Under-sink shutoff valves, also called fixture shutoffs or stop valves, allow you to turn off the water to the sink (or other fixture) without having to use the home's main shutoff. These inexpensive little valves rarely get used, and when they do, sometimes they leak. If this happens to you, you can simply replace the valve with a new valve that matches the old one. Identifying which type of valve you have is a good first step in replacing it.
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Straight Shutoff Valve
Straight stop valves are typically found when the water supply pipe comes up from below the floor or cabinet. The fixture supply tube connects to the top of the valve in the same line as the supply pipe. The handle of a straight stop is located in the middle of the valve body, between the inlet and outlet ports.
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Three-Way Stop Valve
Three-way stop valves have an inlet and two outlets. These are often seen under kitchen sinks, where they are used to feed both the hot tap of the faucet as well as the dishwasher. Three-way stops can come in a few different configurations. Some are cross-shaped and have the two outlet ports facing in opposite directions, some have outlets in an "L" configuration, and some have outlets in a "Y" configuration.
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Compression Shutoff Valve
Compression stop valves are most commonly used to install a shutoff valve on rigid copper pipe. This type of valve has a brass ring, called a ferrule, and a compression nut that squeezes the ferrule into the pipe connection to make a watertight seal. Compression valves are easy to install with just a pair of pliers or wrenches. You can also remove them and reuse them. Sometimes it is hard to get the old nut and ferrule off of the pipe; in this case, you can remove them with a compression sleeve puller.Continue to 5 of 9 below.
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Copper Sweat Stop Valve
"Sweat" is a plumber's term for soldering. A copper sweat valve is designed to be sweated, or soldered, to a rigid copper pipe. This requires soldering tools, such as a torch, flux, emery cloth, and solder. Sweat valves are not easily removed once they are installed because they have to be heated to melt the solder so you can pull the valve off of the pipe.
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Iron Pipe Stop
Iron stop valves have a threaded female inlet port with iron-pipe-size threads. This type of valve is commonly found on galvanized or brass threaded pipe, but it can be adapted to other types of pipe by using a male iron pipe adapter that connects to the pipe and then screws into the shutoff valve.
Iron pipe valves simply screw and unscrew from the end of the pipe. The only tools required are two pliers: one to hold the pipe in place, and the other to tighten the valve.
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PEX Shutoff Valve
The shutoff valves used for PEX tubing have a ribbed inlet port for inserting into the tubing. This type of valve works with either ring-type or pinch-type PEX clamps. Although PEX tools are required for installation (as opposed to push fit valves), these are often the easiest and cheapest way to go, especially if you are already using PEX clamps or pinch rings.
PEX stop valves can be removed, but you have to cut off the ring. This often results in damage to the pipe, which usually means the pipe needs to be shorted to get fresh section of pipe for the new valve.Continue to 9 of 9 below.
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Push Fit Shutoff Valve
Push fit, or push-in, shutoff valves are very easy to install and can be used with copper, PEX, and CPVC pipe. These valves simply push onto the pipe. The valve grips onto the pipe with metal teeth and creates a watertight seal with a plastic O-ring. They are also removable, using a simple tool sold by the manufacturer.