Don’t Let Your Control System Control You
Regular maintenance ensures valves remain healthy. If your system is operating properly, you should physically inspect all valves at least every 12 weeks to check for tubing leaks and other abnormalities. Pressure gauges should be checked to ensure each valve is performing as designed. If you find something wrong, refer to the appropriate instruction manual, which may be available online.
Because valves are under pressure, care should be taken to bleed the pressure before a valve is taken apart. For example, in a 6-in. valve with 100 psi in the line, at least 2,800 pounds of force is trying to push off the valve cover.
Pilot System ShutOff Ball Valves
Exercise the main valve’s three pilotisolating valves, which are located in front of the strainer on the upstream side of the valve, on the bonnet over the top of the valve, and below the pressure-reducing pilot on the valve downstream. Turning the isolating ball valve a quarter turn to the closed position and returning it to the open position is sufficient. In the open position, the isolating valve’s handle lines up with its body.
Air in the Pilot System
Air, the pilot system’s primary enemy, causes false readings and poor valve operation. Bleed air from the valve bonnet. If the valve is equipped with a position indicator, a bleed cock will be located on top of the position indicator. Open the bleed cock slightly by turning the handle counterclockwise.
If the valve doesn’t have a position indicator, bleed air from the valve’s high point. If the water runs clear and no air bubbles are seen in the position indicator’s glass, close the bleed cock. If air is present, indicated by foamy white water, run the water until the air dissipates.
Pilot systems rely on a supply of clean water, usually taken from the valve inlet. External or flush clean strainers can be installed. If an external strainer is installed, an occasional flush is a good idea. Cleaning the strainer screen for 3–5 seconds is usually sufficient. After you’ve gained some experience, you’ll know whether flushing should be conducted for a longer period.