GB2190991A

GB2190991A - Heat pump for solvent cleaning apparatus

Info

Publication number: GB2190991A
Application number: GB8611475A
Authority: GB
Inventors: John Lewis
Original assignee: Kerry Ultrasonics Ltd
Current assignee: Kerry Ultrasonics Ltd
Priority date: 1986-05-10
Filing date: 1986-05-10
Publication date: 1987-12-02
Anticipated expiration: 2006-05-10
Also published as: GB2190991B; GB8611475D0

Abstract

A solvent cleaning apparatus is disclosed which includes a heat pump 22, pressure sensing means, 34, for detecting pressure increases in the heat pump 22 and disconnecting the pump from its power supply when the pressure in the pump increases above a predetermined value, switch means 40, 42 for enabling the sensing means 34 only during rapid mode of the heat pump 22 and indicator means for indicating excess pressure during rapid mode. <IMAGE>

Description

SPECIFICATION Heat pump This invention concerns solvent cleaning apparatus including a heat pump.

Solvent cleaning apparatus including a heat pump in general has a container for the solvent, typically a halogenated hydrocarbon, and a heat pump with heating and cooling elements arranged to supply heat to the solvent to boil and vapourise it, and thereafter to remove heat from the vapourised solvent to condense it and return it to the container.

During use of such apparatus, the pressure of the refrigerant in the heat pump can rise to unacceptably high levels for many reasons. In order to prevent serious damage to the apparatus by such pressure rises, a pressure detector is usually provided in the heat pump which disconnects the pump from its electrical power supply when the pressure of the refrigerant becomes too high. An indicator is often provided to show that the apparatus has been immobilised for this reason.

While such devices do protect the heat pump from excessive pressure increases both during rapid mode, when rapid heat transfer to the solvent is required to bring about its boiling and during normal mode when refluxing of the solvent occurs and cleaning is effected, they fail to distinguish between faults occurring in these two modes. This leads to service engineers being called out to repair solvent cleaning apparatus which itself simply needs cleaning and It has been found that impurities in the solvent resulting from the use of such solvent cleaning apparatus form deposits on the heat transfer element which transfers heat from the refrigerant in the heat pump to the solvent. The result is relatively poor heat transfer to the solvent during the rapid mode, with a consequent increase in refrigerant temperature and pressure.The pressure detector is activated and the power supply is cut off.

According to the present invention there is provided, solvent cleaning apparatus including a heat pump, pressure sensing means for detecting pressure increases in the heat pump and disconnecting the pump from its power supply when the pressure in the pump increases above a predetermined value, switch means for enabling the sensing means only during rapid mode of the heat pump, and indicator means for indicating excess pressure in the heat pump occurring only during rapid mode.

In addition to providing an indication of excess pressure occurring during rapid mode, the apparatus desirably also includes means for indicating the occurrence of excess pressure during normal mode. This can be provided by a further pressure sensor activated by a further switch during the normal mode of the heat pump, a further indicator being provided to indicate excess pressure during normal mode. It is, of course, possible for a single pressure sensor to be used and for the occurrence of excess pressure to be switched so that in rapid mode it activates an indicator for a fault in rapid mode and in normal mode it activates an indicator for a fault in normal mode.

An embodiment of cleaning apparatus in accordance with the present invention will now be described, by way of example, with referende to the accompanying drawing which is a block diagram thereof.

In the drawing, the apparatus has a container or tank 10 divided into two compartments 12 and 14 by a dividing wall 16. Compartment 14 is filled with a solvent, for example trichlorotrifluoroethane, until it overflows and partially fills compartment 12.

Compartment 12 has a solvent boilding coil 18 which forms a part of a heat pump 22.

The coil 18 is arranged to heat and boil the solvent to produce a solvent vapour region above it. Below the open top of the tank 10 but above the two compartments 12 and 14 are cooling coils 20 which form the evaporator of the heat pump 22. The coils 20 are arranged to condense solvent vapour rising from the boiling liquid and deposit condensed vapour into a peripheral channel 24 below the coils 20. The channel 24 drains into a water separator and optional inter-cooler 26. An overflow pipe 28 returns condensate from the separator 26 to compartment 14. Since solvent is continuously supplied to compartment 14, the solvent in compartment 14 remains relatively clean.

Cleansing of articles in the tank 10 can be carried out in known manner.

The heat pump 22 is shown in rapid mode, during which excessive refrigerant pressure build-up is most likely.

A compressor 30 compresses refrigerant which passes via a strainer 32 to the boiling coil 18. Refrigerant passing from coil 18 is fed to a refrigerant accumulator 38 and thence to a flow reversing valve 40. The valve 40, shown in rapid mode, passes refrigerant to a restrictor 46.

Refrigerant leaving the restrictor 46 is cooled in a condenser coil 34 cooled by a fan 48. Cooled refrigerant is then passed via the reversing valve 40 to the inter cooler 26 and thence to the cooling coils 20 before being returned to the compressor 30. The reversing valve 40 is controlled to switch between rapid mode as shown and normal mode in which the 'U' shaped member is moved to the right by a control circuit 42 activated by a temperature sensor 41 on the tank 10. When the solvent boils, hot vapour rises and heats the sensor 41 which results in the valve 40 being moved into normal mode.

The speed of the fan 48 is controlled by a control circuit 50 connected to a temperature sensor 52 which senses the temperature of the refrigerant in the compressor 30.

In normal mode, refrigerant passes from the compressor 30 to the valve 40 as described above for rapid mode. Thereafter, the refrigerant is cooled in the coil 34 by the fan 48, and cooled refrigerant expands and cools further on passing through the restrictor 46. The resulting cooled refrigerant is passed via the inter-cooler 26 to the coils 20 which reflux solvent vapour back to the channel 24.

The refrigerant conduit 31 from the compressor 30 to the strainer 32 has two refrigerant pressure sensors 34 and 36. Once pressure sensor is connected to an indicator circuit which reacts to excessive pressure build up in the conduit 31 in a short time, typically during rapid mode, and the other is connected to an indicator circuit which reacts to excessive pressure build up in the conduit 31 in a longer time, typically during normal mode. Of course, a single pressure sensor could be used to detect excessive pressure, different indicators being used to indicate excessive pressure on start up or during normal operation. In this latter case, the excessive pressure detected to would be the same, whereas if two sensors are used, as illustrated, they could be selected to react to different pressures. Where two switches are used, the switch which functions in rapid mode and gives and indication of contamination may, for example, be arranged to function at a lower pressure than the other switch which serves to indicate a conventional high pressure warning. Typically a pressure difference of 15 p.s.i.

can be used with the high pressure warning being set, for example at 425 p.s.i.g.

Claims

1. Solvent cleaning apparatus including a heat pump, pressure sensing means for detecting pressure increases in the heat pump and disconnecting the pump from its power supply when the pressure in the pump increases above a predetermined value, switch means for enabling the sensing means only during rapid mode of the heat pump, and indicator means for indicating excess pressure during rapid mode.

2. Apparatus according to claim 1, including further pressure sensing means for detecting pressure increases and disconnecting the pump from its power supply during normal mode of the heat pump when the pressure therein increases above a predetermined value, further means for enabling the further sensing means only during normal mode of the heat pump, and further indicator means for indicating excess pressure in the heat pump occurring only during normal mode.

3. Apparatus according to claim 1, including further switch means for enabling said sensing means only during normal mode of the heat pump, and further indicator means for indicating excess pressure in the heat pump occurring only during normal mode.

4. Solvent cleaning apparatus substantially as herein described with reference to the accompanying drawing.