How to Size Steam Traps

Law of the L.A.M.B.S.

• 1

  Understand the parameters required for sizing a stream trap by remembering the acronym "L.A.M.B.S." Load refers to the amount of condensation the trap must handle. Application means how the trap will be used. Modulated or constant asks which type of steam supply will be used. Back pressure refers to the pressure at the trap outlet (normally just atmospheric.) Supply pressure measures the steam pressure at the steam outlet.

• 2

  Manually figure the steam trap size by plugging L.A.M.B.S. information into a standardized formula available on manufacturers' websites. Adjust the calculation's results if necessary by adding a safety margin. The operating differential, which is the difference between the supply pressure and back pressure at the stated condensate load, must be within 80% of the maximum differential, the straight supply pressure with no subtraction for back pressure. Most major manufacturers also provide software, usually available at no charge on CD or by download. Armstrong's Steam-A-ware software is an example. Enter the L.A.M.B.S. data as requested and let the software calculate condensate loads, apply the safety factors, recommend the most efficient steam trap and print out specifications.

• 3

  Select the proper steam trap size from either a capacity chart, a sawtooth curve, or a log-log graph included in the manufacturer's product information. Sawtooth graphs represent the performance of multiple steam trap models across a range of pressures in two test modes, where one mode shows maximum diameter orifices for the pressure, and the other shows performance at pressures below the maximum. These are represented, respectively, by a heavy and a light graph line, with model numbers displayed along the axis. The log-log charts plots actual trap capacity vs. maximum/minimum inlet pressure on a grid for various models.

Advantages and Disadvantages of Major Types

• 4

  Advantages of the most common mechanical "inverted bucket" steam traps include a resilience to high pressures and a good tolerance to water hammer conditions. In failure mode, the valve remains open, making them safer for certain applications. Disadvantages of mechanical steam traps include the small size of the air vent in the top of the bucket, which only allows it to vent air very slowly and may become clogged. The hole cannot be enlarged without affecting trap dynamics and function. Also, the higher temperature of superheated steam may damage its water seals.

• 5

  Float-thermostatic traps provide large ports and handle high capacities. They self-adjust to light or heavy loads and are housed in heavy-duty cast iron bodies. Their disadvantages include vulnerability to water hammer damage to the sensitive float mechanism. In failure mode, the trap remains closed They do not withstand freezing temperatures and cannot be installed in exposed areas. They have a fixed pressure ceiling of 175 psig.

• 6

  A chief advantage of the thermostatic, or disk-type trap, is its small size and wide adaptability for installation. In many cases, they are only slightly larger than the steam pipe itself. Disadvantages center on long-term reliability and the vulnerability of the sealing surfaces to water hammering and steam abrasion, resulting in leakage.