Technical information


Proportional solenoid valves
Introduction
The key to the operation of a proportional valve is a balance established between the forces in action on the plunger.

These balanced forces include a mechanical force provided by a spring specially developed for proportional valves and a magnetic force created by the current level passing through the coil.

The spring force is proportionaly opposed by the magnetic force.

1 Coil
2 Spring
3 Plunger
4 Magnetic field
FMagnet Magnetic force
FSpring Spring force

Power supply
Often, one hears that proportional valves react porportionnaly to the voltage supplied. However, in practice, the current passing through the valve will heat the coil and eventually increase the internal resistance.
At constant voltage, increasing the resistance will provoke a current drop and thus a drop of the magnetic force. As a result, the valve will tend to slowly close.

To avoid this problem, one can use a stabilized current supply. The current supply will be independent of the coil resistance.

The only draw-back is that such a device is more expensive than a voltage supply.

Sealing
To ensure a positive shut-off when the valve is de-energized, there is always a voltage/current offset before obtaining a flow (liftoff point).

Control
Usually, a closed control loop circuit and a pressure (or flow) sensor are used with the power supply.
If high precision is not an issue, one can also use an open control loop

Essential parameters
Our catalogue presents a series of standard proportional valves. However, in order to guarantee the correct operation of our products for a given application, it is essential to provide the following parameters to FAS engineering:

  • Maximum pressure
  • Minimum pressure
  • Maximum flow
  • Back-pressure range
  • Fluid type
  • Ambient temperature range
  • Fluid temperature range.