Steam is supplied to a process heater through a modulating control valve. The valve modulates to reduce steam flow as the outlet set point is reached which causes an increase in pressure drop across the control valve.


Back pressure against the steam trap is the sum of the static pressure in the system plus pressure required to lift the condensate overhead. As an example, assume the lift to the overhead return is 20' and the static pressure on the return is 10 psig. A lift of 2.33' is equal to 1 psig. The back pressure due to lift is 8.6 psig (20 divided by 2.33). The total back pressure against the trap is the sum of 10 psig plus 8.6 psig or 18.6 psig.

The capacity of a steam trap is a combination of the trap size and pressure differential across the trap. As the pressure differential decreases, the capacity of the trap is reduced.

In our example, as the control valve modulates; a point will be reached where the trap will no longer be able to pass the condensate resulting in stalling of condensate in the equipment. This creates hammering, loss of output, and other problems associated with flooded equipment.

To eliminate the condensate stalling problem; a pump must be installed to overcome the back pressure.

If a motor driven pump is selected, caution must be exercised in proper selection of the pump to avoid cavitation and failure of the pump due to hot condensate.

If you are having problems with hammering, erratic output temperatures, corrosion, and equipment failures; call us for application details.