Gardner Denver PUREAIR EWD99E, Руководство по эксплуатации и обслуживанию

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compressors in sequence mode. If it is desired to dictate the complete initial sequence manually, wait
until the previous machine decrements one position and then place the next desired compressor in
sequence mode. If it is acceptable to let the master determine the initial sequence, simply wait until the
master has decremented its rotation number once, and then place all remaining compressors in
sequence mode. Remember that once a master is established, no further self-decrementing is done by
the individual compressors. Instead, they will wait until the master assigns them a rotation number.
Rotation numbers are displayed in the bottom display line, with the mode indication. For example, the
mode indication for the current master is SEQ1; for the first lag compressor, SEQ2; second lag, SEQ; etc.
2. HOW THE “AUTO SENTRY W” CONTROLS PRESSURE WHILE SEQUENCING
Each compressor operates exactly the same as if it were in AUTO mode with one exception: it has a
dynamic unload point. The initial unload point is determined by the equation shown above. A
compressor is started when the system pressure drops below its programmed load point, after waiting for
[ ‘LAG START INTERVAL’ times (rotation number - 1)] seconds. This prevents all lag compressors from
starting at once. Note that a compressor’s [‘LAG START INTERVAL’ times (rotation number - 1)] timer is
not reset to zero until that compressor is started or until another unit in the system stops. This means that
the time for the next lag compressor to come on may be somewhat less than ‘LAG START INTERVAL’.
EXAMPLE:
In a three compressor sequence system, UNLOAD PRESSURE = 100 PSI; LOAD PRESSURE = 90 PSI;
LAG START INTERVAL = 15 seconds. The lead compressor is running alone, maintaining 90-100 PSI
when an air tool is brought on line causing the air demand to exceed the capacity of the lead compressor.
When the pressure drops to 90 PSI, the #2 unit times out its 15 second timer and starts. It takes 5
additional seconds for the pressure to rise above 90 PSI. The #3 unit whose timer was initially set at 30
seconds (15 x [3 - 1]), has counted down 20 seconds (the total time that system pressure was below 90
PSI). If air demand increases again, the pressure will have to fall below 90 PSI for only 10 seconds more
to start unit #3.
As was previously stated, a lag compressor’s unload point (PSET for short) is [UNLOAD PRESSURE -
3(rotation number - 1)]. Thus in the above example, the first lag compressor (rotation #2) has a PSET of
97 PSI; the second lag, 94 PSI, and so on. But look what happens in an eight compressor installation:
The eighth compressor will have an initial unload point of [100 - 3(8 - 1)], or 79 PSI. Does this mean that
an eight compressor installation must operate 21 PSI below the desired operating point when all
compressors are running? NO! This is where the AUTO SENTRY W dynamic unload point control takes
over.
This is how it works: Whenever the system pressure is below the programmed LOAD PRESSURE, the
PSET of each lag compressor is incremented 1 PSI every thirty seconds. Thus, after a short interval
(about five minutes in this example), the PSET of the last sequenced compressor will climb up until either
it equals the LOAD PRESSURE, or a decrease in demand causes the actual system pressure to rise
above the LOAD PRESSURE. It can be seen then, that except for short periods just after a sudden
increase in demand, the AUTO SENTRY W, with its dynamic unload point control, will maintain system
pressure between the limits of LOAD PRESSURE and UNLOAD PRESSURE. Remember, LOAD and
UNLOAD PRESSURE values are programmed by the operator so the operating range is completely
programmable and predictable.
Dynamic unload point control will also work in reverse of the operation described above. Obviously,
incrementing unload points will cause overlap of the compressors’ modulation ranges. While this enables
us to maintain a higher pressure than competitor’s sequencers, overlap is undesirable as demand
decreases, because a system could end up with several compressors cycling instead of running the
minimum number of fully loaded compressors. To overcome this, as pressure rises through the range
between LOAD and UNLOAD, the lag compressors’ set points are now decremented, reversing the effect
described above during periods of high demand. The AUTO SENTRY W keeps track of all functions at all
times so there is never any mix-up of unload points and the proper rotation sequence is always
maintained.