Valves

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Pneumatics without valves is like driving cars without motors - possible in theory, but unimaginable in practice.
The function of valves is generally limited to controlling the flow direction or the quantity of air. Valves can be subdivided into different categories.

Actuation types

Electrically actuated valves

The most frequent type of actuation for valves is electrical voltage. A solenoid is actuated, thus making the valve switch. These valves are frequently designated as solenoid valves.

Elektrisch betaetigtes Ventil.png


Electrically actuated valves

 

Pneumatically actuated valves

If valves are switched using compressed air, they tend to be called pneumatic valves. Instead of an electrical connection, this valve has another connection for compressed air.

Pneumatisch betaetigtes Ventil.png


Pneumatically actuated valve

 

Mechanically actuated valves

This type of actuation is is experiencing quite a revival as part of safety-orientated pneumatics. The valve can be actuated directly via a moving part (e.g.
a pneumatic cylinder). This reduces the number of interfaces required and thus the number of possible error sources.

Mechanisch betaetigtes Ventil.png


Mechanically actuated valves
 

Manually actuated valves

In terms of design, these vales are comparable with mechanically actuated valves. However, instead of levers, rollers or plungers, these valves have a hand lever, a knob or sometimes a pedal switch.

 

Muskelkraft betaetigtes Ventil.png


Manually operated valves


Control types

Directly actuated valves

For a valve to switch, there must always be a movement within the valve. In the simplest cases only a seal is moved, but frequently it is a valve piston which may have several seals. Through the movement of the piston or the seal, the air is directed from one channel to another, or blocked or enabled.
With directly actuated valves, the movement of the valve piston or the seal can be triggered directly by the actuating element (solenoid coil, lever, pedal switch, etc.). This means the switching function of the valve is independent of the operating pressure, and is also suitable for vacuum applications. However, the force required for moving the valve piston increases proportionally to the size of the valve. On solenoid actuated valves, the solenoid coil is frequently larger than the actual valve.

Direktgesteuertes Ventil.png
Directly actuated valve

Indirectly actuated valves

Indirectly actuated valves are also designated as pilot actuated valves.
The task of the actuating element (solenoid coil, lever, pedal switch, etc.) is only to open or close a small pilot bore. The actual movement of the valve piston is generated by the medium - in this case air.
The major advantage of this type of actuation is that a low force is sufficient to switch even large valves. On a solenoid valve, this means that a small coil with low power consumption is able to switch a large valve.
However, this only works if pressure is actually applied.

 

Indirektgesteuertes Ventil.png
Indirectly actuated valve



Function

Directional control valves

The most common directional control valves are:

  • 2/2-way valves

    This valve simply blocks or opens a flow. It can be compared to a slide in a watercourse. Slide open - water flows. Slide closed - water doesn't flow.

  • 3/2-way valves

    The function of this valve is as follows: either the compressed air flows from 1 to 2 through the valve, or 1 is blocked while port 2 is exhausted via port 3. In practical

    applications, this valve could be used, for example, for actuating a single-acting cylinder. The air flows from 1 to 2, and the cylinder extends. Then the cylinder is not supplied

    with air and the air can escape from 2 to 3 and the cylinder retracts again.

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

Pressure regulators, shut-off and flow control valves

Druckregelventil.png Rueckschlagventil.png Drosselventil.png Drosselrueckschlagventil.png
The pressure regulator has the task of
adjusting the preset pressure of the medium
A non-return valve allows air to flow in one direction, while flow in the other direction is blocked (shut-off valve) With a flow control valve, the cross section
is narrowed and therefore the air flow rate is reduced
The one-way flow control valve is a combination of a non-return valve and a flow control valve.
The air can flow unhindered in one direction; in the other direction it is blocked by a non-return valve, and forced through the throttle point.

 


Proportional valves

                           Proportionalventil.png                                                          Stetigventil.png    

Proportional pressure valves Proportional flow control valves                          Proportional directional control valves

Logic valves

These include shuttle valves (also known as OR valves) and dual-pressure valves (AND valves)


ODER.png            UND.png
      OR valves                      AND valves

Links

Article in Wikipedia on valves