Water check valves are one of many manifestations of the popular and highly useful check valve, a valve that oversees and ensures unidirectional fluid flow. Water check valves are much like their cousins, but instead of controlling the flow of any liquid or gas, water check valves work only with water. Water check valves are essentially backflow prevention devices, meaning that they prevent water from flowing in the wrong direction and causing malfunction. In the case of potable water, backflow is especially dangerous because it could cause pollution or contamination. Water check valves are used in a variety of systems, such as fire hydrants, dishwashers, irrigation systems, water mains, domestic and commercial washing machines, plumbing systems and rainwater harvesting systems.
Generally speaking, most water check valves are composed simply of an inlet port, an outlet port and a stopper mechanism. To work, water flows in through the inlet port, where it puts forward-direction pressure on the valve. A properly functioning valve will respond by allowing the stopper mechanism to displace slightly. It will only open in one direction; the pressure from a flow from the other side, rather than opening it, will create an airtight seal by pushing the stopper back into its hole, and the valve will only open again when the forward pressure is greater than the back pressure.
To accommodate the diverse applications that they serve, water check valves come in a variety of sizes and styles. The diameter of the stopping device, which may be a ball, a piston or a disc, is very important in terms of to what it is mounted; if the passageway to which the valve is mounted is smaller than the valve, it cannot be used. Thus, customers must take special care to note diameter sizes when they are shopping for valves for their applications. Common styles incorporated into the water check valve world include ball valves, diaphragm check valves, tilting disc check valves, stop-check valves, lift-check valves, inline check valves, duckbill valves and pneumatic non-return valves. Ball check valves are water check valves that have a spherical ball for their closing member, or movable part that blocks the fluid flow. Some ball check valves are equipped with a spring loading mechanism, which helps hold the ball in place. For those ball check valves without this mechanism, the valve is kept shut by a reverse flow that keeps the ball at the seat and sealing it. Next, diaphragm check valves are normally closed valves that stay closed using a flexible rubber diaphragm. To work, it is essential that pressure on the upstream end be greater than pressure on the downstream end by an adequate pressure differential, or certain amount. When the pressure is high, the valve opens, and when it is low, it closes. Tilting disc check valves, also known as swing check valves, are water check valves that are equipped with a disc, or movable component that blocks water flow, that swings on a trunnion or hinge. The disc either swings off the seat to permit forward flow or swings onto the seat to obstruct reserve flow. A prominent and relevant example of this type of water check valve is the flapper valve found connected to toilet flush lever. Likewise, clapper valves, another variation on tilting disc check valves, are water valves found in firefighting applications. Still another is the backwater valve, which are used in sanitary drainage systems to block the backflow, or return flow, of sewage water. The next type of water check valves, stop-check valves, are valves are designed with override control so that they can stop water flow at any time, no matter the direction of the flow nor the pressure of the flow. This can be done by an external mechanism. In addition, stop-check valves also engage in normal check valve behavior, as they can automatically close in response to inadequate forward pressure or return flow. Following this, the lift-check valve is a water check valve in which the disc, also known as the lift, may be displaced and lifted up off its seat. This displacement is typically either caused from higher pressure from the inlet, or upstream, fluid. When the disc is lifted, it is allowed to flow to the outlet, or downstream, side. It is held in on a vertical line by a guide, which ensures that it is later able to return to its seat. This return takes place when the pressure lowers and lowers the disc down with it. When the valve is on its seat, reverse flow is disallowed.