Check valve

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industrial non-return valves made of a nickel alloy

A check valve is a component that allows a fluid ( liquid , gas ) to flow in only one direction.


Non-return valve, schematic diagram

In the case of spring-loaded check valves, the closing element is closed in one direction by the spring, while in the other direction it is released by the pressure of the flowing fluid. Either a ball , a cone , a flap or a membrane is pressed into the respective seal seat . Is in the forward direction , a pressure of which can overcome the restoring force of the spring, the sealing element is lifted from the seat and the flow is free.

In the case of non-return valves without a spring, the sealing element is pressed into the sealing seat either by gravity or the flow pressure of the flowing fluid.


According to function

  • Backflow preventer or backflow preventer - general designation e.g. B. with device connection valves for connecting a dishwasher or a washing machine, in order to prevent water from flowing back from the connection hose into the drinking water line when the water is shut off.
  • Convection barrier, convection brake, gravity brake - in contrast to the backflow preventer, mostly easier to move (corresponds to a lower pressure loss through the valve), since it is not relevant to safety; also with slight, planned leakage:
    • to enable pressure equalization in the blocking direction (e.g. in the event of slight volume changes due to temperature differences)
    • to allow air bubbles to pass through in the direction of flow, while at the same time preventing thermal convection.

According to type

  • Non-return valve - application e.g. B. as a gravity brake or backflow preventer in the heating circuit and hot water circulation as well as a backflow preventer in the domestic sewage system
  • Check valve, in two designs:
    • Non-return valve - also common in building installations in combination with an angle seat valve or free- flow valve (= KFR valve ). or as a filter-pressure reducer-backflow preventer combination, as well as spring-loaded and in an inverted installation eye as a flow monitor in the gas installation and as a water stop (hose burst protection) on household appliances
    • Ball check valve


Check valves

Check valve for use in infusion therapy
  • simple, with two straight olives, entirely of glass found in the laboratory using
  • after Friedrichs-Antlinger made of glass, with exchangeable valve cone made of plastic
  • sterile check valve made of plastic for infusions
  • Check valve, built into the water jet pump

Ball check valve


Ball check valve

The ball check valve consists of a constriction that is closed by a ball. The ball is pressed onto the constriction by gravity or a spring and closes the passage. The medium cannot flow through. Such valves are usually hermetically sealed in the blocked direction .

If the medium presses against the force of gravity or the spring on the ball from below and the force of the medium on the ball outweighs the force of the spring, the medium can flow through the valve.

Check valve, unlockable

Special check valves can be released in the blocking direction. To do this, either a bypass is opened or the movable sealing element is (mechanically) held back from the seal seat to allow free flow in both directions. In contrast to some other controllable valves (directional control valves), the valve is absolutely tight in the "locked position" and can thus handle loads such as B. keep hydraulic cylinder safe or close the weight of the sealing element. A typical application is the hydraulic jack. The check valve holds the load securely. The hydraulic piston can only move back when the bypass valve is opened.

Non-return valve

Schematic diagram of the non-return valve - the flow of liquid pushes the plate to the left, which releases the flow opening
Non-return valve for water pipes

In the case of a check valve, the flow of the medium, gravity or a spring ensure that the valve is blocked. The sealing body is designed in the form of a flat plate or a plate. A bolt or pin is used for guidance. An example of the application of this type of construction is the bicycle flash valve or the valve on car tires .

Convection lock, convection brake, gravity brake
Convection brake for installation in a 1 "pipe union,

This special form of the non-return valve is used in thermal solar systems , hot water, heating and ventilation systems, where it prevents unwanted free convection within the system and thus heat loss (e.g. when there is no solar radiation or within parked system parts). These check valves are usually designed in such a way that they offer little resistance to the volume flow and are not completely tight against the direction of flow, in order to enable volume equalization during cooling and, in the case of liquid media, the passage of gas bubbles (so-called air lock).

Non-return valve, backflow valve

Non-return valve, schematic diagram

For liquid media, medium nominal sizes (approx. 80–600 mm) and all pressure levels (up to 600  bar ), simple, deadweight-controlled non-return valves are often used. They are manufactured with flange or welding ends and are usually made of cast iron , cast steel or forged steel .

Check valves differ from poppet valves in that the sealing element is rotatably mounted on one side, while it is axially guided in poppet valves.

Non-return valves are used in sewer pipes (underground pipes ) of buildings if there are drainage objects below the backflow level, in order to prevent dirty water from being pushed back into the domestic sewage pipes when the public sewer system is overloaded .

Non-return valves are occasionally installed in the heating flow and in the hot water circulation line behind the pump to prevent the hot water from flowing back.


Check valves on a fire department monitor
  • In the strainer to firefighting pump, a check valve prevents the suction hose is idling, when the pump is not in operation.
  • Noticebolts at drop jacket hydrants
  • Twin check valves in hydraulic linear drives
  • Tire valve on vehicle tires
  • Venous valves cause the blood to flow in the right direction.
  • A combined free- flow valve with a backflow preventer ( KFR valve ) is usually an angle seat valve with a built-in check valve

Web links

Commons : Check valves  - collection of pictures, videos and audio files