Algas SDI VAPORAIRE M-Series, Operation & Maintenance Manual

Page: 32 / 72

Operation
4-24
Algas-SDI Operations & Maintenance Manual – P/N - 54264
MULTIPLE VENTURI SYSTEM
WARNING
The sequencer is mounted in an explosion proof control enclosure.
If the enclosure is opened for testing or for adjusting, be sure that
no LPG vapor is present around the enclosure. The electrical
arcing that occurs when the switches and relays within the
enclosure operate is a possible source of explosive ignition.
SEQUENCER
Operation
The
SEQUENCER
is a PLC controller that uses a pressure transmitter to
monitors mixed gas pressure in the surge /accumulator tank. The
SEQUENCER
controls 1 - 10 venturi valves. All electronics are in the explosion proof box.
When mixed gas pressure in the surge/accumulator tank pressure decreases
below mixed gas pressure setpoint, the
SEQUENCER
energizes the number of
solenoid valves necessary to re-establish the proper mixed gas pressure. The
SEQUENCER
controls the rate and sequence in which the solenoid valves are
turned on and off. The venturi solenoid valves energize upon command from the
SEQUENCER
to allow LPG vapor to enter the venturi(s).
VAPORAIRE’s that requiring more than 8 venturis will have an additional Output
Module attached to the PLC.
VENTURI SEQUENCING
The
SEQUENCER
opens the venturis progressively in sequence, so they are all
used equally. They are controlled in a first on -first off rotation. For example: if
five venturis are used and the load requires two venturis on with one cycling, the
following numbered venturis will come on in sequence: #1, #2, and #3. When the
pressure is satisfied, #1 will shut off. When more pressure is needed, #4 will
come on leaving #2, #3 & #4 on. The venturi to shut off next is #2 and the next
one to come on is #5. In the next sequence, #3 will shut off and #1 will come on.
That rotation will continue every cycle to insure even wear of the venturi check
valves, solenoid valves, and pressure regulators.
The
SEQUENCER
uses the signal from the mixed gas pressure transmitter to
control the venturi solenoid valves to maintain mixed gas pressure at the desired
setpoint.
The flow rate and the LPG vapor/air ratio of each venturi is predetermined by the
venturi design and the vapor motive pressure. Each venturi is strictly an “on-off”
device; flow through each is either 0% or 100%. Up to 10 LPG vapor/air mixing
venturis can be controlled by the
SEQUENCER
. For even function and wear the
venturis are operated in a progressive sequence. This also results in longer
cycle times for each venturi and consequently a better LPG vapor/air mixture.
The
SEQUENCER
uses two potentiometers to control the mixed gas pressure.
See the section on pressure adjustment instruction.