US3073255A

US3073255A - Hydraulic pumping units

Info

Publication number: US3073255A
Application number: US408007A
Authority: US
Inventors: Gratzmuller Jean Louis
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-02-05
Filing date: 1954-02-03
Publication date: 1963-01-15
Anticipated expiration: 1980-01-15

Description

Jan. 15, 1963 J. L. GRAT'ZMULLER HYDRAULIC PUMPING UNITS v '7 Sheets-Sheet 1 FIG! Filed Feb. 3, 1954 Im/enfor mm a Jan. 15, 1963 J. L. GRATZMULLER 3,073,255

HYDRAULIC PUMPING nuns Filed Feb. 5, 1954 '7 Sheets-Sheet 2 Fig.2

LnO:

" InvenT r by M r AfCarnQy Jan. 15, 1963 J. L. GRATZMULLER 3,073,255

HYDRAULIC PUMPING UNITS Filed Feb. 5, 1954 '7 Sheets-Sheet 3 Jan. 15, 1963 J. L. GRATZMULLER 3,0 3, 55

HYDRAULIC PUMPING UNITS Filed Feb. 3, 1954 7 Sheets-Sheet 4 FIGS 4 56 Invenmr b flmmr Jan. 15, 1963 J. L. GRATZMULLER 3,073,255

HYDRAULIC PUMPING UNITS Filed Feb. 3, 1954 7 Sheets-Sheet s FIG.6

Invenmr b7 {hawk/W Attorneys Jan. 15, 1963 .1. L. GRATZMULLER ,0

HYDRAULIC PUMPING UNITS Filed Feb. 5, 1954 7 Sheets-Sheet 6 Inventor by M WW Jan. 15, 1963 J. L. GRATZMULLER 3,073,255

HYDRAULIC PUMPING UNITS 7 Sheets-Sheet '7 Filed Feb. 3, 1954 m. D a J w 8 G. F m w y ,5 m W? //m 72%7 m Q 5 .1 W 9 m 51% Inventor W. pa

by M PM Attarne s Utlit ttes Patent ice 3,073,255 HYDRAULIC PUMPING UNITS Jean Louis Gratzmuller, Paris, France Filed Feb. 3, 1954, Ser. No. 408,007 Claims priority, application France Feb. 5, 1953 3 Claims. (Cl. 103-204) The present invention relates to a hydraulic pumping unit adapted to furnish a liquid under a high pressure.

An object of the invention is to provide a hydraulic pumping unit of this type comprising a pump capable of ensuring a continuous operation without any risk of unpriming nor jamming in any condition of service without resorting to intricate and thus expensive arrangements.

Another object of the invention is to establish an absolutely effective separation between the pump cylinder, on the one side, and the crank-case, on the other side.

A more specific object of the invention is to ensure the above-mentioned absolutely effective separation by means of an annular space constituted by a peripheral groove formed on the piston and/or in the inner wall of the cylinder and to establish a permanent and free communication between said annular space and a liquid mass maintained under a pressure slightly higher than the maximum possible pressure in the crank-case, so that, on the one hand, during the delivery stroke, the liquid to be fed through the pumping unit is prevented from penetrating into the crank-case of the pump and, on the other hand, during the sucking stroke, air from said crank-case is prevented from being sucked into the cylinder.

In the case of a stationary pump, the crank-case of which is at atmospheric pressure, the usual head provided by the liquid tank suflices to maintain the required pressure difference, while, in the case of an aircraft pump, for example, it suflices to maintain in the liquid tank a pressure slightly higher than the pressure in the crank-case, Whatever the absolute value of the latter.

Still another object of the invention is to provide the hydraulic pumping unit with non-return ball valves of the type described in the co-pending patent application Ser. No. 406,262 filed Jan. 26, 1954 by applicant (now Patent No. 2,899,974) for Non-Return Ball Valve for Reciprocating Hydraulic Pumps.

A further object of the invention is to provide a hydraulic pumping unit comprising a pump of the abovedescribed type completed by a supercharging device such as a gear pump, which permits ensuring a full filling of the pump cylinder during each sucking stroke without any fluid leakage toward the crank-case.

Still another object of the invention is to interpose, between the feeding tank and the inlet of the pump, means to vary a cross-section of the feeding circuit, which permits adjusting at will the output of the pumping unit by starving the pump input.

A more specific object of the invention is to use as cross-section adjusting means, for the purpose described in the preceding paragraph, a simple tap, e.g. provided with a needle member.

Another specific object of the invention is to use, as the above-mentioned cross-section varying means, a regulator capable of continuously adjusting said cross-section as a function of any desired parameter.

With this purpose in view, it is a more particular object of theinvention to provide such a regulator, the movable member of which is controlled by means responsive to the output pressure of the pump.

This last arrangement permits solving in a particularly efiicient, simple and cheap manner, the problem of the regulation of a pump sucking rate as a function of the output pressure.

A further object of the invention is to provide a hydraulic pumping unit of the type described comprising a pump provided with an annular space interposed between its piston and cylinder and fed with a pressure slightly higher than the pressure in its crank-case to etficiently insulate the same from said pump cylinder, in combination with at least one of the following elements: means to adjust the sucking rate of the unit as a function of the output pressure, a cock for manually controlling said sucking rate and a supercharging pump to facilitate the filling of the main pump cylinder.

Another object of the invention is to interpose between the piston and the cylinder of the pump, in addition to the above-mentioned annular space, a second annular space disposed axially between the first one and the crank-ease, said second annular space being fed from a tank containing a lubricating liquid, that portion of the piston which is comprised between said second annular space and the pump chamber being fitted in the cylinder with a clearance sufliciently greater than that of the remaining portion of the piston to prevent said piston portion. from making metal-to-metal contact with the cylinder.

Due to this arrangement, the pump is adapted to be used for pumping liquids which usually would cause jamming of the piston in the cylinder, such as gasoline.

In the following description, at liquid having such jamming properties will be called gasoline, while a liquid having lubricating properties will be called oil.

With the above-described arrangement, the first annular space and the inlet of the pump will be connected with a gasoline tank, while the second annular space wil lbe connected with an oil tank, so that only that portion of the piston which is never in contact with the cylinder will be in the gasoline circuit, while the oil will ensure the lubrication between the guiding portion of the piston and the cylinder.

In this arrangement, the oil pressure in the second annular space is preferably slightly higher than. the gasoline pressure in the first one, so as to prevent any gasoline leakage into the oil.

Still another object of the invention is to provide a gasoline pumping unit comprising a pump provided with two annular spaces, as described above, in combination with one or more of the previously mentioned supercharging, hand-controlling and sucking rate regulating elements.

Other objects and advantages of the invention will be, apparent from the following detailed description, together with the accompanying drawings, submitted for purposes of illustration only and not intended to define the scope of the invention, reference being had for that purpose to the subjoined claims.

In these drawings:

FIG. 1 is a diagrammatic partly .sectional view of a hydraulic pumping unit comprising a pump made of two effectively separated portions according to the invention, a regulator for automatically adjusting the sucking rate of said pump, a cock for manually controlling'said sucking rate and an additional superch-arging pump.

portion of the pump of FIG. 2 provided with a sucking rate regulator.

FIG. 6 shows a hydraulic pumping unit comprising amanually actuated cock for controlling the sucking rate of the pump.

FIG. '7 shows another hydraulic pumping unit compris- 3 ing an additional super-charging gear pump interposed in the feeding circuit of the main pump.

FIG. 8 is a partly sectional view, with parts broken away, of a gasoline pump according to the invention.

FIG. 9 is an axial sectional detail view of the device shown in FIG. 8.

Referring to the drawings, and more particularly to FIGS. 2 and 3, there are shown at 1 the crank-case and at 2 the barrel of the pump screwed in the top wall 20 of said crank case.

Inside the barrel 2 are stacked: a member 3 constituting the cylinder of the pump, a member 4 in which is formed the intake valve, a member 5 in which is formed a delivery valve and a plug member 6, which, in the example shown, is screwed in the threaded end of barrel 2 and holds in place the whole assembly of the above described members, suitable packing rings such as 7, 8 and 9 being interposed between the relevant members of the stack.

It is to be noted that the packing rings 8' and 9 ensure tightness both between

members

3 and 4 and members 5 and 6, respectively, and between said members and the inner wall of barrel 2.

Members

3, 4, 5 and 6 are preferably made of a metal having the same coefficient of thermal expansion as barrel 2, so as to avoid any leakage or destruction of the packing rings, as the temperature of the pump varies in operation.

It will be understood that this mode of assembling the various members of the pump by merely stacking them permits a rapid and easy assembling and dismantling of the pump. 10a is the inlet of the pump to which the liquid is fed through a suitable pipe 10b. 11 is the outlet provided through plug 6. The intake valve which, in the example shown, is of the type described in the above cited patent application, essentially comprises a ball 51 cooperating with a seat 12 and guided and centered by a tubular extension 13 of member 4. The liquid is sucked int-o the pump through inlet 10a, a passage 14 and lateral holes 16 drilled through the wall of the tubular extension 13 in the near vicinity of seat 12.

The delivery valve which is formed in member 5 comprises a ball 17 cooperating with a seat 18. This last valve, of a more conventional type, offers between ball 17 and its cylindrical housing, sufficient annular clearance to permit flowing of the liquid towards outlet -11. Both valves are provided with abutment means to limit the lifting stroke of their respective ball, said abutment means being each constituted by a gudgeon pin '19.

It is obvious that both valves may be of the'type described in the above cited application, if preferred.

'It is to be noted that the delivery valve is located directly above the intake valve, said valves being both so designed that the air which could be accumulated in the pump cylinder before the pump is started will tend naturally to escape through outlet 11.

As mentioned above, according to the invention, a complete separation is provided between barrel 2 and crank-case 1, said separation being ensured by an annular space formed between the plunger piston 21 and cylinder 3, said space freely communicating with the liquid tank, as shown in FIG. 1.

In the example shown in FIG. 2, the annular space 52 is formed by a portion 22 of reduced diameter of piston 21, said portion extending over an axial length of the piston 21 at least equal to the stroke of said piston, so as to establish a permanent communication through at least one passage 24 with an annular chamber 23 constantly communicating in turn through a fitting 25 and an individual pipe 58 with the tank 57.

The long piston part extending between the pump chamher and the portion 22 of reduced diameter already ensince a good tightness. However, leakages can still occur,

particularly when'the pump delivers liquid under a very high pressure.

It will be readily understood that these leakages will return to the liquid tank through the free communication offered by pipe 58 rather than forcing their Way between the lower part of the piston and cylinder towards the crank-case 1.

Another important advantage of maintaining the annular space 52in permanent and free communication with the tank 57 is to ensure in said space a constant liquid pressure slightly greater than the pressure in the crankcase 1. Due to this liquid pressure seal, air cannot be sucked into the pump chamber during the suction stroke.

Still another advantage of the complete separation between barrel 2 and crank-case 1 is that of permitting the use in the latter of any desired lubricant, whatever the nature of the liquid delivered by the pumping unit.

As shown in FIG. 4, it is possible, in certain cases, to suppress the special independent duct 58 and to establish a permanent communication between the annular chamber 23 and, hence, the annular space 52 and a space upstream of the intake valve, the inlet port 14 of which is at the same pressure as the feeding tank, by means ofv passages 26. This simplified arrangement may be adopted, in particular, when the feeding tank is located in the near vicinity of the pump, so that no objectionable loss of pressure is to be feared.

On the contrary, when such losses of pressure could happen in the main feeding pipe 10b, e.g. in the case when the feeding tank is located at a considerable distance from the pump, it will be preferred to adopt the embodiment described with references to FIGS. 1 to 3 in which the presence of the independent duct 58 through which no forced circulation of liquid takes place maintains with safety in the annular space 52 the slight above mentioned over-pressure.

It goes without saying that it is possible, within the scope of the invention, instead of providing a portion of reduced diameter in the piston, to provide a portion of enlarged diameter in the cylinder along a suitable axial length to obtain an annular space similar to 52, both dispositions being combined if required.

Referring again to FIGS. 2 and 3, piston 21 is reciprocated by means of an eccentric 27 freely pivoted around a crank-pin portion 28 of a shift, the same being generally indicated at A.

Shaft A is journalled into cylindrical bearing surfaces 29 and 30 of different diameters directly bored in two opposed walls of crank-case 1.

As mentioned above, said crank-case is made of a metal having a high coefficient of thermal expansion and a low modulus of elasticity such as aluminium. Because of this arrangement, it is possible to journal shaft A directly in the above described bearing portions bored in crank-case 1 without any risk of jamming.

Thus, a certain flexibility of the crank-case walls and the high coefiicien-t of thermal expansion of the metal of said walls ensure a good operation of the pump without providing any special bearings to journal shaft A.

The connection between piston 21 and the eccentric 27 is designed to constitute a universal joint.

The end of piston 21 is engaged in a hole in a pivot pin 31 freely rotatable in a cylindrical housing 32 of the eccen. tr-ic 27, the connection between pivot pin 31 and piston 21 being ensured by a cylindrical gudgeon pin 33. Since the hole'in pin 31 is large enough to permit some movement of the piston around the pin 33 as an axis, this assembly constitutes a universal joint. 7

The assembling of the various members of the mechanical driving connection is made easier by the hereunder described constructive anrangement. A passage 34 is provided through the eccentric 27, so that it suflices to bring the cylindrical holes provided in pivot pin 31 by an angular displacement around the axis of the cylindrical housing 32 into registration with said passage 34 after having introduced the end of piston 21 into its hole in said pin 31, whereupon the cylindrical gudgeon pin 33 may be easily passed through its three cylindrical housings provided in contains the liquid to be pumped.

the end of piston 21 and .in pivot pin 31 on either side of said piston end.

Once the piston is brought back into its normal position, the cylindrical gudgeon pin 33 finds itself automatically imprisoned. This universal joint feature permits avoiding the difficulties of providing complete accuracy in the relative positioning of piston 21 with respect to shaft A. As already mentioned above, the

journalled portions

29 and 30 of shaft A have different diameters, while shaft A proper offers an end 35 of reduced diameter adapted to be journalled in bearing surface 29, a crank-pin portion 8 of greater diameter and, finally, a portion 36 of still greater diameter adapted to be journalled in the bearing surface 30 of the crankcase 1.

This arrangement permits mounting the shaft by introducing the same with its reduced end 35 ahead, first into the bearing surface 39, then into the eccentric 27 and, finally, into the bearing surface 29. Once shaft A is mounted as just described, it is secured by means of a plug 38 provided with a hole through which passes the end 37 of shaft A on which a suitable driving member, such as a pulley 39, is keyed.

The lubrication of shaft A is ensured by ringssuch as 40 freely suspended on shaft A and held in depending position, e.g. by a piano wire 41 held in turn by studs 124. inclined passages 42 and 43 ensure the circulation of the lubricating oil in the bearing portions in which shaft A is journalled.

In order to avoid leakages of lubricating oil at the driven end of the shaft, there is formed on said shaft end a frustoconical portion 44, while an annular groove with a rounded cross-section 45 is provided in plug 38. The firusto-conical portion 44 of the shaft and said fixed groove 45, in which the edge of portion 44 slightly penetrates ensure a projection of the leaking oil when shaft A is rotated into groove 45 from which said oil flows through the inclined passage 43 into the pump 113.

The pumping unit shown in FIG. 1 comprises a pump of the type described with reference to FIGS. '2, and 3. The outlet 11 of the pump is connected with the utilization circuit of the pump unit through a duct 55, while the return duct 56 of said circuit leads to the tank 57 which In this embodiment, the annular space 52 communicates, as previously, through at least one radial passage 24 with an annular chamber 23 provided between cylinder 3 and valve 2 and hence, with an additional orifice 25 which is connected through a separate duct 58, to the tank 57.

In the example shown in FIG. 1, there are successively interposed from upstream to downstream on the duct 59 which ensures the feeding of the pump through inlet 10, a gear pump 60 for super-charging the main pump, a cock 61 for manual adjustment of the feeding rate and a regulator 62 automatically varying said feeding rate as a function of the pressure at the outlet 11. Each of said additional apparatus, which may be used separate- 1y or in any combination with a pump according to FIGS. 2 and 3 is described in detail hereunder.

In the complete pumping unit, shown in FIG. 1, it is obvious that the super-charging gear pump '60 could be eliminated during the periods when cock 61 and/ or regulator 62 create a negative pressure at the pump inlet. However, it is more convenient to have the super-charging pump permanently connected, than to provide a switching device which would unduly increase the cost of the pumping unit; such permanent connection is made feasible by the provision of a bypass 99 (see FIG. 7).

The feeding rate regulator shown in FIG. is mounted in the pump barrel 2, in 'a second cylindrical bore parallel to that containing the pump and communicating .at its lower end -(in the drawing) with the feeding duct 59 of the pump, through a radial passage 63 with the inlet 10, and through another radial passage '64 with the delivery port 65 of the pump located downstream of the delivery valve 17 and leading to outlet '11.

In the regulator cylindrical bore, there are mounted by a mere stacking (see details in FIG. 5) a valve body 66 provided with an axial passage 67 formed with a seat 68 for a valve movable member which is constituted by .a ball 69, the lifting of which is controlled by a plunger piston 70; a cylinder member 71 in which said piston is slidably mounted and which is provided with oblique ports 72 leading to an annular groove and establishing a communication between the feeding duct 59, through the axial passage 67 controlled by the ball 69, and the radial port 63 and, hence; the inlet 10, the regulator body pro-per 73 communicating through a radial bore 78 and an axial groove 77 with passage 64, port 65 and, hence, with the outlet 11 and, finally, to hold the whole assembly against an annular shoulder adjacent the lower end of the bore, a threaded plug 74 which is screwed in the upper threaded end of said bore. The tightness of the regulation chamber is ensured by washers 75 and 75a, the latter ensuring concurrently with a third washer 76 the tightness of the controlled communication between the feeding duct and the pump inlet 10. The regulation chamber encloses a disk 79 mounted with a substantial clearance in said chamber on the upper end of a rod 80, the lower end of which is guided with clearance in a sleeve 81 fast with the cylinder member 71 in which the above-mentioned piston 70 is slidably mounted. Piston 70 is mounted on the rod through the intermediary of a kind of universal joint, as shown at 82. Grooves 83 axially spaced along the whole length of piston 70 are provided to reduce the friction between said piston and its cylinder. Finally, springs 84 .and 34a are interposed between disk 79 and the bottom of the regulation chamber. 86, 87 and 88 are threaded plugs tightly closing, with the interposition of packing washers 86a, 87a, 88a, the hole by means of which the members stacked in the bore of the common body 2 may be pushed out for dismantling, as well as the drilling holes through which the radial ports 63 and 64 have been machined.

This device operates as follows:

The utilization pressure in the regulation chamber exerts on piston 70 a thrust tending to apply ball 69 on its seat 68.

Springs 84 are so calibrated as to compensate said thrust for a predetermined value of the utilization pressure. At pressures below this value, springs 84 drive piston 70 upwardly, thus, permitting a more or less substantial lifting of ball 69. Conversely, when the pressure exceeds the above mentioned predetermined value, ball 69 is applied on its seat. In these conditions, when the output pressure of the pump becomes excessive, the cross section of passage 67 controlled by ball 69 is reduced, and thus limits or even completely suppresses, if necessary, the feeding rate into inlet 10 and therefore the rate of discharge of the pump. In spite of the negative pressure which is thus created at the pump inlet, said pump cannot be unprimed due to the fact that the annular groove 52 is permanently filled with oil under a slight overpressure, as explained above.

In the pumping unit shown in FIG. 6, the control of the feeding rate of the inlet 10 of the pump from tank 57 is effected manually by means of a cock, generally indicated at 61 interposed on the feeding duct 59. In the example shown, said cock is essentially constituted by a barrel 89 provided with a chamber 90 communicating at 91 with the upstream portion of duct 59 and at 92 with the downstream portion of said duct. A needle valve 93 controls the communication between the upstream and downstream ends of chamber 90. Said needle is controlled manually by means of a hand-wheel 94 integral with the needle, which comprises a threaded portion 95 screwed in a threaded plug 96 which is screwed in turn in a threaded end of barrel 89. A pack-ing ring 97 is furthermore provided to ensure tightness of the cock. In this case, as previously, the negative pressure which may be created at the inlet 10 of the pump cannot cause any unpriming of said pump, due to the presence of the annular groove 52 (see above).

In FIG. 7, there is shown at 60, the casing of a gear pump interposed in the feeding duct 59. 98 are the gears of said pump, which is preferably completed by a by-pass 99 provided with a pressure-limiting value 100.

In this embodiment, the advantage of the annular space 52 consists in the fact that an increase of the input pressure is capable of causing a leakage of liquid solely between the pump chamber and said annular groove 52 from which the escaping liquid is brought back into the tank through duct 58.

In the embodiment shown in FIGS. 8 and 9, the previously described pump has been completed by a special feature permitting its use for pumping liquids which would be otherwise liable to cause a jamming of the piston in the cylinder (e.g. non-lubricating liquids). This feature which is shown in detail in FIG. 9 essentially consists in the provision of a second annular groove 52a provided, in the example shown, in the periphery of the piston 21 between the first annular groove 52 and the crank-case. Said groove 52a communicates through a port 102 and a duct 102a with a tank 103 containing a lubricating liquid such as oil, said oil tank being so disposed in the example shown, with respect to the tank 57 containing the liquid to be pumped, as to ensure that the pressure in the annular groove 52a is slightly higher than the pressure in the annular groove 52 which, as in the previously described pump, communicates with tank 57, either (and preferably) through a special duct 58, as shown in FIG. 8, or through a port 26 and the feedmg circuit, as shown in FIG. 4.

Moreover, there is provided between the cylinder and that portion of the piston which extends above the second annular groove of the pump chamber 104 a clearance sufliciently greater than the clearance provided between the cylinder and the lubricated portion of the piston to obviate any rnetal-to-metal contact in the portion of the piston which is in the circuit of the liquid to be pumped, which automatically avoids any risk of jamming. The clearances referred to, between the piston and cylinder, are greatly exaggerated in the drawings, for the purposes of illustration. Moreover, the slight over-pressure in the annular groove 52a eliminates any possibility of leakage of the gasoline into the oil, while permitting a slight leakage of oil towards the gasoline circuit.

In this embodiment, it is the pressure of the oil in the annular space 52a which prevents air from being sucked from the crank-case into the pump cylinder, while the gasoline escaping between the piston 21 and the cylinder is permitted to leak through the annular space 52, the port 101 and the pipe 58 towards the gasoline tank 57.

It must be well understood that, while in FIG. 8, the relative positions of the gasoline tank 57 and the oil tank 103 determine the relative pressures to be established in the

annular spaces

52 and 52a, respectively, any other means to maintain the same relation between the pressures in the crank-case, in the annular space 52a and in the annular space 52 may be provided without departing from the scope of the invention. For example, in an aviation pump, where a certain pressure may be maintained in the crank-case and where the pressures in the oil and gasoline tanks are maintained by other means than gravity, the same conditions must be always preserved.

It must be also noted that the arrangement of the type shown in FIGS. 8 and 9, permits the separation between the gasoline circuit and the lubricating circuit provided between the piston and the cylinder, from one side, and the separation of said piston cylinder lubricating system from the lubricating system of the crank-shaft.

This arrangement permits, in particular, to use different lubricatingoils for the piston and the crank-shaft lubrication. By maintaining the pressure diiference between two annular spaces ata proper value and by choosing for the piston a lubricating oil of proper viscosity, the oil leakages can be predetermined and kept at a desired value.

I have designated hereabove by the expression nega-t tive pressure a pressure which is lower than atmospheric pressure.

While the invention has been described with particular reference to a preferred embodiment, it is not intended to limit the scope of the invention to the embodiment illustrated, nor otherwise than by the terms of the subjoined claims.

What is claimed is:

1. A hydraulic pumping unit comprising, in combination, a liquid tank, a reciprocating pump having a crankcase, a cylinder fixedly secured on said crank-case, a plunger piston slidably mounted in said cylinder, driving means in said crank-case operatively connected with the end of said piston, an inlet communicating with said tank through a feeding duct under the control of an intake valve, an outlet provided with a delivery valve and a working chamber formed between said piston and said two valves; a first annular space betwen the wall of said cylinder and an axial zone of said piston spaced from its both ends, means to conduct liquid from said first annular space into said liquid tank, a second annular space between said cylinder and an axial length of said piston spaced from said first annular space and from the driven end of said piston, a reservoir of a lubricating liquid, means to establish a permanent and free communication between said second annular space and said reservoir such that said second space remains filled with lubricating liquid and means to maintain the liquid in said second space under a pressure slightly higher than the pressure in said crankcase, the free end portion of said piston which is comprised between said second annular space and the Working end of said piston being fitted in said cylinder with a clearance sufliciently larger than that of the remaining, guided, portion of said piston to prevent any metal-to-metal contact between said free end portion of the piston and said cylinder.

2. A hydraulic pumping unit according to claim 1, in which said means provided to maintain the liquid in said second space under a pressure slightly higher than the pressure in said crank-case are so adjusted that said pressure is also at least slightly higher than the liquid pressure in said first annular space, whereby said liquid in the first annular space is prevented from leaking towards said reservoir.

3. In a hydraulic pump mechanism, the combination witha barrel provided with an open ended bore, a piston reciprocable in said bore, a housing covering one end of said barrel forming a pumping chamber, means at the other end of said bore for causing reciprocating motion of said piston in said bore, liquid inlet and outlet passages in said housing communicating with said pumping chamber, a suction valve for said inlet passage, and a pressure valve for said outlet passage, of an annular space Within saidbore to intercept leakages of liquid from said pumping chamber past the piston, a feed tank disposed at a higher level than said annular space, a feed duct connecting the liquid inlet passage of the pump to said feed tank, and means including an independent duct also connected to said feed tank for conducting liquid handled by the pump to said annular space at a constant pressure in excess of the pressure at said other end of the bore, but less than the mean pressure in said pumping chamber during the delivery stroke of the pump.

References Cited in the file of this patent UNITED STATES PATENTS 632,001 Stumpf Aug. 29, 1899 1,260,100 Udell Mar. 19, 1918 1,384,097 Schlacks July 12, 1921 I 1,450,135 Clark Mar. 27, 1923 (Other references on following page) UNITED STATES PATENTS 2,410,947 Johnson Nov. 12, 1946 154 59 Made J 1 21 5 2,612,116 LOWlheI'

p

30, 9 1,672,398 Lan :1; 1928 2,645,182 T r ly 1 19 1,743,584 Wiltse Ian, 14, 1930 29678509 Ashton May 18, 1,781,803 Bizzarri Nov. 18, 1930 5 2,691,388 Llvel's 12, 1,971,691 Dilg Aug. 28, 1934 2,081,221 Coberly et a1 May 25, 1937 FOREIGN PATENTS 2,131,749 Ofeldt 001, 4, 1938 407,546 Great Britain Mar. 22, 1934 2,143,637 Vollmann Jan. 10, 1939 415,003 Great Britain Aug. 16, 1934 2,330,781 Langmyhr et a1 Sept. 28, 1943 10

Claims

1. A HYDRAULIC PUMPING UNIT COMPRISING, IN COMBINATION, A LIQUID TANK, A RECIPROCATING PUMP HAVING A CRANKCASE, A CYLINDER FIXEDLY SECURED ON SAID CRANK-CASE, A PLUNGER PISTON SLIDABLY MOUNTED IN SAID CYLINDER, DRIVING MEANS IN SAID CRANK-CASE OPERATIVELY CONNECTED WITH THE END OF SAID PISTON, AN INLET COMMUNICATING WITH SAID TANK THROUGH A FEEDING DUCT UNDER THE CONTROL OF AN INTAKE VALVE, AN OUTLET PROVIDED WITH A DELIVERY VALVE AND A WORKING CHAMBER FORMED BETWEEN SAID PISTON AND SAID TOW VALVES; A FIRST ANNULAR SPACE BETWEEN THE WALL OF SAID CYLINDER AND AN AXIAL ZONE OF SAID PISTON SPACED FROM ITS BOTH ENDS, MEANS TO CONDUCT LIQUID FROM SAID FIRST ANNULAR SPACE INTO SAID LIQUID TANK, A SECOND ANNULAR SPACE BETWEEN SAID CYLINDER AND AN AXIAL LENGTH OF SAID PISTON SPACED FROM SAID FIRST ANNULAR SPACE AND FROM THE DRIVEN END OF SAID PISTON, A RESERVOIR OF A LUBRICATING LIQUID, MEANS TO ESTABLISH A PERMANENT AND FREE COMMUNICATION BETWEEN SAID SECOND ANNULAR SPACE AND SAID RESERVOIR SUCH THAT SAID SECOND SPACE REMAINS FILLED WITH LUBRICATING LIQUID AND MEANS TO MAINTAIN THE LIQUID IN SAID SECOND SPACE UNDER A PRESSURE SLIGHTLY HIGHER THAN THE PRESSURE IN SAID CRANK-CASE, THE FREE END PORTION OF SAID PISTON WHICH IS COMPRISED BETWEEN SAID SECOND ANNULAR SPACE AND THE WORKING END OF SAID PISTON BEING FITTED IN SAID CYLINDER WITH A CLEARANCE SUFFICIENTLY LARGER THAN THAT OF THE REMAINING, GUIDED, PORTION OF SAID PISTON TO PREVENT ANY METAL-TO-METAL CONTACT BETWEEN SAID FREE END PORTION OF THE PISTON AND SAID CYLINDER.