A valve ( lat. Ventus , wind ') is a component used to shut off or control the flow of fluids ( liquids or gases ).
In German, not every shut-off device is called a valve. Fittings such as gate valves , butterfly valves and ball valves are not valves. (However, ball valves and plug valves are often mistaken as ball valves and plug valves , respectively.)
In the case of valves in the narrower sense, a closure part (e.g. plate, cone , ball or needle) is moved approximately parallel to the direction of flow of the fluid. The flow is interrupted in that the sealing surface of the closure part is pressed against a suitably shaped opening, the valve or sealing seat.
Other fittings, which are referred to as valves, although they do not fall under the above definition, are often soft-seated shut-off devices and non- return fittings (e.g. ball , car and bicycle valves ), in which the seal is provided by a rubberized closure part or a rubber membrane ( such as with hose valves and pinch valves ).
The change in the flow rate of valves generally shows a somewhat more linear behavior over the entire setting range than that of taps, slides and flaps. Therefore, in addition to shutting off material flows, valves are ideal for control tasks . Since the fluid is diverted in the area of the valve seat and sealing body, valves cause a higher pressure loss than valves with free flow .
Although colloquially referred to as a "faucet", a classic faucet usually contains one or two poppet valves (newer designs contain ceramic cartridges ). Faucets in the original sense are usually only used when the pressure is low, such as in water tanks and fountains fed by springs .
Valve technology was already used in ancient Greece . For example in the pump of the Ktesibios (see Ktesibios ), an early fire engine
Differentiation according to design and pressure loss
- Angle valve (the connections are at right angles to each other)
Globe valve (the connections are parallel to the direction of flow), whereby the passage can be designed "reduced" (with cross-section reduction) or "equal" (without cross-section reduction).
- Straight seat valve - the shut-off body and actuation axis are at right angles to the direction of flow. This shortens the design and can facilitate operation and flush mounting, in which the pipes are clad or plastered and the valve is often provided with a decorative attachment above the cladding. Simple straight seat valves cause a high pressure loss because the flow of liquid in the valve is deflected several times. A voluminous base body is required to reduce the pressure loss.
- Angle seat valve- The shut-off body and actuation axis are at an angle of approximately 45 ° to the direction of flow; the liquid flow is deflected less strongly, there is a lower pressure loss,
- Free-flow valve - this term is used either synonymously with an angle seat valve or for an angle seat valve with an even further optimized flow path
Directional control valve
- Three-way valves for the controlled mixing of fluid flows, such as those used for temperature control for heating water in heating technology
- Mixing valve - a three-way valve with two inputs and one output; either one of the two inputs can be switched to pass, and a mixture of the material flows in any ratio can be achieved
- Diverting valve - a three-way valve with one input and two outputs; the incoming current is distributed to both outputs or only fed to one output
Differentiation according to type of actuation
- Manually operated valves. Usually with a handwheel or knob, since several turns are usually required to shut off. There are versions with a rising or non-rising spindle. With the latter, the handle does not change its height when operated. With large nominal widths, the actuation force is reduced by interposing a gear.
- (Electrically) motorized valves with valve drive
- (Electro-) magnetically operated valves
- Media-operated valves that are pneumatically or hydraulically controlled enable a large mass flow to be controlled with the use of low actuation energy.
- Multi-stage valves are used to further reduce the actuation force with large nominal diameters . When several valves operated by external media are connected in series, the first one is controlled directly and the other indirectly.
- Valves operated by the medium itself include, for example, check valves
- Foreign media operated valves include, for example, pinch valves ; Valves operated by external media are used to reduce the actuation force or, as indirectly controlled valves, are part of a complex control system.
- Force-controlled valves: A membrane or piston, which is coupled to the magnetic core, is used to seal the actual valve seat. After switching on the electrical current, the core attracts and opens the auxiliary valve seat in the membrane or the piston. The medium standing on the diaphragm or the piston can flow off. This creates balanced pressure conditions in the valve, and the main valve seat is opened via the core / membrane or core / piston coupling. No differential pressure is required with this version. The nominal pressure range begins at zero pressure .
- Pilot operated valves: Pilot operated valves have a 3/2-way pilot solenoid valve. A membrane or a piston is used to seal the actual valve seat. When the pilot valve is closed, the medium pressure can build up via a throttle bore on both sides of the diaphragm. As long as there is a pressure difference between the inlet and outlet, a closing force acts due to the larger area on the upper side of the membrane. When the pilot valve is opened, the pressure above the diaphragm is reduced. The resulting increasing force on the underside now lifts the membrane upwards and opens the valve. Piloted valves require a minimum pressure difference to ensure proper opening and closing.
Differentiation according to task
Valves perform different tasks in a pneumatic or hydraulic system. They offer the fluids ( liquids and gases ) a barrier depending on various factors. There are 4 cases:
- The fluid can simply be hindered when flowing through in both directions (flow control valves),
- or depending on the direction of flow (check valves),
- it can be hindered depending on the pressure (pressure valves),
- or the flow can be controlled on several lines at the same time. (Directional control valves, 3/2 or higher)
Shut-off valves and flow control valves
Flow control valves reduce the flow cross-section or shut off completely. See main article flow control valve . Examples:
- Throttle valve
- Delay valve
- Shuttle valve (OR element)
- Two-pressure valve (AND element)
- Quick-closing valve: A quick-closing valve enables the sudden interruption of a pipe flow. For example, if a generator is suddenly mechanically relieved ( load shedding ), the steam supply can be suddenly interrupted. This prevents the turbine from “running away”.
Quick-closing valves are used in the chemical industry in order to disconnect pipelines as quickly as possible in the event of a fault.
- Globe valve, flow switching valve or 2/2-way valve: shut-off valves with one inlet and one outlet. In the rest position, the core spring, supported by the medium pressure, presses the seal onto the valve seat and closes the passage. After switching on, the core with the seal in the magnet coil is pulled up to the pole face, the valve opens. The electromagnetic force is greater than the sum of the spring force, static and dynamic pressure force.
Check valves only let the medium through in one direction of flow. Special check valves:
- One-way flow control valve
- Quick exhaust valve
- KFR valves are combined free-flow valves with backflow preventer , usually designed as an angle seat valve , the valve disk of which is pressed onto the valve seat by spring force when the valve is open.
Pressure valves obstruct the fluid depending on the pressure. Normally they only become active in a certain pressure range. See main article pressure valve . Examples:
- Pressure relief valve and sequence valve
- Pressure compensator (differential pressure valve )
- Pressure reducing valve
- Pressure control valve
Directional control valves
Three-way valves , four-way valves or higher-order directional valves control the flow like flow control valves, i.e. independent of pressure or direction. They influence several fluid flows at the same time, so they have at least 3 line connections. They can be further differentiated according to the switching positions, i.e. discreet (directional valve as switching valve) and continuous (directional valve as continuous valve ). See main article directional control valves . Examples:
- Proportional valve (directional valve as a proportional valve )
- Control valve (directional valve as a proportional valve)
- Servo valve (directional valve as a proportional valve)
- Direct operated 3/2-way valve (directional valve as switching valve): 3/2-way valves have three connections and two valve seats. One valve seat always remains open or closed alternately. Depending on the connection of the operating medium to the various working connections, there are different functions. The pressure is under the valve seat. When de-energized, a spring presses the lower core seal onto the valve seat and blocks the valve. The line at port A is vented via R. After switching on the electrical current, the core attracts and seals the valve seat at port R via a spring-loaded seal. The medium has passage from P to A.
Differentiation according to the design of the shut-off device
Valves can also be subdivided according to the design of their shut-off body and its mode of operation.
A distinction is made between seat valves and slide valves as modes of action ( closure types): the sealing body moves either in the flow axis or perpendicular to it, i.e. towards the sealing surface (seat) or along it (slide). Differences result from this, in particular in terms of actuation force, wear and susceptibility to failure - e.g. B. by solids in the flow - and in the flow modulation mode. The classic water tap is a seat valve, the beer tap is a slide valve (rotary valve):
- Plate valve (seat valve): The shut-off body is plate-shaped, an example is the typical water tap . See also valve control (internal combustion engines)
- Pipe valve or double seat valve (seat valve): The shut-off body is a pipe section and has two annular sealing surfaces; this achieves pressure-relieved actuation. See also valve control of steam engines
- Piston valve (slide valve): The shut-off body is a piston
- Rolling diaphragm valve : the shut-off element consists of a membrane from one side (as in the spool valve) is more or less freely by rolling the valve cross-sectional area, this construction is, for example, during loading and vent valves used.
- Pinch valve: The shut-off body is the tubular flow channel wall itself.
- Needle valves (seat valve): The conical tip of the shut-off body presses against an annular inlet / outlet opening (e.g. float needle valve in the carburetor of a gasoline engine )
- Ball valve (optionally seat or slide valve): The shut-off body is a ball, in the slide version with a passage.
Other distinguishing features
Furthermore, pneumatic valves can be subdivided according to sealing material (hard / soft sealing) as well as the position of the seal (on the piston / in the housing) and the seal structure. More general differentiation criteria are nominal sizes , nominal pressure ratings and media . A valve can also be distinguished between rising and non-rising spindles . Rising spindles have the advantage that the valve position can be seen from the outside, which is otherwise not the case.
Valves can be used to precisely meter the flow rates in a pipeline and to shut them off safely from the environment. Safety valves, on the other hand, are designed to allow large mass flows in order to be able to quickly compensate for impermissible pressure conditions (e.g. in a container). Valves always have a certain flow resistance , which makes them unsuitable for some applications. In addition, it is very difficult to keep the operating unit absolutely tight .
In the vast majority of vehicles today as driving a gasoline engine in four-stroke design is used in which valves in the valve control are used to control the flow of gas.
Valves, in particular solenoid valves , are often and variedly used in industry: in the field of factory automation for moving cylinders , gripping systems or ejectors , in medical technology for ventilators or dialysis, in the chemical industry, the food industry, water treatment and many other areas.
The leaflet valves on the heart of mammals and the pocket valves in the veins also function as valves.
The term valve is often used as an umbrella term. Depending on the design, synonymous terms such as cock , slide or flap are used.
- Relief valve
- Shut-off valve
- Inlet and outlet valves in four-stroke - combustion engines - see valve control
- Bottom outlet valve
- Flipper valve
- Foot valve = check valve at the lower end of a suction lance that prevents backflow.
- Filling valve
- Cap valve
- Diaphragm valve
- Diaphragm anti-siphon valve
- Needle valve
- Sampling valve , e.g. B. with a flammable discharge tube if biological contamination is to be detected
- Proportional valve
- Pinch valve
- Control valve
- Tire valve , e.g. B. Bicycle valves
- check valve
- Servo valve
- Safety valve
- Control valve
- Proportional valve
- Control valve
- Pressure relief valve
- Valve terminal
- water tap
- Rocker valve
Circuit symbols and circuit diagrams
A comprehensive list of circuit symbols for valves and their type of actuation in fluid technology can be found in the following list of circuit symbols (fluid technology) . Complete pneumatic circuit diagrams contain u. a. Actuators (valves) for controlling the working elements (cylinders).
- Bicycle valve
- Kv value (flow coefficient, flow index) for the design of valves
- ↑ Lucio Russo: The forgotten revolution or the rebirth of ancient knowledge. Springer-Verlag, 2005, ISBN 978-3-540-27707-1 , p. 154 ( limited preview in Google book search).
- ↑ Dietmar Findeisen : Hydro devices for energy control and regulation. Valves. In: Dietmar Findeisen: Oil hydraulics. Manual for hydrostatic power transmission in fluid technology. 5th, revised edition. Springer, Berlin et al. 2006, ISBN 3-540-23880-8 , pp. 557-675, here p. 558, doi : 10.1007 / 3-540-30967-5_4 .
- ↑ Philipp Wahl: Piston valve, seat valve - possible solenoid valves in a technical comparison. Festo AG & Co. KG, sl 2013, ( online ).