Tips & Tricks

1. If you are dealing with a corrosive fluid, choose the valve body and trim material to match the pump casing and impeller. 

2. Velocity is the key to handling abrasive materials. Normal city water velocity is about 7 to 10 F.P.S. (clean liquid). If you have a fluid that is abrasive, keep the velocity as low as possible - without having the particles drop out of suspension. 

3. Always sense pressure where you want to control it. Many control valves and pressure regulators do not function properly simply because they are sensing pressure at one point and being asked to control it somewhere else. 

4. Velocity is the key to handling noise. Noise is energy. When dealing with high pressure drop situations try always to keep the velocities below 0.3 mach. on the inlet pipe, valve body, and outlet pipe. 

5. If you use a transducer in a control loop, specify a positioner on the valve. Otherwise the transducer will rob the actuator of available thrust, and the valve will leak when it is supposed to shut off. 

6. In cavitating fluids - even if the control valve has cavitation trim in it - be sure to allow a straight run of downstream pipe after the valve. If there is a pipe "T"or elbow immediately downstream, the flow will choke out and back up into the valve. 

7. If you use a control valve with a bellows seal in it, try to size the valve so that its normal throttling position is near the bellows "at rest" position. This will minimize wear on the bellows. 

8. Don't use a valve below 10% of flow if at all possible. Even though a valve may have good rangeability, if the valve is used in an abrasive or erosive service (steam), it will not hold up unless it has hardened trim. 

9. If a PLC is being used to control the valves in a system, specify the valves with a linear flow characteristic. 

10. If a control valve is started up and fails to respond - or goes to full open or full closed and stays there - check the controller and reverse the controller's action.