PREVOST LE MIRAGE XLII, Руководство по обслуживанию

Страница: 1218 / 1342

1-4
62--11052
1.5 COMPRESSOR UNLOADERS
The compressor is equipped with unloaders for capacity
control. This consists of a self-contained, cylinder head
hot gas bypass arrangement. (See Figure 1-5)
The compressor unloader system can be controlled with
either a pressure actuated valve or an electrically
actuated (solenoid) valve.
1.5.1 Electric-Controlled Unloaders
The capacity controlled cylinder is easily identified by an
electric 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 1-6. 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 1-7.
1. Discharge Check
Valve
2. Discharge Manifold
3. Solenoid Valve
4. Piston Bypass
Control Valve
5. Cylinder Head
6. Suction Manifold
6
1
2
3
4
5
Figure 1-5. Compressor Unloader
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 1-6, 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.
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
11
1
2
3
4
5
6
7
8
9
10
15
12
13
14
Figure 1-6. Electric--Operated Unloader--
Unloaded Operation
c. Loaded Operation
Discharge pressure bleeds from the discharge manifold
(Figure 1-7, item 15) through the strainer (9) and bleed
orifice (8) 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 (2) 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.