04-01-2013, 03:55 PM
Solenoid Valve Basics
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Switching Functions & Symbols
Most solenoid valves operate on a digital principle. They therefore
possess two distinct states, which are (1) - when the coil is
activated by an electrical current, and (2) - when the valve is resting
(without electricity). Valve functions are defined from the resting
position.
The direct acting or pilot operated solenoid valves may have two
functions:
Normally closed (NC)
A solenoid valve is normally closed (abbreviated - NC) if there is no
flow across the valve in its resting position (with no current on the
solenoid contacts).
Normally open (NO)
A solenoid valve is said to be“normally open” (abbreviated NO)
when it enables fluid to pass in its resting position (with no current
on the solenoid contacts).
Latching or Bi-stable
We manufacture solenoid valves designed for applications where
reduced energy consumption is the determining factor. For these
applications a short electrical impulse enables the solenoid valve
to be opened or closed, and thanks to the residual effects of a
permanent magnet this is sufficient for maintaining the valve in a
particular working position with no electrical energy consumption.
A short impulse of inverted polarity ensures the valve’s return to its
previous position. Electrical power consumption and heating are
almost negligible.
Media Separated Solenoid Valves
Media separated (MS) solenoid valves are specially designed for
transporting corrosive or ultra-pure fluids.
They are designed so that the valve’s membrane (violet) enables
the medium to be separated from the operating part of the valve
(orange) while maintaining a minimum dead (unswept) volume.
Both the membrane and the valve body are highly resistant to
chemical corrosion and can be easily opened for cleaning.
Power Supply
A common assumption is that proportional valves react proportionally
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.