Installation Manual Series CF (excluding encapsulated screw compressors) 23042013 Rev. A / May 2007 11 of 60
4.2 Explanations to the electromo-
tor drive tubing plan
The pressures stated are abso-
lute pressures.
4.2.1 Start-up
Suction valve [4] is closed as no control pres-
sure is applied yet.
To allow for intake of a small amount of air for
pressure build-up, the throttle valve [5] is set
as to provide for a pressure of > 0.1 bar
ahead of the compressor.
An incorrect construction/design of suction
valve might lead to problems/damages
with/of compressor.
Throttle valve [5] is required only
if suction valve [4] does not have
an adjusting possibility for di-
rected leakage (e.g. provision of
bores in a throttle).
Hand switch [23] is closed.
Load position: Electric circuit for relief valve
[16] and the 2/3 way valve [20] is closed.
At the start of the motor, relief valve [16]
closes (idle: open), the 3/2 way valve [20]
opens.
Minimum pressure valve [17] is closed, thus
separating the compressor system from the
mains. Minimum pressure valve must be ad-
justed to a minimum pressure of 4.5 bar.
To protect motor [2] and coupling, starting the
motor should only be possible if there is a
pressure maximum of 2 bar behind the com-
pressor.
4.2.2 Operation under load
When required control pressure has been
reached, the suction valve [4] opens.
Minimum pressure valve [17] opens only after
a pressure of approx. 4.5 bar has built-up in
the compressor system. This pressure en-
sures a sufficient oil supply to the compressor
during operating under load.
The compressor boosts into the mains as
soon as the system pressure ahead of non-
return valve [18] exceeds the pressure of the
mains.
4.2.3 No-load operation
No-load operation is possible:
1. Automatically in case of mains pressure is
higher than the upper switch-point of pres-
sure controller [19].
2. Upon actuation of hand switch [23].
(No-load position: Power supply for relief val-
ve [16] and 3/2 way valve [20] is interrupted).
The sequence is identical:
3/2 way valve [20] closes because of the ab-
sence of current, and suction valve [4] closes
because of the absence of control pressure.
At the same time, the absence of current
opens relief valve [16], the pressure in the
compressor system drops.
Non-return valve [18] separates the com-
pressor system from the mains.
(In addition, minimum pressure valve [17]
closes at a pressure of approx. 4.5 bar.)
As the mains pressure drops and reaches the
lower switch-point, pressure controller [19]
again closes the electric circuit.
This makes relief valve [16] close and 3/2
way valve [20] open. The control pressure
from the mains opens immediately suction
valve [4] by means of non-return valve [22].
Further sequence as described under “Op-
eration under load”.
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