GB2042156A - Improvements in or relating to pressurized liquid medium systems - Google Patents

Abstract

A pressurised liquid medium system, for example a heating system, has two closed liquid medium circuits (7, 8), each of which is connected, via a delivery line (18, 25), a pump (12, 16), and a return line to a low pressure liquid container (10), there being a fully modulating pressure-sensitive valve arrangement between each delivery line and its associated return line to the low pressure liquid container. A pressure-responsive switch arrangement is provided in each delivery line whereby the pumps may be controlled to operate in unison or singly to maintain a predetermined pressure in the liquid medium circuits. <IMAGE>

Description

SPECIFICATION Improvements in or relating to pressurized liquid medium systems This invention relates to pressurised liquid medium systems, for example heating systems of the kind which in operation are pressurised to enable a circulating liquid medium, usually water, to be used at a temperature above its normal boiling point i.e.

its boiling point at atmospheric pressure; and other systems of a generally analogous nature which are pressurised and involve a liquid medium. An example of such an analogous system is a cold water supply system which requires to be pressurised in order adequately to serve users, for example in a high rise apartment building.

According to one aspect of the invention control means for a pressurised liquid medium system, which system has two closed liquid medium circuits each adapted to operate at a pressure greater than atmospheric, comprises two pressure-sensitive valve arrangements respectively for connection between the container and the two circuits for transfer of liquid medium from the respective circuit to a low pressure liquid container, two pumps whose outputs are adapted to be connected in parallel and to the two circuits, means for operating the valve arrangements between a closed and an open condition according to changes in the pressure in the respective circuit within given upper and lower limits, the valve arrangements being capable in the open condition of transferring liquid from the respective circuit, and means for operating the pumps in response to pressure in one or both circuits at least to bring the pressure to a value at which the valve arrangements begin to open.

The invention also includes two pressurised liquid medium circuits connected to a control system as defined bove.

The invention may be performed in various ways and one specific embodiment will now be described by way of example with reference to the accompanying drawing which illustrates diagrammatically control means for pressurised heating systems.

Referring to the drawing, an open low pressure (atmospheric or slightly higher) liquid container 10 for containing, for example water includes means (not shown) controlling the level of liquid, for example a float-controlled inlet valve connected to mains supply.

A suction line 11 connects the container 10 with the inlet to a first pump 12 via filter 13 and isolating valve 14. The line 11 connects through line 15 with the inlet to a second pump 16, in parallel with pump 12, via isolating valve 17.

The outlet from pump 12 connects with a first delivery line 18 through line 21 which includes non return valve 20 and isolating valve 19.

The outlet from pump 16 connects with delivery line 18 through line 22 which includes non return valve 23 and isolating valve 24.

Output lines 21, 22 also connect with a second delivery line 25 respectively through lines 26, 27 including non return valves 28, 29 and isolator valves 30, 31.

The isolator valves 14,19,30,17,24,31 are provided to isolate respectively pump 12 or 16 thereby enabling the shut-down of one of the pumps for maintenance whilst the other continues to function.

Pressure gauges 35,36 respectively connect with lines 18,25 through pressure responsive electrical switches 37,38. One switch 37 is connected to an alarm to indicate when pressure in line 18 falls to an undesirable level, one switch 37 is connected for controlling pump 12. Switches 18 are similarly connected to pumps 12, and to provide an alarm for line 25.

Pump 16 is in a constant run condition.

Delivery line 18 connects with return line 40 leading to a distributor or mixer 9 in tank 10 through a transfer valve 41 spring urged to a closed position and responsive to the pressure in the line 18.

Delivery line 25 connects with return line 42 leading to tank 10 through transfer valve 43 similar to valve 41.

Delivery line 18 connects with a first heating circuit 8 intended to operate at elevated pressure and including for example boiler 32, pump 33 and load 34. The load may for example be radiators for space heating.

Delivery line 25 connects with a second heating circuit 7 intended to operate at elevated pressure, similar to circuit 8. In use of the arrangement, pump 16 is isolated using valves 17,24 and 31 and with transfer valves 41, 43 set to be open at a flow rate respectively equal to the expected maximum return from the first and second heating circuits, pump 12 is energised and set to a delivery rate to give a desired operating pressure in the heating circuits 7, 8, which are full of liquid, with the boilers off. The pressure is indicated on the pressure gauges. Pump 12 is now isolated and pump 16 energised and set to give the same pressure in circuits 7, 8, with transfer valves 41,43 fully open.

It will be appreciated that each pump is capable of delivery the maximum demand of both heating circuits together.

The pressure unit is up to pressure with pump 12 running and passing water via transfer valves 41,43 to the tank.

The isolating valves are now opened and one or both boilers can be started to bring the temperature(s) in the heating circuit(s) to a desired level.

Assume that the boiler in heating circuit 8 is now switched on. The temperature in circuit 8 will rise to the desired level and in doing so transfer valves 41 and 43, which are fully modulating, would compensate for the expansion flow rate in addition to the flow rate from pump 12.

When the liquid in circuit 8 cools, the pressure in the circuit falls, this will be indicated on gauge 35 and valve 41 will move nearer to its seat, that movement being relative to the cooling rate of the system. Some of the liquid delivered by pump 12 will be passing through valves 41 and 43, and the balance of that liquid will be diverted to circuit 8 at a flow rate sufficient to maintain the pressure in the circuit. When the contraction curve has been satis fied all of the water from pump 12 will then be passing through valves 41 and 43.

If, due to a large and sudden load change cooling system 8 cools rapidly, thus causing a large reduction in volume and pressure, and for a short time contracts at such a rate that pump 12 can no longer meet the demand, then pressure falls to a level at which a switch 37 brings pump 16 into operation.

Pumps 12 and 16 then operate together until the pressure in circuit 8 is raised to a level at which switch 37 disengages pump 16. Pump 12 will then maintain the pressure in the circuits under small changes of load as above.

Circuit 7 can act in an identical manner two circuit 8 at the same time, or at a different time. ie Circuit 8 could be on the expansion sequence and circuit 7 could be on the contraction sequence, and in either condition the pumps and respective transfer valves will contain both systems at a safe working pressure, irrespective of expansion or contraction.

Of course both heating circuits 7, 8 may be in use together and under normal operating conditions are maintained at the desired pressure by pump 12 alone, with pump 16 being brought into operation when necessary, as above.

The system may for example have the following characteristics: Maximum expansion through transfer valve 41 or 43 at a pressure of 50 p.s.i.g.

Static (i.e. steady load) condition pressure with pumps 12 and 16 running : 50 p.s.i.g.

Pressure at which transfer valve 41 or 43 fully shuts : 40 p.s.i.g.

Pressure at which a pressure switch 37 or 38 engages pump 16: 42 p.s.i.g.

Claims (10)

1. Control means for a pressurised liquid medium system having two closed liquid medium circuits each adapted to operate at a pressure greater than atmospheric, comprises two pressuresensitive valve arrangements respectively for connection between the container and the two circuits for transfer of liquid medium from the respective circuit to a low pressure liquid container, two pumps whose outputs are adapted to be connected in parallel and to the two circuits, means for operating the valve arrangements between a closed and an open condition according to changes in the pressure in the respective circuit within given upper and lower limits, the valve arrangements being capable in the open condition of transferring liquid from the respective circuits, and means for operating the pumps in response to pressure in one or both circuits at least to bring the pressure to a value at which the valve arrangements begin to open.

2. Control means as claimed in Claim 1 in which the pressure sensitive valve arrangements are each connected to a delivery line from a pump to its respective closed liquid medium circuit and to a return line to the low pressure liquid container.

3. Control means as claimed in claim 1 or 2 in which, the pressure sensitive valve arrangements are in the form of fully modulating valves adapted to compensate for expansion flow rate in the liquid in addition to flow rate from the pumps.

4. Control means as claimed in claim 2, in which each delivery line is provided with a pressure responsive switch arrangement adapted to control the operation of its associated pump.

5. Control means as claimed in claim 4, in which each pressure responsive switch arrangement is provided with a pressure gauge.

6. Control means as claimed in claim 1 or 2 in which the pressure sensitive valve arrangements are each spring loaded towards a valve closed condition.

7. Control means as claimed in claim 1 in which each pump is connected to the delivery lines to both of the closed liquid medium circuits.

8. Control means as claimed in claim 1 or 7 in which isolator valves are provided between the low pressure liquid container, the pumps and the closed liquid medium circuit whereby the closed liquid medium circuits may be operated selectively or in unison.

9. Control means as claimed in claim 1 in which non-return valves are provided in the lines connecting the pumps to the delivery lines to the closed liquid medium circuits.

10. Control meansfora pressurised liquid medium system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.