Pump & Trap Combinations How a Pump-Trap Works
5 PSIG
Operation of a PUMP-TRAP with a Heat Exchanger (HX):
The steam pressure to the HX will vary depending on the flow rate of hot water required by the system. Let’s assume the HX was sized for a maximum flow rate of 40 GPM of HOT water at 140˚F using 30 PSIG steam. When maximum flow rate of water is required, the 30 PSIG steam pressure is more than adequate to push the condensate generated thru the steam trap against the 15 PSIG back pressure. Now, if the hot water requirement reduces from 40 to 20 GPM, the steam flow (lbs/hr) to the Heat Exchanger must drop by about half. Since it is the same size HX, the steam temperature (steam pressure) must also reduce (see table below).
30 PSIG
10 PSIG Head Pressure
balancing line
Total Back Pressure 15 PSIG
Steam Motive Inlet
hot water outlet
cold water inlet
Steam Pressure vs. Hot Water Required
Steam Steam Pressure
Condensate Generated
Flow Rate Water (gallons per minute)
Usage (lbs/hr)
in Heat Exchanger
(PSIG)
(same as steam used)
40 35 32 20
1,900 1,650 1,530
30 15 10
1,900 1,650 1,530
Trap Mode Stall Point Pump Mode
950
-6.6 (Vacuum)
950
TRAP Mode The system is operating with 30 PSIG inlet pressure to the heat exchanger. The Pump-Trap unit functions like a standard float-operated trap. Condensate is pushed thru the pump-trap into the return line by the steam pressure in the HX.
Vent Outlet: Open position, allowing pressure in the pump tank to equal pressure in the heat exchanger, allowing condensate to freely enter Pump-Trap by gravity, even under vacuum. Motive Inlet: Closed position
50 PSIG
30 PSIG
50 PSIG
Condensate gets pushed through Trap
balancing line
15 PSIG
1 TRAPPING Mode: Inlet steam pressure is higher than back pressure. Steam pushes condensate through Pump-Trap.
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