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Regulators

Emerson Climate Technologies

HeadMaster Head Pressure Controls

The application of air-cooled condensers for year-

round operation, or during periods of low ambient

temperature, requires some means of control to main-

tain adequate condensing pressures that ensure proper

system performance. It is essential that proper liquid

refrigerant pressure be controlled to:

1) Maintain liquid subcooling and prevent liquid line

ash gas.

2) Provide adequate pressure at the inlet side of the

Thermostatic Expansion Valve to get enough pres-

sure drop across the valve port.

3) Properly operate systems with hot gas defrost or hot

gas bypass.

4) Provide adequate temperature for operation of heat

reclaim systems.

Without proper control of condensing pressure a

refrigeration system might not perform properly and

components can be damaged. Emerson’s HeadMaster

Control offers an efcient and economical approach to

this common industry problem on air cooled condensers.

The HeadMaster 3-Way Head Pressure Control

eliminates the need for special piping or multiple con-

trol valves. As a single unit it simplies piping and cuts

installation costs.

HeadMaster HP Operation

The HP control is a three-way modulating valve

controlled by the discharge pressure. The charged dome

exerts a constant pressure on top of the diaphragm. At

high ambient air temperature, bypass gas entering Port

B is allowed under the diaphragm where it counters the

pressure of the dome charge. This upward push on the

diaphragm allows the seat disc to seal against the top

seat, preventing ow from Port B (discharge gas) while

ow from Port C is unrestricted (see gure 6).

Figure 6: HeadMaster HP Valve CutAway View

As ambient air temperature falls, an uncontrolled air

cooled condenser will exhibit a corresponding decrease

in head pressure. As the discharge (bypass) pressure

falls, it no longer counters the dome charge pressure

and the diaphragm moves downward, moving the push-

rod and seat disc toward the bottom seat. This allows

discharge (bypass) gas to be metered into the receiver,

creating a higher pressure at the condenser outlet. The

higher pressure at the condenser outlet reduces the ow

from Port C and causes the level of condensed liquid to

rise in the condenser.

The ooding of the condenser with liquid cuts the

available condensing surface. The result is to raise the

pressure in the condenser and maintain an adequate

high side pressure. Figure 7 illustrates a typical appli-

cation of the 3-way control valve. This system is per-

haps the most economical and reliable way to control

discharge pressure. The three-way valve as shown in

gure 6 is a xed, non-adjustable valve. The wholesaler

replacement setting is normally furnished for a pressure

corresponding to 95° to 98°F condensing temperature

for the given system refrigerant.

Figure 7: Typical 3-Way Valve

Head Pressure Control Application

As with all head pressure control applications, addi-

tional liquid receiver capacity is required to prevent loss

of a liquid seal in the receiver when the condenser is

ooded. The receiver must be large enough to hold the

total system charge. The total system charge consists of

the following:

1. An operating charge which is the amount of refriger-

ant needed to operate the system during summer

(high ambient temperature) conditions.

2. An additional charge equaling the amount of refriger-

ant required to ood the condenser with liquid. The

condenser must be lled with liquid to a point where

a minimum head pressure is created for cold weather

(low ambient temperature) conditions.

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