A useful guide for control valve maintenance and operating performance
Whether that brand new control valve in your system is the first one you have ever had to look after or if you are an old hand at valve maintenance with tens of valves in your system, there are a few simple guidelines and reminders for keeping your control valves operating at optimal performance.
1. Regularly inspect your control valves
It is important to physically inspect your valve(s) at least every 12 weeks or so. This inspection is really to check for any leaks in the tubing, check pressure gauges to ensure the valve is actually doing what it is supposed to and generally inspecting for anything that just looks abnormal.
If it is determined that something is wrong, always ensure you have the correct instruction manual for the valve. These days all manufacturers have these available on their websites. As a note of caution, these valves are under pressure and care should be taken to bleed pressure off the valve before you start to take any valves apart.
Pilot system shut off ball valves
Exercise the three isolating cocks on the main valve. These are located in front of the strainer on the upstream side of the valve, on the valve bonnet on top of the valve, and below the pressure-reducing pilot on the valve downstream. Giving the isolating cock a momentary quarter turn to the closed position, then returning it to the open position is sufficient. Open position is when the handle of the isolating cock is inline with its body.
Air in the Pilot System
Air is your number one enemy in the pilot system as it will give false readings and cause poor valve operation. Bleed air from the valve bonnet. If the valve is equipped with a position indicator, on top of the position indicator is a bleed cock. Open the bleed cock slightly by turning the handle counter-clockwise. Otherwise, bleed the air from the high point of the valve. If the water runs clear, and no air bubbles are seen in the glass of the position indicator close the bleed cock. If air is present (the water will be foamy white) run the water until the air is gone.
Pilot systems rely on a supply of clean water, usually taken from the inlet of the valve. Either external or flush clean type strainers can be installed. If an external strainer is installed a simple occasional flush is a good idea. Normally 3 – 5 seconds is sufficient time to clean the strainer screen. Experience will dictate if it needs to be flushed longer than this, but it is unlikely in a municipal system. A number of water utilities install a ball valve on the flushing plug of the strainer, allowing operators to give a short flush everytime they are in the valve station. (This certainly helps to eliminate those problem calls later as a plugged strainer causes a valve to remain open!)
Ensuring the control valve pilot is still operational is a simple task. As a cautionary note – before you make any pressure adjustment, ensure that this is acceptable for the system and any SCADA alarm controls that may be triggered by a change in pressure. To exercise the pressure-reducing pilot, loosen the lock nut on the pilot adjusting screw and turn clockwise to increase the pressure 5 psi above the normal set point. Check that the downstream pressure gauge is tracking the adjustments you are making. Then turn the adjusting screw counter-clockwise to reduce the pressure to 5 psi below the set point. Does the pressure gauge track this also? Finally, turn the adjusting screw clockwise to increase the pressure back to the original set point, and tighten the lock nut. If for some reason the pressure gauge is not moving as you adjust the screw, you either have a bad gauge or a pilot that needs looking at.
Check main valve flows
Just like we all like to take our cars out for an occasional run to give them a good workout, the valves also need to see some decent flow occasionally. During a major fire flow is not a good time to find out your main valve will not open fully.
Get some flow through the valve station to open the the peak demand/fire-flow valve. (This could be as simple as opening a hydrant on the outside of the valve station). If you have stations or vaults that have two valves in in parallel, with one valve handling normal flow and the other valve handling large or fire flows, the larger valve should be operated for a minimum of 5 minutes. This can be done by closing the isolating cock on the downstream side of the smaller valve pilot system (the cock below the pressure-reducing pilot). This will close the smaller valve and cause the larger valve to open and allow flow into the system. The above four steps can be followed for the larger valve while it is in the flowing mode.
This is also a good time to ensure the main line control isolating valves are in good working order. The gate or butterfly valves used to isolate the control valve should also be checked to ensure they are operational if they are needed.
By following this simple routine your valves should give years of trouble free service. Of course such variables as pressures, operational use, water quality (hardness, TDS etc.) all have an effect on the periods between major valve overhauls.
Information was taken from www.singervalve.com in producing this tutorial article.
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