How Reliable Is Your Control Valve 
Maintenance Program?

All mechanical equipment requires maintenance, and control valves are no exception. With the guidance of a regular maintenance plan, you should be checking for leaks in the tubing, monitoring pressure gauges and inspecting equipment for any abnormalities. In most cases, this process should only take 20 to 30 minutes—a small price to pay for peace of mind. In case a problem is detected, always have the correct instruction manual for the valve. Today, many manufacturers provide these on their websites, which operators can access from a mobile device. The following guidelines can help you keep your valves operating at optimal performance. As a note of caution, valves are under pressure, so be sure to bleed pressure off the valve before taking any valve apart.

Ball Valves

Plated steel handles on ball valves often rust away and leave a valve without means of closure, so try to ensure that you have solid stainless handles for longevity. Ensure that ball valves are open. If a ball valve is meant to be left closed, it will typically have a tag to inform you of that. Give each ball valve a quick turn to ensure it still moves, but leave them in the same position you found them.

Pilot Systems

Pilots typically sit in the same position with little internal movement for years of trouble-
free operation, but certain factors 
can cause sluggish behavior or flawed readings. To check your pilot, make slight adjustments to the pressure settings while the valve is in operation. By slowly adjusting the setting screw clockwise and observing the downstream pressure gauge, you can see if the pilot still has operation of the valve. A small move on the adjustment screw should be seen on the pressure gauge needle. Increase the setting by approximately 5 pounds per square inch (psi). Then, assuming the pilot has performed this, turn the adjustment screw counterclockwise and lower the pressure past the normal set point so the gauge reads 5 psi lower 
than normal. Did the pilot and gauge work together? If so, slowly bring the pressure back to normal by turning the adjusting screw clockwise and setting the lock nut. This simple exercise proves the pilot is still working and controlling the valve. If the gauge did not track your adjustments, then take a closer look internally to ensure that nothing has worn out in the pilot. Another thing to look for is pilot diaphragm leakage. If your pilot has water leaking out of a vent hole or through the adjusting screw threads, you have a problem. First, make sure that the water is not just condensation by wiping the water with a cloth. If after a few minutes it starts to drip, then you know you have a leak. Water leakage indicates that you have water in the spring casing; that means there is a problem with the pilot diaphragm. If this is the case, you will have to take it apart and replace that part. The one exception where a leaking pilot is acceptable is for an altitude pilot, which is installed with a copper tail tube designed to relieve water during valve operation, so water will drip 
from it. Leaks and cracks in a pilot system will also affect how a valve operates. Because the valve pilot system relies on a supply of pressurized water, it is susceptible to damage from simple accidents. Over-tightening of flare fittings often results in a small crack that, over time, will cause failure. When you check the valve, look at the entire pilot system to see if the fittings are tight and to ensure that no water is seeping from a joint. The small bore tube and fittings can also break. In some areas, minerals in the water will wear out copper tubing in the bends, so make sure the system looks like it will still 
hold pressure. Air rises to collect at high points, which are usually the pilots and tubing in the control valves. Air is also compressible and, if allowed to remain in the pilot system, it will alter readings and lead to instability. If the valve is installed with a wet type position indicator, air will collect in the sight glass, and the water level will be partially down the glass tube. The small plug or bleed valve installed on the top of the indicator can be opened or removed to vent the air. When venting the indicator, you are venting the main valve bonnet, so the main valve will begin to open.

Strainers

A plugged strainer screen will choke the water supply to the main valve bonnet, causing the main valve to have trouble closing or not close at all. Most strainers are installed with a plug, which allows for a blowdown of the screen without removing it. Remove the plug and install a nipple and ball valve, which allows for simple blowdown. Keeping a screen clean usually takes just a few seconds.

Fittings

Depending on the mineral quality of your water, restriction fittings—small orifices that all pilot systems rely on—can also get blocked. Clear them by drilling them out, soaking them in a solution or replacing them altogether. If you have a valve that struggles to open or close and the strainer has been cleaned—and assuming all needle valves are functional—a plugged or partially blocked line could be the problem.

Valve Diaphragms

Main valve diaphragms rarely tragically fail unless something is in the line that does not belong there. They typically wear out over time or get fatigued because of mineral buildup. A simple test can ensure that the diaphragm is intact. First, isolate the pilot system so no water can get into the valve cover. Then remove the bonnet top plug or open bleed valve on top of the position indicator. The main valve will open, discharging all the water in the bonnet as it does so. Once the valve is wide open, the water should stop flowing. If water continues to flow, the diaphragm is leaking. This will require removing the main valve bonnet and closely inspecting the diaphragm.

Take the Maintenance Test

Download the test here to see how your control valves score.