Chapter 5 – Surge Protection
Surge Analysis and the Wave Plan Method
Supplementary Material: Example Problems and Solutions
Chapter 5 – Problem 5.4
5.4 Consider a hydraulic control valve shown in Figure 5.8. This valve is used as a pressure relief valve on a pipeline system. Suppose the valve is in fully closed position at certain time t and the pilot has just triggered the valve to start opening. The volume of the diaphragm control chamber is 1 liter, the pipe connecting ports C and B is a 1m long 4 mm internal diameter copper tube with a Darcy-Weisbach friction factor of 0.015. The minor loss coefficient for the 4 mm diameter fully open needle valve within the copper tube is 3.
a. If the pressure differential across ports C and B is 5 bar and this differential remains constant throughout the closing cycle, compute the shortest time required to drain the diaphragm chamber effecting the valve opening.
b. If a surge analysis has indicated that the PRV should be opened in 2s to provide the desired level of protection, what changes are needed to the connecting pipe to achieve this?
c. Periodic maintenance of the pilots and the associated tubing is essential to ensure that the PRVs open and close in the desired manner, thus providing relief from extreme pressures. Suppose due to a poor maintenance schedule, there is a 20% increase in the pipe roughness value and the needle valve minor loss coefficient, compute the change in valve opening times determined in parts a and b of this question.
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