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On this model, the same centrifugal pump performs two functions. It produces a vacuum, using a nozzle/venturi arrangement, and it pumps the returned condensate to a boiler. The model also offers a low profile design.
The receiver is divided into two chambers. The lower chamber is used to collect the returned condensate and comes under the same vacuum as the condensate return line. The vacuum in the lower chamber is produced by recycling the water from the upper chamber. Therefore, it is not unusual for the centrifugal pump to be running even though the lower chamber is empty.
The centrifugal pump can be turned on in three ways. The float switch in the upper or lower chamber may send a signal turning it on or the vacuum switch may send a signal. These conditions are further explained in the following animation.
Note: The pump is shown without a motor to improve view of operation.
Gravity returns enter lower chamber of receiver.
WARNING! On initial start-up, the upper chamber must be approximately 1/2 full to ensure the centrifugal pump does not run dry (which can ruin the pump). Water can be poured into the upper chamber through a vent/priming opening on the top of the receiver.
The condensate returns cause the water level in the receiver to rise.
When the float switch in the bottom chamber reaches the high water setting, the float switch sends a signal to turn on the centrifugal pump.
As the high velocity streams of water pass by the air gap, located between the nozzle and the venturi they entrain (i.e., pull) both air and water from the lower chamber up the lift manifold and into the venturi piping.
As the mixture of air and water enters the venturi, it converges in the venturi creating a steady vacuum at the air gap, back through the lower chamber and out the gravity returns piping. As the mixture is discharged out the venturi back into the upper chamber, the air and gases separate from the water. The air, gases and water vapor rise over the baffle and escape through the air vent on the top of the receiver.
As streams of water pass the air gap, the air suction created pulls open the "swing" check valve, drawing air, gases and water from the lower chamber into the upper chamber.
The water level in the upper chamber rises as the water from the lower chamber is pulled up the lift manifold into the upper chamber while the centrifugal pump runs.
When the float switch in the upper chamber reaches the high water setting, the float switch sends a signal to open the discharge valve (typically a solenoid valve) discharging water from the upper chamber. The high velocity streams of water continue to pass the air gap pulling water and air from the lower chamber.
As water is pumped from the upper chamber, the water level in the upper chamber falls.
When the float switch in the upper chambers reaches the low water setting, the float switch sends a signal to close the solenoid valve, cutting off the discharge flow. It may also turn off the centrifugal pump unless the pump is running to maintain the vacuum.
The low water setting of the float switch in the upper chamber is set so that sufficient water remains in the upper chamber to run the centrifugal pump for maintaining a vacuum.
The vacuum sensing line, connecting the vacuum switch to the condensate return piping, detects if the vacuum level in the condensate return line meets the preset conditions.
Note: At installation of unit, the contractor typically moves the sensing line from the tee at the strainer, where the factory connects it, to a place further out the gravity return line.
If the vacuum level does not meet the preset conditions, the vacuum switch sends a signal to turn on the centrifugal pump.
The vacuum in the condensate return line is returned to normal conditions.
When the vacuum level meets the preset conditions, the vacuum switch sends a signal to turn off the centrifugal pump.