Design Pressure and Surge Pressure

Water Hammer derating is commonly used in hydraulic systems so yes you need to derate for additional pressure you expect to encounter.

If you are moving water, then instal pilot operated relief valves (Cla-Val) at the 1/3 and 2/3 points along the pipe. Set them to open at 10 psi over operation pressure. The impulse addition of a water hammer caused by surge is trying the stretch the pipe and the pipe will expand. The valves leak away the small amout of water this impulse requires and the resulting surge pressure is dramatically reduced (+25 psi). It operates much like a surge tank but it is cheaper and it won't break or fill like a tank. I did this for a 20" water pipe that is Eight miles long that had a history of breakage for this same reason. No more breaks or surges. The first valve is sized to discharge the entire pumped flow without damage to the pump or motor just in case the pump turns on a gainst a closed valve. I know it is overkill but it made the system entirely safe.

what is the fluid?

try this www.masterplumbers.com/plumbwatch/pipes99/waterhammer.doc

The fluid is WATER

Yes, you have to add the maximum surge pressure that can rise in pipe system. max. surge pressure=design pressure. It is better to calculate the (not 100% accurate value at first) rise of pressure. Try to find something on the net for quick calculations o surge pressure

Hi.

If the maximum surge pressure = design pressure, then it will be very high.

However, based on ASME B31.3, the Code allows for pressure variation such that it can go beyond the design pressure by 33% for 10 hours per event or 100 hrs per year.

Rgds,

Chan