Steam traps are automatic valves the
function of which is to allow the
condensate to pass while preventing
the passage of steam.
Steam traps are also expected to
pass air and other non-condensible
gases without the loss of steam.
Definition of a Steam Trap
“self-contained valve which automatically
drains the condensate from a steam
containing enclosure while remaining tight
to live steam, or if necessary, allowing
steam to flow at a controlled or adjusted
rate. Most steam traps will also pass non-
condensible gases while remaining tight to
Function of steam traps
• Discharges condensate
• Prevents or limits the discharge of steam.
• Automatically opens and closes (or throttles)
1. — At the saturated steam temperature
2. — Below the saturated steam temperature (also called
• Discharges liquid for freeze protection
• Drains non-condensible gases, such as air and CO2
1. — Start-up
2. — Normal running conditions
• Thermostatic traps.
Traps that are actuated by temperature-
They attempt to sense the difference
between steam and condensate by their
Therefore, this type of trap can
discriminate between steam and cooler
Most thermostatic traps are either
actuated by a bimetallic thermostat or use
bellows filled with vaporizing liquid.
• Thermodynamic traps.
Traps that are actuated by principles
of thermodynamics and fluid
This type uses flash or live steam to
close the valve. Disc traps, piston
traps, and lever traps fall into this
• Mechanical traps.
Traps that are actuated by a float,
which responds to changes in
Float and thermostatic traps,
inverted bucket traps, and open
bucket traps are mechanical trap.
Disc traps utilize the heat energy in hot condensate
and the kinetic energy in steam to open and close
the valve disc.
They sense the difference between liquid, and gas
Piston (or impulse) traps utilize the heat energy in
hot condensate, and the kinetic energy in steam to
open and close a valve.
Like disc traps, they sense the difference between
a liquid, and gas or vapor.
The closed float trap is one of the oldest type of steam traps on
the market, but it is still in widespread use. The opening and
closing of the valve is caused by changes of the condensate level
within the trap shell.
When the trap is empty, the weight of the float closes the valve.
As condensate enters the trap, the float rises and opens the valve,
allowing condensate to be discharged.
Bimetallic steam traps utilize the sensible
heat in the condensate in conjunction
with line pressure to open and close a valve
Bellows traps are thermostatic traps that respond to changes in
the temperature and pressure of the steam supply to open and
close a valve.
The valve actuator is a capsule or bellows filled with a vaporizing
liquid, and because it has both a fixed and a free moving end, it
opens or closes the valve in response to internal pressure
Fixed orifice traps or drainers are seldom used because of their
This device consists of one or more successive orifices. Where two
or more orifices are used, condensate passes through a number of
successive chambers where flashing occurs.
This creates a restricting or choking effect and allows the use of
larger and less dirt-sensitive orifices for a given condensate
capacity. In some designs, these “fixed” orifices are actually
STEAM TRAP APPLICATIONS
industrial steam trapping applications
can be divided into two major
Steam line drip. Drainage of the
condensate that forms in the pipes
delivering steam from a boiler to a
specific point of use.
This helps prevent damaging water
hammer and promotes the delivery of
dryer steam to plant equipment.
Drainage of the condensate that
normally forms when steam is used
to heat liquids, gases, or solids in any
Infrared thermography monitoring
Leakage from a
• ANSI/FCI-85-1: Standard for Production
Testing of Steam Traps
• ANSI/FCI-69-1: Pressure Rating Standard
for Steam Traps
• ANSI/FCI-65-3: Operating Principles and
Standard for Determining Steam Trap
• ANSI/ASME PTC-39.1: Condensate
Removal Devices for Steam Systems
Coating and Paints for traps
Heat resistant aluminium paints
IS 13183 Gr 1 ( for 400-600 deg C )
IS 13183 Gr 2 ( for 200-400 deg C )