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Techniques
for Testing Steam
Trap Operation |
Page 1 2 3 |
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| The frequency of testing traps
depends on the steam pressure and the quality of the traps.
Specific guidelines cannot be established. Optimum frequency
should be determined by noting the percentage of traps
found defective during each inspection. Under some conditions,
monthly testing is required. In less demanding circumstances,
testing every 3 or 4 months is adequate. In most installations,
traps should be tested at least once a year. |
| Every maintenance
shop should have a test stand, similar to the arrangement
shown in Fig. 2, to test traps. This test stand is convenient
and inexpensive. |
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| Fig. 2. Inexpensive
test stand may be used to test steam trap operation. Valves
A, B, C, and D are closed and the trap is attached. Valve
C is cracked and valve D is slowly opened. The pressure-reducing
valve is adjusted to the rated pressure of the trap being
tested, valve C is closed, and valve A is opened slowly,
allowing condensate flow to the trap until it is discharged.
Valve B is then partially opened to allow the condensate
to drain out, unloading the trap. Under this final condition,
the trap must close with a tight shutoff. With some trap
configurations, a small amount of condensate may remain
downstream of the trap orifice. Slow evaporation of this
condensate will cause small amounts of flash steam to flow
from the discharge of the trap even though shutoff is absolute. |
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The test arrangement
may also be used to check the maximum operating pressure of float
and bucket traps. The trap is mounted upside down, and the pressure-reducing
valve is set approximately 50 percent above the maximum operating
pressure of the trap. Then, the trap is carefully rotated to
its normal position. Valve D is then closed, allowing pressure
ahead of the trap to dissipate. The pressure indicated by the
gauge as the trap opens is the maximum operating pressure of
the trap.
A more elaborate trap testing setup is shown in Fig. 3. The procedures
described in Fig. 2 can also be used with the test stand shown in Fig.
3. This arrangement can also be used to check trap capacity. The amount
of cold water entering the system is adjusted so the level in the gauge
glass remains relatively constant. The ability of a steam trap to maintain
dry steam spaces upstream of the trap can also be evaluated. A nominal
load is placed on the trap and the condensate level in the gauge glass,
the pressure, and the temperature indicate the trap's ability to handle
condensate backup. |
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Fig. 3. Another trap testing setup has a gauge glass shunted around the vertical
pipe and a source of high-pressure water supplied through a water injector.
The amount of cold water being injected is measured on the flow meter. Cold
water combines with the steam to form hot condensate. Some steam is required
to heat the water to the operating temperaure of the trap, and this amount
must be added to the meter reading of the cold water to estimate the total
load on the trap. Test procedure described in Fig. 2 may also be used. |
| TABLE III. FACTORS
FOR DETERMINING STEAM LOADS TO FORM CONDENSATE IN SATURATED
STEAM* |
| Steam Pressure, psig |
Factor |
| 2 |
1.16 |
| 5 |
1.17 |
| 10 |
1.19 |
| 15 |
1.20 |
| 20 |
1.21 |
| 25 |
1.22 |
| 30 |
1.23 |
| 40 |
1.25 |
| 50 |
1.26 |
| 60 |
1.27 |
| 75 |
1.29 |
| 100 |
1.32 |
| 125 |
1.34 |
| 150 |
1.36 |
| 200 |
1.40 |
| 250 |
1.43 |
| 300 |
1.46 |
| *To determine steam required
to form condensate in saturated steam, multiply cold water
iced, lb/hr, by factor indicated. |
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Operating temperature of a trap can
be determined with this setup. For example, a thermostatic trap
is attached to the stand and nominal load is added until the
trap discharges. Temperature at discharge is the operating temperature.
Amounts of steam required to heat cold water to form condensate in saturated
steam are given in Table III. For example, assume a system is operating at 125-psig
steam pressure, with a meter reading of 715 lb/hr of cold water. Table III shows
that at 125 psig the load factor is 1.34. Therefore, the total load on the trap
will be 715 X 1.34 = 958 lb/hr of steam. END |
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