Brochure

105
Selection Guides
Selecting the proper steam trap is important in effective
operation of steam systems. Steam traps are automatic
valves that open to pass condensate and close to prevent
the flow of steam. The functions of a steam trap in a
steam system are to:
• Vent air from the system so steam can enter
• Hold steam in the system until the steam latent
heat is removed
• Drain condensate from the system as it is formed
after the latent heat is removed.
Removing condensate from piping helps prevent erosion
and water hammer. Removing condensate from heat
exchangers is required to make room for new steam for
the heating process.
There are many types of steam traps. The Steam Trap
Selection Guide Chart points out system conditions that
may be encountered and suggests the trap type(s) that
may best handle the requirement. Several types of traps
may be used for a specific application.
Factors to consider in selecting the type of trap include:
• Constant or modulating condensate load
• Constant or fluctuating pressure
• Speed of air venting required
• Trap location
TRAP SIZING
1. Determine the maximum condensate load (capacity)
requirement for the trap by one of the following:
– Referring to the manufacturers' specifications for
the system equipment.
– Approximating condensate loads using the
"General Usage Formulas".
– Using the "CalcLoad" Load Calculator available
through "Steam Specialty Component Selector"
on the Hoffman Specialty website or ESP-Plus.
2. Determine the available steam inlet pressure at the
trap (This pressure could be different than supply
pressure at boiler.)
3. Determine the outlet pressure (backpressure) at the
trap discharge. (Pressure against the outlet can be due
to static pressure in return line or due to lifting to an
overhead return).
4. Determine the pressure differential across the trap.
(inlet pressure - outlet pressure = differential pressure).
5. Determine a Safety Factor. The Safety factor will
depend on accuracy in determining condensate load,
inlet and outlet pressures. Recommendations:
– Float & Thermostatic Trap 1.5 to 2.5
– Bucket Trap 2 to 4
– Thermostatic Trap 2 to 4
– Thermodisc Trap 1 to 1.2
6. Multiply normal maximum condensate load (as
determined above) by Safety Factor.
7. Use the Capacity Tables for the selected type of trap
to determine the trap model number.
8. Use Ordering Information Charts to determine the
part number.
Guidelines:
– The trap seat rating must always be higher than the
maximum inlet pressure at the trap.
– When a modulating control valve controls the inlet to
equipment, select a trap size with a pressure rating
greater than the maximum inlet pressure at the trap.
– Trap capacity should be checked at the minimum
differential pressure to assure complete condensate
removal under all possible conditions.
Inverted Bucket Trap Operating Pressure Selection:
• Bucket traps are offered with various orifice sizes that
determine the maximum operating pressure rating.
• A trap with a lower seat pressure rating has a larger
sized orifice than a trap with a higher seat pressure
rating. The larger orifice provides a larger condensate
rating. When the actual operating pressure is higher
than the seat rating, the pressure differential across the
seat will prevent the trap from opening. Thus, an inverted
bucket trap must be selected for the maximum differential
pressure that will be encountered by the trap.
• Trap Capacity Tables show trap capacities at lower
differential pressures than the trap rating. This allows
selection of a trap at various operating points. A trap
with a higher seat pressure rating may be used at lower
pressure differentials. However, the capacity rating at
that pressure differential will be less than the same size
trap with a lower seat pressure rating.
Selecting and Sizing Steam Traps
Steam Traps
Hoffman Specialty
®
Selection Guidelines