Wastage of refrigerant can be reduced by cooling the mixture of gases and thus reducing the ratio. By means of a refrigerated purge device, which cools the mix­ture down to the evaporator temperature (for example, — 35°C in a blast freezer plant), the ratio would become

Vapour pressure of R407C at — 35°C = 1.5 bar Partial pressure of non-condensible gas = 10.2 bar

The ratio now becomes 10 g of R407C lost per kilogram of air.

Automatic gas purgers comprise a collection vessel for the gas mixture with an inbuilt cooling coil connected to the main suction, or with its own refrigera­tion system. Condensed refrigerant returns to the condenser, and any gas remain­ing in the vessel will be non-condensible and can be vented by an inverted bucket trap.

Purging of gases must always be to the open air. The release of ammonia-air mixture is usually made through a flexible tube into a container of water. The water will absorb the ammonia, and any bubbles seen to rise to the surface will be other gases.

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