What is the allowable tolerance for a simmering boiler safety valve, assuming it is not at boiler operating pressure and is less than the blowdown?

The allowable tolerance for a simmering boiler safety valve, when it is not at boiler operating pressure and is below the specified blowdown, is established as 1.5% of the lifting pressure. This standard is in place to ensure that safety valves function correctly and reliably without allowing excessive pressure build-up which could lead to dangerous situations. The 1.5% tolerance provides a balance between operational safety and the precision necessary for the valve's performance.

The tolerances mentioned ensure the safety valve's proper functioning within acceptable limits while accommodating minor variations. In practice, having a defined percentage allows for consistent maintenance and testing protocols that ultimately contribute to the safety and efficiency of the boiler system.