston means moves towards an extended position developing an isolated and evacuated annulus between said shoulder, said piston and cylinder portions, and said seals to produce a vacuum therein whereby upon exhausting pressurized working fluid through said supply and exhaust means said piston means is returned to a retracted position by the force of he vacuum.