Plumbing check valve

Plumbing Check Valve

PVC check valves are typical in residential and commercial plumbing systems.

Figure 1: PVC check valves are typical in residential and commercial plumbing systems.

Plumbing systems distribute water from supply to fixtures and remove wastewater and excess rainwater in buildings. Devices like pipes, valves, tubes, tanks, and fixtures are used for all plumbing needs. A plumbing check valve, also called a one-way valve, restricts the flow of media in a plumbing system to one direction. This article explores the various types of plumbing systems and the role of check valves in each kind.

Table of contents


What is a check valve?

A check valve is a device that allows fluid flow only in one direction. The primary purpose of a check valve is to prevent backflow in the system since a contaminated backflow can eventually contaminate the media upstream. For example, a sewer line check valve ensures that waste can leave but not re-enter the system.

Check valves in plumbing systems

A plumbing system is a series of pipes and serves two purposes: to supply water for use and to get rid of waste. There are different types of plumbing systems like sanitary drainage, stormwater drainage, and potable water. Each of these systems has its unique purpose but all require check valves in order to operate correctly.

Sanitary drainage system

A sanitary drainage system helps clear out wastewater from buildings. The system consists of an array of pipes designed to dispose of waste, like food or laundry detergent, down the drain. The waste is transferred to a local sewer system once it enters the pipes. Cast iron, PVC (Polyvinyl chloride), and chromed brass are used as plumbing materials for sanitary drainage systems.

Special check valves called backwater valves are installed where the building's wastewater enters the municipal sewer. A backwater valve has a hinged disc that rests in the vertical position when wastewater is not flowing through it. When wastewater flows, its pressure pushes the disc open so the wastewater can flow to the sewer system (Figure 2 left). When the wastewater flow diminishes, the disc returns to the vertical position (Figure 2 right). This prevents wastewater or other material from the sewer returning into the building's plumbing system.

A backwater valve in the open position (left) when wastewater flows to the sewer and the closed position (right) when wastewater is not flowing towards the sewer.

Figure 2: A backwater valve in the open position (left) when wastewater flows to the sewer and the closed position (right) when wastewater is not flowing towards the sewer.

Stormwater drainage system

Storm drains are used to carry excess water from a house. As seen in Figure 3, they are grated openings next to a sidewalk or building. A stormwater drainage system consists of a network of structures and pipes under the ground that carries rainwater to a storm sewer and, after that, to ponds, lakes, streams, and rivers. Copper, galvanized iron, CPVC (Chlorinated polyvinyl chloride), or PEX (Cross-linked Polyethylene) are commonly used as plumbing materials for these systems.

In urban areas, stormwater can overload sewage systems, causing flooding and backflows. Check valves prevent contaminated wastewater from flowing back and contaminating clean water supplies. Duckbill check valves are typical in stormwater drainage systems. This valve is composed of a flexible elastomer material that is molded into a bill-shaped configuration, which prevents the flow of fluid by sealing against a seat when the pressure on the inlet side is lower than the outlet side. Duckbill check valves are ideal for stormwater drainage systems for the following reasons:

  • Shape: The valve's bill-shaped design allows for effective sealing against backflow of water and contaminants, which is essential for ensuring that the stormwater drainage system operates as intended.
  • Material: The flexible elastomer material used in the valve's construction can tolerate the high levels of solids, debris, and pollutants that are often present in stormwater systems, which can cause other check valves to become clogged and fail.
  • Low pressure drop: The valve's low-pressure drop reduces the energy required to move water through the system, resulting in improved efficiency and reduced operating costs.
  • Installation direction: The duckbill check can be installed vertically or horizontally, making it suitable for a wide range of applications.
Stormwater drainage system.

Figure 3: Stormwater drainage system.

Potable water system

Potable water (drinking water) comes from several surface and ground sources and is treated to levels that meet federal and state standards for human consumption. A potable water system usually consists of several pipes connected to the main water supply and individual devices, enabling people to use drinking water within a building. Occasionally, a meter on the line displays how much water is being used throughout the building.

Check valves are not the correct solution for protecting potable water systems that connect to municipal water systems. Backflow preventers, which operate similarly to check valves, offer a higher degree of protection and are required in many places around the world when a building's potable water plumbing system connects with the municipal water system.

In well plumbing systems, a check valve is installed between the incoming water line from the well and the water pump and pressure tank. The valve prevents water from flowing backward out of the pump and water tank back into the well when the pump motor has stopped working. Read our article on well pump check valves for more information.

Plumbing check valve materials

Sanitary and stormwater plumbing materials

  • One factor to consider is where the valve is going to be located. If it is a coastal environment with salty air, make sure to have stainless steel components for the check valve as the material is corrosion free and suitable for marine environments.
  • Typically plumbing check valves are made of PVC or cast iron. PVC is commonly chosen for residential plumbing systems, whereas cast iron is chosen for industrial applications requiring stronger valves with high-temperature resistance.

Flow rate and pipe size

The flow rate and pipe size can be used to calculate the fluid flow velocity as follows:

V = Q/A,

  • V: Fluid velocity
  • Q: Flow rate
  • A: Pipe’s cross-sectional area

Certain check valves have specified flow velocity ranges and head parameters. Hence, if these valves are not sized properly, there may be maintenance issues with the system. Increased flow velocities can cause greater slamming potential or water hammer within the check valves.

A low flow velocity results in the chattering of internal components, causing the check valve's closing mechanism to wear away faster than normal. The valve may barely open under low flow conditions, which can damage the seating components and lead to a shorter lifespan.

In short, a flow velocity too low or too high can damage the check valve within a plumbing system; hence it is crucial to get a valve that fits the flow rate and pipe size. Always select a check valve with a broad range of acceptable flow velocities.


What is a check valve in plumbing?

Check valves are installed in pipelines to prevent backflow.

When should you use a check valve on a water line?

A check valve can be used when there is a possibility of mixing different media. The check valve prevents the mixing by preventing the backflow of one medium back into the system.