We’ll need a pipe to get the water from the wellhead to the tank, and on into the house. We’ll need to provide some sort of control to turn the pump on and off. We’ll need to have a pressure gage to know how the system is performing, and a pressure-relief valve to protect the system in case the pump controls fail and the system starts to build too much pressure. Finally, we’ll need a drain valve to drain the tank for servicing. We no longer recommend installing a check valve between the pressure tank and the wellhead – see the paragraph on check valves below. Figure 1 (at right) shows the component layout for a water system with a pre-charged pressure tank.
Solid Setting of the TankThe pressure tank needs to sit on a solid surface. If it is in a basement or garage with a concrete floor, no additional support is needed. If it is outside, some sort of solid pad will be needed. Most pump wholesalers carry either plastic or lightweight pre-cast concrete appliance pads that can be easily carried to the job site, and are much easier to install than pouring a cement pad. They particularly are useful if you are in an area where freezing is not a problem, and the tanks are installed outside where you do not need a big pad for a pump house.
The pressure tank also needs to be accessible for servicing. Today’s pre-charged captive-air tanks are built to last 10 years and longer, but eventually they will need to be replaced, so make sure you leave room to remove the tank.
Plumbing the Pressure TankThe decision as to what type of piping to use – PVC, galvanized steel or copper – depends on local codes and personal preference. I like galvanized steel or copper because it is stronger, and is less likely to be broken if someone kicks it or drops something on it. Many pump installers use PVC in the pump house, and it works fine as long as it is protected from outside forces. It is much faster and cheaper to install. Check your local codes to make sure that the type of piping you plan to use is approved.
The Tank ConnectionSome installers fabricate the tank connections out of galvanized fittings. My preference is to use one of the specialized stainless steel, lead-free brass or galvanized tank tees offered by the water well accessories manufacturers, because they eliminate five or six joints that could leak, and they save time (see Figure 2 on p.18). For future serviceability, be sure to install a union between the tee and the tank or on both sides of the tee, so when it comes time to replace the tank, you don’t have to cut out your old plumbing. It is important that all of the materials used to connect the tank be electrolytically compatible. In other words, if you are using galvanized plumbing, use a galvanized tank tee; if you are using copper piping, use a brass tank tee.
Whether you use a prefabricated or cast tank tee, or make your own, you need to provide four outlets for the following: 1⁄4-inch tap for a pressure gage, 1⁄4-inch tap for a pressure switch, 1⁄2-inch or 3⁄4-inch tap for a pressure relief valve (PRV), and a 1⁄2-inch or 3⁄4-inch tap for a drain valve. You can get a tank tee that has a union going to the tank, with all of these taps included, or you can make the whole thing up with galvanized or copper fittings – your choice.
Pressure Relief ValveThe purpose of having a pressure relief valve (PRV) is to protect the system – and the people and property in the vicinity of the system – from damage should something go wrong and the pump builds up too much pressure. The most common failure that can cause the system to over-pressurize is for the pressure switch to stick in the “on” position. Remember that some submersible pumps, particularly those designed for deep wells, are capable of producing hundreds on pounds of pressure. I have seen pictures of a pump house roof blown off when a pressure tank exploded because the pressure switch stuck, and there was no PRV on the system. Always install a pressure relief valve, and always make sure it is large enough to handle the output of your pump. A 1⁄2-inch PRV is not large enough to protect a 55-gpm pump.
Check Valve IssuesIn earlier articles on this subject, we recommended installing a check valve between the pressure tank and the wellhead, a practice that has been common for years in the ground water industry. However, since sanitary protection should be our primary concern, no belowground potable water line should ever be subjected to a vacuum. With a check valve at the tank, a leak in the drop pipe or any of the in-well check valves would create a vacuum condition that potentially could draw contaminated surface water into the well through a pinhole in the section between the wellhead and the tank. Therefore, we must rely on the in-well check valves to prevent pressure-tank water from draining back into the well when the pump shuts off.
System Isolation ValvesIn order to be able to service the system, without having the water in the house drain back when the plumbing at the tank is opened up, it is a good practice to install a gate valve or ball valve on the house side of the tank tee. Make sure the isolation valve is on the house side of the PRV, and never put an isolation valve between the PRV and the pump.
Finally, you will want to install a union at the wellhead to allow the pump to be pulled without having to cut pipe when it comes time to service the pump.
Next month, we will talk about selecting and sizing submersible pump cable. ’Til then....