Elevated Condensate

Drainage Technique for Constant Pressure

As we've learned, whenever possible, gravity should be used to return condensate to the boiler. Sometimes, however, it is necessary to lift the condensate from the trap outlet to navigate around building obstructions or to compensate for the processing unit. Elevating condensate increases the back pressure at the trap outlet by 1 psia (.06 bar) for every 2 feet (0.61 meters) of elevation. This reduces the pressure differential across the trap by an equal amount, impeding the condensate drainage. If the trap is in constant pressure service, and the differential pressure remains sufficient for proper drainage, then it may be elevated directly from the trap with only a few simple hardware additions.

• Size the riser pipe one size smaller than normal.
• Ensure there is at least one pound of positive differential pressure for every two feet of lift.
• Place a check valve either before or integral to the trap when pressure may be suddenly interrupted or reduced (C or D).
• Place a check valve near the trap outlet in indoor, non-freezing environments (B).
• Place a check vavle at the top of the riser in potentially freezing environments (A).

Drainage Technique for Modulated or Low Pressure

If the trap is in a modulating steam service application or is supplied by steam of a too low pressure, elevating the condensate directly from the trap is not a viable option. In either of these cases, the differential pressure can fall below the minimum necessary to raise the condensate to the return line, resulting in flooded lines or equipment. In such cases there are three options available:

• Using a safety drain that wastes the condensate when there is insufficient pressure to return it.
• Using a pumping trap to raise the condensate.
• Using a vented receiver and pump to return the condensate.