Emerson Fluid Chiller Guia de Resolução de Problemas descarregar pdf (Página 28)

Solenoid Valves

Emerson Climate Technologies

Solenoid Valve Selection

The selection of a Solenoid Valve for a control ap-

plication requires the following information:

1. Fluid to be controlled

2. Capacity required

3. Maximum operating pressure differential (MOPD)

4. Electrical characteristics

5. Maximum working pressure required (MWP)

The capacities of Solenoid Valves for normal liquid

or suction gas refrigerant service are given in tons of

refrigeration at some nominal pressure drop and stan-

dard conditions. Manufacturers’ catalogs provide ex-

tended tables to cover nearly all operating conditions for

common refrigerants. Follow the manufacturer’s sizing

recommendations. Do not select a valve based on line

size. Pilot operated valves require a pressure drop to

operate and selecting an oversize valve will result in the

valve failing to open. Undersized valves result in exces-

sive pressure drops.

The solenoid valve selected must have a MOPD rat-

ing equal to or greater than the maximum possible differ-

ential against which the valve must open. The MOPD or

Maximum Operating Pressure Differential considers the

inlet and outlet valve pressures. If a valve has a 500 psi

inlet pressure and a 250 outlet pressure, and a MOPD

rating of 300 psi it will operate, since the pressure dif-

ference (or 500-250) is less than the 300 MOPD rating.

If the pressure difference is larger than the MOPD, the

valve will not open.

Minimum Operating Pressure Differential

Consideration of the maximum working pressure

required is also important for proper and safe operation.

A solenoid valve should not be used for an application

when the pressure is higher than the valve maximum

working pressure. Solenoid valves are designed for a

given type of uid so that the materials of construction

will be compatible with that uid. Special seat materi-

als and synthetics may be used for high temperature

or ultra-low temperature service. Special materials are

required for corrosive uids. Special attention to the

electrical characteristics is also important. Required

voltage and Hertz must be specied to ensure proper

selection. Valves for DC service often have different in-

ternal construction than valves for AC applications, so it

is important to study the manufacturer’s catalog informa-

tion. Solenoid valves should never be used as a Safety

Shut Off unless specically designed and rated for that

service.

NOTE: No minimum pressure differential – valve

will not operate.

NOTE: Pressure differential greater than minimum

– valve will operate.

50 psig 50 psig 194 psig 200 psig

sP = 0 psig sP = 6 psig

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