check valve
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A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a
valve A valve is a device or Heart valve, natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technical ...
that normally allows
fluid In physics, a fluid is a liquid, gas, or other material that continuously Deformation (physics), deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are Matter, substances wh ...
(
liquid A liquid is a nearly Compressibility, incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of State of matter#Four fundamental states, the four fund ...
or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for
fluid In physics, a fluid is a liquid, gas, or other material that continuously Deformation (physics), deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are Matter, substances wh ...
to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal. An important concept in check valves is the cracking
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
which is the minimum differential upstream pressure between inlet and outlet at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.


Technical terminology

Cracking pressure – Refers to the minimum pressure differential needed between the inlet and outlet of the valve at which the first indication of flow occurs (steady stream of bubbles). Cracking pressure is also known as unseating head (pressure) or opening pressure. Reseal pressure – Refers to the pressure differential between the inlet and outlet of the valve during the closing process of the check valve, at which there is no visible leak rate. Reseal pressure is also known as sealing pressure, seating head (pressure) or closing pressure. Back pressure – a pressure higher at the outlet of a fitting than that at the inlet or a point upstream


Types of check valves

A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a ball. In some ball check valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow. Ball check valves are often very small, simple, and cheap. They are commonly used in liquid or gel minipump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other
pump A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the metho ...
s, and refillable dispensing syringes. Although the balls are most often made of metal, they can be made of other materials; in some specialized cases out of highly durable or inert materials, such as
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
. High pressure
HPLC High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to p ...
pump A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the metho ...
s and similar applications commonly use small inlet and outlet ball check valves with balls of (artificial) ruby and seats made of sapphire or both ball and seat of ruby, for both hardness and chemical resistance. After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement. Therefore, such valves are made to be replaceable, sometimes placed in a small plastic body tightly-fitted inside a metal fitting which can withstand high pressure and which is screwed into the pump head. There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring. Ball check valves should not be confused with
ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...
s, which is a different type of valve in which a ball acts as a controllable rotor to stop or direct flow. A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position. This type is used in
respirator A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including wikt:fumes, fumes, vapor, vapours, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main cat ...
s (face masks) with an exhalation valve. A swing check valve or tilting disc check valve is a check valve in which the disc, the movable part to block the flow, swings on a
hinge A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other ...
or
trunnion A trunnion (from Old French "''trognon''", trunk) is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development. Alternatively, a trunnion is a shaft that positions a ...
, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle. Although swing check valves can come in various sizes, large check valves are often swing check valves. A common issue caused by swing check valves is known as water hammer. This can occur when the swing check closes and the flow abruptly stops, causing a surge of pressure resulting in high velocity shock waves that act against the piping and valves, placing large stress on the metals and vibrations in the system. Undetected, water hammer can rupture pumps, valves, and pipes within the system. The flapper valve in a flush-toilet mechanism is an example of this type of valve. Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank drains and the flapper falls due to gravity. Another variation of this mechanism is the clapper valve, used in applications such
firefighting Firefighting is the act of extinguishing or preventing the spread of unwanted fires from threatening human lives and destroying property and the environment. A person who engages in firefighting is known as a firefighter. Firefighters typically ...
and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure. Another example is the backwater valve (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters. Such risk occurs most often in sanitary drainage systems connected to combined sewerage systems and in rainwater drainage systems. It may be caused by intense rainfall, thaw or flood. A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure (normal check-valve behavior), it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure. A lift-check valve is a check valve in which the disc, sometimes called a ''lift'', can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow. An in-line check valve is a check valve similar to the lift check valve. However, this valve generally has a spring that will 'lift' when there is pressure on the upstream side of the valve. The pressure needed on the upstream side of the valve to overcome the spring tension is called the 'cracking pressure'. When the pressure going through the valve goes below the cracking pressure, the spring will close the valve to prevent back-flow in the process. A
duckbill valve A duckbill valve is a check valve, usually manufactured from rubber or synthetic elastomer, and has 2 (or more) flaps, usually shaped like the beak of a duck. It is commonly used in medical applications to prevent contamination due to backflow. ...
is a check valve in which flow proceeds through a soft tube that protrudes into the downstream side. Back-pressure collapses this tube, cutting off flow. A pneumatic non-return valve. A reed valve is a check valve formed by a flexible flat sheet that seals an orifice plate. The cracking pressure is very low, the moving part has low mass allowing rapid operation, the flow resistance is moderate, and the seal improves with back pressure. These are commonly found in two stroke internal combustion engines as the air intake valve for the crankcase volume and in air compressors as both intake and exhaust valves for the cylinder(s). Although reed valves are typically used for gasses rather than liquids, the Autotrol brand of water treatment control valves are designed as a set of reed valves taking advantage of the sealing characteristic, selectively forcing open some of the reeds to establish a flow path. A flow check is a check valve used in hydronic heating and cooling systems to prevent unwanted passive gravity flow. A flow check is a simple flow lifted gravity closed heavy metal stopper designed for low flow resistance, many decades of continuous service, and to self-clean the fine particulates commonly found in hydroninc systems from the sealing surfaces. To accomplish self cleaning, the stopper is typically not conical. A circular recess in a weight that fits over a matching narrow ridge at the rim of an orifice is a common design. The application inherently tolerates a modest reverse leakage rate, a perfect seal is not required. A flow check has an operating screw to allow the valve to be held open, the opposite of the control on a stop-check valve, as an aide for filling the system and for purging air from the system. Multiple check valves can be connected in series. For example, a double check valve is often used as a
backflow prevention device A backflow prevention device is used to protect potable water supplies from contamination or pollution due to backflow (plumbing), backflow. In water distribution systems, water is normally maintained at a significant pressure to enable water to ...
to keep potentially contaminated water from
siphon A siphon (from grc, σίφων, síphōn, "pipe, tube", also spelled nonetymologically syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in a ...
ing back into municipal water supply lines. There are also ''double ball check valves'' in which there are two ball/seat combinations sequentially in the same body to ensure positive leak-tight shutoff when blocking reverse flow; and piston check valves, wafer check valves, and ball-and-cone check valves.


Applications


Pumps

Check valves are often used with some types of pumps. Piston-driven and
diaphragm pump A diaphragm pump (also known as a Membrane pump) is a pump#Positive-displacement pump, positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or Polytetrafluoroethylene, teflon diaphragm (mechani ...
s such as metering pumps and pumps for
chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it ...
commonly use inlet and outlet ball check valves. These valves often look like small cylinders attached to the pump head on the inlet and outlet lines. Many similar pump-like mechanisms for moving volumes of fluids around use check valves such as ball check valves. The
feed pump A boiler feedwater pump is a specific type of pump used to pump feedwater into a boiler (steam generator), steam boiler. The water may be freshly supplied or returning Condensation, condensate produced as a result of the condensation of the steam ...
s or
injector An injector is a system of ducting and nozzles used to direct the flow of a high-pressure fluid in such a way that a lower pressure fluid is Entrainment (hydrodynamics), entrained in the jet and carried through a duct to a region of higher pre ...
s which supply water to steam
boiler A boiler is a closed pressure vessel, vessel in which fluid (generally water) is heated. The fluid does not necessarily boiling, boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including ...
s are fitted with check valves to prevent back-flow. Check valves are also used in the pumps that supply water to water slides. The water to the slide flows through a pipe which doubles as the tower holding the steps to the slide. When the facility with the slide closes for the night, the check valve stops the flow of water through the pipe; when the facility reopens for the next day, the valve is opened and the flow restarts, making the slide ready for use again.


Industrial processes

Check valves are used in many fluid systems such as those in
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent Chemical element, elements by physical separation m ...
and
power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the electricity generation, generation of electric power. Power stations are generally connected to an el ...
s, and in many other industrial processes. Typical applications in the nuclear industry are feed water control systems, dump lines, make-up water, miscellaneous process systems, N2 systems, and monitoring and sampling systems. In aircraft and aerospace, check valves are used where high vibration, large temperature extremes and corrosive fluids are present. For example, spacecraft and launch vehicle propulsion propellant control for reaction control systems (RCS) and Attitude Control Systems (ACS) and aircraft hydraulic systems. Check valves are also often used when multiple gases are mixed into one gas stream. A check valve is installed on each of the individual gas streams to prevent mixing of the gases in the original source. For example, if a fuel and an oxidizer are to be mixed, then check valves will normally be used on both the fuel and oxidizer sources to ensure that the original gas cylinders remain pure and therefore nonflammable. In 2010, NASA's Jet Propulsion Laboratory slightly modified a simple check valve design with the intention to store liquid samples indicative to life on Mars in separate reservoirs of the device without fear of cross contamination.


Domestic use

When a sanitary potable water supply is plumbed to an unsanitary system, for example lawn sprinklers, a dish washer or a
washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and i ...
, a check valve called a backflow preventer is used to prevent contaminated water from re-entering the domestic water supply. Some types of
irrigation sprinkler An irrigation sprinkler (also known as a water sprinkler or simply a sprinkler) is a device used to Irrigation, irrigate (water) agricultural crops, lawns, landscapes, golf courses, and other areas. They are also used for cooling and for the cont ...
s and
drip irrigation Drip irrigation or trickle irrigation is a type of micro-irrigation system that has the potential to save water and nutrients by allowing water to drip slowly to the roots of plants, either from above the soil surface or buried below the surface. ...

drip irrigation
emitters have small check valves built into them to keep the lines from draining when the system is shut off. Check valves used in domestic heating systems to prevent vertical convection, especially in combination with
solar thermal Solar thermal energy (STE) is a form of energy and a technology Technology is the application of knowledge to reach practical goals in a specifiable and Reproducibility, reproducible way. The word ''technology'' may also mean the product ...
installations, also are called gravity brakes.
Rainwater harvesting Rainwater harvesting (RWH) is the collection and storage of rain, rather than allowing it to run off. Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit (well, shaft, or borehole), Aquifer storage and recov ...
systems that are plumbed into the main water supply of a utility provider may be required to have one or more check valves fitted to prevent contamination of the primary supply by rainwater. Hydraulic jacks use ball check valves to build pressure on the lifting side of the jack. Check valves are commonly used in inflatables, such as toys, mattresses and boats. This allows the object to be inflated without continuous or uninterrupted air pressure.


History

Frank P. Cotter developed a "simple self sealing check valve, adapted to be connected in the pipe connections without requiring special fittings and which may be readily opened for inspection or repair" 1907
U.S. patent 865,631
.
Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''Random House Webster's Unabridged Dictionary''.
; 1856 – 7 January 1943 ...

Nikola Tesla
invented a deceptively simple one-way valve for fluids in 1916, called a
Tesla valve A Tesla valve, called a valvular conduit by its inventor, is a fixed-geometry passive check valve. It allows a fluid to flow preferentially in one direction, without moving parts. The device is named after Nikola Tesla, who was awarded in 1920 ...
. It was patented in 1920
U.S. patent 1,329,559
.


Images

File:Swing Check valves.JPG, Hastelloy check valves File:Wafer check valve--The-Alloy-Valve-Stockist.JPG, Stainless steel wafer check valve File:Inconel-Tilting disc check valve--The-Alloy-Valve-Stockist.JPG, Inconel check valve File:Inside-tilting-disc-check-valve-The-Alloy-Valve-Stockist.jpg, Inside view of a tilting disc inconel check valve File:Flanged-Nozzle-check-valve-The-Alloy-Valve-Stockist.JPG, Flanged nozzle inconel check valve or axial check valve File:Clappered.JPG, This Siamese clappered inlet allows one or two inputs into a
deluge gun A deluge gun, fire monitor, master stream or deck gun is an aimable controllable high-capacity water jet used for manual firefighting or automatic fire protection systems. Deluge guns are often designed to accommodate foam which has been injecte ...
. File:Inside-wafer-check-valve-The-Alloy-Valve-Stockist.JPG, Inside hastelloy check valve, wafer configuration File:Large-swing-check-valve-The-Alloy-Valve-Stockist.jpg, Large carbon steel swing check valve File:Nozzle-check-valve-disc-The-Alloy-Valve-Stockist.jpg, Disc for an alloy check valve also known as axial check valve File:Wafer-check-valve-The-Alloy-Valve-Stockist.JPG, Wafer check valve File:Plastic Check Valve.jpg, Plastic Check Valve File:he_release_valve_seadweller.jpg, Integrated Helium release valve as used by the Rolex Sea-Dweller diving watch


See also

*
Diode A diode is a two-Terminal (electronics), terminal electronic component that conducts Electric current, current primarily in one direction (asymmetric electrical conductance, conductance); it has low (ideally zero) electrical resistance and co ...

Diode
, the electrical analog of a check valve * Top feed * Vacuum breaker * Reed valve *
Ball valve A ball valve is a flow control device which uses a hollow, perforated and pivoting ball to control fluid flowing through it. It is open when the ball's hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve h ...

Ball valve
*
Butterfly valve
Butterfly valve
*
Control valve
Control valve
*
Gate valve
Gate valve
*
Globe valve
Globe valve
*
Diaphragm valve
Diaphragm valve
*
Needle valve
Needle valve


References


External links


Working Principle of Spring Check ValvesCheck Valves Tutorial
The operation, benefits, applications and selection of different designs, including lift, disc, swing and wafer check valves are explained in this tutorial

a scaled down version of Tesla's original fluidic diode. *, Tesla's original fluidic diode
a test of a design showing very poor performance
– n.b. the test protocol did not match the conditions described in the patent)

{{Backflow Plumbing valves Steam boiler components Firefighting equipment Valves