Parker S7A Installation Information

Type S7A
August, 2001
Installation Information
Refrigerating Specialties Division
309672
Coil Assembly. One coil size
fits all Refrigerating Specialties
Industrial solenoid valves
Plunger Needle
Assembly
Piston-plug
Assembly
Manual Opening Stem
Seal Cap
Fig. 1
Solenoid Valve
TYPE S7A
Port Size 3/4"-1" (20-25mm)
Compact, low capacity, wafer mount sole-
noid valve for service with most refrigerants
and their corresponding lubricants. Re-
quires R/S industrial coils offered as open
frame, optional remote pilot lights or encap-
sulated, optional integral pilot light. Both
coil styles available with 18 in. leads or DIN
connector.
Purpose
A solenoid valve is an electrically operated device used
to control the flow of liquids or gases in a fully open or
fully closed configuration. Solenoid valves do not
modulate; they either permit or prevent fluid flow in the
normal direction.
Principles of Operation
The S4A, S4W, S5A, S7A, S7F and S8F are normally
closed pilot operated solenoid valves that employ the
Refrigerating Specialties Industrial operator and the
corresponding selection of R/S industrial coils. Starting
from the closed position, the plunger needle is seated in
the pilot port preventing pilot stream flow. Energization
of the solenoid coil forms a magnetic field, drawing the
plunger upward. The plunger strikes the needle lifting it
out of its seated position. This permits pilot stream flow
through the seat. De-energization of the solenoid coil
breaks the magnetic field and permits the spring-
assisted needle to return to seat, interrupting the pilot
stream flow.
S7A
When energized, the pilot port is opened. This permits
flow of the trapped refrigerant from the top of the piston,
which reduces pressure above the piston. The piston is
then forced upward by the upstream pressure acting on
the piston-main valve. This opens the valve port to allow
flow through the valve. This piston-main valve is then
held up magnetically by the plunger-needle assembly
and no pressure drop is required to keep the valve open.
If no pressure difference across the valve is present
when the solenoid coil is energized, the plunger-needle
assembly, opening the valve lifts the piston main valve
off the seat. When de-energized the pilot port is closed
and the pressure above and below the piston-main valve
is equalized through the bleed hole in the piston. The
weights of the plunger-needle and the piston-main valve
assembly cause the piston-main valve to drop it its seat
and stop the flow. The pressure difference across the
valve, acting upon the area of the valve seat, holds the
piston-main valve in a tightly close position.
1