Trane TRG-TRC012-EN Slide Valve Operation

24 TRG-TRC012-EN

notes

period three

Compressor Capacity Control

The slide valve is operated by a piston and cylinder assembly. Extension and

retraction of the operator shaft positions the slide valve along the compressor

rotors.

High-pressure refrigerant vapor, controlled by 2 solenoid valves, is fed to or

bled from this assembly in order to position the valve. To close the slide valve

and load the compressor, the load valve is opened and the unload valve is

closed. This allows high-pressure refrigerant vapor to enter the cylinder from

the discharge of the compressor, extending the operator shaft and moving the

slide valve so that it covers more of the rotor length.

Conversely, to open the slide valve and unload the compressor, the load valve

is closed and the unload valve is opened. This allows the high-pressure

refrigerant vapor to bleed out of the cylinder into the low-pressure area within

the compressor housing. A spring helps return the piston, retracting the

operator shaft and moving the slide valve such that the rotors are more

uncovered. This reduces the effective length of the rotors, which are

compressing vapor.

On shutdown the unload solenoid valve is energized and the spring drives the

slide valve to the fully-unloaded position. This ensures that the compressor

always starts fully unloaded.

When both solenoid valves are closed, the operator shaft holds the slide valve

at its current position.

Slide Valve Operation

to low-

pressure

compressor

housing

high-pressure

refrigerant vapor

slide valve

operator

shaft

spring

spring piston

piston cylinder

cylinder

load

valve

valve unload

unload

valve

Figure 36