Parker S7A Manuale di servizio

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

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