Proportioning valve

A proportional valve, a proportional valve, which not only allows discrete switch positions by means of a proportional magnet, but a smooth transition of the valve opening. Proportional valves are used in hydraulic and pneumatic applications especially where variable flow rates are required. There is a proportional flow control valves as valves having an input and an output, and a directional valve with more than two working ports. They usually have a non- linear flow characteristic and are only suitable for control tasks.

Designs

Proportional valves are electromagnetic or self-operated valves which any intermediate positions can take between open and closed. Electromagnetically driven valves have a solenoid, which pushes against spring most. If he presses against the fluid pressure itself, the valves open when de-energized, which may be beneficial as part of other constructions. Serves the valve, for example. directly control the movement of a cylinder, however, recommended that a valve that closes when de-energized. The active electromagnet then acts as a spring against passive force. Electromagnetic proportional valves are available for pneumatic and hydraulic applications.

Medium -controlled proportional valves are controlled with hydraulic fluid. It comes from other proportional valves. To serve medium controlled proportional valves as ' main' stage (s) in multi-stage systems. As pistons and cylinders are pneumatically other position not good without regulation, there is no medium-controlled pneumatic proportional valves.

Proportional valves are usually constructed as a piston valves. That is, the shut-off member is an axially displaceable piston most connecting side mounted inlet and outlet openings, or closing. There are also conical valve and poppet valve forms, for example. as feedforward control.

A valve has two working ports, such as input and output, it is according to the object, a flow control valve, also called a throttle valve, but it may also be regarded as a special form of the directional valve, that is, as a 2/2-way valve, whatever its internal structure. You can, after establishing his simultaneously piston, cone or disc valves. Way valves higher order there are only a piston valve, a construction of a 5/3-way valve in plate design would be too complicated.

In a proportional spool valve, the piston is the one -way switching valve is not dissimilar. Because the intermediate positions be availed between open and closed, however, he receives a slightly different form. It results from the desired flow characteristic, which describes the dependence between drive current and flow.

Proportional valves, especially single-stage hydraulic versions may require a considerable electromagnetic force.

Examples

Single-stage pneumatic proportional throttle valve

A simple proportional pneumatic valve controls the air passage opening of a shut-off plate with the help of an electromagnet, and a counteracting spring. If the coil of the electromagnet overcoming the restoring force of the spring, the valve opens as in the degree to which the current increases in the electromagnet.

Single-stage pneumatic proportional directional valve

Driving a single-stage - direct operated proportional directional control valve must be different from that of a switching -way valve, not much. Connecting a linearly movable piston of the openings to the inputs and outputs or closing of a solenoid and a spring that moves one or the other direction. In this example, however, a blocking position in the energized state is desired, during which there is no air flow. That's with a 5 /3 way valve, unfortunately, in the middle position, which requires additional changes. The coil must be able to move the piston operates in two directions. This can be accomplished here. with 2 coils and 2 springs. The coils are arranged so that they pull the piston in opposite directions. This normally is only one of them in operation. Electroless provision in the center position via the springs.

Pilot operated proportional throttle valve for low pressure water

A two-way proportional valve or the proportional throttle valve for water may be designed as a pilot-operated two-stage, and thus the diaphragm valve. Said movable membrane is a mechanical connection between the main stage and pilot precursor. It is used for pressures of about 10 bar. When de-energized, the spring pushes the piston to the dish-shaped shut-off downward. This, in turn, pushes the closure member with the conical closure member, which is mounted in the center of the circular diaphragm, downward, thereby closing the valve.

Does the coil the piston up, initially the outlet nozzle opening in the closure member. Thus, the fluid from the pressure source input (P) flows through two nozzles to the exit. The pressure above the membrane thereby decreases and pulls it upwards, namely so far that the outlet nozzle to again, and the pressure is balanced and under the membrane. Thus the main stage goes on, but only to the extent permitted by the piston and thus the control current in the coil. In the way the electromagnetic coil force is amplified by the fluid pressure.

After dropping of the coil current, the spring force takes over again, the closing of the valve.

A direct-operated three-way proportional valve for hydraulic transmission

Frequently proportional valves can be found in the hydraulic oil. In the 3-way valve shown in the picture, the solenoid pushes the left of center against the spring, which is to the right. It is up to no coil current Ip, there is still 100 % flow from A to T ( tank) and P ( pressure source ) to B. If the coil current is turned on and has, for example, half of the necessary for full scale maximum, as in the next image moves the piston to the right, and closes the openings.

The drawn differential transformer (LVDT, left) is an optional component for measuring the position of the piston. It is used for the electronic control. The valve can for example be placed exactly in the locked position, with about 50% of coil current, and this blocking position can be checked before actually moving a cylinder or something similar.

A direct-operated three-way proportional valve with two coils

The hydraulic version of the pneumatic proportional directional valve of the section used again further up 2 coils and 2 springs to normally reach the locked position. But coils directly operated hydraulic proportional valves need more power and more space than the pneumatic version, so they are not located next to each other but on two different pages. Each of them moves in a different direction, is at rest so that the valve to.

Two-stage three-way proportional valve

Are larger hydraulic volume flow control, proportional valves can connected in series to two -stage valves ( cascaded) to be. The precursor then moved instead of a cylinder the piston of the main stage and the main stage then moves the cylinder or whatever. The main stage is then a medium controlled proportional valve. The space behind the respective end of the main valve piston is connected as a cylinder with two working connections of the precursor.

Coverage

The control edges are the parts on the valve piston, the seal or release the openings to the working line ports A and B. They are ultimately responsible for the flow of the valve. You will be proportional valves on both sides about the opening of the working line, here it is on A. This overlap is referred to in directional control valves as positive overlap. It separates the different pressure ranges and seals with it. While opening only the dead zone must be overcome, then the proportional valve opens slowly. Why have standard proportional valves usually a non- linear flow characteristics which are only suitable for control tasks. The dead zone of overlap must be compensated, for example, control technology.