Reed valves are a type of check valve

Check valve

A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....

 which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. Modern versions often consist of flexible metal or composite materials (fiberglass

Fiberglass

Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...

 or carbon fiber

Carbon fiber

Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...

).

Traditional

Reed-valves, normally a leather

Leather

Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...

 flap covering a hole, are amongst the earliest form of automatic flow control

Flow control valve

A flow control valve regulates the flow or pressure of a fluid. Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges.Control valves are normally fitted with actuators and positioners...

 for liquids and gases. They have been used for thousands of years in water pump

Water Pump

Water Pump is one of the neighbourhoods of Gulberg Town in Karachi, Sindh, Pakistan. It is near main Water Pump that supplies fresh water to the city of Karachi....

s and for hundreds of years in bellows

Bellows

A bellows is a device for delivering pressurized air in a controlled quantity to a controlled location.Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet...

 for high-temperature forge

Forge

A forge is a hearth used for forging. The term "forge" can also refer to the workplace of a smith or a blacksmith, although the term smithy is then more commonly used.The basic smithy contains a forge, also known as a hearth, for heating metals...

s and musical instruments such as church organs and accordion

Accordion

The accordion is a box-shaped musical instrument of the bellows-driven free-reed aerophone family, sometimes referred to as a squeezebox. A person who plays the accordion is called an accordionist....

s. In nature, heart valve

Heart valve

A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...

s operate in a somewhat similar fashion.

Pumps

Reed valves are used in some reciprocating compressor designs, and in the pumping element of some musical instruments, large and small.

Two-stroke engines

Reed valves are commonly used in high-performance versions of the two-stroke engine, where they control the fuel-air mixture admitted to the cylinder. As the piston rises in the cylinder a vacuum is created in the crankcase

Crankcase

In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...

 beneath the piston. This vacuum opens the valve and admits the fuel-air mixture into the crankcase. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber

Combustion chamber

A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...

.

Composite materials are preferred in racing engines, especially in kart racing

Kart racing

Kart racing or karting is a variant of open-wheel motorsport with small, open, four-wheeled vehicles called karts, go-karts, or gearbox/shifter karts depending on the design. They are usually raced on scaled-down circuits...

, because the stiffness of the petals can be easily tuned and they are relatively safe in failure. High-speed impact takes its toll on all reed valves, with metal valves suffering in fatigue

Metal Fatigue

Metal Fatigue , is a futuristic science fiction, real-time strategy computer game developed by Zono Incorporated and published by Psygnosis and TalonSoft .-Plot:...

. The physical inertia of reed valves means that they are not as entirely precise in action as rotary valve

Rotary valve

A rotary valve is a type of valve in which the rotation of a passage or passages in a transverse plug regulates the flow of liquid or gas through the attached pipes. The common stopcock is the simplest form of rotary valve...

s, a rotary valve engine may run better than a reed valve engine at a small rpm range but the reed valve engine often runs better over a wider rpm range. More sophisticated designs partly address this by creating multi-stage reeds with smaller, more responsive reeds within larger ones that provide more volume later in the cycle. Nevertheless, current technology favors reed valves almost to the exclusion of rotary valves due to their simplicity and low implementation costs.

Pulse jets

Reed valves are used in the cheap but inefficient pulse jet engine

Pulse jet engine

A pulse jet engine is a type of jet engine in which combustion occurs in pulses. Pulsejet engines can be made with few or no moving parts, and are capable of running statically....

, such as the one used by the Argus

Argus Motoren

Argus Motoren was a German manufacturing firm known for their series of small inverted-V engines and the V-1 pulse jet engine.-History:...

 engine in the German V-1 (flying bomb). The valves at the front of the cylindrical engine are opened by the low pressure in the combustion chamber caused by the resonance of the air column in the engine, fuel

Fuel

Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

 is squirted into the combustion chamber and ignited by the hot combustion gases of the previous cycle. Once the charge has expanded and mostly left the engine, pressure inside drops again to below-atmospheric values and the reed valve allows fresh air to enter and the cycle be repeated. Some ram-air pressure due to forward motion helps scavenging and filling the combustion chamber with the new, fresh air charge, thus improving the power of the engine at higher speeds.

Design and modelling

Reed valves are designed considering the pressure gradient

Pressure gradient

In atmospheric sciences , the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location. The pressure gradient is a dimensional quantity expressed in units of pressure per unit length...

 and mass flow

Mass flow

Mass flow, also known as mass transfer and bulk flow, is the movement of material matter. In physics, mass flow occurs in open systems and is often measured as occurring when moving across a certain boundary characterized by its cross-sectional area and a flow rate. In engineering and biology it...

 . The pressure gradient is used to evaluate the valve lift during open condition; the lift and overall component geometry (considering also a pressure loss coefficient) are then used to calculate the mass flow. For high speed applications (compressors and engines) the dynamic response has to be considered. A simple approach consists in the evaluation of first eigenvalue that is compared with exciting frequency.
Design of reed valves can be refined using simulations. The dynamic of petals can be studied neglecting the coupling between fluid and structure: in this case the evolution of the structural part are simulated using lumped parameters models or FEM models, discharge coefficients at various valve lift are evaluated with experiments or CFD simulations.
The study of the complete system needs an integrated Fluid-structure interaction

Fluid-Structure Interaction

Fluid-structure interaction is the interaction of some movable or deformable structure with an internal or surrounding fluid flow. Fluid-structure interactions can be stable or oscillatory...

model.