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Publication numberUS2965036 A
Publication typeGrant
Publication dateDec 20, 1960
Filing dateJul 8, 1957
Priority dateJul 8, 1957
Publication numberUS 2965036 A, US 2965036A, US-A-2965036, US2965036 A, US2965036A
InventorsWood Louis S
Original AssigneeWood Louis S
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Automatic dual pump single-multiple stage low-high pressure fluid supply means
US 2965036 A
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Description  (OCR text may contain errors)

5 Sheets-Sheet 1 LOW-HIGH PRESSURE FLUID SUPPLY MEANS Dec. 20, 1960 L. s. WOOD 2,965,036

AUTOMATIC DUAL PUMP SINGLE-MULTIPLE STAGE Filed July 8, 1957 INVENTOR. [00/5 5 14 000 BY W Dec. 20, 1960 s. WOOD 2,965,036

AUTOMATIC DUAL PUMP SINGLEMULTIPLE STAGE LOW-HIGH PRESSURE FLUID SUPPLY MEANS Filed July 8, 1957 3 Sheets-Sheet 2 Z3 c5 INVENTOR.

Dec. 20, 1960 L. s. WOOD 2,965,036

AUTOMATIC DUAL PUMP SINGLE-MULTIPLE STAGE LOW-HIGH PRESSURE FLUID SUPPLY MEANS Filed July 8, 1957 3 Sheets-Sheet 3 3o 5 Q? 4 i is; E c

20 0 P1 I 2 [J 1 f 5 ZZJILAJ l \l\ E 22 \23 INVENTOR.

4 TTOR/Vy AUTOMATIC DUAL PUMP SINGLE-MULTIPLE p r sou now-mou PRESSURE FLUID SUPPLY Louis S. Wood, 1615 Grant Blvd, Findlay, Ghio Filed July 8, 1957, Ser. No. 670,437

2 Claims. (Cl. 103-10).

This invention relates to an improved low-high pressure hydraulic fluid supplymeans which normally functions as a single stage high volume low pressure fluid supply to a hydraulic motor such as a power cylinder or the like and which automatically changes to function as a two stage low volume high pressure fluid supply responsive to a predetermined increased back-pressure from an increase in the connected load on the hydraulic motor.

Under normal conditions, gear type pumps operate at certain maximum pressures for which they are designed. When the connected load on the hydraulic fluid pressure supply system of which the pump is an element requires the gear pump to operate under a greater than normal maximum pressure, and the gear pump is over-powered to provide such increased pressure, the said gear pump soon fails to function. In many installations, however, the hydraulic motor means and the hydraulic fluid; supply system is required to handle peak or heavier than normal loads which overloads the pump. To furnish a larger gear pump and increase the power means employed to drive it whereby to permit the hydraulic fluid supply system to operate under peak load pressure is not only expensive but is ofttimes cumbersome or wasteful.

The present invention, among other applications, is particularly well adapted to supply hydraulic fluid under pressure to such hydraulic motor means as the hydraulic power cylinders of hydraulic lifts, hydraulic rams and other hydraulic cylinder operated equipment such as dump truck bodies and tail gate loaders where the load thereon fluctuates from light to heavy according to conditions which either repeat during each cycle of operation of the hydraulic motor means or which occur as a result of unusual or above normal peak loading of the hydraulically operated equipment.

Accordingly, the primary object of this invention is to provide a simple, inexpensive selfoperating single-multiple stage low-high pressure hydraulic fluid supply system ineluding a dual pump and control means therefor which will normally deliver relatively low pressure hydraulic fluid into a hydraulic motive system, and which will autodraulic fluid pressure supply means and system con.-

sisting of a dual gear pump driven from a single power means which normally operates in parallel to provide a high volume-low pressure hydraulic fluid source to a hydraulic motor means such as a hydraulic power cylinder and which automatically changes to a series operation to provide a low volume-high pressure hydraulic fluid source resmnsive toan increase, in the load requirements on the hydraulic motor means.

A further object of theinvention is to. provide a simple,

inexpensive, hydraulic pressure. fluid source comprising thecombination of a dual gear pump consisting of two gear pump units driven. by a single power means through a single drive shaft and including an automatic control means and hydraulic circuit adapted to cause the said pump units to function either as a single stage relatively low pressure pump or as a two stage relatively high pressure pump to supply hydraulic fluid under either low or high pressures to a hydraulic motor means responsive to the pressure required to operate the said hydraulic motor means as determined by variations in the loading of the equipment operated thereby.

Other objects of the invention will become apparent. by reference to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a longitudinal sectional view of a dual gear pump of a type preferably employed as an element of the hydraulic pressure fluid supply means and system embodying the invention.

Fig. 2 is a vertical sectional view taken substantially on the line 22 of Fig. 1.

Fig. 3 is a sectional view through a conventional check valve preferably employed.

Fig. 4 is a longitudinal sectional view of the improved automatic pressure control valve means employed in the hydraulic system showing the valve element thereof in its low pressure position causing the dual pump means to operate as a single stage low pressure high volume hydraulic fluid supply means.

Fig. 5 is a longitudinal sectional view similar to Fig. 4 except that the valve element of the automatic pressure control valve means is shown in its high pressure position causing the dual pump means to operate as a two stage high pressure low volume hydraulic fluid supply means.

Fig. 6 is a cross sectional view taken on the line 6,--6 of Fig. 4.

Fig. 7 is a, cross sectional view taken on the line 7-7 of Fig. 4.

Fig. 8 is a cross sectional view taken on the line 8-8 of Fig. 4.

Fig. 9 is a flow diagram of a hydraulic fluid pressure supply means and system embodying the invention including a dual gear pump consisting of two pump units powered from a single power source and control means therefor, with the hydraulic fluid supply valve leading therefrom to a hydraulic cylinder or other fluid motor shown in its Oif position.

Fig. 10 is a flow diagram of the hydraulic fluid pressure supply means and system disclosed in Fig. 9 with the hydraulic fluid supply valve leading therefrom in its On position, and with the automatic low-high pressure control valve preferably employed disposed in its low pressure position. I

Fig. 11 is a flow diagram of the hydraulic fluid pressure supply means and system disclosed in Figs.v 9 and Hi with the hydraulic fluid supply valve leading therefrom in its On. position, and with the automatic low-high pressure control valve in its high pressure position.

Referring now to the drawings wherein like numerals refer to like and corresponding parts throughout the several views, the illustrative embodiment of the invention will now be described in detail. Although the pump and control means employed in the invention have been shown throughout the drawings as separate elements, it is obvious that the invention may readily be practiced by those skilled in the art by incorporating the several elements thereof in the pump housing, thereby reducing the cost of manufacture and assembly of separate elemerits, and also facilitating and reducing the cost of installation of the invention in hydraulically powered equipment with which it may be employed.

The particular single-multiple stage low-high pressure hydraulic fluid supply means embodying the invention disclosed in the drawings includea dual gear pump 20 consisting of a housing 21 having two gear pump units 22 and 23 therein mounted on common shafts 24 and 25 driven by a single power means (not shown) through one of the two shafts 24 or 25'. The pump unit-22 is provided with an inlet 224 and an outlet 225, and the pump unit 23 is provided with an inlet 234 and an outlet 235. The said gear pump 20 supplies low-high pressure hydraulic fluid through a suitable hydraulic circuit including a pressure selector valve 27 and a check valve 28 from a reservoir 26 to a connected load L such as a hydraulic cylinder or other hydraulic motor means (not shown). The said selector valve 27 preferably includes a spring loaded valve spool 29, which, when in its normal position, causes the gear pump units 22 and 23 of the dual gear pump 20 to operate in parallel at a low pressure and high volume, the said selector valve spool 29-being shiftable responsive to a predetermined back-pressure from said connected load L to cause said gear pump units 22 and 23 of the said dual gear pump 20 to operate in series at a relatively high pressure and a relativey low volume. The check valve 28 prevents hydraulic fluid in the said hydraulic circuit from return ng to the reservoir 26 during the high pressure-low volume series operation of the pump units 22 and 23 of the dual gear pump 20.

An On-Olf flow control valve 30 is preferably provided in the hydraulic circuit for establishing and shutting off the flow of hydraulic fluid from the said fluid supply systern to the connected load L. When the said flow control valve 30 is in its On position, hydraulic fluid under either low or high pressure, as determined by the backpressure created by the connected load L, is supplied by the single-multiple stage low-high pressure fluid supply system to the said connected load L. When the said flow control valve 30 is in its Off position, hydraulic fluid is returned to the reservoir 26 from said pump 20, and the said single-multiple stage low-high pressure hydraulic fluid supply system operates as a recircu'ating single stage system under zero pressure. Obviously. the invention may be practiced by the use of other hydraulic circuits to and from the connected load L, it being important that the hydraulic circuit employed be such as will permit the selector valve 27 to funct on responsi e to back-pressure from the connected load L to cause the dual gear pump 20 to automatically change from a single stage low pressure operation to a two stage high pressure operation responsive to increased loading on the hydraulic cylinder or other hvdraulicmotor means herein designated as the connecter load L.

The particular dual gear pump 20 preferably employed as an element of the invention is shown in Figs. 1 and 2, and consists of a housing 21 having therein two separate gear pump units 22 and 23. each including a pair of meshing pump gears 221 and 222, and 231 and 232 respectively. Each said pair of meshing pump gears 221 and 222, and 231 and 232 are rotatably mounted in pump chambers 223 and 233 respectively provided in the said dual gear pump housing 20. A separate in et and a separate outlet as indicated by the arrows in Fig. 2 is provided to and from each of the pump chambers 223 and 233. The said inlets and outlets may be reversed if the pump is run in the direction opposite to that ind cated by the arrows in Fig. 2. The pump gears 221 and 231 are mounted on a common shaft 24, while the pump gears 222 and 232 are mounted on a common shaft 25. The said shafts 24 and 25 extend through both pump chambers 223 and 233 and through shaft bores 32 and 33 respectively in the central portion of the housing 21 between the said pump chambers 223 and 233. End caps 211' and 212 are provided at opposite ends of the pump housin 21 and serve as end covers for the pump chamhers 223 and 224 respectively. The sa d end caps 211 and 212 are secured onto the pump housing 21 by such means as studs 210. 4

One end of each of the said shafts 24 and 25 is rotatably supported on roller bearings 34 in the end cap 211. The

other end of each of the said shafts 24 and 25 extends through the end cap 212, and is rotatably supported on roller bearings 35 in the said end cap 212. Both said shafts 24 and 25 are rotatably supported on roller bearings 36 located in the said shaft bores 32 and 33 through the central portion of the housing 21. A suitable fluid seal 37 is provided in the end cap 212 around each shaft 24 and 25, and the pump chambers 223 and 233 are each provided with Wear plates 33 at each end thereof adjacent the pump gears therein.

The outer end portion of each of the shafts 24 and 25 of the dual gear pump extending from the end cap 212 j thereof is provided with a keyway 39 to permit either of the said shafts 24 or 25 to be coupled to drive means such as a power take-off from an' engine transmission, an electric motor, or the like (not shown). The shaft 24 or 25 to which the power is applied becomes the drive shaft, while the other shaft becomes the driven shaft. As illustrated in Fig. 1, two of the meshing pump gears 221, 222, 231 and 232 are mounted on the drive shaft which may be the shaft 24, two are mounted on the driven shaft 25. The said shafts 24 and 25 are each provided with a keyway 40 therein at each pump gear thereon, and each of the said pump gears is provided with a mating keyway 41 therein. All but one of the said meshing pump gears 221, 222, 231 and 232 are keyed by keys 42 to the shaft upon which they are mounted. In the particular dual gear pump 20 illustrated in Figs. 1 and 2, the pump gear 221 is not keyed to the pump shaft 23. This construction provides flexibility in the installation and drive of the dual gear pump 20 and assures perfect meshing and wearing-in of all of the pump gears of both units 22 and 23 of the said dual gear a valve spool bore 51 longitudinally therethrough to accommodate a reciprocable valve spool 29 having a stem 52 and two longitudinally spaced lands 53 and 54. End caps 55 and 56 secured on the ends of the housing 50 by suitable studs 57 close the ends of the valve spool bore 51, and suitable gaskets 58 make the said end closures fluid tight. The stem 52 of the said valve spool 29 slidably extends through a central aperture 550 in the end cap 55, and an O-ring 59 provides a fluid seal between the said valve spool stem 52 and the end cap 56.

The said selector valve housing 50 is provided with three longitudinally spaced cored fluid passages 60, 61 and 62 therein disposed around and in communication with said valve spool bore 51. A selector valve inlet 70 communicates with the center annular fluid passage 61, and

' a selector valve inlet 71 communicates with the right hand annular fluid passage 62. A selector valve outlet 72 communicates with the right hand annular fluid passage 62, and a selector valve outlet 73 communicates with the left hand annular fluid passage 60, see Figs. 4-8 inclusive.

The valve spool bore 51 is preferably enlarged at its right hand end as best shown in Figs. 4 and 5 to provide a back pressure chamber 510 into which the frusto-conical end 540 of the land 54 of the valve spool 29 enters when the said valve spool 29 is spring urged by a compression spring 63 to its normal or low pressure position as shown in Fig. 4. The said frusto-conical end 540 of the land 54 of the valve spool 29 rests against the end cap 56 of the selector valve housing 50 when the valve spool 29 is in its said low pressure position. The said compression spring 63 is disposed around the stem 52 of the valve pool 29 and between the end cap 55 and the land 53 thereof. A sleeve 64 is pressed into the left end of the valve spool bore 51 as shown in Figs. 4 and 5 to limit the movement of the valve spool 29 to its high pressure position as shown in Fig. 5. Suitable longitudinal bores 530 are provided through the land 53 of the valve spool 29 to prevent entrapment of hydraulic fluid in the valve spool bore 51 between the end cap 46 and the land 53.

The movement of the valve spool 29 from its normal or low pressure position as shown in Fig. 4 to its high pressure position as shown in Fig. 5 is accomplished when suflicient back-pressure is developed in the selector valve outlet 72. The said back-pressure in the selector valve outlet 72 is applied to the frusto-conical end 540 of the right hand land 54 of the valve spool 29 through fluid passages 65 and 66 leading from the selector valve outlet 72 to the back-pressure chamber 510 and the right hand end of the valve spool bore 51.

The location, length and spacing of the lands 53 and 54 of the valve spool 29 is such in relation to the fluid passages 69, 61 and 62 that, when the valve spool 29 is spring urged to its low pressure position, to the right as shown in Fig. 4, fluid from the outlet of the gear pump unit 22 of the dual gear pump unit 20 will enter the selector valve inlet 71 and pass through the fluid passage 62 and out through the selector valve outlet 72. At the same time fluid from the outlet of the gear pump unit 23 of the said dual gear pump unit 20 will enter the selector valve inlet 70 and pass through the fluid passages 61 and 62, which are open to each other through the valve spool bore 51, and out through the said selector valve outlet 72. Thus, when the valve spool 29 of the selector valve 27' is urged under the pressure of the compression spring 63' into its normal low pressure position as shown in Fig. 4, the gear pump units 22 and 23 of the dual gear pump 20 operate in parallel at a relatively low pressure and relatively high volume, see Fig. 10.

The said location, length and spacing of the lands 53 and 54 of the valve spool 29 is also such in relation to the fluid passages 60, 61 and 62 that, when the vave spool is urged to its high pressure position, to the left as shown in- Fig. 5', by back-pressure from the connected load L building up in the back-pressure chamber 510 sufliciently to overcome the spring load of the compression spring 63 on the valve spool 29, fluid from the outlet of the gear pump unit 23 of the dual gear pump 20 will enter the selector valve inlet 70 and pass through the fluid passages 61 and 60, which are open to each other through the valve spool bore 51, and out through the selector valve outlet 73 from whence it passes to the inlet of the gear pump unit 22. Then, fluid from the outlet of the gear pump unit 22 will enter the selector valve inlet 71 and pass through the fluid passage 62 and out through the selector valve outlet 72. Thus, when the valve spool 29 of the selector valve 27 is moved under hydraulic backpressure from the connected load L to its high pressure position shown in Fig. 5, the gear pump units 23 and 22 of the gear pump 20 operate in series. at a relatively high pressure and relatively low volume, see Fig. 11.

By referring to the hydraulic circuit diagrams in Figs. 9, and 11, it will be observed that a suitable check valve 28 is placed in the supply line A leading from the reservoir 26 to the inlet 224 of the gear pump unit 22. This check valve 28 prevents back-flow to the reservoir 26 from the pressure lines CD from the outlet 235 of the gear pump unit 23 to the inlet 224 of the gear pump unit 22 of the dual gear pump during the high pressure-low volume operation of the low-high pressure fluid supply means as indicated in Fig. 9. The said check valve 28 may be a ball check valve as shown in Fig. 3 consisting of a housing 80 having a fluid passage 81 therethrough including an inlet 82 and an outlet 83. A ball seat 84 is threaded in the inlet 82. A ball check 85 is positioned in the fluid passage 81 and is held in proximity to the ball seat 84 by such means as a pin 86. Obviously, any suitable one-way check valve 28 may be used.

A typical installation of an improved low-high pressure hydraulic fluid supply means embodying the invention is shown diagrammatically in Figs. 9, l0 and 11. Referring first to the hydraulic circuit d'agram in Fig. 9, when the dual gear pump 20 is being driven, and the flow control valve 30 is in its Oif position, hydraulic fluid from-a reservoir 26 is supplied viathe. supply line A to the intake 224 and 234 respectively of each gear pump unit 22 and 23 of the dual gear pump 20, and, since there is no backpressure from the connected load L, the valve spool 29 of the selector valve 27 remains in its normal low pressure position shown in. Fig. 4 to which it is constantly urged by the compression spring 63 as hereinbefore described, and, hydraulic fluid passes from each gear pump unit 22 and 23 through pressure lines B and C and the said selector valve 27, and, through a pressure line B, the flow control valve 30 and the return line F back to the reservoir 26. According to the cycle of operation illustrated in Fig. 9, the said gear pump units 22- and 23; of the dual gear pump 20 are operating in parallel at substantially zero pressure.

Referring now to the hydraulic circuit diagram, in Fig. 10, the same hydraulic cycle as described above for Fig. 9 obtains, except that the flow control valve 3.0 is in. its On position, and hydraulic fluid under low pressure from the dual gear pump 20 is applied to the connected load L through the pressure line G rather than being returned to the reservoir 26. In other words, in the cycle of operation illustrated in Fig. 10, said gear pump units 22 and 23 of the dual gear pump 20 are still operating in parallel, but at a low pressure.

The low-high pressure hydraulic fluid supply means of the invention operates according to the hydraulic cycle disclosed in Fig. 10 furnishing hydraulic fluid under a relatively low pressure and high volume from the gear pump units 22 and 23 of the gear pump 20 operating in parallel until the connected load L creates a back-pressure in the chamber 510 of the selector valve 27 sufliclent to overcome the spring load of the compression spring 63 on the valve spool 29 as hereinbefore described.

Whenever the low-high pressure hydraulic supply means embodying the invention is operating at a low pressure and high volume according to the hydraulic cycle disclosed in Fig. 10, and whenever the back-pressure in the chamber 510 of the selector valve 27 increases responsive to an increase in the connected load L sufliciently to overcome the spring load of the compression spring 63 normally urging the valve spool 29 to its low pressure position shown in Fig. 4, the valve spool 29 moves to its high pressure position shown in Fig. 5". As shown diagrammatIcally in the. hydraulic circuit diagram in Fig. 11, bydraulic fluid from the reservoir 26 is now supplied through the supply line A to the intake 234 of the gear pump unit 23, is pumped from the outlet 235 of the gear pump unit 23 via the pressure line C. to and through the selector valve 27', passes from the said selector valve 27 via the loop low pressure line D to the inlet 224 of the gear pump unit 22, is pumped from the outlet 225 of the gear pump unit 22 vfa the pressure line B to and through the selector valve 27, through the flow control valve 30, which is in its On position, and through the pressure line G to the connected load L. The said gear pump units 23 and 22 of the dual gear pump 20 are now operating in series, but at a high pressure and a relatively low volume.

By employing a compression spring 63 in the selector valve 27 having a lower or higher resistance to compression, the particular pressure at which the improved lowhigh pressure hydraulic fluid supply means embodying the invention will change in operation automatically from a low pressure operation to a high pressure operation can be established. For example, assuming that each pump unit 22 and 23 of the dual gear pump 20 will operate in parallel at a certain volume up to 1000 p.s.i., and the compression spring 63 of the selector valve 27 will permit its valve spool 29 to shift from its low pressure position shown in Fig. 4 to its high pressure position shown in Fig. 5 responsive to a 1000 p.s.i. back-pressure in the backpressure chamber 510 thereof, then, as soon as the backpressure in the back-pressure chamber 510 of the selector valve 27 increases to 1000 p.s.i., the said valve spool 29 7 thereof will shift to its high pressure position shown in Fig. 5, and the hydraulic fluid supply means of the invention will operate with the pump units 23 and 22 thereof in series at pressures from 1000 to 2000 p.s.i., but at onehalf the said certain volume.

If, in the same example, the compression spring 63 of the selector valve 27 would permit the valve spool 29 thereof to shift from its low pressure position to its high pressure position at a back-pressure of 500 p.s.i. in the back-pressure chamber 510 of the selector valve 27, then the pump units 22 and 23 would normally operate in parallel up to 500 p.s.i., and would automatically change from a parallel to a series operation to operate in series from 500 to 2000 p.s.i., but at one-half the said certain volume.

Obviously, the automatic dual pump single-multiple stage low-high pressure fluid supply means of the invention may be employed in many operational combinations and in many different types of installations where a relatively low pressure high volume of hydraulic fluid is required to operate a hydraulic cylinder or other hydraulic motor means rapidly under light loading and relatively slower under relatively heavier loads.

Although but a single embodiment of the invention has been disclosed and described in detail, it is obvious that many changes may be made in the size, shape, arrangement and detail of the various elements of the invention as defined by the appended claims.

I claim:

1. A dual gear pump and control means therefor in a hydraulic circuit including therein a reservoir and adapted to be connected with a load such as a hydraulic motor means wherein said dual gear pump and its control means supplies hydraulic fluid at low pressure and high volume and at high pressure and low volume selectively responsive to variations in back pressure in said control means, said dual gear pump consisting of two like capacity adjacent gear pump units each including an inlet and an outlet and a pair of like meshed gears, a pair of drive shafts each mounting one gear of each said pump unit, each gear except one being keyed to the drive shaft on which it is mounted permitting said dual gear pump to be driven by either of said two drive shafts, said hydraulic circuit connecting said reservoir to said dual gear pumps including a selector valve means therein normally providing hydraulic fluid flow from the outlets of said dual gear pump units, said hydraulic circuit including a loop from the outlet of one gear pump unit to the inlet of the other, .said selector valve means being spring loaded in one position to cause said pump units of said dual gear pump to operate normally in parallel at low pressure and high volume, said selector valve means being movable responsive to a back pressure predetermined by the spring loading thereof to cause said pump units to operate in series at high pressure and low volume, and a check valve in said hydraulic circuit operable independently of said selector valve means to prevent back-flow of hydraulic fluid from said loop at the inlet of said other pump unit when said pump units are series operated.

2. A dual gear pump and control means therefor in a hydraulic circuit including therein a reservoir and adapted to be connected with a load in the formof a hydraulic motor means wherein said dual gear pump and its control means supplies hydraulic fluid at low pressure and high volume and at high pressure and low volume selectively responsive to variations in back pressure in said control means, said dual gear pump consisting of two like capacity adjacent gear pump units each including an inlet and an outlet and a pair of like meshed gears, a pair of drive shafts each mounting one gear of each said pump unit, each gear except one being keyed to the drive shaft on which it is mounted permitting said dual gear pump to be driven by either of said two drive shafts, said hydraulic circuit connecting said reservoir to said dual gear pumps including a selector valve means therein normally providing hydraulic fluid flow from units of said dual gear pump and from the outlets thereof, said hydraulic circuit including a loop from the outlet of one pump unit through said selector valve means to the inlet of the other pump unit, said selector valve means being spring loaded in one position to cause said pump units to operate normally in parallel at low pressure and high volume, said selector valve means being movable responsive to a back pressure predetermined by the spring loading thereof to cause said pump units to operate in series at high pressure and low volume, and a check valve located in said hydraulic circuit operable independently of said selector valve means preventing backflow from the inlet of said other pump means to the reservoir when said pump units operate in series.

References Cited in the file of this patent UNITED STATES PATENTS 2,255,560 Fieber et a1 Sept. 9, 1941 2,526,964 Muller Oct. 24, 1950 2,599,701 Eames June 10, 1952 2,626,570 Armington et a1 Jan. 27, 1953 2,655,109 Walker Oct. 13, 1953 2,665,637 Lauck Jan. 12, 1954 2,780,172 Coar Feb. 5, 1957 FOREIGN PATENTS 994,357 France Aug. 8, 1951

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Classifications
U.S. Classification417/62, 418/200
International ClassificationF04C14/02, F04C14/00
Cooperative ClassificationF04C14/02
European ClassificationF04C14/02