Parker S7A Service manual

RefrigeratingSpecialtiesDivision 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.
Type S7A
August, 2001
Installation Information
Fig. 1
Coil Assembly. One coil size
fits all Refrigerating Specialties
Industrialsolenoidvalves
PlungerNeedle
Assembly
Piston-plug
Assembly
ManualOpeningStem
SealCap
309672

RefrigeratingSpecialtiesDivision 2
Installation
Refer also to Safety Installation Bulletin RSBCV. Do
not remove the protective covers from the inlet and
outlet of the valve until ready to install. They protect the
interior from dirt and other foreign matter.
Select a location for installation where the valve will be
easily accessible for adjustment and maintenance. Avoid
locations where personnel, traffic, material handling or
other equipment may damage the valve. If the valve
surfaces will be cold, avoid areas where ice may accu-
mulate in the body.
Before installing the valve, check to see that all chips,
scale, dirt and other foreign material are removed from
the pipes; also be sure the arrow on the valve body is
pointing in the flow direction. Remove the protective
covers from the valve.
Mount valves with R/S Industrial operators (S4A, S4W,
S5A, S7A, S7F and S8F) only in horizontal pipeline with
solenoid at the top; they will work properly only in this
position.
In a liquid line the Solenoid Valve should be near the
expansion valve inlet. It is advisable to install the RSF
close coupled companion strainer ahead of the valve for
protection against dirt and chips.
Install with the arrow on the valve body in the direction
of flow. If the valve is backwards, the flow will not be
stopped when the valve is electrically de-energized.
Solenoid Valves can stop flow only in the direction from
normal inlet to normal outlet (as shown by the arrow on
the body). If reversal of pressure occurs in the system
so the outlet pressure exceeds the inlet pressure the
main valve plug will be blown away from its seat and
reverse flow will occur. If a system has this type of
pressure reversal (as encountered during hot gas
defrost with liquid recirculation systems), a check valve
such as Refrigerating Specialties Division Type CK4A
will need to be added. Check valves must be installed
downstream to avoid trapping liquid.
If the valve is to be insulated be sure to allow access to
the manual opening stem and strainer cover.
Do not insulate the coil or coil housing.
Connect the solenoid lead wires only to an electrical
supply source as indicated on the solenoid coil. The
power source must be capable of supplying full, constant
voltage. The wires to which the solenoid leads are
connected must be of suitable gauge, and must be
insulated and enclosed appropriate to the voltage and
the environmental or conformity requirements.
Forpartsselectionsee Bulletin30-92,latestedition.
Forsolenoid coil availabilitysee RSBCVlatest edition.
MM INCH
A282 11.1
B102 4
C157 6.2
D216 8.5
E261 10.3
F239 9.4
H117 4.6
J180 7.1
N25 1
P13 0.5
DIMENSIONAL DATA