ZA200902819B - Pump - Google Patents

Description

THIS INVENTION relates to a pump.

Pumping small volumes of a fluid to high pressures is often problematic.

Pumps used for such applications often suffer from seal failure. A pump capable of reliably pumping small volumes of a fluid, and in particular a hot viscous fluid such as hot grease, to a high pressure of at least 300 bar, comprising few components would be desirable.

According to the invention, there is provided a pump which includes an intake cylinder holding an intake piston arranged for reciprocal movement inside the intake cylinder between a cylinder full position and a cylinder empty position, the intake cylinder having an intake port; a discharge cylinder holding a discharge piston arranged for reciprocal movement inside the discharge cylinder between a cylinder empty position and a cylinder full position, the discharge cylinder having a discharge port and being in one way fluid communication with the intake cylinder; and a drive arrangement drivingly to displace the intake piston and the discharge piston in unison in reciprocating fashion in their associated cylinders so that when the intake piston is in its cylinder full position the discharge piston is in its cylinder empty position, and when the intake piston is in its cylinder empty position the discharge piston is in its cylinder full position.

Preferably, the intake cylinder and the discharge cylinder are linearly . aligned or co-axial, with the cylinder empty position of the intake piston being at an end of a stroke of the intake piston proximal to the cylinder empty position of the discharge piston which is also at an end of a stroke of the discharge piston. - The intake port of the intake cylinder is preferably in a side wall of the intake cylinder, between ends of the intake cylinder. The intake port may be elongate, having a length dimension in a direction parallel to a length direction of the cylinder or x

A parallel to a stroke direction of the intake piston. The length of the intake port may be at least 20%, preferably at least 30%, more preferably at least 40%, e.g. about 44% of the length of the stroke of the intake piston. Preferably, an end of the intake port coincides with the cylinder full position of the intake piston, so that during displacement of the intake piston from its cylinder full position to its cylinder empty position, the intake piston initially travels the length of the intake port, before leaving the intake port behind.

The intake cylinder may include a breather opening into the intake cylinder to prevent a vacuum from building up in the intake cylinder during displacement of the intake piston from its cylinder empty position to its cylinder full position, before the intake piston travels past the intake port. In one embodiment of the invention, the breather is in the form of a breathing passage having an outlet at one end thereof through the intake piston into the intake cylinder, and an inlet at another end thereof from the environment outside the pump. The breathing passage may include a non- return valve allowing flow through the breathing passage from the inlet to the outlet only.

The intake piston may be seal-less.

The intake cylinder and the discharge cylinder may be longitudinally spaced with at least one fluid transfer passage with a non-return valve between them to provide one way fluid communication from the intake cylinder to the discharge cylinder.

In one embodiment of the invention, there is a plurality of parallel transfer passages, e.g. four transfer passages, between an end of the intake cylinder and an end of the discharge cylinder, with a single non-return valve opening and closing all of the transfer passages simultaneously as required.

The discharge port of the discharge cylinder may lead from the discharge cylinder immediately adjacent the non-return valve of the transfer passage or transfer passages, between the transfer passage or transfer passages and the cylinder empty position of the discharge piston. In one embodiment of the invention, the discharge cylinder has two parallel discharge ports.

The pump may include a valve block between the intake cylinder and the discharge cylinder, with the transfer passage or transfer passages and the discharge port or discharge ports extending through the valve block and with the non-return valve of the transfer passage or transfer passages being located inside the valve block. If desired, the valve block may also house a non-return valve for the discharge port or discharge ports.

The discharge piston may include a seal. The seal may be of the kind which expands outwardly towards the discharge cylinder when pressure is applied, i.e. during displacement of the discharge piston from its cylinder full position to its cylinder empty position. This seal may thus be cup-shaped.

An end portion of the discharge cylinder remote from the discharge port may be tapered, widening towards the discharge port. Advantageously, this configuration assists in guiding the seal of the discharge piston into the discharge cylinder without damaging the seal.

The drive arrangement may include at least one intake piston push rod and at least one discharge piston push rod, the intake piston push rod and the discharge piston push rod being arranged to move in unison. In one embodiment of the invention, the drive arrangement includes a pair of parallel intake piston push rods, the intake piston push rods being parallel to and flanking a discharge piston push rod.

The drive arrangement typically includes a motion translator to translate rotary movement provided by a drive, such as an electric motor, into linear movement of the pistons. The motion translator may be an eccentrically mounted cam-wheel with the push rods arranged to follow the cam=wheel during rotation of the cam-wheel. In one embodiment of the invention, the cam-wheel has a cam ring with radially inner and radially outer circular cam surfaces, with the push rods engaging both of the inner and outer cam surfaces. Preferably, the push rods engage the inner and outer cam surfaces by means of bearings between which the cam ring passes. With this arrangement, it is not necessary to bias the push rods in any way to ensure that the push rods engage the cam surfaces, as the cam surfaces are locked in-between the bearings ensuring that the cam ring pushes the push rods during stroking of the pistons in one direction and pulls the push rods during stroking of the pistons in an opposite direction.

The ends of the push rods remote from their associated pistons may be held in a common locating block. The locating block may be attached to the bearings with one or more bearing carriers. Slides may be provided for guiding the bearings and the bearing carriers in a reciprocal linear path on rotation of the cam-wheel.

The ends of the push rods remote from their associated pistons may pass through a base to which the intake cylinder and the discharge cylinder are mounted, and from which the intake cylinder and the discharge cylinder are spaced. The intake cylinder and the discharge cylinder may be spaced from the base by means of an extension cylinder within which one of the push rods is received for reciprocal movement relative to the extension cylinder. Advantageously, by making use of an extension cylinder, it is possible to submerge the intake cylinder and the discharge cylinder in a fluid to be pumped, whilst positioning most of the drive arrangement, and in particular the motion translator above the fluid.

The invention will now be described, by way of example only, with reference to the diagrammatic drawings in which

Figure 1 shows a vertically partially sectioned front view of a pump in accordance with the invention; and

Figure 2 shows a vertically partially sectioned side view of the pump of Figure 1.

Referring to the drawings, reference numeral 10 generally indicates a positive displacement pump in accordance with the invention. The pump 10 is particularly suitable for pumping small volumes of a hot viscous fluid such as hot grease, to a high pressure, e.g. 300 bar or higher.

The pump 10 comprises, broadly, an intake cylinder 12 holding an intake piston 14, a brass discharge cylinder 16 holding a discharge piston 18, and a drive arrangement 20 drivingly to displace the intake piston 14 and the discharge piston 18 in reciprocating fashion and in unison in their associated cylinders 12, 16.

The intake piston 14 is arranged for reciprocal movement inside the intake cylinder 12 between a cylinder full position, as shown in Figures 1 and 2, and a cylinder

. | 6 empty position in which the intake piston 14 is at an end of its stroke nearest to the discharge cylinder 16. Similarly, the discharge piston 18 is arranged for reciprocal movement inside the discharge cylinder 16 between a cylinder empty position as shown in Figures 1 and 2, and a cylinder full position at an end of the stroke of the discharge piston 18 where the discharge piston 18 is furthest from the intake cylinder 12. The drive arrangement 20 is configured drivingly to displace the intake piston 14 and the discharge piston 18 in unison so that when the intake piston 14 is in its cylinder full position the discharge piston 18 is in its cylinder empty position, and when the intake piston 14 is in its cylinder empty position the discharge piston 18 is in its cylinder full position. In the illustrated embodiment of the invention, both pistons 14, 18 have a stroke of 80mm.

The intake cylinder 12 has an elongate intake port 22 in a side wall of the intake cylinder 12, between ends of the intake cylinder 12 or, in other words, between 156 ends of the stroke of the intake piston 14. The intake port 22 has a length dimension which is parallel to a stroke direction of the intake. piston 14 and has a length which is about 44% of the length of the stroke of the intake piston 14. One end of the intake port 22, which in the drawings is a lower end of the intake port 22, coincides with the cylinder full position of the intake piston 14, i.e. where the intake piston 14 is at one end of its stroke. As will be appreciated, during displacement of the intake piston 14 from its cylinder full position to its cylinder empty position, the intake piston 14 thus initially travels the length of the intake port 22, before leaving the intake port 22 behind before reaching the end of the stroke of the intake piston 14, and then travelling back towards the cylinder empty position of the intake piston 14.

A portion 26 of the intake piston 14 protrudes from an open end 24 of the intake cylinder 12. The portion 26 of the intake piston 14 is thus external of the intake cylinder 12. A breathing passage 28 with an inlet 30 in the portion 26 of the intake piston 14, and an outlet in an end face of the intake piston 14, into the intake cylinder 12, is provided through the intake piston 14. The breathing passage 28 houses a non- return valve 29 (see Figure 2) which allows flow through the breathing passage 28 from the inlet 30 to the outlet into the intake cylinder 12 only. In use, the breathing passage 28 and its associated non-return valve 29 prevent a vacuum from building up in the intake cylinder 12 during displacement of the intake piston 14 from its cylinder empty p position towards its cylinder full position, before the intake piston 14 travels past the intake port 22.

Advantageously, the intake piston 14 does not have a seal between the intake piston 14 and the intake cylinder 12. There is thus no seal which can be damaged by contact with the intake port 22, reducing the number of components of the pump 10 subject to wear and tear.

The intake cylinder 12 and the discharge cylinder 16 are co-axial, as can be clearly seen in Figures 1 and 2. As the intake piston 14 and the discharge piston 18 are arranged to move in unison, the cylinder empty position of the intake piston 14 is at an end of the stroke of the intake piston 14 proximal to the cylinder empty position of the discharge piston 18 which naturally is also at an end of the stroke of the discharge piston 18. The cylinder full position of the intake piston 14 and the cylinder full position of the discharge piston 18 are at ends of their associated cylinders 12, 16 which are furthest from each other.

The pump 10 includes a valve block 32 between the intake cylinder 12 and the discharge cylinder 16. Both the intake cylinder 12 and the discharge cylinder 16 are screwed into the valve block, on opposed faces of the valve block 32 so that the valve block 32 spaces the intake cylinder 12 and the discharge cylinder 16. Four transfer passages 34 (only two of which are visible in the drawings) extend through the valve block 32 between the intake cylinder 12 and the discharge cylinder 16. A single : non-return valve 36 is located inside the valve block 32. The non-return valve 36 opens . and closes all four of the transfer passages 34 simultaneously, ensuring one-way fluid communication from the intake cylinder 12 to the discharge cylinder 16.

The discharge cylinder 16 has a pair of parallel discharge ports 38 (see

Figure 2) extending through the valve block 32. Only one discharge port 38 is visible in

Figure 2. Although ends 40 of the discharge ports 38 are blocked, the discharge ports 38 lead into a valve chamber holding a non-return valve 42. A delivery line 44 is attached to the valve block 32, with the non-return valve 42 being between the delivery line 44 and the discharge ports 38, ensuring one-way fluid communication from the discharge cylinder 16 through the delivery line 44 only.

The discharge piston 18 has a cup seal 46 which expands outwardly towards walls of the discharge cylinder 16 during displacement of the discharge piston 18 from its cylinder full position to its cylinder empty position. In order to assist in guiding the cup seal 46, the discharge cylinder 16 is tapered, widening over the length of the discharge cylinder 16 towards the discharge ports 38.

The discharge cylinder 16 is screw-threadedly attached to an end of an extension cylinder 48 which is mounted to a base 50 by means of a holding flange 52.

The extension cylinder 48 thus spaces the discharge cylinder 16, and hence also the valve block 32 and the intake cylinder 12, from the base 50.

A 20mm diameter discharge piston push rod 54 runs inside the extension cylinder 48 and projects through the holding flange 52 and the base 50. One end of the discharge piston push rod 54 is screw-threadedly attached to the discharge piston 18.

The extension cylinder 48 is flanked by a pair of intake piston push rods 56. The intake piston push rods 56 are parallel to the extension cylinder 48 and the discharge piston push rod 54 and extend through the valve block 32 and also extend through the holding flange 52 and the base 50. Ends of the intake piston push rods 56 remote from the base 50 are held in a locating block 58, to which the portion 26 of the intake piston 14 is also attached. The portion 26 of the intake piston 14 is also parallel to the intake piston push rods 56.

The drive arrangement 20 includes a motion translator in the form of an eccentrically mounted cam wheel 60 with a cam ring 62 defining radially inner circular cam surfaces 64 and a radially outer circular cam surface 66. By means of the cam wheel 60, rotary movement provided by a drive, such as an electric motor (not shown), is translated into linear movement of the push rods 54, 56.

In order to transfer motion from the cam wheel 60 to the push rods 54, 56, the push rods 54, 56 are connected to the cam wheel 60, and more particularly to the cam ring 62, by means of bearings 68. A pair of bearings 68 engage the radially inner circular cam surfaces 64, on opposed sides of the cam wheel 60 and a pair of spaced bearings 68 engage the radially outer circular cam surface 66, from below as shown in

A

Figure 2 of the drawings. The bearings 68 are mounted in between two spaced bearing carriers 70 which also receive a lower portion of the cam wheel 60 between them. The bearing carriers 70 in turn are attached to a locating block 72 which also holds the ends of the push rods 54, 56 extending through the holding flange 52 and the base 50. Two slides 71 guide the bearings 68 and the bearing carriers 70 during reciprocal movement of the bearings 68 and the bearing carriers 70.

The cam wheel 60 is mounted to a drive shaft 74 passing through a pair of spaced cover plates 76 mounted to the base 50. The cover plates 76 protect the cam wheel 60. One of the cover plates 76 provides a base against which a gearbox for a drive, such as an electric motor, can be mounted in order drivingly to rotate the drive shaft 74.

In use, the drive shaft 74, and thus the cam wheel 60, is rotated by a drive such as an electric motor, typically via a gearbox mounted to one of the cover plates 76.

As the cam ring 62 of the eccentrically mounted cam wheel 60 passes between the upper and lower bearings 68 as shown in the drawings, the push rods 54 and 56 are displaced in reciprocating fashion together during rotation of the cam wheel 60. In

Figures 1 and 2 of the drawings, the push rods 54, 56 are thus displaced upwardly and downwardly in reciprocating fashion as the cam wheel 60 is rotated. At least the intake cylinder 12 is in use submerged in a fluid which it is desired to be pumped, for example a hot viscous fluid such as hot grease. During displacement of the intake piston 14 from the cylinder full position as shown in Figures 1 and 2, towards its cylinder empty position, fluid that entered the intake cylinder 12 through the intake port 22 is pushed through the transfer passages 34 into the discharge cylinder 16. This transfer of fluid is assisted by the discharge piston 18 being displaced from its cylinder empty position as shown in Figures 1 and 2 of the drawings, to its cylinder full position, thereby also drawing the fluid into the discharge cylinder 16. On the downward stroke of the intake piston 14 and the discharge piston 18, the non-return valve 36 closes and the discharge piston 18 forces the fluid through the discharge ports 38 into the delivery line 44. At the . same time, the intake piston 14 travels back down through the intake cylinder 12.

Initially, before the intake piston 14 reaches the intake port 22, fluid enters the space between the intake piston 14 and the intake cylinder 12 through the breathing passage 28, thus preventing a vacuum from building up inside the intake cylinder 12, or at least ’ PZ reducing such a vacuum. Once the intake piston 14 has reached the intake port 22, the fluid enters the intake cylinder 12 directly through the intake port 22. The intake piston 14 and the discharge piston 18 then reach the ends of their downward strokes and the cycle is repeated as the intake piston 14 and the discharge piston 18 again simultaneously move upwards inside their associated cylinders 12, 16. During upward displacement of the intake piston 14, the non-return valve 29 prevents fluid from flowing back through the breathing passage 28 and out through the inlet 30.

The pump 10, as illustrated, can reliably pump molten grease at temperatures of around 90°C to pressures of between 300 bar and 500 bar. The pump 10, as illustrated, is sized to pump 57 litres per hour of molten grease but as will be appreciated, with small modifications to the cylinders 12, 16 and pistons 14, 18 higher or lower flow rates can be achieved. The pump 10 has relatively few components compared to conventional pumps used for similar applications and has been found to be extremely reliable.

Claims (15)

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1. A pump which includes an intake cylinder holding an intake piston arranged for reciprocal movement inside the intake cylinder between a cylinder full position and a cylinder empty position, the intake cylinder having an intake port; a discharge cylinder holding a discharge piston arranged for reciprocal movement inside the discharge cylinder between a cylinder empty position and a cylinder full position, the discharge cylinder having a discharge port and being in one way fluid communication with the intake cylinder; and a drive arrangement drivingly to displace the intake piston and the discharge piston in unison in reciprocating fashion in their associated cylinders so that when the intake piston is in its cylinder full position the discharge piston is in its cylinder empty position, and when the intake piston is in its cylinder empty position the discharge piston is in its cylinder full position.

2. The pump as claimed in claim 1, in which the intake cylinder and the discharge cylinder are linearly aligned or co-axial, with the cylinder empty position of the intake piston being at an end of a stroke of the intake piston proximal to the cylinder empty position of the discharge piston which is also at an end of a stroke of the discharge piston.

3. The pump as claimed in claim 1 or claim 2, in which the intake port of the intake cylinder is in a side wall of the intake cylinder, between ends of the intake cylinder, the intake port being elongate, having a length dimension in a direction parallel to a length direction of the cylinder or parallel to a stroke direction of the intake piston.

4. The pump as claimed in claim 3, in which an end of the intake port coincides with the cylinder full position of the intake piston, so that during displacement of the intake piston from its cylinder full position to its cylinder empty position, the intake piston initially travels the length of the intake port, before leaving the intake port behind.

5. The pump as claimed in any of claims 1 to 4 inclusive, in which the intake cylinder includes a breather opening into the intake cylinder to prevent a vacuum from building up in the intake cylinder during displacement of the intake piston from its cylinder empty position to its cylinder full position, before the intake piston travels past the intake port.

6. The pump as claimed in any of claims 1 to 5 inclusive, in which the intake piston is seal-less.

7. The pump as claimed in any of claims 1 to 6 inclusive, in which the intake cylinder and the discharge cylinder are longitudinally spaced with at least one fluid transfer passage with a non-return valve between them to provide one way fluid communication from the intake cylinder to the discharge cylinder.

8. The pump as claimed in claim 7, in which the discharge port of the discharge cylinder leads from the discharge cylinder immediately adjacent the non- return valve of the at least one fluid transfer passage, between the at least one fluid transfer passage and the cylinder empty position of the discharge piston. ’

9. The pump as claimed in any of claims 1 to 8 inclusive, in which an end portion of the discharge cylinder remote from the discharge port is tapered, widening towards the discharge port.

10. The pump as claimed in any of claims 1 to 9 inclusive, in which the drive arrangement includes a motion translator to translate rotary movement provided by a drive into linear movement of the pistons.

11. The pump as claimed in any of claims 1 to 10 inclusive, in which the drive arrangement includes a pair of parallel intake piston push rods, the intake piston push rods being parallel to and flanking a discharge piston push rod, the intake piston push rods and the discharge piston push rod being arranged to move in unison.

12. The pump as claimed in claim 10 and claim 11, in which the motion translator is an eccentrically mounted cam-wheel with the push rods arranged to follow the cam-wheel during rotation of the cam-wheel, the cam-wheel having a cam ring with radially inner and radially outer circular cam surfaces, with the push rods engaging both of the inner and outer cam surfaces.

13. The pump as claimed in claim 11 or claim 12, in which ends of the push rods remote from their associated pistons are held in a common locating block, with the locating block being attached to bearings with one or more bearing carriers.

14. The pump as claimed in any of claims 11 to 13 inclusive, in which end portions of the push rods remote from their associated pistons pass through a base to which the intake cylinder and the discharge cylinder are mounted, and from which the intake cylinder and the discharge cylinder are spaced by means of an extension cylinder within which one of the push rods is received for reciprocal movement relative to the extension cylinder. :

15. The pump as claimed in claim 1, substantially as herein described with reference to and as illustrated in any of the drawings. Dated this 23rd day of April 2009 ADAMS & ADAMS APPLICANTS’ PATENT ATTORNEYS