Plumbing: Two-Way Check Valve

Two-Way

• Two-way check valves are the simplest valves in terms of design and are also called dual-check valves. These valves are sometimes used to prevent back-flow, but due to their lack of safety features, this is usually not recommended. The two-way models have a valve opening at either end, and their basic construction makes them unsuitable for venting purposes. It is impossible to gauge-test them to make sure they are working properly.

Back-Flow

• Back-flow is contaminated water that needs to be kept out of potable, or drinking, water. As contaminated water flows out for disposal, a check valve ensures that it does not reverse direction in the piping and re-enter as drinking water. A double check valve is recommended for use as a back-flow preventer. In this case it is essential that a two-way valve with extra security in the form of exhaust test ports be used. Keeping back-flow out of homes is a necessary measure for public health and safety.

Two-Way Uses

• Use a two-way check valve in applications where a check valve is not needed for safety purposes. These valves are often used in-line before the home's water meter. The purpose of the check valve in this location is to prevent any back-flow from causing the meter to run backward. A water meter that does this will not give the utility company an accurate measurement of the home's water usage.

Correct Installation

• No matter what type of check valve you choose, it must be installed correctly to fulfill its purpose. This becomes very important when installing a valve as a back-flow preventer. Many valves look similar on both sides. Fortunately, they are usually equipped with arrows on their labels. The arrows indicate the direction of water flow, beginning with inlet and ending with outlet. Match the arrows to the direction the water flows through the pipe.