Chapter 10: Heating and Purifying Water Check valves: These valves allow fluid to flow in only in one direction. The most common are swing valves, which have a little gate that swings like a dog door that’s constrained to only one direction. The best ones are made of bronze, and they’re very reliable. Because the gate is gravity forced, swing valves only work when they’re horizontal or tilted upward. Don’t use spring check valves; they load pumps too much, which constricts flow. Pipe unions: These connectors join two pipes without solder or permanent connection. Pipe unions are commonly used to interface with all collectors, so you can remove the collector from the system for servicing or replacement without having to cut pipe. Drain valves: Drain valves are part of every solar water system because they are the means to drain the fluid out of the system (maintenance, weather safety, and so on). Ball valves are most reliable; they use a spinning ball with a big hole, constrained in a socket. They’re either on or off. Gate valves (such as the faucets used on your backyard hoses) have a twist handle that regulates the amount of flow by means of a gate lowered into the fluid path. People don’t use them much on solar heating systems because you rarely want a valve that’s partially open. Relief valves: These valves protect against pressure buildup (on the top of your water heater you’ll likely see one). They’re required for every closed loop system (see the earlier “Exploring Water Heating Systems” section). Be careful; relief valves can pop open at any time, and they spray the area with whatever’s in the pipes or tank they’re protecting. If they’re on a hot water tank, it’s going to be hot water. If they’re in a solar system, the hot water may be super heated. In general, always use a drainage tube with a relief valve so that if the valve does open, you channel the flow to a safe location, such as under an enclosed porch. Tempering valves (mixing valves): These valves have three ports: cold in, hot in, and mixed output. A twist handle controls the output temperature at your faucet. Tempering valves provide very important anti-scald protection and are always part of solar water heating systems. Don’t be cheap here! Motorized valves: These valves are controlled electrically. They can be either off-on or proportional (a mixture of off and on, or an ability to control the amount of flow). The type chosen is a function of the application. For example, in most system applications, off/on is all that is required, and these valves are cheaper and easier to operate.
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