What is the maximum allowable blowback on a safety relief valve set for 100 psig?

The maximum allowable blowback on a safety relief valve is an important consideration for ensuring the proper functioning and safety of boiler systems. For a safety relief valve set at 100 psig, the accepted industry standard is that the blowback, which is the difference between the set pressure and the actual pressure the valve may reach during operation, should not exceed 4 psi.

This means that when a safety relief valve that is set to open at 100 psig is subjected to system fluctuations, it may safely experience pressure fluctuations up to 104 psig before being considered out of compliance. Operating beyond this limit can lead to safety risks and potential damage to the boiler and associated systems.

In this context, the other options represent pressures beyond that 4 psig threshold, potentially causing unsafe conditions. Thus, the determination that 4 psig is the correct answer stems from established safety practices designed to maintain effective operation of safety relief valves within acceptable safety parameters.