Brochure

Parker Hannifin Corporation
Climate & Industrial Controls Group
Cleveland, OH
Catalog CIC-2003-1/US
Refrigeration Solenoid Valves
254
Coil De-energized
Valve Closed
Operating Principles
Introduction
Solenoid valves are highly engineered products which
can be used in many diverse and unique system appli-
cations. This section provides a brief overview of the
components and functional varieties of solenoid valves.
General Information
Valve Construction and Basic Operation
A solenoid valve is an electronically operated device. It
is used to control the flow of liquids or gases in a posi-
tive, fully-closed or fully-open mode. The valve is com-
monly used to replace a manual valve or where remote
control is desirable. A solenoid is operated by opening
and closing an orifice in a valve body which permits or
prevents flow through the valve. The orifice is opened
or closed through the use of a plunger that is raised or
lowered within a sleeve tube by energizing the coil. The
bottom of the plunger contains a compatible sealing
material, which closes off the orifice in the body, stop-
ping flow through the valve.
The solenoid assembly consists of a coil, plunger and
sleeve assembly. In a normally closed valve, a plunger
return spring holds the plunger against the orifice, pre-
venting flow through the valve. When the coil is ener-
gized, a magnetic field is produced raising the plunger
allowing flow through the valve. In a normally open
valve, when the coil is energized, the plunger seals off
the orifice stopping flow through the valve.
Operating Principles Technical Information
Two-Way Solenoid Valves
Two way valves control flow in one direction. They may
be direct operated or pilot operated.
Direct Operated Solenoid Valves
Direct operated solenoid valves function to directly
open or close the main valve orifice, which is the only
flow path in the valve. Direct operated valves are used
in systems requiring low flow capacities or in applica-
tions with low pressure differential across the valve
orifice. The sealing surface that opens and closes the
main valve orifice is connected to the solenoid plunger.
The valve operates from zero pressure differential to
maximum rated pressure differential (MOPD) regard-
less of line pressure. Pressure drop across the valve is
not required to hold the valve open.
Coil Energized
Valve Open
Pilot Operated Valves
Pilot operated valves are the most widely used solenoid
valves. Pilot operated valves utilize system line pres-
sure to open and close the main orifice in the valve
body. In a piston style valve, the main orifice is held
closed with a piston seal pressed against the main
orifice by the combined fluid pressure and spring
pressure. In a normally closed valve, the piston is
shifted or opened when the pilot operator is energized.
This allows process fluid behind the piston to evacuate
through the valve outlet. At this point, the system line
pressure moves the piston opening the main orifice of
the valve allowing high capacity flow through the valve.
When energizing the coil of a normally open valve, fluid
pressure builds up behind the piston forcing the piston
to seal the main orifice of the valve.
Coil De-energized
Valve Closed
Coil Energized
Valve Open