ACCUMULATION OF PRESSURE TEST - BOILER

ACCUMULATION OF PRESSURE TEST  ( BOILER)


1. Classification societies require that when initially fitted to boiler, safety valves must be subjected to an accumulation of pressure test to ensure the valves are of correct discharge capacity for the boiler. 

2. To conduct such a test, all feed inlets and steam outlets to and from 
the boiler respectively, must be closed, and maximum firing rate arranged.

 3. Accumulation of pressure must then not exceed 10 % of the working pressure. 

4. Duration of test (water permitting) is not to exceed 15 minutes for cylindrical boilers and 7 minutes for water tube boiler. In the case of water tube boilers the test may be waived if damage to superheaters or 
economizers could result from the test. 

5. The safety valves must be capable of releasing the maximum amount of steam the boiler can evaporate, while still keeping within the 10 % accumulation of pressure rule. 

6. This rule is necessary because having calculated the cross sectional area for the valve bore, the valve lid must be able to lift at least ¼ of the valve bore in order to provide full steam flow.

7. However as the valve lifts, the force to compress spring also increases, and so the  higher the valve lift the greater the increase in boiler pressure. 

8. The Classification Societies limit this accumulation of pressure to 10% of the maximum allowable working pressure for  the boiler.

9. This means that the lift of an ordinary spring-loaded mitre valve, although mechanically able to lift D/4, would be very limited under these conditions, and the valve would have to be very large to give the required throughput.

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