Cylinder lining for hydraulic pump

A hydraulic pump includes a pump housing block, a rotary drive shaft and plural pumping assemblies extending radially from the rotary drive shaft. Each pumping assembly includes a reciprocating piston, a cylinder lining, and a piston return spring mounted between the piston and the lining. The cylinder linings are inserted into the pump block from the outside and a detachable latching device secures the linings to the block. The cylinder lining, the piston and the piston return spring can be easily removed and replaced after the latching device, for instance a locking ring, has been removed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a hydraulic pump of the kind which 
includes a pump housing block which is provided with means for driving a 
piston axially forwards and backwards, a piston-receiving cylindrical 
bore, inlet and outlet passageways which connect with the cylinder and 
through which hydraulic fluid is drawn by suction into the cylinder and 
discharged therefrom respectively, wherein each of the passageways 
includes a respective check valve which determines the direction in which 
hydraulic medium will flow in respective passageways. 
2. Description of the Related Art 
Hydraulic piston pumps are subjected to wear on surfaces which move 
relative to one another, particularly on the piston and the surfaces of 
the cylinder bore in which it moves. Such wear is accentuated when the 
components move at a relatively high speed, and when the pump works at 
high pressures and is kept working for long periods of time. 
The operational efficiency of hydraulic pumps which are subjected to such 
heavy loads as those inferred above will be gradually impaired or the pump 
will malfunction, which means, in turn, that the pump must be replaced or 
repaired. However, the pump normally comprises only one part of a working 
machine, which must be taken out of operation while the faulty hydraulic 
pump is being dealt with. 
In the case of known radial piston pumps, which are used as hydraulic 
pumps, a number of pump devices are disposed radially around a pump 
housing block in a star-like configuration, said block including a drive 
shaft which is common to the pump devices and which includes an eccentric 
which coacts with said devices. When such a radial piston pump is in need 
of repair, it is necessary for an operator or fitter to dismantle each of 
the pump devices from the block, wherein bolts must be loosened, replaced 
and re-tightened, and a relatively large working space is required around 
the pump itself to enable the replacement of pump devices in the pump 
housing block of the machine in which the hydraulic pump is fitted. 
Prior publication DE-A-2,317,089 discloses a paint spray which includes a 
paint conduit having incorporated therein at least one check valve, to 
form a paint pump chamber of which one wall consists of a diaphragm which 
is driven reciprocatingly by pulsating hydraulic pressure generated by a 
piston which is reciprocatingly movable in a cylinder lining that can be 
fitted loosely in a bore. It is necessary to dismantle the paint pump 
chamber before access can be had to the cylinder lining. The bore which 
receives the lining opens into the hydraulic reservoir at a level beneath 
the surface of the hydraulic fluid. 
Prior publications GB-A-1,302,163 and U.S. Pat. No. 4,968,220 relate to 
hydraulic pumps where the pump must be dismantled before the cylinder 
lining/piston can be changed, this work being relatively complicated. 
Consequently, no hydraulic pump can be repaired on site in practice and it 
is therefore necessary in practice to take the whole of the assembly which 
includes the hydraulic pump to a workshop, in order to repair the pump. 
SUMMARY OF THE INVENTION 
Accordingly, one object of the present invention is to provide a hydraulic 
pump construction which will enable the pump to be repaired quickly and 
simply within the confines of a relatively small space and with the use of 
a relatively small number of tools. 
This object is achieved with the inventive hydraulic pump. 
One essential feature of the invention is that the pump housing block has a 
cylinder which opens out onto the outside of the block, and that a 
cylinder lining can be inserted loosely into the cylinder and supported 
against the cylinder wall. A releasable latching device, such as a 
groove-seated locking ring, is fitted to prevent the lining moving out of 
the cylinder in a direction towards the outer side of the block. The 
lining has at least one opening which passes through its cylinder wall and 
establishes communication between the hollow interior of the cylinder 
lining and hydraulic fluid passageways in the block. Disposed 
circumferentially around the outer surface of the lining are labyrinth 
seals which define a circumferentially extending passageway into which the 
passageways in the pump housing block discharge and into which the opening 
or openings in the lining also discharges or discharge. This enables the 
cylinder to have a circular-cylindrical shape and also enables the lining 
to be circular-cylindrical in shape and to adopt any position of rotation 
within the cylinder. The groove which receives the aforesaid locking ring 
is located at the outer end of the cylinder, wherein the locking ring may 
support directly against the outer end of the lining. The actual lining is 
cup-shaped and includes external flanges or fins which, as mentioned, seal 
against the cylindrical wall so as to establish a seal against the flow of 
hydraulic fluid axially in the cylinder, between the lining and the 
cylinder wall. 
The outer end of the cylinder lining may include a somewhat enlarged flange 
which is received on a corresponding shoulder or ledge in the outer 
end-region of the cylinder bore, so as to define a definite axial position 
for the cylinder lining radially inwards, while the groove-seated locking 
ring defines the position of the lining radially outwards. 
The piston drive means may comprise a rotatable shaft having an eccentric 
which acts on the radially inner end of the piston. 
The inventive hydraulic pump may advantageously include at least two 
piston/cylinder assemblies which are driven by a common drive means and 
which are mutually spaced circumferentially around the rotational axis of 
the drive means. 
The radially inner end of the piston may include a support f or a return 
spring which acts against a support surface on the lining, wherein the 
piston support and the spring are both dimensioned to enable them to be 
removed through the cylinder bore or barrel. 
This will enable an insert assembly comprised of the cylinder lining, the 
return spring and the piston to be removed readily from the pump as soon 
as the locking ring has been dismantled in a conventional way, and quickly 
replaced with a new, corresponding assembly which is locked in place with 
the aid of the groove-seated locking ring. 
The invention will now be described in more detail with reference to an 
exemplifying embodiment thereof and also with reference to the 
accompanying drawing, in which

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a pump housing block 1 having a rotatable shaft 2 which 
is rotated by means of a motor, not shown. The shaft 2 is provided with an 
eccentric 3 which is embraced by a bearing 4. Two cylindrical bores 5 are 
disposed radially to the shaft 2 and extend out through the outside of the 
block 1. The cylinder 5 includes a pump means 6 comprising a cylinder 
lining 61 which receives a pump piston 63, wherein a spring 62 is mounted 
between the lining 61 and the piston 63 and functions to return the piston 
63 towards the eccentric 3 on bearing 4. The lining 61 includes an 
end-flange 611 which is received in a corresponding recess 51 (see FIG. 3) 
and locked with a locking ring (not shown) seated in a recess 52 (FIG. 3) 
intended therefor. The piston 63 has a piston part 631 which fits in the 
lining barrel 615, and a support plate 632 which alternates with the 
bearing 4. The lining is provided on its bottom part with a plurality of 
openings 616 which penetrate the wall of the lining, and sealing flanges 
612-614 which define a labyrinth seal are mounted on the outside of the 
lining on both sides of the axial position of the openings 616. 
An inlet passageway 8 which includes a check valve 9 opens out into the 
cylinder wall 5 at the location of the lining opening 616, and an outlet 
passageway 10 which includes a check valve 11 also opens out into the 
cylinder wall 5 at an axial position which corresponds to the location of 
the opening 616 in the lining 61. The passageways 8 for the two pump 
devices can be supplied with hydraulic medium from a common source, and 
pressure lines 10 from the two pump devices are conveniently combined to a 
common pressure channel. 
The whole of the pump device 6 can be removed by dismantling the locking 
ring 7 from its groove 52, and then replaced with a new pump device, after 
which the locking ring 7 is refitted. The ease with which the pumping 
devices can be removed and replaced enables repair work to be carried out 
by less qualified personnel in the proximity of the hydraulic pump when so 
required, even on site and in the shortest time. 
The cylinder bores open out onto the outside of the block at easily reached 
locations, wherein the locations may also be exposed so as to be readily 
seen for inspection purposes and when changing pump assemblies (cylinder 
lining, piston and spring) and so that any leakage of hydraulic fluid that 
might occur can be readily seen in the inspection, such leakage often 
indicating the need to change a pump assembly. The bores are also 
positioned to enable the pump inserts or assemblies to be withdrawn and 
inserted with no difficulty. Furthermore, the pump is oriented and 
designed so that no appreciable amounts of hydraulic fluid will run-out 
via the lining-receiving bore in the block when changing a pump insert, 
either from the pump housing chamber which contains the shaft 2 or through 
any of the inlet and outlet passageways 8, 10. The inventive hydraulic 
pump is normally contained in a protective casing, which can be easily 
removed to expose the actual hydraulic pump, i.e. the pump housing block. 
A pump insert can be removed easily, by dismantling the latching means 
which is located in an accessible position in the outermost part of the 
cylinder bore. In addition to removing or opening the pump housing casing, 
all that is needed is to remove a locking ring from its groove in the 
outer end of the bore in order to be able to withdraw the pump assembly 
and replace this assembly with another which, after being inserted, is 
locked in place by means of the locking ring. 
It will be obvious to the skilled person that the locking ring and its 
associated groove in the peripheral surface of the bore can be replaced 
with some other readily removable latching arrangement of a known kind 
which, when removed, will immediately enable a pump assembly to be 
changed.