scope:

Steam trap hot condensate flow capacities can be measured in accordance with ANSI/ASME PTC 39 or ISO 7842 standards. Steam trap manufacturers should publish capacity tables or graphs according to the aforementioned standards in order for users to select the correct steam trap to discharge the condensate load required by their application.

Calculation of the condensate load requirement that the steam trap needs to discharge is just as important as having an accurate flow capability. Under-sizing of the steam trap due to poor load information can lead to poor process performance or dangerous water hammer. Over-sizing the steam trap, while removing some condensate, may cause unnecessary steam leakage under low flow conditions and may shorten the life of the trap.

If the equipment manufacturer lists the heat output of the steam equipment that needs to be drained, the condensate rate can be estimated using this information. Generally, equipment manufacturers provide the heat output in BTU/hr. In that case, divide the BTU/hr output by the operating steam pressure latent heat (Table 1) to estimate the condensate generation rate from that equipment. For a more precise calculation, the steam quality, which can be referred to as wetness, must be considered to adjust for the actual lowered latent heat available.

Example: 2,500,000 BTU/hr @ 30 psig steam

When selecting the trap type, size, and required discharge capacity, consideration must be given to whether the steam pressure is steady state or modulating. The calculation shown in the example above is maximum condensate load at full pressure.

When the heat output rates from the equipment are unknown, estimated calculations for heat load using other sources of data can be utilized.

PURPOSE

The purpose of this standard is to help estimate steam trap condensate loads using generally accepted formulas. The calculated result is then used to size a trap with sufficient safety factor to discharge the necessary flow throughout the positive pressure differential range without being grossly oversized.