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Pump-Trap Combinations

Pump-Traps

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.



Solution: Use a Pump-Trap to Avoid Condensate Back-up & Improve Temperature Control

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.



Using 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).

TRAP Mode

When inlet steam pressure is greater than back pressure, it will function as a steamtrap.

PUMP Mode

When inlet steam pressure is less than back pressure, it will function as a pump.

Condensate rises to a level that the float triggers the inlet steam valve and closes the vent valve. Full line pressure steam (50 PSIG) enters thru the inlet valve on top of the pump body to discharge the condensate. Because of check valves, condensate will not flow back to HX and is discharged to the condensate return line. Unit will continue to operate and cycle in pump mode as long as pressure in the HX is below back pressure. Pump-Trap will also operate in vacuum conditions.

PMPT

The PMPT low-profile pressure motive pump has an Internal Steam Trap for applications requiring compact design due to spatial constraints. It is an excellent choice for drainage of various modulating process equipment. The pump body is made of ductile iron or stainless steel. ASME “UM” code stamp is available.

Includes: Body, Cover, Internal mechanism, Check valves and Internal Steam Trap.

WPT

The WPT Series are stand-alone pump units with an appropriately sized External Steam Trap pre-assembled at the factory and mounted on a common base plate, allowing for simple installation. The WPT Series should be used when capacity requirements exceed the PMPT (pump with internal steam trap).

Includes: Body, Cover, Internal mechanism, Check valves and External Steam Trap

PMPT with receiver

Ductile Iron Pump-Trap Combination with Internal Steam Trap

Includes: Pump-Trap, Steel Receiver, Isolation Valve(s), SS Check Valves, Piping, and mounted on a Steel Base..