Sizing a steam trap: PMO, PMA, TMO and condensate recovery

Once you have chosen the trap type, sizing remains. An undersized trap floods the line; an oversized one wastes steam and wears out sooner. It takes only a few, precise figures.

Differential pressure

Discharge capacity depends on the differential pressure between inlet and outlet: ΔP = upstream pressure − downstream backpressure. Beware: the condensate-return backpressure (and any lift) reduces the available ΔP and therefore the flow that can be discharged.

The nameplate limits: PMO, PMA, TMO

• PMO — maximum operating pressure at which the trap works correctly.
• PMA — maximum allowable pressure of the body (construction/safety limit).
• TMO — maximum operating temperature allowed.

Operating conditions must stay within these limits; superheated steam calls for careful checking of TMO and PMO.

Condensate load and safety factor

Estimate the condensate load (kg/h): maximum at start-up (cold warm-up) and at running conditions. On the running load apply a typical safety factor of 2–3 to cover transients and ΔP drop. Check that the trap capacity at that ΔP exceeds the increased load.

Condensate recovery

Condensate is hot, already-treated water: returning it to the boiler feed tank recovers sensible heat, cuts make-up water and blowdown, and saves fuel. Where pressure allows, flash steam is also recovered at low pressure. Good trap sizing is the basis of efficient recovery.

For selection support, request a quotation from the request for quotation page or start from the selector.