US2556426A - Pump structure - Google Patents

Description

J. F. HOFFER PUMP STRUCTURE June 12, 1951 2 Sheets-Sheet 1 Original Filed Feb. 9, 1942 W im June l2, 1951 J, F, HOF-FER 2,556,426

' PUMP STRUCTURE 2 Sheets-Sheet 2 Original Filed Feb. 9, 1942 Patented June 12, 1951 PUMP STRUCTURE James F. Hoifer, Detroit, Mich., assigner to Ex- Cell.-O Corporation, Detroit, Mich., a corpora? tion of' Michigan.

Original application February 9, 1942, Serial No.

429,998. Divided and this. application December 1, 1944, SerialNo. 566,066

The present invention relates to improvements in pumps and has particular reference to a new and improved pump structure which is especially suited for supplying fuel in metered charges at a relatively high pressure to. an internal combustion engine.

One of the objects of the invention is to provide a novel pump structure comprising a high pressure delivery pump, a low pressureprimary pump for supplying fuel to the delivery pump, and auxiliary pump means for removing fuel and lubricant leaking from said delivery pump.

Another object is to provide a new and improved pump structure of the foregoing character in which the fuel and lubricant leaking from the delivery pump are not intermingled.

A further object is to provide a novel primary pump having an inlet passageY connected to an enlarged surge chamber or accumulator within the pump body.

Another object is to provide a new and improved transfer pump unit comprising`r a primary pump for transferring fuel to a delivery pump and having a pressure controlled plunger, which plunger serves also as. the pumping element of an auxiliary pumpv for removing fuel leaking from the delivery pump.

.A further object is to provide a novel pump unit comprising a primary pump for transferring fuel to a delivery pump and having a reciprocatory piston which serves.. alsov as the piston of an auxiliary pump for removing lubricant leaking from the delivery pump.

Still another object is to provide a new and improved pump structure including a delivery pump and a primary pump for supplying fuel to the delivery pump, said pumps having a novel drive connection for effecting synchronous operation.

Further objects and advantages will become apparent as the description proceeds.

lin the accompanying. drawings,

Figure l is a fragmentary verticalV sectional view of a pump structure embodying the features of my invention, part of the structure being shown in side elevation.

Fig. 2 is a top plan View of a transfer pump unit forming part of the structure.

Fig. 3 is a side elevation of the transfer pump unit.

Fig. l is a left-end elevation.

Fig. 5 is a right-end elevation.

Fig. 6 is a transverse vertical sectional view taken along line S--Gof Fig. l.

Fig. '7 is a fragmentary detail sectional view taken along line 7.-1 of Fig. 6.

12 Claims. (Cl. 1'03-5) Fig. 8 is an enlarged sectional view through a valve forming part of the transfer pump unit.

Fig. 9 is a fragmentary sectional view taken along line 9 9 of Fig. 6.

Referring more particularly to the drawings, the pump structure, illustrating the invention, comprises generally a delivery pump I for discharging fluid under a relatively high pressure, and a transfer pump unit, including a primary pump 2 for supplying or transferring fluid under a relatively low pressure to the inlet of the delivery pump I, and two auxiliary pumps 3 and 4 respectively for scavenging accumulated fluid leaking from the pumping means of the delivery pump, and accumulated lubricant leaking from or circulating through the driving mechanism of the delivery pump. The pumps 2', 3 and 4 are combined in a unit assembly, and are operated in timed relation to each other and to the delivery pump I'.

The high pressure delivery pump I may be of any desired form or type, and is herein disclosed for purposes of illustration as an adjustable metering and distributing fuel pump like that disclosed in my Patent No. 2,265,232, issued December 9, 1941. In the present instance, the fuel delivery pump I comprises a housing 5 adapted to be mounted on a suitable support, such as the crank case of an internal combustion engine. A cylinder body 6 is mounted in one end of the housing 5, and is formed with a central bore lv and with a plurality of parallel pump cylinders 8 arranged in angularly spaced relation about the bore. A plurality of pump pistons 9 are reciprocably disposed in the cylinders 8, and are urged outwardly by compression springs Ill. Mounted in the other end of the housing 5 is a driving mechanism for effecting reclprocation of the pistons 9 in uniformly timed sequence. This mechanism comprises a plurality of actuating plungers or tappets I I reciprocably guided in the' housing 5, and disposed in axial alinement, and in end abutting engagement, respectively with the pistons 9. A rotary swash plate I2 ccacts with the plungers II, and is operable by a central drive shaft I3 in axial alinement with the bore I. The pressure ends of the pump cylinders 8 open respectively through outlet check valves III to a plurality of delivery lines I5, and have individual inlet ports IS opening in a common transverse plane from the bore 'I. A groove II is formed in the periphery of the bore l, and is open to an inlet passage I8 connected to a low pressure fluid supply line I9. Mounted in the bore 'l is a rotary valve member 20 having a relief' area 2l adapted to effect communication between the ports I and the groove I1, and having a narrow land area 22 movable successively across the ports to close each port during a predetermined portion of the working stroke of the associated piston 9. The valve member 2Q is operatively connected to the shaft I3 for rotation thereby in timed relation to the reciprocation of the pistons 3.

In the operation of the delivery pump I, predetermined quantities of uid, such as liquid fuel, are discharged under a relatively high pressure and in timed sequence to the delivery lines I5. Any fuel leaking from the closed ends of the cylinders Z along the pistons 9, .and from the groove i? inwardly along the valve member 2G, will pass into the left-end portion of the interior of the housing 5 between the cylinder body 5 and the pump driving mechanism. Similarly, any lubricant leaking inwardly along the plungers II will pass into the right-end portion of the interior of the' housing 5 between the cylinder body 5 and the driving mechanism.

The transfer pump unit comprises a generally rectangular body 23 which is normally disposed in a horizontal position, and which is formed at the top with a flat marginal flange or plate 25 adapted to be secured in position against a mounting surface 25 on the underside of the delivery pump housing 5. Preferably, the plate 2li is located by a plurality of diagonally spaced dowel pins 2e and is secured to the housing 5 by four corner bolts 2l. A marginal gasket 2 is inserted between the housing 5 and the plate 24 to obtain a duid-tight connection.

The bottom wall of the pump housing intermediate the pumping unit and the drive mechanism, is formed with an opening 29 which is circumscribed by the marginal surface 25, and which hence is closed by the plate 25 of the to form two open reservoirs or sumps 3B and 3! which are arranged respectively to collect fuel and lubricant leaking from the pumping unit and the drive mechanism into the housing 5 and then dripping or draining through the opening 29. A transverse rib or dam 32, rising to the top level of the plate 2li, separates the sumps 3Q and 3l to prevent intermingling of the leakage fuel and lubricant. The fluids collecting in the sumps and 3i are removed by the auxiliary pumps 3 and l as is hereinafter more fully described.

The primary pump 2, for transferring fuel to the supply line I9 of the pump I, comprises a longitudinal medial cylinder 33 formed in and opening through the body 23. One end of the cylinder is closed by a plug 3d, and the other end is formed with a counterbore 35 constituting an auxiliary cylinder and defining an outwardly facing annular stop shoulder 35. A sleeve nut 37 is threaded into the outer end of the counterbore 35 to close the latter.

Opening respectively to opposite sides of the cylinder 33 in a common transverse plane intermediate its ends are an inlet port 38 and an outlet port 39. The inlet port 38 is connected through an inlet check valve G9 with a supply passage il which extends to one end of the body 23. A suction line l2 leading from a suitable source of fuel, such as a supply tank (not shown) is detachably connected to the cody 23 and communicates with the outer end of the passage 4I.

The inlet check valve comprises a valve passage intersecting the supply passage 4I and opening vertically through a. valve seat 54 to a actuating plunger or tappet II. body 23. The top face of the plate 24 is recessed 4 valve chamber d5. The chamber is closed at the top by a screw plug A5, and connects with the port 39. A suitable valve member 41 is slidably guided in the plug 45, and is normally urged by a compression spring 48 into engagement with the seat 4d.

Formed in the body 23 and connected to the inner end of the supply passage 4I is a large bore-49 which serves as a surge chamber or accumulator. The outer end of the bore 49 is closed by a plug 55, and the two plugs 34 and 5E! are secured in position by a lock screw 5 I.

The outlet port 39 is connected through an outlet check valve 52 to a delivery passage 53 which extends to one end of the body 23, and is connected with the supply line I3 leading to the inlet of the pump I. The outlet check valve 52 comprises a valve chamber 54 'formed in one side of the body 23, and closed by a screw plug 55. The chamber 54 opens through a valve seat 56 to the outlet port 39, and intersects the delivery passage 53. A suitable valve member 51, slidably guided in the screw plug 55, is normally urged into engagement with the seat 53 by a coiled compression spring 58.

A relief valve 53 is connected to the chamber 54 to dissipate excessive pressures in the event of abnormal operating conditions. The valve 59 has an inlet passage 69 controlled by an adjustable spring-seated ball valve member 6I and has an outlet passage 62 opening to the sump 39.

Reciprocably mounted in the cylinder 33 intermediate its ends is a pump piston I63. Preferably, the piston 63 is driven by the delivery pump I in timed relation to the pistons 9. The drive connection comprises a vertical pin 54 which is formed at the upper end with a sleeve 65 fitting snugly about and rigidly locked to the lowermost The lower end of the pin 5ft extends with a close t into a diametrical bore 65 in the piston 63 substantially midway of its ends. vA relatively large vertical bore 6'! in the body 23 opens downwardly from the sump 35, and fully intersects the cylinder 33 to permit the drive connection and to accommodate the translation of the pin 54. The bore 6'! is somewhat larger in diameter than the cylinder 33, and hence provides vertical passages 58 at opposite sides of the piston 33 adapted to receive fuel from the sump 39.

One end of the piston 63, having an end face 59, constitutes the active end in the primary pump 2. At the end of the pressure stroke, the piston face 39 advances substantially to the plane of the inlet and outlet ports 38 and 39. To prevent blocking of these ports, suitable arcuate grooves I0 are formed in opposite sides of the piston 53 at the end face 69.

In operation, movement of the piston 53 on its outward stroke away from the ports 38 and 39 will cause the flow of fuel from the supply tank through the inlet valve 40 in whatever amount is required to ll the cylinder 33, and movement of the piston in the reverse direction on the pressure stroke will cause the discharge of fuel under pressure through the outlet check valve 52 to the supply line I9 for the delivery pump I.

A pressure control plunger 1I is reciprocable in the left end of the cylinder 33 in opposed relation to the active end of the piston 63, and coacts therewith to define the pressure chamber of the pump 2. The plunger has an enlarged peripheral flange or head 'I2 freely reciprooable in the auxiliary cylinder 35, and adapted to limit inward movement by engagement with the stop: 36; The plunger 1 I. isA urged inwardly by spring pressure, and iny effect constitutes a yieldable end Wall of the pump pressure chamber.. In the present instance, the spring means comprises two coaxialv compression springs 13 and I4 which at one end bear against a flange 1.5 on a pilot sleeve. 13 seated in the sleeve nut 31., and which atl the other end engage in a centering recess 1 in the head 12.

The displacement of the piston 63 is normally equal to and preferably in excess of the maxi.- mum requirements ofthe associated fuel injection pump and the. pressure control plunger Tl isoperable automatically to vary the-volume of fuel actuallyl delivered in accordance with. the. existing requirements. at a predetermined maximum pressure. If atany time the full displacement of the piston 63 is required, the springs f3l and 1.4 will maintain the head. 1.2 against the stopA 36 toy constrain the plunger 1| against movement out of its innermost position. In. the event that. the full displacement of the piston 63 isf not required, the pressure inv the cylinder 33' will cause the plunger 1| to move outwardly during the pressure stroke of the piston 63 so that onlyv part. of the displacement of the piston will be discharged through the valve 52. In. the subsequent suction stroke of the piston 63; the plunger 12| will. move inwardly to maintain the fuel' iin the.l cylinder 33 under a. predetermined maximum discharge pressure until the head 12 again engages. the stop 36, and. thereafter fuelpin an amount sui'cient to; ref-lll the cylinder will enter through the valve 40.. If no fuel is required by the delivery pump the plunger 1| willtravel in synchronism with the piston '63,

thereby resulting in zerodelivery.` Consequently,

the pump 2 isv self-relieving tov supply the demands. of the delivery pump fromv zero to maximum at the maximum delivery pressure.

Thev auxiliary pump 3. utilizes the counterbore 35 as a cylinder, and thel plunger 1|? as' a piston, and is operable to take leakage fuel from the sump 3B and transfer it to the source. of. supply for the delivery pump or to some other convenient place.. The pump 3 hasan inlet passage 1.8 which connects: at one end with the bottom ofi the bore' 61,. and which opens at the other end' through a. port 19` to the outer end portion of thev cylinderl 33. The piston 1-'|` serves to uncover the port 19 when in its innermost position in the cylinder 33,. and to close the port upon initial. movement out of this position. In the present instance, the piston 1| is formed beneath the head 12; with a peripheral groove 8|) adapted to communicate with the port 19v when the head 12.V engages the stop 36,. and with a plurality of apertures 8f| opening from the groovev 80 through the. head 12 to complete the flow connection to the cylinder 35.

The pumpv 3 has an outlet check valve 82 mounted in' the sleeve 16- andl adapted for connection to a return line 8-3. be of any suitable form, andi in the present instance (see Fig.. 85)" comprises a body 64: having a valve passage |35 with. a seat 86. A ball. valve member 81 is normally urged against the seat Sift by' a coiled' compression spring 88 which is. confined"v in the body 84 by a tubular* pilot sleeve 89; Preferablynltering elements 90 are mounted in. opposite ends of the valve body 845.v

Inl operation, it will'V be seen that the plunger 1"|I performs the dual function of controlling the effective displacement. of the pump 2 ata given maximurnpressure in accordance with the re- The valve 8.2 may' quirements of the pump I, and at the same time of serving as they piston of. the `pump 3. Upon inward movement of the piston 1| t0 the right into engagement with the stop 36, a suction is created in the cylinder 35, and the port 19 is opened' to admit. fuel from the sump 30. Upon outward movement of the piston 1|, the port '1.9 is cut off, and thereafter the fuel in the cylind'er 35 is compressed and discharged through the valve 82 into the line 83 for return to the fuel supply tank. While the pump 3 is operative only as. an incident. to the reciprocation of the plunger 1|, the latter is reciprocated enough in. the normal operation of the pump structure to. remove: all the leakage fuel accumulating iny the pump 30.

The auxiliary pump 4, for removing lubricant leaking from the housing 5 and collecting into the sump 3|, utilizes the right end of piston 63 as the pumping element and the closed end of the cylinder 33 as the cylinder or pressure chamber.' 9|... Thus, the piston 63' is of the double acting. type, its pressure stroke for the pump 2 being the: suction stroke for the pump 4, and its suction stroke for the pump 2 being the pressure stroke for the pump 4.

The" cylinder 9| has anl inlet port 92 which opensr from the sump 3|, and which is uncovered by the piston. 63 at the end of the suction stroke and is closed in the initial movement of the piston on the pressure: stroke. The cylinder 9| also has an outlet passage 93 which opens through the body 2.3: to. the top` face ofv the flange 24- in registration with a passage 94 through the housing 5i for. returning. the discharged lubricant to the crank case of the engine. The gasket 23 between the body 5- of the pump I and the mounting plate 24" of the pump 2 is suitably apertured to establish communication between the passages 93 andV 94; Inserted in the passage 33y is. an outlet check valve unit 95 of the same type as the valve 82.

In operation, the piston 63 uncovers the inlet port 92 at the end of the suction stroke in the cylinder 9| to permit the entry of accumulating lubricating oil from the sump 3|. On the pressure stroke of the pump- 4, the piston 63l will dis charge-the lubricant from the cylinder 9| through the passages 93 and 94 and. valve 95 to the engine crank case.

The dam 342y prevents the fuel and lubricant collecting respectively in the sumps 36 and 3| normally from intermingling. If either of the auxiliary pumps 3 or 4 should fail to operate properly to transfer thel fluid collecting in the corresponding sumps, the associated sump would nll up and the fluid therein would overow the darn 32. Means is provided for indicating such abnormal condition of operation, and in the presenti instance, this means comprises two longitudinal grooves 96 formed in the top of the dam at opposite sides of the vertical bore 61, and arranged tov catch any overflow from either sump. The grooves are connected through vertical down-flow passages 91 to two relatively large bores 98 formed in. opposite sides of the body 23. Suitable lters 99 are mounted in the bores 98. In theV event of any overflow, fluid will pass to the filters 99, and indicate that at least one of the pumps 3 and 4 is not operating properly. From'. the character of the fluid noticeable at the filters 93, the offending pump can be identified.

Means is also provided for reciprocating the plunger 1li manually to prime the pump without.I cranking the engine when the pump is idle.

The means for this purpose comprises an actuating plunger IGI) which extends reciprocably through a bore lill in the body 23.. One end of the plunger Iil projects for engagement with the head l2, and the other end projects from the body 23 for engagement by the rounded free end of a lever arm |02 fixed on a rock shaft W3. The latter is journaled in parallel spaced lugs or Webs i534 integral with one end of the body 23. A hand lever |85 may be nxed on the shaft 183 for actuating the latter. Normally, the springs i3 and ifi acting through the head 'l2 tend to move the piston ll in its suction stroke, and to swing the lever It to the right. Additional spring means may, however, be provided for insuring movement of the lever 95 to the right independently of the piston ll. This spring means comprises a plunger 06 reciprocable in a bore lill parallel to the bore IDI in the body 23, and urged outwardly by a coiled compression spring H33 into engagement with the lever arm M32. By alternately actuating the hand lever IE5, first in one direction against the action of the springs 13, 'M and Hi8, and then in the reverse direction, pumping reciprocation will be imparted to the piston ll, independently of the operation of the pump 2. The piston 'il will, on its outward stroke, take in fuel through the valve 4G, and on its pressure stroke discharge fuel through the valve 52.

The present application is a division of my copending application Serial No. 429,998, filed February 9, 1942 (now Patent No. 2,383,483).

I claim as my invention:

l. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on the underside of said housing and constituting a closure therefor, said transfer pump unit including a primary pump operable in timed relation to said delivery pump and having a discharge line connected to the inlet of said pumping unit, an auxiliary pump operable as an incident to the operation of said primary pump to remove to an external point from said housing fluid leaking thereto from said pumping unit, and a second auxiliary pump operable in synchronism With said primary pump for removing to an outside point from said housing lubricant leaking thereto from said driving unit.

2. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on the underside of said housing and constituting a closure therefor, said transfer pump unit including a primaiy pump operable in timed relation to said delivery pump and having a discharge line connected to the inlet of said pumping unit, and including an auxiliary pump operable in synchronism with said primary pump and having a discharge line independent of said primary pump and said first mentioned discharge line for removing to an outside point from said housing lubricant leaking thereto from said driving unit.

3. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on the underside of said housing and constituting a closure therefor, said transfer pump unit including a primary pump operable in timed relation to said delivery pump and hav- (Effi ing a discharge line connected to the inlet of said pumping unit, and including an auxiliary pump operable as an incident to the operation of said primary pump and having a discharge line independent of said primary pump and said first mentioned discharge line to remove to a point external from said housing and transfer pump unit iiuid leaking thereto from said pumping unit.

4. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on said housing and constituting a closure therefor, said transfer pump unit including a primary pump operable in timed relation to said delivery pump and having a discharge line connected to the inlet of said pumping unit, an auxiliary pump operable in timed relation to said primary pump to remove from said housing iluid leaking thereto from said pumping unit, and a second auxiliary pump operable in syrichronism with said primary pump for removing from said housing lubricant leaking thereto from said' drive unit.

5. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on said housing and constituting a closure therefor, said transfervpump unit including a primary pump operable in timed relation to said delivery pump and having a discharge line connected to the inlet' of said pumping unit, an auxiliary pump operable in timed relation to said primary pump to remove from said housing uid leaking thereto from said pumping unit, and a second auxiliary pump operable'in synchronism With said primary pump for removf ing from said housing lubricant leaking lthereto from said drive unit, said primary and auxiliary pumps having independent outlet passages to prevent intermingling of the uids discharged therefrom.

6. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on and enclosing the underside of said housing and formed in the top with a first sump located to collect fluid leaking from said pumping unit, and a second sump located to collect lubricant leaking from said driving unit, said transfer pump 'unit including a primary pump for supplying fluid to the inlet of said pumping unit, an auxiliary pump for transferring fluid from said `first sump, and an auxiliary pump for transferring fluid from said second sump.

7. A pump structure comprising, in combination, a delivery pump having a housing enclos'- ing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on and enclosing the underside of said housing and formed in the top with a sump located to collect fluid leaking from said pumping unit, and 9. second sump separated from said rst sump by a dam and located to collect lubricant leaking from said driving unit, said transfer pump unit including a primary pump for supplying fluid to the inlet of said pumping unit, an auxiliary pump for transferring uid from said first sump separate from the delivery of said primary pump, and an auxiliary pump for transferring iluid from said second sump l separate from the delivery of said primary pump.

8. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on and enclosing the underside of said housing and formed in the top with a sump located to collect uid leaking from said pumping unit, and a second sump separated from said iirst sump by a dam and located to collect lubricant leaking from said driving unit, said transfer pump unit includ-ing a primary pump for supplying uid to the inlet of said pumping unit, an auxiliary pump for transferring fluid from said rst sump separate from the delivery of said primary pump, and an auxiliary pump for transferring fluid from said second sump separate from the delivery of said primary pump, all of said pumps being operable in timed relation.

9. A `pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit in one end and a driving unit in the other end, and a transfer pump unit mounted on and enclosing the underside of said housing and formed in the top with a sump located to collect fluid leaking from said pumping unit, and a second sump separated from said :trst sump by a dam and located to collect lubricant leaking from said driving unit, said transfer pump unit including a primary pump for supplying uid to the inlet of said pumping unit, an auxiliary pump for transferring fluid from said rst sump separate from the delivery of said primary pump, and an auxiliary pump for transferring fluid from said second sump separate from the delivery of said primary pump, and means for indicating the overflow of fluid from either sump across said dam.

10. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit, and a transfer pump unit mounted on and enclosing the underside of said housing and formed in the top With a sump 1ocated to collect fluid leaking from said pumping unit, said transfer pump unit including a primary pump for supplying fluid to the inlet of said pumping unit, and an auxiliary pump having an inlet open to said sump and a discharge line leading directly from said auxiliary pump independently of said primary pump for .transferring uid from said'sump separate from the delivery of said primary pump.

11. A pump structure comprising, in combination, a delivery pump having a housing enclosing a pumping unit, and a transfer pump unit mounted on and enclosing the underside of said housing and formed in the top w-ith a sump having a dam and located to collect iluid leaking from said pumping unit, said transfer pump unit including a primary pump for supplying fluid to the inlet of said pumping unit, and an auxiliary pump for transferring uid from said sump separate from the delivery of said primary pump, and means for indicating the overflow of .fluid from said sump across said dam.

12. A pump structure comprising, in combination, a fuel delivery pump having a plurality of reciprocatory pump pistons reciprocable in timed sequence to deliver metered charges of fuel, a plurality of reciprocatory tappets for operating said pistons, and means for reciprocating said tappets, and a primary pump having a cylinder body mounted on said delivery pump and formed with an opening in the top communicating with the interior of said delivery pump, a piston reciprocable in said cylinder body and having a diametrical bore intermediate its ends, a drive pin rigidly anchored at one end to one of said tappets for movement therewith and extending transversely therefrom through said opening into said diametrical bore to establish a drive connection for said piston, and means for supplying fuel to said cylinder body during the suction stroke of said piston and discharging fuel from said cylinder body to the inlet of said delivery pump during the pressure stroke of said piston.

JAMES F. HOFFER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,535,643 Astrom Apr. 28, 1925 2,093,003 Bowman Sept. 14, 1937 2,160,735 Hoffer May 30, 1939 2,214,257 Pfauser Sept. 10, 1940 2,265,232 Hoffer Dec. 9, 1941 2,310,370 Hoifer Feb. 9, 1943 2,331,462 Denigan Oct. 12, 1943 2,383,483 Hoiler Aug. 28, 1945

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