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THERMOSTATIC EXPANSION VALVE (TXV)

All 581J units have factory-installed nonadjustable thermostatic

expansion valves (TXV). The TXVs are bleed port expansion

valves with an external equalizer. TXVs are specifically designed

to operate with Puron

or R-22 refrigerant. Use only factory au-

thorized TXVs. See Fig. 18.

Fig. 18 — Thermostatic Expansion Valve (TXV) Operation

TXV Operation

The TXV is a metering device that is used in air conditioning and

heat pump systems to adjust to the changing load conditions by

maintaining a preset superheat temperature at the outlet of the

evaporator coil. See Fig. 19.

The volume of refrigerant metered through the valve seat is de-

pendent upon the following:

1. Superheat temperature is sensed by the cap tube sensing

bulb on suction the tube at the outlet of evaporator coil.

This temperature is converted into pressure by refrigerant

in the bulb pushing downward on the diaphragm which

opens the valve using the push rods.

2. The suction pressure at the outlet of the evaporator coil is

transferred through the external equalizer tube to the

underside of the diaphragm.

3. The needle valve on the pin carrier is spring loaded, exert-

ing pressure on the underside of the diaphragm. Therefore,

the bulb pressure equals the evaporator pressure (at the

outlet of the coil) plus the spring pressure. If the evapora-

tor load increases, the temperature increases at the bulb,

which increases the pressure on the topside of the dia-

phragm, pushing the carrier away from the seat, opening

the valve and increasing the flow of refrigerant. The

increased refrigerant flow causes increased leaving evapo-

rator pressure which is transferred through the equalizer

tube to the underside of the diaphragm. This causes the pin

carrier spring pressure to close the TXV valve. The refrig-

erant flow is effectively stabilized to the load demand with

a negligible change in superheat.

Fig. 19 — TXV Sensor Bulb Location

OUTLET

INLET

PUSHRODS

DIAPHRAGM

NEEDLE

VALVE

SPRING

DISTRIBUTOR

FEEDER TUBES

CAPILLARY TUBE

COIL

BULB

EXTERNAL EQUALIZER TUBE

TXV SENSOR

BULB

CLAMP

CIRCUIT 1

CIRCUIT 2

TXV

(CIRCUIT 2)

TXV

(CIRCUIT 1)

TXV SENSOR

BULBS

TXV

SENSOR

BULBS

Brand	Bryant
Model	Preferred Series
Category	Air Conditioner
Language	English

Bryant Preferred Series User Manual

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