WARNING
Inside the valve, there is a very heavy, tight spring. Provided the valve is intact, the spring presents no
danger when dismantling.
High-stage units
For high-stage units, the cold-start valve is equipped with a large spring which creates a 2.0 bar [30
psi] pressure in the oil separator (above suction pressure) for lubrication of the compressor.
Once the compressor is running it begins to force gas to the condenser at connection P2.
As the condenser heats up, the pressure begins to rise as the compressor suction pulls down in
pressure. As soon as a differential pressure has developed between the condenser and suction
side,these pressures act across a piston inside the cold-start valve to partially overcome the
spring force. When the differential pressure reaches and exceeds 2.0 bar [30 psi], the piston fully
overcomes the spring force and powers the valve fully open for a very low operating pressure drop.
Booster applications
For booster applications, the valve is equipped with a light spring, which produces 0.5 bar [7 psi]
oil pressure above suction pressure before it fully powers open. An oil pump is required to ensure
compressor lubrication.
The unit is also equipped with a suction check valve by-pass. The oil separator will slowly
bleed down to approximate system suction pressure when the unit is stopped. This allows the
compressor drive motor to have an easier start, and the discharge check valve will seat more
.
Note:
For alarm descriptions and shutdown or cut-out parameters, refer to the separate
control system manual.
SAB 283-355 A-Frame OHU 6042 and OHU 7650 (including ATEX) Screw Compressor Unit
50
