PRESSURES IN A DAIRY FARM VAT REFRIGERANT PAD OPERATED ON REFRIGERANTR22

Farm milk vats are fitted with refrigeration systems to chill and pres erve the milk until collection for transportation to the processing pl ant. In response to the New Zealand Ozone Layer Protection legislation , some of the vat refrigeration systems were converted from R12 to R22 . The refrigerant evaporator is part of the vat floor and could be dam aged by the higher saturation pressures of R22. Of particular concern was the washing of the vat with hot water at 60-degrees-C, during an i nterruption to the power supply, which could cause very high pressures with R22. Measurements in a vat showed that the pressure obtained was very much lower because the refrigerant migrated to the lower-tempera ture suction-pipe system. However, the pressures were still high enoug h to damage vats constructed before 1988. Vats constructed between 198 8 and 1990 are stronger and can resist the pressures, although the eff ect on long-term life is unknown.