Like every other piece of mechanical equipment we use, a control valve does require some maintenance. As budgets are stretched and time is tight, it can be tempting to ignore checking on valves that are often located in underground vaults and give years of operation without complaint, but eventually like everything else, they will fail. This article looks at 8 simple steps that if undertaken occasionally will help to eliminate valve failures that always seem to occur at the most inconvenient times.
Here’s a simple checklist to use every time you look in on a pressure reducing valve:
1. Check for broken or leaking pilot systems
The valve pilot system relies on a supply of pressurized water. Leaks and cracks in a pilot system will certainly have an affect on how a valve operates. Unfortunately the very nature of pilot systems makes them susceptible to damage from simple accidents like tools being dropped to the deliberate notion (which is false), that they could be used as a stepping point! The small bore tube and fittings can break. Over tightening of flare fittings often results in a small crack that overtime will fail. Whenever you visit the valve, take a close look at the entire pilot system. Are the fittings tight? Is there water seeping from a joint? In some parts of the country it is not uncommon to find that the minerals in the water will even wear out copper tubing on the bends. Take a close look and ensure that everything still looks like it will hold pressure. Remember, the pressure you have in the main water line is the same pressure going through the pilot system. Inspect and rectify any potential issues you find.
2. Air in the pilot system
Unlike water, 1 air is compressible and if allowed to remain in the pilot system it will give erroneous readings. The pilot will have trouble maintaining a stable valve and therefore it is generally a good idea to get rid of air that will collect in the pilot system. Air loves to collect at high points and typically that means the pilots and tubing in the control valves. If the valve is installed with a wet type position indicator, you will see air collected in the sight glass and the water level will be part way down the glass tube. There will be either a small plug or bleed valve installed on the top of the indicator and opening or removing this will vent the air. Remember – when venting the indicator you are effectively venting the main valve bonnet so the main valve will begin to open.
3. Dirty strainer
Plugged strainers are common reason that control valves fail. A dirty strained screen is essentially chocking the water supply to the main valve bonnet which means the main valve will either have a lot of trouble closing or may not even close at all. Most strainers are installed with a plug, which allows for a blow down of the screen without removing it. A good solution is to remove the plug and install a nipple and ball valve, which allows for very simple blow down whenever you are around the valve. Usually only a few seconds is all that is required to keep a screen clean.
4. Plugged fittings
Assuming the strainer is clean, don’t assume that everything else in the pilot line will be free and clear. Restriction fittings (those small orifices that all pilot systems rely on), can and do get blocked. Depending on the mineral quality of your water it is possible to have these plugged solid. This either requires the fitting to be drilled out or soaked in a solution to clean them or simply replaced. Typically the latter ends up being the most cost effective choice as time is worth a lot more than having the luxury of messing around with a fitting while you have the water system shut off.
Anytime you have a valve that struggles to open or close and the strainer has been cleaned, and assuming all needle valves etc. are ok, then a plugged or partially blocked line is worth exploring.
5. Worn main valve diaphragms
Main valve diaphragms can last for years. It is all dependent on system pressure, usage and minerals in the water. Generally they do not catastrophically fail instantly unless there is something in the line that does not belong there. Typically diaphragms just wear out over time or due to mineral build up get fatigued. A simple test to ensure your diaphragm is still intact is to 1) isolate the pilot system so no water can get into the valve cover, 2) remove bonnet top plug or open bleed valve on top of position indicator. 3) Main valve will open, discharging all the water in the bonnet as it does so. 4) Once valve is wide open the water should stop flowing. 5) If water continues to flow even with valve wide open, that would be an indication that the diaphragm is leaking. This will require removing the main valve bonnet and closely inspecting the diaphragm.
6. Check the Pilot Diaphragm
Anytime you see water dripping out of the control pilot it is not a good thing. An exception to this would be an altitude pilot, which is installed with a copper tail tube signifying that it is designed to relieve water during valve operation.
However, most pilots are supposed to keep the water on the inside and so if you come across a pilot with water leaking out of a vent hole or through the adjusting screw threads then you have a problem. Make sure that the water is actually running and not simply condensation, a quick wipe with a cloth and a few minutes of observation will confirm a leak.
If water is leaking this is an indication that you have water in the spring casing and that would indicate that you have a problem with the pilot diaphragm. That means you will have to take it apart and replace that part.
7. Pilot not tracking
Pilots typically sit in the same position with very little internal movement for years of trouble free operation. However, just like the main valve, there are things that can cause sluggish behavior or erroneous readings that will affect the system eventually. A simple pilot check is to make slight adjustments to the pressure settings while the valve is in operation. By slowing adjusting the setting screw clockwise and observing the downstream pressure gauge, it is possible to see that 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 psi. Then assuming the pilot has performed this, turn the adjustment screw counter clockwise and lower the pressure past normal set point so the gauge now reads 5 psi lower than normal. Did the pilot and gauge work together? If they did then 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 for some reason the gauge did not track your adjustments then it is time to take a closer look internally at the pilot to ensure that nothing has worn out.
8. Ball valve handles
Firstly, make sure they are open. If a ball valve is supposed to be left closed it will typically have a tag informing you that this is normally a closed valve. It will not hurt to actually give each ball valve a quick turn just to ensure they still move, but ensure you leave them in the same position you find them.
Of course, this is assuming you still have handles on your ball valves. Plated steel handles on ball valves often rust away leaving a valve without any means of closure. Try to ensure you have solid stainless handles on all of your ball valves.
These 8 simple steps can certainly alleviate future problems and if performed at least once will give a benchmark for maintenance frequencies required in your system valves. Unfortunately no two water systems are alike and often even in one network, two valves can require differing amounts of attention. Hopefully these simple steps will allow you to eliminate problems before they occur and focus on all the systems issues that you may be facing.