GB2096708A

GB2096708A - Improvements relating to pumping apparatus

Info

Publication number: GB2096708A
Application number: GB8202846A
Authority: GB
Original assignee: Whitehead & Poole
Current assignee: Whitehead & Poole
Priority date: 1981-01-30
Filing date: 1982-02-01
Publication date: 1982-10-20
Also published as: GB2096708B

Abstract

A sensing device is provided in pumping apparatus e.g. for pumping slurry and operates an alarm or stops the pump's motor (16, 18) should a predetermined limit be sensed. As described a slurry pump has a counting device (50) which counts the number of strokes executed by the drive piston (18) in a specific period of time. A comparison device (54), receives an output signal from the counting device (50) and compares it with a pre-set signal from a selector device (56). When the output signal of the counting device reaches the level of the pre-set signal of the selection device, a control device terminates operation of the apparatus, and energises an alarm to alert an operative. A comparator unit (58) also compares the output signals of the counting device 50 with previous output signals thereof, and stops the apparatus and energises the alarm should the signals differ by a predetermined amount. For details of the electronic circuitry reference should be made to the description and drawings. <IMAGE>

Description

SPECIFICATION Improvements relating to pumping apparatus Description of invention This invention is concerned with improvements relatiny to liquid pumping apparatus.

In the filtering of slurries, it is common practice to use a fluid-powered pumping apparatus adapted to pump the slurry into a filter press, liquid constituent of the slurry being exuded through the walls of the filter press, leaving filter cake, comprising predominantly solid material within the filter press.

A conventional type of pumping apparatus utilised in this operation comprises a pumping device, comprising a pumping piston reciprocably mounted in a pumping cylinder to cause slurry to be drawn through an inlet port into the cylinder, and to be pumped from the cylinder through an outlet port into the filter press. Such apparatus conventionally also comprises an operating device comprising a drive piston reciprocably mounted in a drive cylinder, and which is connected to the pumping piston by a connecting member, the admission of fluid under pressure to one of two ports of the drive cylinder causing the drive piston, and hence the pumping piston, to move.As the drive piston reaches an uppermost position, a valve operates to reverse the application of fluid under pressure to the drive cylinder, and as the drive piston reaches its lowermost position, the valve is operated again to reverse the application of fluid under pressure to the drive cylinder.

During operation, as the pumping device delivers slurry to the filter press, and the filter press fills, resistance to flow of slurry into the filter press increases, and the stroke rate of the pumping device reduces. Under normal circumstances, an operative would take no action untii the rate of operation of the device reached a low speed, or stalled, whereupon he would shut down the apparatus, disconnect the filter press from the outlet port thereof, and connect an empty filter press to the apparatus.

The point at which operation of the apparatus is terminated may be determined by a timer but this is often not accurate, since the time taken to fill a filter press may vary, with variations in the solid content of a batch of slurry. Most conveniently therefore, termination of operation of the apparatus is effected manually by the operative.

Clearly, during the terminal part of the filling of the filter press, the work rate of the apparatus is significantly lower, and there comes a point before filling is completed, at which it is no longer economical to maintain the apparatus and the filter press connected together, in order solely to complete the filling operation.

The rate of reduction in stroke speed, and the point at which it is no longer economic to maintain the apparatus and the filter press connected together, will be dependent upon the particular pumping operation concerned, including the percentage dry solid content, the particle size and the type of filter press being filled.

According to this invention, there is provided a pumping apparatus comprising a sensing device responsive to the rate of operation of the apparatus fo produce zn output signal which is functional of said rate of operation, and a control device which is operative to terminate operation of the apparatus or to energise an alarm to alert an operative, in dependence upon information derived from the output signal.

This invention is particularly useful in the application to apparatus of the kind used to pump slurry into a filter press, the apparatus being operated by fluid under pressure.

Thus the output signal may be applied to the control device, to cause the control device to operate to terminate operation of the apparatus or to energise said alarm when the output signal reaches a predetermined magnitude. Said predetermined magnitude may be an upper limit, corresponding to a higher speed than is desirable, whereby operation of the apparatus may be terminated in the event of an unduly high speed being attained.

Altematively, or in addition, said predetermined magnitude may be a lower limit corresponding to a speed below which continued operation of the apparatus is no longer economical, whereby operation of the apparatus may be terminated in the event of 3 filter press to which the apparatus is connected becoming substantially filled.

Thus during a normal run of the pumping apparatus, the rate of operation will initially be high, and will reduce dung the run as the filter press is tilled. Such reduction will be sensed by the sensing device, and the apparatus will thus be shut down or the alarm may be energised to advise the operative to so shut down the apparatus during the desired latter part of the pumping operation, over which the pumping apparatus is operating at reduced delivery rate, or the alarm may be energised to advise the operative to so shut down the apparatus.

Preferably the control device comprises a comparison device which compares the output signal with a preset signal, and which is operative, as said output signal moves towards the preset signal in magnitude to terminate operation of the apparatus.

Thus, during a normal run of the pumping apparatus, the initial rate of operation may be high, said rate falling somewhat exponentially towards zero as the filter press is filled. As the rate of operation falls, the output signal will converge with the preset signal, and when the values of these are the same, the operation of the pumping apparatus is shut down.

Preferably the control device comprises a selection device which is adapted to provide a preset control signal of desired value, which may be selected by the operative before commencement of the run, aependent upon the nature of the slurry being pumped and the filter press being filled. Thus, the selection device may, at the will of the operative, be operated to provide a preset signal which corresponds to a pumping rate below which continued operation of the pumping apparatus is inefficient and powerwasteful.

It will of course be appreciated, that the control device will also operate to terminate operation of the apparatus, or to energise the alarm in the event that the rate of operation of the apparatus as sensed by the sensing device, falls below the optimum rate for reasons other than that of the filling of the filter press. Thus for example, should one of the valves controlling the flow of slurry into or from the pumping apparatus become blocked, causing the pumping apparatus to be ineffective or partially ineffective and to reduce in speed, operation of the apparatus will also be terminated orthe alarm will be energised by the control device.

Most desirably, the control device is operative both to terminate operation of the apparatus and to energise an alarm, which may be a visual signal or an audible signal or both, to alert the operative to the situation.

The present invention has been devised particularly for use in pumping apparatus of the kind comprising a pumping piston reciprocably mounted in a pumping cylinder to cause slurry to be drawn through an inlet into the cylinder, and pumped from the cylinder through an outlet into a filter press, such apparatus conveniently comprisingan operating device comprising a drive piston reciprocably mounted in a drive 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 an uppermost position, a valve is operated to reverse the application of fluid under pressure to the drive cylinder, and when the drive piston reaches its lowermost position, the valve is again operated to reverse the application-of fluid under pressure to the drive cylinder. Pumping apparatus of this kind is particularly described in U.S. Patent Specification No. 2,035,447A.

Thus, the sensing mechanism preferably comprises a counting device operative to count the number of strokes of the operating piston in a specific interval of time, but as an alternative, the sensing mechanism may comprise a measuring device operative to measure the time taken by the operating piston to complete a specific number of strokes.

For example, the selection device is adapted to be operated to provide a preset signal which corresponds to a pumping rate of two and twenty strokes per minute, or a corresponding range of time intervals, where the sensing device comprises a measuring device to measure the time taken to complete a specific number of strokes.

Thus, during a normal run of the pumping device, the initial rate of operation may be thirty strokes per minute, and the control device will be operative to terminate operation of the pumping apparatus and/or to energise the alarm when the stroke rate falls to the preselected pumping rate.

it is however to be appreciated that the invention may be utilised in pumping apparatus other than of the kind set out in the last preceding paragraph but three: for example, the invention may be utilised in conjunction with diaphragm pumps, or with a continuous delivery type of pumping apparatus, such as a rotary pumping apparatus.

Additional difficulties are encountered in pumping operations of the kind with which this present invention is concerned, due to that the pumping cycle often taking several hours, and it being inconvenient to have the machines attended permanently.

Thus problems may be incurred during a pumping run, which do not necessarily involve the rate of operation of the apparatus becoming unduly high or unduly low, but which it would be desirable to detect at an earlier stage as possible.

For example, in the filtering of slurries, on occasion the filter press ruptures, and the pumping apparatus will continue operation to pump slurry into and from the filter press until the problem is noticed by an operative, who must then shut down the pumping apparatus disconnect the filter press and clean up the mess.

Thus, a pumping apparatus of the kind set out in the last preceding paragraph but sixteen preferably comprises a comparator unit by which output signals of the sensing mechanism are compared with previous output signals thereof, and which is operative to terminate operation of the apparatus to energise the alarm in dependence upon information derived from a comparison of said signals. Thus for example, each output signal produced by the sensing device may be compared with the value of the immediately preceding output signal produced by the sensing device, to produce a control signal dependent upon the difference between successive output signals.

Thus, the comparator unit may be operative to shut down the pumping apparatus, to energise the alarm in the event that the comparator unit detects a variation between successive output signals greater than a predetermined magnitude.

Preferably the comparator unit comprises a variable control, by which said predetermined magnitude (at which the operation of the pumping apparatus is shut down or the alarm is energised) may be varied to a desired magnitude.

Thus during a normal operation of the pumping apparatus, successive output signals compared by the comparator unit will show a continued reduction in such successive values, whilst the difference between successive output signals will be within a predetermined magnitude. In the event that the filter press ruptures, the sensing device will respond to an increase in the rate of operation of the pumping apparatus, to produce a large output signal, and the comparator unit will detect such an increase as being in excess of said predetermined magnitude, and will cause the pumping apparatus to be shut down.

Similarly, in the event of an interruption to the flow of slurry to the pumping apparatus, as may be occasioned by a blockage at the inlet valve, or a blockage of the outlet valve preventing flow of slurry from the pumping apparatus, a similar large disparity between successive output signals will cause the comparator unit to shut down operation of the pumping apparatus.

Preferably, pumping apparatus in accordance with this invention comprises both a comparison device and a comparator unit hereinbefore mentioned.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of a pumping apparatus which is a preferred embodiment of this invention and which has been selected for the purposes of illustrating the invention by way of example. In the accompanying drawings: FIGURE 1 is a schematic view of the pumping apparatus which is the preferred embodiment of this invention; FIGURES 2, 3, 4 and 5 are circuit diagrams of control mechanism of the apparatus; FIGURES 6 and 7 are schedules of parts used in the control mechanism; FIGURE 8 is a circuit diagram of a gp module of the apparatus; and FIGURE 9 is a schematic view of a logic rack thereof.

The pumping apparatus which is the preferred embodiment of this invention is basically similar to the apparatus described in U.K. Patent Specification No. 2,035,447, to which reference should be made for details not disclosed herein.

Said pumping apparatus comprises a pumping device comprising a cylinder 6, a piston 8 mounted for reciprocating movement in the cylinder to cause liquid (in the preferred embodiment a slurry) to alternately be drawn through an inlet valve (not shown) through an inlet port 10 into the cylinder 6, and to be forced from the cylinder 6 through an outlet port 14, through a further one-way valve (not shown) to a filter press (not shown) connected to the outlet port 14.

The apparatus also comprises a fluid pressure operating device comprising a cylinder 1 6 and a drive piston 18, mounted for rediprocating movement in the cylinder 1 6. 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 connecting rod 20.

The apparatus also comprises a control mechanism 40, comprising a valve mechanism 28 operative to control the admission of fluid under pressure to the cylinder 1 6. In a first condition of the valve mechanism, fluid under pressure is supplied to an upper port of the cylinder 16, a lower port thereof being connected to sump, and in'a second condition of the valve mechanism fluid under pressure is applied to said lower port of the cylinder 16, with the upper port being connected to sump. The valve mechanism is moved between its first and second conditions by momentary energisation of solenoid 34 or 36.

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.

Signals from the reed switches, as they are closed under the influence of the magnet 38, are applied to the control mechanism 40.

The normal operation of the control mechanism, to control the valve mechanism 28 in accordance with signals delivered to the control mechanism by the sensors 42, 44, is as described in the above mentioned U.K. patent specification, and will not be described herein further.

However, additional to the features described in said above mentioned patent specification, the control mechanism of the pumping apparatus which is the preferred embodiment of this invention comprises a sensing device responsive to the rate of operation of the apparatus to produce an output signal. In particular, the sensing device comprises a counting device 50 to count the number of strokes executed by the drive piston (as detected by movement of the cross head by the sensors 42 and 44) in a specific period of time, and which is operative to produce an output signal which is proportional to the number so counted.

The control mechanism further comprises a control device 52, which is operative to terminate operation of the apparatus in dependence upon information derived from the output signal. In particular, the control device comprises a comparison device 54 to which the output signal produced by the counting device is applied, and a selection device 56 which applies a preset signal of desired value (selected at the will of the operator) to the comparison device. The comparison device compares the output signal produced by the counting device 50 with said preset signal, and operates to terminate operation of the apparatus automatically when the output signal falls to the level of said preset signal, and to activate an audible and visual alarm 70 to alert the operative in charge.

The control mechanism also comprises a comparator unit 58, to which the output signals produced by the counting device are continuously applied, and which compares successive output signals to produce a comparative value. Said comparator unit also is operative to terminate operation of the apparatus in dependence upon information derived from said comparative value.

For this purpose, the control mechanism also comprises a variable control 60 adapted to produce a control signal of desired value (set by an operator), said control signal being applied to the comparator unit, and compared with the comparative value obtained by comparing successive output signals. Thus, when the comparative value exceeds the control signal, as would be occasioned in the event of a sudden substantial increase or decrease in the rate of operation of the pumping apparatus, operation of the apparatus would be terminated by the comparator unit.

A typical run of the pumping apparatus which is the preferred embodiment of this invention will now be described briefly, with reference to the accompanying drawings.

A start and stop button on the control mechanism will control motor operation, with a pilot lamp to indicate motor running.

On starting, the pump will first reverse to the limit switch 42, and then cycle alternately in forward and reverse directions between two limit switches.

The counting device 50 counts the number of forward strokes completed in successive sampling periods. Although the sampling period may be varied in accordance with the nature of the pumping operation (e.g. ram speed), the period will not be altered once a pumping operation has commenced. A typical interval for the sampling period is one minute. Sampling periods are synchronised with the pump stroke, so that they always commence as the pump leaves the reverse limit switch 42 at the start of a forward stroke. At the end of each sampling period the number of strokes counted is placed in a circuit store, which thus always holds the number of the last completed sampling period.

The selection device 56 comprises a selector switch adapted to be set at a level of between 3 to 14 strokes per minute, enabling the operator to set time operations for the lowest limit for economic pumping. Logic circuits compare the switch and store numbers, to trip the contactor when the stored number falls below the switch setting.

During the counting period, arithmetic circuits continuously monitor the difference between the increasing count and the stored number. At any instant that the count exceeds the stored number by a predetermined amount, the contactor will trip. The trip difference can be set by a switch, from 2 to 7 strokes per minute.

On initial starting, the stored number is zero, but logic circuits prevent cutting out of either trip until the store has been loaded from the first sampling of the stroke rate.

Although the control mechanism has been described hereinabove in relation to the termination of operation of the apparatus a) when the stroke rate falls below that which has been decided as being economically viable, and b) in the event of a sudden increase in the rate of operation of the apparatus, it will readily be appreciated that the control mechanism may readily be adapted to operate to terminate operation of the apparatus, on other eventualities.

Although the invention has been described herein in relation to a pumping apparatus having electrical sensors 42, 44 to trigger change-over at valve 28 and to provide a counting input to the control, the invention may be used on pumping apparatus having other forms of change-over trigger, such as mechanically actuated devices.

Claims

1. A pumping apparatus comprising a sensing device responsive to the rate of operation of the apparatus to produce an output signal which is functional of said rate of operation, and a control device which is operative to terminate operation of the apparatus or to energise an alarm to alert the operative, in dependence upon information derived from the output signal.

2. Apparatus according to Claim 1 adapted for use in the pumping of a slurry into a filter press, the pumping apparatus being operated by fluid under pressure.

3. Apparatus according to one of Claims 1 and 2 wherein the output signal is applied to the control device, to cause the control device to operate to terminate operation of the apparatus or to energise the alarm when the output signal reaches a predetermined magnitude.

4. Apparatus according to Claim 3 wherein said predetermined magnitude is an upper limit.

5. Apparatus according to one of Claims 3 and 4 wherein said predetermined magnitude is a lower limit.

6. Apparatus according to any one of Claims 3 to 5 wherein the control device comprises a comparison device which compares the output signal with a preset signal, and which is operative, as said output signal moves towards the preset signal in magnitude, to terminate operation of the apparatus or to energise the alarm.

7. Apparatus according to any one of Claims 3 to 6 wherein the control device comprises a selection device which is adapted to provide a preset signal of desired value.

8. Apparatus according to any one of the preceding claims wherein when the control device is operative both to terminate operation of the apparatus, and to energise an alarm to alert the operative to the situation.

9. Apparatus according to any one of the preceding claims comprising a pumping piston reciprocably mounted in a pumping cylinder to cause slurry to be drawn through an inlet into the cylinder, and pumped from the cylinder through an outlet into a filter press, such apparatus comprising an operating device comprising a drive piston reciprocably mounted in a drive 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.

10. Apparatus according to Claim 9 wherein the sensing mechanism comprises a counting device operative to count the number of strokes of the operating piston in a specific interval of time.

11. Apparatus according to Claim 9 wherein the sensive mechanism comprises a measuring device operative to measure the time taken by the operating piston to complete a specific number of strokes.

12. Apparatus according to any one of Claims 9, 10 and 11, as appendant to Claim 6, wherein the selection device is adapted to be operated to provide a preset signal which corresponds to a pumping rate of two and twenty strokes per minute.

13. Apparatus according to any one of the preceding claims comprises a comparator unit by which output signals of the sensing mechanism are compared with previous output signals thereof, and which is operative to terminate operation of the apparatus in dependence upon information derived from a comparison of said signals.

14. Apparatus according to Claim 1 3 wherein each output signal produced by the sensing device is compared with the value of the immediately preceding output signal produced by the sensing device, to produce a control signal dependent upon the difference between successive output signals.

1 5. Apparatus according to Claim 14 wherein the comparator unit is operative to shut down the pumping apparatus, or to energise the alarm, in the event that the comparator unit detects a variation between successive output signals greater than a predetermined magnitude.

16. Apparatus according to any one of Claims 13, 14 and 15 wherein the comparator unit comprises a variable control, by which said predetermined magnitude may be varied to a desired magnitude.

1 7. Apparatus for pumping a slurry into a filter press, constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

18. Any novel feature or novel combination of features hereinbefore described and/or shown in the accompanying drawings.