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2.2.2 RO Pump Pressure Sensor - PS2
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This pressure sensor is used to protect the system from operating over the setpoint pressure.
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The system can produce 10 GPM (Standard Flow) or 15 GPM (High Flow) of RO below 200 psi at a water temperature
above 40F.
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This pressure set point is to allow the use of membranes that might be lower-pressure or cold-water membranes.
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This situation may occur as the membranes reach the end of life or if feed water drops below 40 F.
2.2.3 RO Product Flow Sensor - ROFLO
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This sensor provides the feedback signal to the pump controller to adjust RO Pump speed and pressure to achieve
the desired RO fl ow rate. The programmed fl ow rate is adjustable on the PLC settings screen.
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This sensor provides a 4-20 mA signal to the controller and the calibration is set in the controller software. This
allows the operator to adjust the requested fl ow based on the tank level. As the tank level decreases, the fl ow is set
to increase. This approach allows the unit to generate RO at the lowest energy cost to meet the fl ow required by the
tunnel.
'RO Production' turns on when the tank level drops to 75% and fi lls it back to 95%.
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Verify the RO pump turns on when the tank level drops to 75% tank level.
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Once the re-pressurization pump is commanded off, the unit will keep running continuously until the level reaches
100%. The system will wait 15min then initiate a RO MEMBRANE FLUSH CYCLE before shutting down.
During the fl ush cycle, the RO pump circulates a few gallons of RO water to the feed side of the membranes.
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RO water pulls deposits from the surface of the membranes. The fl ush water (RO water) remains in the dirty
(concentrate) side of the membranes until the next production cycle.
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Using this method, the feed (concentrate side) of the membranes will always be cleaning the membranes between
the RO production cycles.
The tank is divided into three sectors which allow fl exibility in set-up. The objective is to allow the unit to adjust fl ow based on
tank level with lower fl ow rates as the tank is nearing 100% full and higher fl ow rates as the tank approaches empty.
The 'RO Production Turn On' level is adjustable and will normally be set in the 60% range. In the screen shot above the oper-
ator has set this number to 80%. Based on the settings above the unit will ramp from 0 GPM to 8 GPM when the tank reaches
80% full condition.
2.2.4 Tank Level Sensor
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The tank sensor is a low-pressure sensor that measures the static water head pressure based on the depth of water
in the tank.
The 0-5 psi sensor is scaled to a 4-20 mA signal. This signal is used to request fl ow rate based on the tank level. This
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signal is an input to the PLC which is used to modify the fl ow request based on the tank level.
2.2.5 Recirculation Flow Switch
The recirculation fl ow switch verifi es that the recirculation loop fl ow (the combined fl ow of the recirculation fl ow and
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reject fl ow) is operating at more than 12 GPM of fl ow during operation.
This switch protects the membranes from fouling, verifying that Valve C is open and the recirculation and reject fl ow
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orifi ces are not blocked during RO production. If the reject fl ow orifi ce or the recirculation orifi ce becomes blocked
it would increase RO recovery and potentially damage the membranes. The switch will not close if the RO pump
pressure is less than 70 psi.
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System Overview
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