GB1575724A - High pressure water supply systems - Google Patents

Description

(54) HIGH PRESSURE WATER SUPPLY SYSTEMS (71) We, WARWICK PUMP & EN GINEERING COMPANY LIMITED, a British Company, of Oxford Road, Berinsfield, Oxford OX9 8LZ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to high pressure water supply systems, and to a control circuit for controlling a series of pumps supplying such a system.

As high pressure water systems become more widely used in industrial environments it is becoming increasingly attractive to replace a number of individual machines throughout the plant with a high pressure main system to which the hose and lance assembly may be connected at a number of outlets. This gives the cleaner operative the possibility of moving quickly and easily round the plant carrying only the hose and lance and connecting into the main at a suitable take-off point adjacent to the area to be cleaned. The main may carry either hot or cold water at pressures typically between 500 and 2000 psi (pounds per square inch). This system has been found particularly useful in food factories, abattoirs, engineering plants, larger garages etc.

Although the ring main itself may be expensive to install, the equivalent of say 6 5hp machines scattered throughout the works can be installed in one central plant room and the cost of a central installation will be substantially less than 6 individual units. Servicing, obviously, is far simpler with all the units in one position and it is easier to use waste heat should any be available in the plant to provide hot water, if this is required.

Since a relatively large amount of power is used to raise water to the high pressures involved, it is important to have a control system which allows as little high pressure water as possible to be lost within the circuit without being used for cleaning.

In the most elementary systems, the pump is switched on before any cleaning commences and continues to operate at full power, the water either being used on any cleaning lances which are attached to the system, or sent to waste through a relief valve. This has the disadvantage that all the energy put into the water is recovered as heat through the relief valve which may raise the recirculated water to dangerously high temperatures.

An improved control system has a pressure sensitive switch which, with the single pump, senses a fall in system pressure and starts the pump and will switch off the pump if the pressure rises above a pre-set level, a level normally set when no lance is in use.

This system also offers a low pressure cut-out device so that the whole circuit is switched off should the circuit pressure fall below the pre-set level (e.g. 200 psi in the case of a 1200 psi circuit), thereby indicating that there has either been a fracture in a pipe or a fault in the system.

This pressure switch oriented system may be extended to drive a number of pumps in parallel by having several switching elements operated by the same pressure switch, each set to slightly wider pressure ranges. For example on a 1200 psi circuit, if the pressure should fall to 1150 psi pump number 1 is started and, providing the nozzle on the cleaning lance matches the pump output, the pressure will rise to 1200 psi. If, however, a second lance is switched on pressure will again fall and on reaching say 1100 psi pump number 2 will be started.

Similarly pumps numbers 3 and 4 start at 1050 and 1000 psi. The "off" elements might be set at 1350, 1400, 1450, and 1500 psi.

It will become evident that as more pumps are added to the system the change in pressure in the circuit when each additional pump is switched off or on becomes smaller. For example in a four pump, 3 gpm (gallons per minute) system running at 1200 psi with one pump running, when the second lance is switched on the pressure will fall to 300 psi, whereas with three pumps running, when the fourth lance is switched on the pressure will fall only to 675 psi.

There is obviously a limit to the number of pumps which can be operated satisfactorily by this system, since eventually the differential becomes unacceptably small.

It is, however, very attractive to have a large number of small pump units, and, indeed, for preference each pump unit should match the "standard" cleaning lance proposed for the system. For instance a system in a food factory might have a requirement for a main with 50 take-off points, of which, at any one time, up to 10 might be in use, each lance being designed to deliver 3 gpm at 1200 psi. If the system were driven by 2 pumps each of 15 hp, and each capable of delivering 15 gpm at 1200 psi, when one lance only is in use the pumps will be delivering an excess of 12 gpm which would have either to be dumped to waste or stored in a very large accumulator in order to avoid the pump switching on and off excessively frequently.The storage system although attractive because of its simplicity requires an extremely large accumulator in order to avoid the wide pressure fluctuations in the circuit and/or the requirement for the pump to start and stop very frequently. Ten pumps, however, each delivering 3 gpm could equally well drive the system and with the control circuit described below are able to offer a number of significant advantages. The circuit could also, of course, be driven by 5 pumps at 6 hp or in a number of other combinations.

It will become evident that if a large number of smaller units is used, the required volume of accumulator to prevent one pump switching on and off excessively frequently becomes considerably smaller (for instance in the event of an incorrectly sized nozzle (e.g. 42 gpm) being used in the circuit).

The object, therefore, of this invention is to provide a control circuit which may operate in conjunction with with one simple 4 stage pressure switch device, such as is manufactured by the Warwick Pump and Engineering Company, such that a number of pumps can be arranged to be turned on and turned off sequentially according to the demand of the system.

According to the present invention, there is provided a control circuit, for controlling a series of pumps supplying a high pressure ring main in which a pressure switch device sensitive to pressure in the main has first and second switches actuated respectively when pressure falls below a predetermined lower limit or rises above a predetermined upper limit, the control circuit being adapted in response to actuation of the first switch to start up the pumps sequentially with a first predetermined delay between the starting of successive pumps until the pressure in the main exceeds said lower limit, and in response to actuation of the second switch to stop pumps sequentially with a second predetermined delay between stopping of successive pumps until the pressure in the main falls below said upper limit.

The principle of this invention is that if the pressure switch device detects an underpressure condition in the circuit, for instance caused because one lance has been turned on, this control circuit will start a pump and continue to start further pumps each after a short delay, until the system pressure again rises above the lower pressure limit. Similarly to turn the pump off, each time a lance is released the system pressure will rise and pumps will commence to turn off sequentially after a short delay until the system pressure falls below the upper pressure limit or all the pumps have been switched off.

With a 4 stage pressure switch device, as referred to above, the two remaining stages in the pressure switch may be used: (a) as an underpressure control, to detect an unacceptably low pressure in the circuit, e.g.

because a pipe has burst, and disenable the whole system so that it requires manual intervention to re-start it; and (b) to detect an overpressure situation where, possibly due to a fault in circuitry, the pressure has risen to an unacceptably high level, and again the entire circuit is disenabled.

An example of appropriate circuitry is shown in the accompanying drawings, in which only two circuit elements are shown corresponding to two pumps. However, it can be seen that a control system of this type can control any number of pump units, merely by adding an appropriate number of elements to the circuit. Therefore it enables a circuit to be built initially with, say, 4 pumps and then expanded with the addition of further pumps without difficulty.

It is also possible to adjust the operating pressure of the entire circuit by merely selecting an alternative pressure switch device in which the individual switches are actuated at different pressures.

In the drawing: Figure 1 shows a control circuit, Figure 2 shows a power circuit, and Figure 3 shows a logic circuit.

The circuit is shown in three distinct sections.

The power circuit. Motors 1, 2 etc are controlled by contactor elements C1, C2 etc and protected by Thermal overload elements TOL1, 2 etc. in a completely conventional manner. The circuit is drawn single phase but may of course equally be three phase.

The control circuit, which energises the contactor operating elements C1, C2 etc. In order that power can reach the operating elements PSW 4 and PSW 1 must both be made. PSW 1 will be open when the circuit is at rest and it is therefore bridged by the spring return "start" switch to allow the circuit to be manually held running until the operating pressure of PSW 1 has been reached. PSW 4 senses system overpressure, and when this occurs it cuts out all control power and shuts the pumps down. For simplicity this element is shown operating directly although in practice a mechanical or electrical latch such as a relay is added so that it has to be manually reset once it has operated.The emergency stop button is provided in a prominent position and may be limited to a low voltage circuit with additional emergency stop buttons situated remotely from the equipment (a continuous low voltage line incorporating a number of normally closed stop buttons holding in the coil of a relay wherein normally open contacts form the "emergency stop" switch).

"Test" and "off" switches are provided in each circuit so that each pump may be taken out of service or run without affecting any other. Switches TOL 1, TOL 2 etc are provided to shut down a pump should the thermal element in the power circuit detect an overload condition.

The switches R1, R2, etc. control the circuit during normal operation and are operated by operating elements El, E2 etc shown in the logic circuit.

Logic Circuit. The logic circuit energises operating elements El, E2, etc. under certain circumstances. Each pump has its own operating element El, 2, etc. and its own logic board B1, 2, etc. shown inside the dotted lines. Each logic board is identical and is connected to its neighbour by connections 7, 8, 10, 11 and 12. Line 10 is continuous throughout and is in the 1 condition if PSW 2 is made. PSW 2 is made if the circuit pressure falls to a preset level indicating that more pumps should be turned on. Similarly line 11 is continuous and is in the 1 condition if PSW 3 is made.

PSW 3 is made if the circuit pressure rises to a preset level indicating that pumps should be turned off as system demand has fallen.

With the system at rest, if a lance valve is opened PSW 2 will close and send a signal through delay T in B1 to AND element 1 which will also receive a signal from line 10 and will therefore turn on. Two NOR elements 3 and 4 linked to form a latch are set by the signal at la. The output is amplified by amplifier 5, signals are sent down lines 8a and 7 in B1, and element El is energised to start pump 1. This will cause the circuit pressure to rise and will break PSW 2. If however it does not rise before the signal sent down line 7 has passed delay T in B2, NOR gates 3 and 4 in B2 will "set" in the same way energising E2 and in turn sending a signal to B3 through line 7 in B2.

If a lance is turned off the pressure will rise and PSW 3 will be made, sending a signal down line 11. If pumps 1 and 2 only, for example, are running, there will be no signal at line 8 in B2 since pump B3 is not running. Inverter 6 will have sent a signal through delay S to AND element 2, however, and as PSW 3 makes, AND element 2 in B2 is turned on sending a signal through 2a to NOR element 4 which will "reset" the latch to the 0 condition in turn de-energising amplifier 5, relay R2 and taking away the 1 signal from lines 8a and 7 in B2. Pump 2 will then stop, the circuit pressure will fall and PSW 3 will reopen.If, however, for instance because two lances were turned off simultaneously, the pressure did not fall fast enough to open PSW 3 before the 0 signal, passing down 8a and 8 and inverted to a 1 by inverter 6 in B1, had passed through delay S in B1, the operation described above would be repeated and R1 would be de-energised also after delay S.

It should be noted that this circuit may be built with either relays or solid state logic elements and that solid state has been used by way of example only.

WHAT WE CLAIM IS: 1. A control circuit for controlling a series of pumps supplying a high pressure ring main in which a pressure switch device sensitive to pressure in the main has first and second switches actuated respectively when pressure falls below a predetermined lower limit or rises above a predetermined upper limit, the control circuit being adapted in response to actuation of the first switch to start up the pumps sequentially with a first predetermined delay between the starting of successive pumps until the pressure in the main exceeds said lower limit, and in response to actuation of the second switch to stop pumps sequentially with a second predetermined delay between stopping of successive pumps until the pressure in the main falls below said upper limit.

2. A control circuit as claimed in claim 1, wherein a four stage pressure switch device is employed, two of the stages forming said first and second switches, and the two remaining stages being used respectively as an under pressure control to detect an unacceptably low pressure in the circuit, and as an over pressure control to detect an unacceptably high pressure in the circuit,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. and protected by Thermal overload elements TOL1, 2 etc. in a completely conventional manner. The circuit is drawn single phase but may of course equally be three phase. The control circuit, which energises the contactor operating elements C1, C2 etc. In order that power can reach the operating elements PSW 4 and PSW 1 must both be made. PSW 1 will be open when the circuit is at rest and it is therefore bridged by the spring return "start" switch to allow the circuit to be manually held running until the operating pressure of PSW 1 has been reached. PSW 4 senses system overpressure, and when this occurs it cuts out all control power and shuts the pumps down. For simplicity this element is shown operating directly although in practice a mechanical or electrical latch such as a relay is added so that it has to be manually reset once it has operated.The emergency stop button is provided in a prominent position and may be limited to a low voltage circuit with additional emergency stop buttons situated remotely from the equipment (a continuous low voltage line incorporating a number of normally closed stop buttons holding in the coil of a relay wherein normally open contacts form the "emergency stop" switch). "Test" and "off" switches are provided in each circuit so that each pump may be taken out of service or run without affecting any other. Switches TOL 1, TOL 2 etc are provided to shut down a pump should the thermal element in the power circuit detect an overload condition. The switches R1, R2, etc. control the circuit during normal operation and are operated by operating elements El, E2 etc shown in the logic circuit. Logic Circuit. The logic circuit energises operating elements El, E2, etc. under certain circumstances. Each pump has its own operating element El, 2, etc. and its own logic board B1, 2, etc. shown inside the dotted lines. Each logic board is identical and is connected to its neighbour by connections 7, 8, 10, 11 and 12. Line 10 is continuous throughout and is in the 1 condition if PSW 2 is made. PSW 2 is made if the circuit pressure falls to a preset level indicating that more pumps should be turned on. Similarly line 11 is continuous and is in the 1 condition if PSW 3 is made. PSW 3 is made if the circuit pressure rises to a preset level indicating that pumps should be turned off as system demand has fallen. With the system at rest, if a lance valve is opened PSW 2 will close and send a signal through delay T in B1 to AND element 1 which will also receive a signal from line 10 and will therefore turn on. Two NOR elements 3 and 4 linked to form a latch are set by the signal at la. The output is amplified by amplifier 5, signals are sent down lines 8a and 7 in B1, and element El is energised to start pump 1. This will cause the circuit pressure to rise and will break PSW 2. If however it does not rise before the signal sent down line 7 has passed delay T in B2, NOR gates 3 and 4 in B2 will "set" in the same way energising E2 and in turn sending a signal to B3 through line 7 in B2. If a lance is turned off the pressure will rise and PSW 3 will be made, sending a signal down line 11. If pumps 1 and 2 only, for example, are running, there will be no signal at line 8 in B2 since pump B3 is not running. Inverter 6 will have sent a signal through delay S to AND element 2, however, and as PSW 3 makes, AND element 2 in B2 is turned on sending a signal through 2a to NOR element 4 which will "reset" the latch to the 0 condition in turn de-energising amplifier 5, relay R2 and taking away the 1 signal from lines 8a and 7 in B2. Pump 2 will then stop, the circuit pressure will fall and PSW 3 will reopen.If, however, for instance because two lances were turned off simultaneously, the pressure did not fall fast enough to open PSW 3 before the 0 signal, passing down 8a and 8 and inverted to a 1 by inverter 6 in B1, had passed through delay S in B1, the operation described above would be repeated and R1 would be de-energised also after delay S. It should be noted that this circuit may be built with either relays or solid state logic elements and that solid state has been used by way of example only. WHAT WE CLAIM IS:

1. A control circuit for controlling a series of pumps supplying a high pressure ring main in which a pressure switch device sensitive to pressure in the main has first and second switches actuated respectively when pressure falls below a predetermined lower limit or rises above a predetermined upper limit, the control circuit being adapted in response to actuation of the first switch to start up the pumps sequentially with a first predetermined delay between the starting of successive pumps until the pressure in the main exceeds said lower limit, and in response to actuation of the second switch to stop pumps sequentially with a second predetermined delay between stopping of successive pumps until the pressure in the main falls below said upper limit.

2. A control circuit as claimed in claim 1, wherein a four stage pressure switch device is employed, two of the stages forming said first and second switches, and the two remaining stages being used respectively as an under pressure control to detect an unacceptably low pressure in the circuit, and as an over pressure control to detect an unacceptably high pressure in the circuit,

both said under pressure control and said over pressure control disenabling the entire circuit when they are activated.

3. A control circuit for controlling a series of pumps supplying a high pressure ring main, substantially as herein described with reference to the accompanying drawing.