What valve arrangement is necessary for blowoff piping when the allowable working pressure exceeds 100 pounds per square inch?

In systems where the allowable working pressure exceeds 100 pounds per square inch, the use of two slow-opening valves in the blowoff piping arrangement is essential for safely managing pressure and preventing sudden changes in pressure that could lead to operational hazards. Slow-opening valves are designed to progressively open, allowing for a gradual release of pressure and minimizing the risk of water hammer or other adverse effects that can arise from rapid pressure changes.

The rationale for using two slow-opening valves is to create a double block and bleed configuration. This setup enhances safety by ensuring that, in the event of maintenance or operation, the system can isolate and safely manage pressure. The first slow-opening valve can be closed to prevent backflow, and the second slow-opening valve can be gradually opened to allow safe venting or drainage.

In contrast, quick-opening valves are not suitable for situations where high pressure is present, as they can lead to sudden surges in flow that might be hazardous in a high-pressure system. Thus, using two slow-opening valves aligns with safety protocols and best practices in high-pressure boiler operations.