Control valves are responsible for keeping and maintaining variables such as pressure, flow etc., within the required optimal operating range. Control valves also reduce wastage, thus increasing energy efficiency. They also improve profitability and environmental sustainability. However, control valves are often overlooked and not adequately maintained despite providing enormous benefits. Faulty control valves can cost the business a considerable amount of money and may also cause a shutdown of operations. Here is a definitive guide for the selection, maintenance and repair of control valves:
It is significant to note that a majority of control valves in use today are oversized, which undermines the purpose of the control valve in controlling the variables affecting an operation precisely. Control valves must operate over a wide range of flow, exhibit shorter dead time, and respond with a high stroking speed to be suitable for the operation. The faster a control valve responds to minor changes, the better a process can be controlled. The sizing of the control valve is significant; an undersized valve doesn’t have the capacity to handle the required flow, while oversized valves are sensitive and challenging to get the required objectives. When selecting a control valve, the rule of thumb is to choose the size, so it operates at 80% of the required flow rate.
Period inspection and maintenance of control valves are a must for optimum performance. Check the control valve for air or fluid leaks and loose bolts. They should also be inspected periodically for any abnormal sound, vibration, or other damage signs. The routine maintenance procedure includes cleaning the control valve to ensure that there is no trapped debris or dust, lubricating to ensure smooth operation of moving parts and tightening other control valve accessories to minimize leakage. Standard tests like closure tests, stroke tests, and auxiliary piping inspection are done to decrease the chances of future failure or damage. A stroke test is generally conducted under full flow conditions to discover any leakages; in ideal conditions, the control valves must have zero leakage. Stroke tests are performed to ensure the control valves operate smoothly under adverse environmental conditions by exposing them to strokes under full flow conditions. Periodic inspection should also be extended to auxiliary piping systems to find any scaling, rusting, pressure damage, bending bowing or loose connections.
There are several instances where the control valves might need a replacement or repair. Some of them are – when the valve leaks internally beyond its allowable range, when it leaks externally and when the control valve fails to perform. To repair your control valves, close the system’s flow and depressurize it. After that, dismantle the control valve from the system by dismantling all the electric and pneumatic connections. After that, inspect your control valve and replace the damaged parts with spare parts or replace it. You must remember to calibre the control valve for optimum performance after installation.