What is a valve

Valves: shapes, areas of application

Valves are used for control; they are operated in various ways, particularly in fluid technology (pneumatics & hydraulics). A Valve regulates the direction of flow or the amount of air or liquid that should flow through a pipe. In fluid technology, valves can be distinguished by various parameters.

Valves have an executive function in the control process. The task of valves is usually limited to controlling the direction of flow and / or the amount of air (pneumatics) or fluid (hydraulics). On the one hand, valves are used to determine exactly how much fluid (liquid & gas) is allowed to pass through a line. On the other hand, valves sometimes completely block lines so that no more liquid or gas can penetrate them. With this control function, valves are exposed to great dynamics and must therefore be durable and reliable.

In German, not every shut-off device is called a valve. Fittings such as gate valves, butterfly valves and ball valves are not valves.

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 by pressing the sealing surface of the closure part 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 mostly soft-sealing shut-off devices and check valves. This means that the seal is achieved by means of a rubberized closure part or a rubber membrane (as is the case with hose valves and pinch valves, for example).

Valves distinction

How a valve is constructed depends on the type of valve. Valves can be distinguished by various parameters: the shape, the type of actuation of the valve, the type of control, the valve function and the design of the shut-off body.

Valve shapes

Valves can be divided into:

  • Globe valve (inlet and outlet are parallel in the direction of flow), whereby the passage can be designed "reduced" (with cross-section reduction) or "equal" (without cross-section reduction).
  • Angle valve (inlet and outlet are at right angles to each other)
  • Angle seat valve (the shut-off body is (usually) inclined 45 ° to the direction of flow), a straight-way valve with lower pressure loss than a straight seat valve
  • Three-way valves for the controlled mixing of fluid flows, such as those used for temperature control for heating water in heating technology

Types of actuation of valves

A valve can be controlled in different ways. For example, electromagnetically, mechanically, with compressed air or by hand / foot.

  • Electromagnetically operated valves (solenoid valves): These valves are controlled by electrical voltage. An electromagnet is responsible for ensuring that the valve reacts. These types of valves are most commonly used.
  • Valves operated with compressed air (pneumatic valves, pneumatic valves): Here, the compressed air is the trigger for the valve. A compressed air connection is therefore required on the valve.
  • Mechanically operated valves: These valves are controlled and operated directly, e.g. by a pneumatic cylinder. Due to the direct control, there are fewer interfaces and thus the error rate also decreases. Mechanically operated valves are therefore very popular in fluid technology.
  • Muscle-operated valves (manually operated valves): In terms of their function and structure, valves operated by muscle force are similar to mechanically operated valves. However, the trigger here is a button, foot switch or lever that has to be operated by hand and directly controls the valve.

Control types of valves

When a valve regulates the amount or direction of fluid, there is always movement in it, for example when a valve piston moves. The valve piston can be triggered indirectly or directly, which is why a distinction is made between indirectly controlled valves and directly controlled valves when controlling valves.

Direct operated valve
With direct control, the valve piston is actuated directly - i.e. without an intermediate step. For example by means of a solenoid, a switch or a push button. A directly controlled valve is used in the vacuum sector because it is not dependent on the general working pressure. However, the greater the size of the directly controlled valve, the greater the force required.

Indirectly controlled valve
An indirectly controlled valve (pilot operated valve) works e.g. via a compressed air control connection. The valve piston is not triggered directly by an actuating element, but by compressed air that is released with the help of a pneumatic button. So you first press the pneumatic button (lever, push button, etc.). This releases compressed air that moves the valve piston. The advantage of an indirectly controlled valve is that, unlike the directly controlled valve, it requires much less force. However, it is also dependent on sufficient working pressure.

Function valves

The functions of valves are different:

Directional control valves
A directional valve controls the path of the working medium (compressed air, liquid) by releasing or blocking the medium or determining its direction of flow. There are different types of directional control valves. They are named after the number of connections and switch positions. The first number in the designation stands for the number of connections, the second number indicates the number of switch positions. A 3/2-way valve (read: 3-dash, 2-way valve), for example, has three connections and two switching positions. The most common types of directional control valves are:

  • 2/2-way valves
  • 3/2-way valves
  • 4/2-way valves
  • 5/2-way valves
  • 5/3-way valves

Pressure, shut-off and flow valves
A Pressure valve (Pressure control valve) ensures that the pressure of the compressed air is set correctly.

A Check valve blocks the path of the working medium in one direction and releases another path for it. An example of a check valve is a check valve that is installed as a safety valve so that there is no pressure drop.

A Flow valve controls the speed of the fluid by changing the cross-section of the opening. An example of a flow control valve is a one-way flow control valve. It slows the flow of the medium in one direction while the fluid can flow unhindered in the other direction.

Proportional valves
With a proportional valve, the output value changes in relation to the entered value. This means, for example, the more force acts on a valve, the greater its flow rate.

Logic valves
Logic valves can be subdivided into two-pressure valves and shuttle valves.

A Two-pressure valve has two pressure connections and a working connection. The medium is only forwarded to the working connection if pressure is created on both pressure connections at the same time. The two-pressure valve is therefore also referred to as an AND valve.

A Shuttle valve also has two pressure connections and a working connection. However, the medium is already forwarded to the working connection here if only one pressure connection is under pressure. There does not have to be pressure at both pressure connections at the same time, which is why the shuttle valve is also known as an OR valve.

Trailer control valves

Design of the shut-off body

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 the operating 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 slide valve):

Examples are:

  • 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 piece of pipe and has two ring-shaped sealing surfaces; pressure-relieved actuation is thereby achieved. See also valve control of steam engines
  • Piston valve (slide valve): The shut-off body is a piston
  • Rolling diaphragm valve: The shut-off body consists of a diaphragm which, by rolling, more or less releases the valve cross-sectional area from one side (as with a slide valve), this type of construction is used, for example, for ventilation valves.
  • 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.

Terms used in valves

There are a few important terms related to valves:

  • Main connections: These are the compressed air connection, consumer connection and ventilation
  • Control connections: Control connections are the reset connection and the switching connection
  • Switching: Switching is the process when the valve changes from its initial position to the controlled position
  • Reset: This is what happens when the valve returns to its rest position
  • ways: Number of connections
  • Positions: Number of possible positions (= number of squares in circuit diagrams)
  • function: Working diagram of the valve in the rest position (= right square in circuit diagrams)
  • Seals for valve covers

Overlap with valves

If the shut-off body in a valve is piston-shaped, there are different types of overlap. The overlap means the sealing length between the control edge of the piston and the control edge of the annular groove. There are three different types of overlap for directional control valves: negative overlap, positive overlap and zero overlap.

a) Overlap zero
The so-called Zero cut the control edges of the piston and ring groove exactly match. No volume flow can therefore flow in the starting position. However, this occurs very quickly when the shut-off body is moved.

b) Positive coverage
In this case, the shut-off body is longer than the annular groove. So the control edges are not on top of each other. As a result, a volume flow can only occur when the piston has passed the overlap.

c) Negative coverage
Here the piston is shorter and smaller than the ring groove. Here, too, the control edges are not directly on top of each other, but in contrast to the positive overlap, in this case a volume flow can already flow in the starting position of the shut-off body (floating position).

Variants overlap valves

Areas of application for valves

Valves are ubiquitous in pneumatics and hydraulics. In addition to fluid technology, valves are also used in other areas:

  • Motor vehicles (e.g. EGR valve)
  • Bicycles (e.g. Schrader valve)
  • Water treatment (e.g. solenoid valve)
  • Medical technology (e.g. valves with piezo technology)
  • chemical industry
  • food industry
  • mechanical engineering

Explosion-proof valves

Also in Explosion protection valves play a role. Explosion-proof valves are used in flammable and explosive occasions used. These include, for example, dust removal systems with flammable media. Another use case is in explosive pipelines or devices where valves are used as pressure relief devices for explosive pipelines or devices.

Explosion-proof valves generally include two types of valves:

  1. Eliminate the source of the explosion automated valve (Examples: safety valve in the boiler, dust collector in front of the smoke outlet).
  2. Avoidance high heat or electrical sparks (examples: explosion-proof ball valves, explosion-proof gate valves or explosion-proof butterfly valves that are equipped with electrical or pneumatic drives to prevent or delay an explosion.

Manufacturer

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In the ATEXshop there are explosion-proof pumps and valves for professional users in Ex area.

Category "Valves: Shapes, Areas of Application"