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Solenoid Valves

Emerson Climate Technologies

Direct Acting Solenoid Anatomy

What Are Solenoid Valves?

A solenoid valve consists of two distinct but integral

acting parts, a coil and a valve. See drawing below for

complete valve anatomy.

Solenoid Valves

In most refrigeration applications, it is necessary to

start or stop the ow in a refrigerant circuit to automati-

cally control the uids in the system. An electrically

operated solenoid valve is usually used for this purpose.

Its basic function is the same as a manually operated

shut off valve, but by being solenoid actuated, it can be

positioned in remote locations and may be conveniently

controlled by simple electrical switches.

Solenoid valves can be operated by a thermostatic

switch, oat switches, low pressure switches, high pres-

sure switches or any other device for making or breaking

an electric circuit, with the thermostatic switch being the

most common device used in refrigeration systems.

Principles of Solenoid Operation

Solenoids are either direct acting or pilot operated.

The application determines the need for either of these

types. The direct acting valve is used on valves with low

capacities and small port sizes. The pilot operated type

is used on the larger valves, eliminating the need for

larger coils and plungers.

1. Direct Acting

In the direct acting type valve, as discussed under

Solenoid Valve operation, the plunger is mechanically

connected to the needle valve. When the coil is ener-

gized, the plunger pulling the needle off the orice is

raised into the center of the coil. A direct acting valve will

operate from zero pressure differential to its maximum

rated pressure differential, regardless of the line pres-

sure.

The direct acting type valve is only used on small

capacity circuits because of the increased coil size that

would be required to counter the large pressure dif-

ferential of large capacities. The required coil would be

large, uneconomical, and not feasible for large capacity

circuits. To overcome this problem on large systems,

pilot operated solenoid valves are used.

The coil is nothing more than electrical wire wound

around the surface of a cylindrical form usually of circu-

lar cross section. When an electric current is sent thru

the windings, they act as an electromagnet. The force

eld that is created in the center of the solenoid is the

driving force for opening the valve. Inside is a moveable

magnetic steel plunger that is drawn toward the center

of the coil when energized.

The valve contains an orice through which uid

ows when open. A needle or rod is seated on or in the

orice and is attached directly to the lower part of the

plunger.

When the coil is energized, the plunger is forced

toward the center of the coil, lifting the needle valve off

of the orice and allowing ow. With a normally-closed

valve, when the coil is de-energized, the weight of the

plunger and in some designs, a spring, causes it to fall

and close off the orice, thus stopping the ow through

the valve. Less common are normally-open valves which

are open when the coil is de-energized.

Enclosing Tube

Top Plug

Assembly

Return Spring

Plunger Assembly

Collar

Body

Assembly

O-Ring

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