Carrier TRANSICOLD 05G, Операция и обслуживание, Страница: 8 / 23

1-4
1.5 COMPRESSOR UNLOADER
The 6 cylinder 05G compressor can be applied with 2
bank of unloading.
There are two types of compressor unloader systems;
the first one is the hot gas bypass and the second is the
suction cutoff. They are easily distinguished from each
other by observing the bottom side of the compressor
cylinder head, it is either blank (Hot gas bypass) or has a
cover plate (Suction cutoff).
The two types of compressor unloader systems can
be controlled with either a pressure actuated valve or an
electrically actuated (solenoid) valve.
1.5.1 HOT GAS BYPASS UNLOADER
The compressor is equipped with an unloader for
capacity control. This consists of a self-contained,
cylinder head bypass arrangement (See Figure 1-4)
which is electronically controlled by the temperature
controller.
The capacity controlled cylinder is easily identified by
the solenoid which extends from the side of the cylinder
head. When the solenoid energizes, the cylinder unloads
allowing discharge gas to circulate as shown in Figure 1-5.
The unloaded cylinder operates with little or no pressure
differential, consuming very little power. A de-energized
solenoid reloads the cylinder as shown in Figure 1-6.
2
1
3
4
5
6
1. Discharge Check
Valve
2. Discharge Manifold
3. Solenoid Valve
4. Piston Bypass
Control Valve
5. Cylinder Head
6. Suction Manifold
Figure 1-4. Compressor Unloader --- Hot Gas Bypass
a. Major Working Parts
1. Solenoid and valve system
2. Spring loaded piston type bypass control valve
3. Spring loaded discharge check valve
b. Unloaded Operation
Pressure from the discharge manifold (Figure 1-5,
item 15) passes through the strainer (9) and bleed orifice
(8) to the back of the piston bypass valve (7). Unless bled
away, this pressure would tend to close the piston (6)
against the piston spring (5) pressure.
With the solenoid valve (1) energized the solenoid
valve stem (2) will open the gas bypass port (3).
Refrigerant pressure will be bled to the suction
manifold (10) through the opened gas bypass port . A
reduction in pressure on the piston bypass valve will take
place because the rate of bleed through the gas bypass
port is greater than the rate of bleed through the bleed
orifice (8)
.
When the pressure behind the piston has been
reduced sufficiently, the valve spring will force the piston
bypass valve back , opening the gas bypass from the
discharge manifold to the suction manifold.
Discharge pressure in the discharge manifold will
close the discharge piston check valve assembly (14)
isolating the compressor discharge manifold from the
individual cylinder bank manifold.
The unloaded cylinder bank will continue to operate
fully unloaded until the solenoid valve control device is
de-energized and the gas bypass port is closed.
10
11
12
13
4
6
5
15
14
1
9
2 3
8
7
1. Solenoid Valve
2. Valve Stem
3. Gas Bypass Port
4. Spring Guide
5. Spring
6. Piston
7. Piston Bypass Valve
8. Bleed Orifice
9. Strainer
10. Suction Cavity
11. Cylinder Discharge
Valve
12. Valve Plate
13. Cylinder Suction
Valve
14. Discharge Piston
Check Valve
Assembly
15. Discharge Manifold
Figure 1-5. Compressor Cylinder Head Unloaded ---
Hot Gas Bypass
c. Loaded Operation
Discharge pressure bleeds from the discharge
manifold (Figure 1-6, item 15) through the strainer (9)
and (8) bleed orifice to the solenoid valve stem (2)
chamber and the back of the piston bypass valve (7).
With the solenoid valve (1) de-energized the solenoid
valve stem will close the gas bypass port (3).
Refrigerant pressure will overcome the bypass valve
spring (5) tension and force the piston (6) forward closing
the gas bypass from the discharge manifold to the suction
manifold (10).
Cylinder discharge pressure will force open the
discharge piston check valve assembly (14). Refrigerant
gas will pass into the compressor discharge manifold.