Atlas Copco XAMS 1150 CD7 T3 APP Instruction Manual page 21

The compressor is provided with a continuous
pneumatic regulating system and a blow-off valve
(BOV), which is integrated in the unloader assembly
(UA). The valve is closed during operation by outlet
pressure of the compressor element and opens by air
receiver pressure when the compressor is stopped.
When the air consumption increases, the air receiver
pressure will decrease and vice versa. This receiver
pressure variation is sensed by the regulating valve
(RV) which, by means of control air to the unloader
assembly (UA), matches the air output to the air
consumption. The air receiver pressure is maintained
between the pre-selected working pressure and the
corresponding unloading pressure.
When starting the compressor, the throttle valve (TV)
is kept closed via receiver pressure. The compressor
element (CE) takes in air and pressure builds up
inside the receiver (AR). The throttle valve (TV) is
closed. The air output is controlled from maximum
output (100%) to no output (0%) by:
1. Speed control of the engine between maximum
load speed and unloading speed (the output of a
screw compressor is proportional to the rotating
speed).
2. Air inlet throttling.
If the air consumption is equal to or exceeds the
maximum air output, the engine speed is held at
maximum load speed and the throttle valve (TV) is
fully open.
If the air consumption is less than the maximum air
output, air receiver pressure increases and the
regulating valve supplies control air to throttle valve
(TV) to reduce the air output and holds air receiver
pressure between the normal working pressure and
the corresponding unloading pressure. Unloading
pressure = normal working pressure + 1 bar (14.5 psi).
When the air consumption is resumed, the blow off
valve (BOV) closes and the throttle valve (TV)
gradually opens the air intake and the electronic speed
regulator increases the engine speed.
The construction of the regulating valve (RV) is such
that any increase (decrease) of the air receiver
pressure above the pre-set valve opening pressure
results in a proportional increase (decrease) of the
control pressure to the throttle valve and the
electronic speed regulator.
Part of the control air is vented into the atmosphere,
and any condensate discharged, through the vent
holes (VH).
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