Air Brake System Leakage
When a soap suds check of all coninfections in apparatus air brake systems fails to indicate the source of excessive leak-down, there is one more test that should be made that can’t be made with soap suds, advises Herbert L. Metcalfe, field sales-service engineer in Braintree, Mass., for Peter Pirsch & Sons Co.
In the usual system, Metcalfe says, the check valve between the air compressor outlet and the No. 1, or wet, tank cannot be checked with soap suds. The quickest way to check this valve is to build up the air system to the cut-off pressure, shut off the engine and allow the apparatus to stand for five minutes. Then loosen or remove the tubing nut on the compressor side of the check valve. If there is a continuing air flow, the valve seat is gone. Usually the valve seat is Punched through as though by a doughnut cutter. Replacement of the valve seat is all that is needed, Metcalfe advises.