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.
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