Testing Steam Traps - Xylem Bell & Gossett Hoffman Speciality Series Engineering Data Manual

Where a test valve is installed in the trap dis-
charge piping, visual inspection is the most
positive method of testing.
Thermostatic Traps, and F & T Traps modulate
in operation. The discharge should be steady.
Bucket Traps and Disc Traps cycle and the
discharge should be intermittent. The trap is
often discharging condensate above 212°F.
When this high temperature condensate dis-
charges to atmosphere flash steam may be
present. Flash steam is normal and is not an
indication of trap failure. Flash steam is a low
velocity white colored discharge with a large
stream of condensate. If the trap is blowing
live steam it will be at high velocity—a clear
area will be present ahead of where the steam
begins to condense. Then, a bluish steam will
begin and there will be less condensate along
with the steam.
When no test valve is installed other methods
may be used.
When the piping ahead of the steam trap is
cold, this is an indication that the trap has
failed in a closed position.
Temperature measuring devices may be used
to test thermostatic traps. The temperature
immediately ahead of the trap should be
lower than the steam coil, radiator, etc.
Listening devices may be used to test traps
that cycle, these include Bucket Traps and
Disc Traps. As the linkage or disc opens, a
low pitch sound occurs as condensate dis-
charges. The linkage or disc closing can then
be heard. No other sound should follow. A
trap blowing live steam will have a higher pitch
whistle as steam blows across the orifice.
F & T Traps modulate and discharge at satura-
tion temperature. A fast response tempera-
ture scanner may be used to test operation.
You will be looking for two-phase flow in the
discharge line. Two-phase flow has steam in
the discharge line and will be over 212° F.
along the piping. Flash steam normally con-
denses in a short length of piping and will
drop in temperature along the pipe. Live
steam carried through the pipe will maintain a
near constant temperature.
Where several traps are used in similar appli-
cations make a comparison between different
trap discharge temperatures. You will soon be
able to pick out a defective trap. Both a listen-
ing device and a temperature scanner should
be available to spot trap problems.
Sight checkers provide a positive way to
check steam traps. A sight checker would be
installed in the outlet piping from the trap.
When the trap opens the ball check lifts off
the seat. It can be seen moving inside the
glass enclosure. When the trap closes the
ball should seat. If the trap is blowing live
steam the ball will move inside the housing.
Many independent trap survey companies will
do field testing of traps. Due to the high cost
of waste energy from defective steam traps, a
trap survey normally has a good payback.
START
HAS STEAM
NO
WAIT FOR
SYSTEM
STABILIZATION
STABILIZED?
YES
NO
IS TRAP IS STEAM
HOT? TURNED ON?
YES
PRESSURE
YES
TRAP?
YES
TRAP HAS
WHAT
PROBABLY
KIND OF
FAILED CLOSED
TRAP?
OR IS AIRBOUND
Check list–step by step

Testing Steam Traps

Objective:
Determine if trap is performing properly & efficiently.
Types of Tests:
Temperature, pressure, flow.
How to Check:
Listening device, temperature device, visual.
Listening Devices:
Screwdriver, stethoscope, ultrasonic tester.
Temperature Devices:
Gloves, water gun, crayons, pyrometer, infrared.
Real Reason:
Hot-cold, Go/no go, Repair or replace.
Chapter 5
Testing Steam
Traps
TURN
NO
STEAM
ON
A SYSTEM
NO
PROBLEM
TO
FIND AND
CORRECT
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