Heavy Duty Balanced Opposed Compressors - Ariel Corporation

FOR MODELS: JGZ AND JGU SECTION 4 LUBRICATION
switch will be open until the button is pushed and the contact will close. If a momentary push
button switch is NC then when it is taken out of the box the switch will be closed until the
button is pushed.) This does not apply to divider block monitoring devices.
Divider block device manufacturers have "simplified" things for the mechanic. Normally
Open (NO) refers to the state the switch is in when the divider block is cycling or the unit is
running. An NO switch means that when the unit is running the shutdown switch is open or
non-failsafe. If a wire falls off or is cut while the unit is running the control system will never
stop the unit. If the device is damaged or a wire has come loose at startup the control system
would never know there is a problem. An NC switch means that when the unit is running
the shutdown switch is closed or failsafe. Now if a wire falls off or is cut the control system
will detect that the switch is open and shutdown the unit.
Ariel recommends using a NC (failsafe) switch. However, when a NO (non-failsafe) switch
is used, Ariel recommends testing the shutdown circuits at least once a month.
II. Proximity switch - This is a device that will sense the position of the divider block piston
and will produce a switch change of state or a pulse every time the pin changes position. This
device must be combined with a PLC or some other counter/timer device to produce the shutdown.
Some devices on the market will open the switch when the pin is toward the left and
close when the pin is toward the right. Others will produce a 0.5 second pulse when the pin
moves from left to right. If this is used it is the responsibility of the control system to sense the
switch cycling and stop the unit if a block stops cycling.
APPLICATION NOTES - Proximity Switch
Ariel recommends setting up the control system to find the time between cycles triggered
when the switch transitions from off to on. See Figure 4-7 suggested control system block
diagram.
1. Shutdown time with no lubrication - The distribution block cycle times will vary
slightly from cycle to cycle. Seeing 12 seconds one cycle then 15 seconds the
next then 14 the next is normal. The recommended shutdown time is: 2 times the
design cycle time + 30 seconds limited between 30 seconds and 3 minutes.
LIMIT (2 x design cycle time + 30 seconds) 30, 180
Design cycle time is found on the compressor lube sheets or tag on the compressor.
2. DE-BOUNCE and latching circuits - Depending on the device and control system
scan time it may be necessary to include de-bounce hardware and/or software.
Some of the devices do not have built in de-bounce circuits and can cause a fast
control system to double or triple count. Other times it may be necessary to latch
the input thus allowing the control system to detect only the first transition from
low to high. This becomes significant when displaying the cycle time for the operator
to set the pump flow rates and when calculating the total oil through the
divider block.
3. Suggested Operator Displays:
Divider block cycle time - The operator will need to set the lube system pumps according
to the recommended divider block cycle times. It is helpful for the operator
to have a display of divider block cycle time in seconds. This will be used to adjust
the lube pumps as the pumps wear out and when the pumps are replaced to set
divider block cycle times.
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