Steam Trap Selection
39
A QUICK GUIDE TO THE SIZING OF STEAM TRAPS
Need To Know:
1. The steam pressure at the trap—after any pressure drop through
control valves or equipment.
2. THE LIFT, if any, after the trap.
Rule of thumb: 2 ft. = 1 psi back pressure, approximately.
3. Any other possible sources of BACK PRESSURE in the
condensate return system.
e.g. A) Condensate taken to a pressurized DA. tank.
B) Local back pressure due to discharges of numerous traps
close together into small sized return.
4. QUANTITY of condensate to be handled. Obtained from
A) Measurement, B) Calculation of heat load (see page 24), and
C) Manufacturer’s Data
5. SAFETY FACTOR—These factors depend upon particular
applications, typical examples being as follows:
General With Temp. Control
Mains Drainage x2 —
Storage Heaters x2 —
Space Unit Heaters x2 x3
Air Heating Coils x2 x3
Submerged Coils (low level drain) x2 —
Submerged Coils (siphon drain) x3 —
Rotating Cylinders x3 —
Tracing Lines x2 —
Platen Presses x2 —
Rule of thumb: Use factor of 2 on everything except Temperature
Controlled Air Heater Coils and Converters, and
Siphon applications.
How To Use
The difference between the steam pressure at the trap, and the total
back pressure, including that due to any lift after the trap, is the
DIFFERENTIAL PRESSURE. The quantity of condensate should be
multiplied by the appropriate factor, to produce SIZING LOAD. The
trap may now be selected using the DIFFERENTIAL PRESSURE and
the SIZING LOAD.
Example
A trap is required to drain 22 lb/h of condensate from a 4" insulated
steam main, which is supplying steam at 100 PSIG. There will be a lift
after the trap of 20 ft.
Supply Pressure = 100 psig
Lift = 20 ft = 10 psi approx.
Therefore
Differential Pressure = 100 – 10 = 90 psi
Quantity = 22 lb/hr
Mains Drainage Factor = 2
Therefore Sizing Load = 44 lb/hr
A small reduced capacity Thermo-Dynamic® steam trap will easily
handle the 44 lb/h sizing load at a differential pressure of 90 psi.