Pumping apparatus for pumping liquids such as slurrys

A pumping apparatus for pumping liquids such as slurrys comprises a pumping cylinder/piston (6,8) driven by the piston/cylinder (16,18) of an operating device, the supply of fluid under pressure either to an upper port (16a) of the cylinder (16), or the lower port (16b) of the cylinder, being controlled by valve mechanism (28). The valve mechanism is moved between two conditions, in which it supplies fluid under pressure to one or other of said ports consequent upon the arrival of a member (20) connecting the two pistons (8,18) at one or other of its extreme positions of movement. Alternatively, or in addition, the fluid pressure circuit powering the operating device includes a regenerative branch, through which fluid under pressure flows from the low pressure side of the operating device directly back to the high pressure line of the fluid circuit, upstream of the motor supplying fluid under pressure. In this manner, the apparatus can operate both at an initial high speed, under relatively low resistance to pumping, while utilizing a power source which is smaller than would otherwise be required. In this manner, not only is a saving of energy obtained, but (because of a reduction of work done on the fluid) water cooling of the fluid circuit may be dispensed with.

DESCRIPTION OF INVENTION 
This invention is concerned with improvements relating to liquid pumping 
apparatus. 
In, for example, the pumping of liquids such as sewage slurry into a filter 
press, conventionally there is used apparatus comprising a pumping device, 
comprising a pumping piston reciprocably mounted in a cylinder to cause 
slurry to be drawn through an inlet port into a chamber, conveniently 
afforded by the cylinder, and pumped from the chamber through an outlet 
port into the filter press. The apparatus also comprises an operating 
device comprising a drive piston reciprocably mounted in a cylinder and 
which is connected to the pumping piston by a connecting member, the 
admission of fluid under pressure to one of two inlet ports of the drive 
cylinder causing the drive piston, and hence the pumping piston, to move. 
As the drive piston reaches its uppermost position, it is necessary to 
operate a valve to reverse the application of fluid pressure to the drive 
cylinder, and when the drive piston reaches its lowermost position, it is 
necessary to operate the valve again to reverse the application of fluid 
under pressure to the drive cylinder. 
At present, operation of the valve is effected by a linkage connected to 
the piston rod, or a cross-head thereof, movement of the linkage to an 
from its extreme positions effecting switching of the valve in a 
mechanical operation. Such a method is not only cumbersome, but is also 
dangerous, in that it is difficult or impractical to fully enclose the 
moving parts of the apparatus, for example by a safety screen. 
According to the invention there is provided apparatus suitable for use in 
the pumping of a slurry and comprising a pumping device which comprises a 
cylinder and a piston mounted therein, and which is operative to cause 
liquid to be drawn through an inlet port and expelled through an outlet 
port, an operating device comprising a cylinder and piston mounted 
therein, valve mechanism which is operative to control the admission of 
fluid under pressure to the cylinder of the operating device, and a 
connecting member extending between the piston of the pumping device and 
the piston of the operating device, the apparatus comprising control 
mechanism which comprises two sensor members respectively responsive to 
the connector member of a part fixedly secured thereto reaching its two 
extreme positions of movement, to cause switching of the valve mechanism. 
The moving parts of apparatus of the kind set out in the last preceding 
paragraph may readily be enclosed behind a safety screen, conveniently in 
the form of a perspex screen, reducing the possibility of injury to 
personnel supervising operation of the apparatus. 
The sensor members may be provided by switches (e.g. micro switches) which 
are positively actuated by the connector member, or such part fixedly 
secured thereto. Whereas such switches may form part of a fluid pressure 
circuit of the control mechanism, to reduce response time, it would, in 
such circumstances, be necessary to position the control mechanism close 
to the valve mechanism. Thus, advantageously such switches form part of an 
electrical circuit of the control mechanism. 
Preferably, however, the sensor members are provided by proximity switches 
responsive to the presence of the connector member, or such part fixedly 
secured thereto, at the extreme positions of movement, without any 
mechanical inter-action therebetween. Most conveniently the proximity 
switches are reed switches which are switched at the extreme positions of 
movement of the connector member by the proximity of a permanent magnet 
fixedly secured to the connector member, or a cross-head thereof. However, 
other forms of proximity switches, such as switches responsive to change 
in electrical capacitance, may be utilised. 
It will of course be appreciated that the sensor members may be so 
positioned as to be activated immediately prior to the connector member 
reaching its extreme positions, especially where the control mechanism 
and/or the valve mechanism operates under a brief time delay. 
Additionally, it will be appreciated that the term "extreme positions of 
movement" refer to the extreme positions actually reached by the control 
member, irrespective of whether or not the control member is capable of 
further movement in one or both directions. 
Alternatively, or in addition, presently available apparatus for pumping 
liquids such as sewage slurry into a filter press suffers from 
disadvantages in relation to the difficulty of the pump meeting the 
different pumping parameters which prevail at different times of a pumping 
cycle. 
For example, at the beginning of a pumping cycle, the resistance of flow of 
the slurry into the filter press is minimal, and it is thus desirable for 
the pump to operate at a high a speed as possible. Conversely, towards the 
end of the pumping cycle, as the filter press fills, resistance to pumping 
of slurry in to the filter press increases, and the requirement is 
therefore for the apparatus to pump slurry at a lower rate, at a high 
pressure. At the end of the cycle, in order to subject the slurry in the 
filter press to the highest possible pressure, it is desirable to maintain 
the pump at stall conditions for a short period of time, during which 
period there is no flow of slurry into the filter press. 
A typical existing apparatus, to overcome the problems of significantly 
varying rates of flow of fluid under pressure during different times of 
the cycle, uses a motor which is capable of delivering fluid at both high 
pressure and high flow rates. During the initial part of the cycle, the 
resistance to pumping movement of the piston is small, and fluid is 
retained from the low pressure side of the operating device to the sump of 
the hydraulic circuit. However, as resistance to pumping increases, and 
the pump demand for fluid under pressure decreases, fluid is returned 
directly to the sump from the high pressure side of the fluid circuit by 
way of a dump valve. This necessitates that a considerable amount of work 
is done on the fluid throughout the cycle, and in general such pumps have 
power requirements which are excessive in relation to the work which the 
apparatus is required to do, and it is in general necessary that such 
pumps comprise cooling circuits for the pressure fluid thereof. 
It has been suggested to overcome this problem, that two pumps be provided, 
one which operates initially at high speed and at low pressure, the second 
of which operates during a later stage of the pumping cycle at low speed 
and high pressure. This is however unnecessarily expensive and seems by 
the present Applicants to be a typical example of the expression "using a 
sledge hammer to crack a walnut". 
Thus, according to this invention there is also provided apparatus for use 
in the pumping of a slurry and comprising a pumping device comprising a 
cylinder and a piston mounted therein, and which is operative to cause 
liquid to be drawn through an inlet port and expelled through an outlet 
port, an operating device comprising a cylinder and piston mounted 
therein, a fluid pressure circuit which includes a fluid sump, a motor 
operative to pump fluid under pressure to the operating device and valve 
mechanism operative to control the admission of fluid under pressure to 
the operating device, a connecting member extending between the piston of 
the pumping device and the piston of the operating device, wherein in each 
pumping operation of the apparatus, part of the fluid flowing from the low 
pressure side of the operating device is returned directly to the high 
pressure side of the fluid circuit and part is returned to the sump of the 
fluid pressure circuit. 
Preferably, the said part of the fluid which is returned directly to the 
high pressure side of the fluid circuit is returned thereto through a 
venturi device. 
Advantageously, there is provided in the low pressure side of the operating 
device, a valve which is normally in a first condition in which part of 
the fluid flowing from the low pressure side of the operating device is 
returned directly to the high pressure side of the fluid circuit and part 
is returned to the sump of the fluid circuit, said valve being moved from 
its first condition to a second condition in consequence of an increase in 
the pressure of fluid on the high pressure side of the operating device to 
a predetermined pressure, in which second condition fluid flowing from the 
low pressure side of the operating device is returned preferentially 
directly to the sump of the fluid pressure circuit. 
Preferably, but not necessarily, the feature set out in the last preceding 
three paragraphs, is included in apparatus of the kind set out in the last 
preceding paragraph but twelve.

The apparatus which is the preferred embodiment of this invention comprises 
a pumping device comprising a cylinder 6, a piston 8 mounted for 
reciprocating movement in the cylinder 6 to cause liquid (in the preferred 
embodiment a sewage slurry) to alternately be drawn through an inlet valve 
10 into the cylinder chamber 12, and to be forced from the chamber 12 
through the outlet valve 14 into filter press (not shown) connected to the 
outlet valve. 
The apparatus also comprises a fluid pressure operating device comprising a 
cylinder 16 and a drive piston 18, mounted for reciprocating movement in 
the cylinder 16. A connecting member in the form of a rod 20 extends 
between the piston 8 and the piston 18, a cross-head 22 being fixedly 
secured to the connected rod 20. 
The cylinder 16 is mounted on a trunnion 24, tie rods 26 passing through 
apertures in the head 22 guiding the connecting rod for linear, axial 
movement. 
The apparatus also comprises a fluid pressure circuit which includes a 
fluid sump 27, a motor 26 operative to pump fluid under pressure from the 
sump 27 to the operating device, and valve mechanism 28 operative to 
control the admission of fluid under pressure to the cylinder 16 (FIG. 4). 
The valve mechanism 28 is connected to the motor by a high pressure line 
30, and to the sump of the source by a low pressure line 32. The valve 
mechanism 28 is a bi-stable latch-type valve, being stable in a first 
position (FIG. 4) in which fluid under pressure is supplied through the 
valve mechanism to an upper inlet port 16a of the cylinder 16 by line 56, 
a lower inlet port 16b thereof being connected via line 58 to the sump, 
and a second position in which fluid under pressure is supplied to the 
lower inlet port 16b of the cylinder, the upper inlet port 16a being 
connected to the sump. The valve mechanism may be moved from its first to 
its second position by momentary energisation of a solenoid 34, and from 
its second position to its first position by momentary energisation of a 
solenoid 36. 
A pumping operation involving the use of the apparatus involves a series of 
pumping strokes, in which the upper inlet port of the cylinder 16 is 
connected to the high pressure line, in which the piston 8 is moved to 
pump slurry from the cylinder chamber 12 into a filter press, alternating 
with a series of intake strokes, in which the valve mechanism is in its 
second position, with the lower inlet port being connected to the high 
pressure line. 
Mounted on the cross-head 22 is a permanent magnet 38, and mounted adjacent 
to the positions occupied by the magnet at the two extreme positions of 
movement of the cross-head are upper and lower limit sensors 42, 44 
respectively, provided by magnetically operated reed switches. These reed 
switches form part of control mechanism 40 of the apparatus, adapted to 
control the application of the fluid under pressure to the cylinder 16 by 
operation of the valve mechanism 28. 
Extending between the lines 32 and 58 is a branch line 60, operative in 
which is a one-way valve 62. The line 60 extends to the radial port of a 
venturi device 64, located axially along the high pressure line 30. 
Extending from line 58 is a return line 68, which extends directly to the 
sump (that is, not by way of the valve mechanism 28). Operative across the 
line 68 is a relief valve 66, which normally adopts a first condition to 
block the line 68. However, when pressure in the high pressure line 56 
reaches a predetermined maximum pressure, this pressure is operative, 
through line 70, to move the valve 66 from its first condition to a second 
condition, in which fluid may flow preferentially from the lower port 16b 
of the cylinder 16 directly to the circuit sump. 
A sequence of operations of the accompanying apparatus will now be 
described starting from the position shown in FIG. 4 of the drawings, 
various switches and relays being shown in FIGS. 5 and 6. 
Upon closing of the start switch C, with the bi-stable (latch) valve 
mechanism 28 in its first position shown in FIGS. 4 and 6, fluid under 
pressure is supplied to the upper inlet port of the cylinder 16, causing 
the piston thereof to downstroke, causing other liquid with which the 
cylinder 6 has previously been primed, to be forced from the cylinder 
chamber 12 through the outlet valve 14. 
Fluid displaced by the piston 18 from the cylinder 16 will flow through the 
lower port 16b via line 58, the valve 66 being during this stage of the 
pumping operation, in its first (closed) condition. A majority of liquid 
flowing along line 58 will pass through the valve mechanism 28, and will 
be returned by way of line 32, to the sump. However, some of this fluid 
will be returned, by way of the branch line 60, to the radial port of the 
venturi device 64, and will re-enter the high pressure line 30 directly. 
The advantage of this arrangement is as follows: 
During an initial part of the pumping cycle, when resistance to flow of 
slurry from the apparatus into the filter press is minimal, the piston 18 
will downstroke at a rapid rate, and thus fluid will flow from the lower 
inlet port 16b of the operating device at a high flow rate. The speed of 
flow of fluid under pressure along line 30 during this part of the pumping 
cycle is sufficient to enable up to 30% of the fluid exiting from the 
cylinder 16 to be returned directly to the high pressure line 30, without 
significant pressure loss in the high pressure line 30. By this means, 
fluid under sufficient pressure to carry out the pumping cycle during an 
initial sequence of pumping strokes may be provided, by means of a fluid 
pressure motor which is capable of delivering fluid at a flow rate less 
than that which is theoretically required, to sustain the pumping 
operation at its maximum rate. 
When the magnetic element 38 reaches a position adjacent to the lower limit 
switch 44, the proximity of the magnet to the switch 44 causes the switch 
44 to close, and (since switch S1 is closed) causes a brief energisation 
of the solenoid 34 to move the valve 28 to its second position. Closure of 
the lower limit switch 44 similarly energises relay R1 (which may if 
desired be time-delayed) which opens switch S1 and closes switch S2. 
With the valve mechanism 28 in its second position, fluid under pressure is 
provided through the lower port of the cylinder 16, forcing the drive 
piston to upstroke, causing in turn the pumping piston 18 to draw fluid 
from source through the inlet valve 10 into the cylinder chamber 12. 
It will of course be appreciated that, during the intake stroke of the 
pumping apparatus, the one-way valve 62 operative across line 60 prevents 
flow of fluid under pressure into the cylinder 16 through the lower inlet 
port 16b, and that, during the intake stroke, there is no "regenerative" 
recirculation of fluid from the low pressure side of the fluid circuit 
directly back into the high pressure side of the circuit. 
When the cross-head 8 reaches a position in which the magnetic element 38 
is adjacent to the upper limit switch 42, the proximity of the said magnet 
to the reed switch causes the reed switch 42 to close. Since the switch S2 
is also closed, this causes energisation for a brief period of the 
solenoid 36, which causes the valve mechanism to return to its first 
position. However, closing of the upper limit switch 42 also energises 
relay R2, which opens switch S2 and closes switch S1. 
In the use of the apparatus, an alternating sequence of pumping and intake 
steps is repeated, until the filter press approaches a condition in which 
it is substantially filled. In such a condition, flow of fluid under 
pressure through line 30 and through the venturi device 64 is insufficient 
to generate any significant "pull" of the fluid along line 60, and valve 
62 becomes in effect closed. As the pressue detected in line 56, on a 
pumping cycle of the apparatus, approaches a predetermined maximum a gauge 
72 is operated, and is effective to cut out the electrical control of the 
valve mechanism 28, and the by-pass line 74, together with the restrictor 
76 and one-way valve 78 operative therein, is effective to centralise the 
spool of the valve mechanism 28. In its centralised position, the valve 
provides for significantly reduced flow of fluid under pressure from line 
30 to line 56, and significantly reduced flow of fluid from line 58 to 
line 32. 
However, the pressure at which the gauge 72 is operative, is also effective 
to open the relief valve 66, allowing fluid to flow directly from line 58 
to the sump 27 preferentially directly. 
Thus, upon reaching stall condition, some flow of fluid under pressure from 
line 30 to line 56 is permitted, to maintain the pressure on the drive 
piston 18, to maintain the filter press firmly packed. 
Should the apparatus stall with the magnet 38 adjacent to one or other of 
the limit switches 42 and 44, by the use of the relays R1 and R2 neither 
of the two solenoids 34 or 36 will be continuously energised. 
The apparatus comprises a guard in the form of a safety screen 50, 
comprising two curved sections 52 and 54, which may be of transparent, 
reinforced plastics material or may be wire mesh. Advantageously the 
section 54 is mounted for pivotal movement, and may be opened (as shown in 
FIG. 2) should acceptance to the interior be requires. Advantageously, the 
door is interlocked with the control mechanism, so that operation of the 
apparatus is shut down, when the door is opened.