GB2170869A

GB2170869A - Pumping systems

Info

Publication number: GB2170869A
Application number: GB08503571A
Authority: GB
Inventors: John Harp
Original assignee: Thomas Willett and Co Ltd
Current assignee: Thomas Willett and Co Ltd
Priority date: 1985-02-12
Filing date: 1985-02-12
Publication date: 1986-08-13
Also published as: GB8503571D0; CA1265955A; GB2170869B

Abstract

Pumping apparatus, typically incorporating one or more hydraulically actuated reciprocating pump units (P1, P2, P3), for handling slurry or the like, includes sensors (15, 16) monitoring the outflow characteristics, e.g. pressure and flow rate, and a control unit (17) coacting with the drive means (12) of the unit(s) to keep the power output developed in the pump outflow (11) at a substantially constant level. The drive is preferably by means of a hydraulic pump (13) driven by an electric motor (14). <IMAGE>

Description

SPECIFICATION Pumping systems This invention relates to pumping systems particularly but not exclusively for handling such materials such as slurry or sludge having high content of solids, particularly but not exclusively the transfer of such materials over substantial distance utilising high pressure small bore pipelines.

Under practical conditions the volume of material to be handled by a pumping system may vary widely at different times as may the consistency and other properties of the material, for example the ratio of solids content and fluid content and this will affect the flow characteristics of the material in the particular pipeline. For maximum efficiency and safety of operation it is desirable that the pipeline is kept fully charged at all times with delivery from the output end of the pipeline taking place at a substantially constant rate and pressure regardless of fluctuations in input. Where the pumping system is part of a water treatment plant or sewage or effluent disposal plant voids in the pipeline flow may become filled with flammable gases such as methane giving rise to danger of explosion.

The object of the invention is to provide a pumping system which will substantially meet the above desirable requirements and which will operate automatically and reliably under service conditions in a wide range of applications.

One kind of pump known for the purposes referred to above such as handling slurry or sludge comprises a ram-type piston or other displacement member mounted for reciprocation in a cylinder having inlet and outlet ports for admission and discharge of materials to be pumped, and power actuated drive means, commonly a hydraulic ram, linked to the displacement member and actuated to effect reversal of the latter at the end of each stroke.

Said ram is usually operated by a hydraulic pressure system whose prime mover is an electric motor driving a hydraulic power pump.

While the ram-type pump may be double-acting utilising the displacement member to define a variable volume chamber at each end of the cylinder, a single acting arrangement is more commonly employed particularly for heavy duty high pressure applications. Double or single acting pumps as defined above are hereinafter referred to as "reciprocating pump units of the kind described".

A plurality of such units may be operated in a pumping system in parallel with each other and controlled for sequential operation of their displacement members as described in our copending British Patent Application No.

8414341 dated 5th June 1984 and to which reference is made for further details.

According to one aspect of the present invention we provide pumping apparatus comprising one or more reciprocating pump units of the kind described, a delivery duct through which outflow from the unit or units passes in use, control means operatively connected to regulate operation of drive means of the unit or units, sensing means responsive to a pro- perty or properties of outflow within the delivery duct in use, and feedback means applying a signal or signals which are a function or functions of said property or properties to the control means to maintain the power output from to the pump unit or units developed in said outflow at a substantially constant level during operation.

Conveniently said sensing means include a pressure transducer providing a direct reading of the pressure at any given time in the delivery duct and a flow rate recorder monitoring the rate of flow therethrough, signals therefrom being applied in the control means to regulate the drive means of the pump unit or units by maintaining the power applied therein at said constant level.

In one example of the invention, as applied to a pumping system of the kind described in our said co-pending patent application, said signals will be applied to a microprocessor based programmable logic controller (PLC) and which also provides other control functions of the system, for servo control of a flow regulator in the hydraulic power drive circuit whereby the wattage exerted by said drive means is maintained at a substantially constant level.

According to a further aspect of the invention we provide a method of operating pumping apparatus in which the pressure and flow rate at the output from the apparatus is automatically monitored and applied to regulate the power applied by the apparatus in use to said output whereby the power so applied is held at a substantially constant predetermined level.

It will be appreciated that the invention may be applied to various types of pumping systems and is not restricted to the reciprocating pump units of the kind described.

One example of a pumping system incorporating the invention is illustrated by the accompanying diagrammatic drawing.

In the drawing three signal acting reciprocating pump units of the kind described, P1, P2 and P3 are shown which are connected in parallel between a suction or inlet duct 10 and a common outflow or delivery duct 11, the latter extending to a long distance small bore pipeline. The pumping system in this example is used for long distance transfer of sludge, the hydraulic ram drives of the three units being controlled and operated sequentially in the manner described in our said co-pending patent application 8414341. The rams of each unit are connected to a common hydraulic drive and control module 1 2 which is powered by a hydraulic drive pump 13 driven by an electric motor 14.

Positioned in the delivery duct 11 adjacent to the common output from the pump units is a pressure transducer 15 and, immediately downstream of this, a flow rate transducer 16.

These transducers operate to constantly monitor the pressure and flow rate in duct 11 providing signals which are fed to an automatic control unit 17 which incorporates a microprocessor based programmable logic controller (PLC). Control unit 17 regulates the operation of the hydraulic control module 12 to provide said sequential operation of pump units P1-3 as described in greater detail in our said co-pending application.

Control unit 17 also functions to apply the signals derived from the transducers 15 and 16 to provide an output signal which is a function of the pressure and flow rate sensed in duct 11 and this is fed back to the hydraulic module 12 to regulate the power applied thereby to the actuating rams of the pump units, in this example by adjusting a flow control device in the hydraulic circuit.

Where P is the power needed to drive the pump units, F is the flow rate and P is the pressure then P2FXPXConstant The PLC of control unit 17 is pre-programmed to maintain the power output at a substantially constant preset level and this will be maintained despite any variations in input rate to the pump units and/or the consistency or other physical characteristics of the material being pumped, for example variations in solids/liquid content.

Control in this way ensures that the pipeline is always kept fully loaded and operates with optimum efficiency and substantially constant material output at the delivery end.

As the actual useful work done by the pump units, i.e. the delivery through duct 11 is being directly monitored and the power requirements is being automatically adjusted by control of the hydraulics which are applied directly to the pump rams a very efficient and accurate closed loop feedback system is provided. This is much more responsive, reliable and accurate than known power consumption monitoring systems which "read" the current consumption of the electric drive motor and attempt to regulate operation accordingly.

Claims

1. Pumping apparatus comprising one or more reciprocating pump units of the kind described, a delivery duct through which outflow from the unit or units passes in use, control means operatively connected to regulate operation of drive means of the unit or units, sensing means responsive to a property or properties of outflow within the delivery duct in use, and feedback means applying a signal or signals which are a function or functions of said property or properties to the control means to maintain the power output from the pump unit or units developed in said outflow at a substantially constant level during operation.

2. Apparatus as in Claim 1 wherein the sensing means is responsive to the pressure of said outflow in use.

3. Apparatus as in Claim 1 or 2 wherein the sensing means is responsive to the flow rate of said outflow in use.

4. Apparatus as in Claim 1 wherein the sensing means includes a pressure transducer providing a direct reading of the pressure at any given time in the delivery duct and a flow rate recorder monitoring the rate of flow therethrough.

5. Apparatus as in Claim 4 wherein the signals from the transducer and recorder are operatively applied in the control means to regulate the drive means of the pump unit or units by maintaining the power applied therein at said constant level.

6. Apparatus as in any preceding claim wherein there are a plurality of pump units operating in parallel and controlled for sequential operation of their displacement members.

7. Apparatus as in any preceding claim wherein the feedback means includes a microprocessor based programmable logic controller (PLC) which also provides other control functions of the apparatus.

8. Apparatus as in any preceding claim including a hydraulic power drive circuit for actuating the unit or units, the control means including a servo controlled flow regulator in said circuit responsive to the feedback means whereby the wattage exerted by said drive means is maintained at a substantially constant level.

9. Pumping apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

10. A method of operating pumping apparatus in which the pressure and flow rate at the output from the apparatus is automatically monitored and applied to regulate the power applied by the apparatus in use in said output whereby the power so applied is held at a substantially constant predetermined level.

11. A method of operating pumping apparatus substantially as hereinbefore described with reference to the accompanying drawing.