Section 5
SEQUENCING TIMERS FOR
EFFICIENT OPERATION
21
5. SEQUENCING TIMERS FOR EFFICIENT OPERATION
5.1 RECOVERY TIME AND DELAYED START TIMER
The Recovery Timer is used to keep machines from starting, loading or unloading all at
the same time. The Delayed Start timer is used to keep machines from starting
unnecessarily due to temporary load changes. These timers and the Lowest Pressure
Parameter are used to tune a system so that it is energy efficient but still responds to
system demand changes.
Delaying loading and starting of machines will make the system more efficient, but must
be balanced against system demands. For example delaying the start of a machine will
be more energy efficient but could cause system pressure to drop below desired levels.
The Recovery Timer is used in conjunction with the load and unload parameters. There
are also two calculated parameters derived from the load and unload settings. These are
the Sequencing Unload and Sequencing Load pressures. The Sequencing Unload
pressure is 2 psi below the unload setting. The Sequencing Load pressure is 2 psi above
the load setting.
For example, if the Unload Parameter is set to 110 and the Load Delta parameter is set
to 10 then:
110 psi = Unload pressure; all machines unload above this pressure
108 psi = Sequencing unload pressure; trim machine unloads above this pressure
102 psi = Sequencing load pressure;next machine in sequence loads below this
pressure
100 psi = Load pressure, all machines load below this pressure
If the system pressure goes above 110 (e.g. 111) for any reason, all machines will
unload immediately (regardless of recovery timer). If the system pressure goes below
100 (e.g. 99) all running machines will load (regardless of recovery timer). The recovery
timer only comes into play if the pressure is between 108-110 (for unloading), or 100-102
(for loading). The following examples will describe operation.
If system pressure drops below the Load Pressure setting, but is above the Lowest
Pressure setting, then the Delayed Start Timer is used to time the start of the next
machine in sequence. This timer starts at 120 seconds but will time out sooner if the
pressure drops. The length of time is prorated over the difference between the Load
Pressure setting and the Lowest Pressure setting.
For example:
A compressor’s Load pressure is 100 psi and the Lowest Pressure setting is 70 psi.
If the System Pressure is above 100 and drops to (and stays at):
99, the machine will start in about 120 seconds (2 minutes)
NOTE
The recovery timer is an accurate timer. However, because of system delays
caused by variables like filtering and communications, recovery time may vary
from 0 to 5 seconds. If, for example, the recovery timer is set to 10 seconds, the
actual delay may be from 10 to 15 seconds.
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