Room pressure relief valves
A correctly sized relief valve that operates in both under and over pressure situations, is vital to protect the sealed room structure.
In many CA stores the relief valve is either undersized or incorrectly located. Another problem often encountered by our service engineers is relief valves that are set at too high a pressure providing little or no protection for the sealed room.
The opening pressure should be 8 to 10 mm both positive and negative. In rooms with large or oversized evaporators, the pressure created can be two or three times greater than the standard pressure settings for relief valves. This problem can be overcome by modifying blower fan start up sequences and installing additional relief valve capacity.
Maintenance of relief valves is also important. For our VA type waterless valves, these can be washed in detergent and rinsed with clean water. A quick check as you walk past the room can be useful: just lift the shaft on both sides of the valve to ensure the valve is not sticking.
Room expansion bags
The purpose of these bags is to initially compensate for pressure changes in the room by drawing room atmosphere from the bag or putting atmosphere into the bag to avoid bringing in outside air that will raise the room oxygen level.
There is a ratio of room size to expansion bag capacity which is seldom achieved due to cost of the bags and suitable locations. The smaller bags generally installed will still provide a positive benefit on room atmospheres. Care in location of the bags (away from hot surfaces) and correctly sized pipework between the bag and the room are also important issues.
