VMAC – Vehicle Mounted Air Compressors
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3.3 Speed Control
The PREDATAIR60 has the facility to signal for a higher engine
speed under high air demand conditions and for a lower engine
speed under low air demand conditions.
Most work trucks either have a built in electrically activated idle up
system or an after-market product may be available which will
provide this function.
It is not essential that the two speed feature be used, it is entirely
acceptable to run the PREDATAIR60 constantly at a fixed engine
rpm and pump GPM. There are, however, several advantages to the
two speed feature which should be considered when deciding
whether to go with two speed or single speed operation.
Two speed operation offers these advantages:
• lower fuel consumption.
• lower noise.
• lower wear rate on engine, hydraulic pump and compressor.
• greater latitude for flexible service intervals.
• better cold start behavior.
The preferred approach for speed control is to keep the hydraulic
flow as low as possible when the PTO first starts, then when the
PREDATAIR60 is engaged, the engine idles up for the desired
performance.
For single speed operation, the throttle would idle up to achieve the
desired CFM when the PREDATAIR60 is engaged (Figure 15).
For two speed operation, speed 1 is activated when the
PREDATAIR60 is engaged. This is set for the minimum desired
CFM. Speed 2 is connected to the purple wire and set to the
maximum desired CFM (Figure 16).
Always allow for efficiency loss as the hydraulic oil heats. Operate
the system for at least one hour at full load and monitor hydraulic
flow at speed 1 and speed 2 (if applicable). Adjust as required to
ensure that speed 1 flow does not drop below the minimum
requirement. A flow meter should be temporarily plumbed into the
PREDATAIR60 return line to confirm actual hydraulic flow.
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