A stop check valve on a boiler feedwater line is not selected simply because reverse flow is possible. The real question is whether one valve must perform three duties at the same location: allow stable forward flow from the feed pump, close automatically against reverse flow when the pump trips or pressure reverses, and provide a manual stop function when the line or boiler needs to be isolated. ...

Yes, a butterfly valve can control flow and may remain partly open, but only when the valve, actuator and operating range have been selected for throttling service. A line-size on-off butterfly valve held near the closed position can suffer poor control, cavitation, noise, vibration and concentrated seat or disc erosion. Partial opening is not inherently harmful; operating at the wrong opening for...

A wafer ball valve usually fits a tight piping layout better because its body is shorter and lighter than a conventional flanged ball valve. This saves axial space, but the shorter valve may still be difficult to use if there is little room for through-bolts, flange separation, the handle or the actuator. Compare the complete installation and maintenance envelope, not face-to-face length alone. &n...

A plug valve that becomes hard to turn usually has excessive plug-to-seat friction, incorrect adjustment, pressure-related loading, or resistance in the drivetrain. Do not begin with generic grease or more actuator torque. Identify the valve design and determine whether resistance changes with line pressure and valve position.   Identify the Plug Valve Before Treating the Symptom   A lub...