Hi Bill,

The PRDS valves (AKA turbine bypass valves) that I am familiar with are in-line valves that are supported via the pipe. Of course it is important to know accurately what the total weight of the unit is so that hangers can be designed. Remember to include the weight of the cooling water piping that is transferred to the valve.

With these valves, the "bore thrust" forces due to internal pressure are self balancing. In a piece of pipe without a valve, the bore thrusts impinge upon components such as elbows and since the thrust is equal and opposite, the forces balance AS LONG AS THERE IS STRUCTURAL CONTINUITY (continuous pipe wall). If there is a structural discontinuity (e.g., an expansion joint interrupts the continuous pipe wall), there would be a pair of opposite forces to be addressed by design. With the PRDS valve in-line, there is a "high pressure (inlet) side and a "low pressure" outlet side but since both the HP and LP impinge upon the PRDS valve and some other component in the opposite directions the pressure remains balanced (discounting the possible structural discontinuity).

It is also important to know if the valve fails open or fails closed. What would happen if the flow of coolant were to be interrupted? Would the steam flow be shut down by the valve or would the downstream piping be subjected to higher than design pressure and temperature (expansion)? Just something else to think about.

DeZurik, Copes-Vulcan has an interesting Bulletin (Bulletin 1163 in PDF form) on the internet at:

http://www.dezurik.com/Literature_PDF/1163.pdf

What do the rest of you folks think?

Best regards, John.