Pump & Trap Combinations Why use a Pump-Trap?
Heat Exchanger System with Steam Trap
Problem: Condensate Backs Up Into Heat Exchanger The diagram shows a temperature control valve delivering steam to a Heat Exchanger that is using steam to heat water. Condensate formed in the heat exchanger is being discharged through the steam trap into the condensate return line. This particular application demonstrates what happens when the return line is elevated and/or pressurized. The plant steam pressure on the inlet side of the control valve would be adequate to purge (push) the condensate through the trap and into the return line. However, the steam pressure in the heat exchanger is controlled by the valve and is dependent on the demand of the system. When the demand for HOT water is low, the steam pressure in the Heat Exchanger falls below the back pressure and the system backs up with condensate, creating unstable temperature control and waterhammer. This undesirable condition, referred to as Stall, occurs when the steam pressure in the heat exchanger falls to or below the system back pressure due to a decrease in the demand (flow rate)of hot water.
condensate return line pressure
Steam Pressure of 10 PSIG in heat exchanger cannot overcome total back pressure causing condensate to back up
steam control valve
50 PSIG
temperature controller
air vent
condensate return
Steam
temp sensor
Condensate backs up into heat exchanger
Total Back Pressure 15 PSIG
hot water outlet
F&T TRAP
cold water inlet
If Inlet Pressure is not higher than Back Pressure ,
Condensate will back up
BACK PRESSURE
Heat Exchanger System with Pumping Trap
Solution: Use a Pump-Trap to Avoid Condensate Back-up & Improve Temperature Control
steam control valve
condensate return line pressure
50 PSIG
temperature controller
Steam Pressure
To eliminate condensate backing up (STALL), the standard float trap is replaced with a PUMP-TRAP. When steam pressure in the Heat Exchanger is greater than the back pressure, the steam pressure will push the condensate through the Pump-Trap and it functions like a standard float-operated trap. When the steam pressure to the Heat Exchanger drops below the back pressure, the condensate backs up inside the PUMP-TRAP, raising the float. When the trip point of the mechanism is reached, the high-pressure steam valve will open to drive the condensate out.
air vent
condensate return
50 PSIG
Steam
temp sensor
higher pressure steam used to pump condensate can overcome back pressure
balancing line
hot water outlet
pump exhaust
Total Back Pressure 15 PSIG
cold water inlet
condensate drains by gravity into pump tank
inlet check valve
outlet check valve
PUMP TRAP
Solution: Steam Trap is Replaced with Pump-Trap Combination
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Tel: 610-495-5131 • Pottstown PA • USA •• www.watsonmcdaniel.com
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