Keeping Control Valves and Actuators in Healthy Condition

The control valve operates a flowing fluid, such as gas, steam, water, or chemical to take care of the load disturbance and keep the regulates as close as possible
1.0) General Thumb rules to keep Control valves & Actuators in Healthy Condition
1) Keep valve Stem Polished without any abrasions. This is to prevent any gland leakages.
2) Keep minimum Clearance between Valve plug & the guide bushing. This will avoid any Plug Vibrations.
3) Gland leakages are common in steam valves due to high temp. & Pressure ,Saturation & Temp gradient between Body & Gland area . Greasing the gland area will help greatly. Keep the greasing valve in place. Do not just plug the Greasing inlet.
4) Generally, valves are selected with flow tending to open. This is to have a stable valve.
5) Sometimes the line vibrations create Pneumatic leakages. Try using Flexible Pneumatic Hoses instead of stiff tubing.
6) It is a good idea to paint the valves with different colors to differentiate between air to close / Air to open / Shutdown valves.
7) Reversing of valve actions can be carried out at Positioner / DCS such that uniform signal of 4-20 ma will go on the valve i.e. 4 ma ---0% open & 20 ma --- full close. This is to avoid any confusion by Inst. Tech.
8) Similarly, split ranging can be done at DCS level. Signal on the valve will be uniform 4 – 20 ma
9) SOV Monitoring can be done by monitoring the section currents periodically. If any significant increase is observed in any section, individual section currents can be monitored. Increase in SOV Current indicates the weakening of Insulation.
10) The air filter regulator output setting should be done as per Manufacturers' Recommendations. Higher value can affect valve operation time. The lower value can affect valve operation itself. 11) ‘Unit spare valve’ strategy could help in reducing shut downtime requirement. It also allows more time for the valve under maintenance.
11) Typical flashing and cavitation services can be handled by choosing special trims, higher body size, superior body and trim material.
12) Some valves are prone to erosion even after taking control measures. Installed parallel spare valve could be a handy strategy.
13) Balanced design trims in control valves help in achieving lower actuator size but the need for the sealing ring can prove to be costlier and less reliable performance of the valve due to its leakage through seal ring.
14) Control valves in Chlorine and Phosgene services require “euro color ” grade which is of the higher specification in terms of body thickness bonnet gland packing design.
15) Surface hardening techniques are used for mitigating eroding services like flashing or fluid containing solid particles at high velocity. Stelliting of trim parts, nitriding, ceramic coating, tungsten carbide application etc.

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