A standard method for instrumenting a control valve is termed the “double block and bleed,” which is illustrated in Figure P1.22.

Under normal conditions, valves a to c are open and valves d and e are closed. Answer the following:

• Explain, carefully, the sequence of opening and closing valves required in order to change out the valve stem on the control valve (valve b).
• What changes, if any, would you make to Figure P1.22 if the process stream did not contain a process chemical but contained process water?
• It has been suggested that the bypass valve (valve d) be replaced with another gate valve to save money. Gate valves are cheap but essentially function as on-off valves. What do you recommend?
• What would be the consequence of eliminating the bypass valve (valve d)?

Transcribed Image Text:

a Gate Valve Globe Valve d 오무 Control Valve e Gate Valve Chemical Sewer Figure P1.22 Double Block and Bleed Arrangement for Problem 1.22