626

7,800

1/2

833,000

2,500

——3—0,—00—0

®Based on 100-psig differential pressure across the orifice. fcBased on steam value of $3/1000 lb. Cost will scale in direct proportion for other steam values.

®Based on 100-psig differential pressure across the orifice. fcBased on steam value of $3/1000 lb. Cost will scale in direct proportion for other steam values.

A major problem facing the energy conservation manager is diagnosis of open traps. The fact that a trap is blowing through can often be detected by a rise in temperature at the condensate receiver, and it is quite easy to monitor this simple parameter. There are also several direct methods for checking trap operation. Figure 6.15 shows the simplest approach for open condensate systems where traps drain directly to atmospheric pressure. In proper normal operation, a stream of condensate drains from the line together with a lazy cloud of flash steam, produced as the condensate throttles across the trap. When the trap is blowing through, a

Table 6.14 Operating Sounds of Various Types of Steam Traps

Trap

Proper Operation

Malfunctioning

Disk type (impulse of thermodynamic)

Opening and snap-closing of disk several times per minute

Rapid chattering of disk as steam blows through

Mechanical type (bucket) Cycling sound of the bucket as Fails open—sound of steam it opens and closes blowing through

Fails closed—no sound

Mechanical type (bucket) Cycling sound of the bucket as Fails open—sound of steam it opens and closes blowing through

Fails closed—no sound

Thermostatic type Sound of periodic discharge if Fails closed—no sound medium to high load; possibly no sound if light load; throttled discharge

Condensate

Fig. 6.15 Visual observation of steam trap operation in open system, (a) Proper operation, (b) Improper operation.

Fig. 6.15 Visual observation of steam trap operation in open system, (a) Proper operation, (b) Improper operation.

well-defined jet of live steam will issue from the line with either no condensate, or perhaps a condensate mist associated with steam condensation at the periphery of the jet.

Visual observation is less convenient in a closed condensate system, but can be utilized if a test valve is placed in the return line just downstream of the trap, as shown in Figure 6.16. This system has the added advantage that the test line may be used to actually measure condensate discharge rate as a check on equipment efficiency, as discussed earlier. An alternative in closed condensate return systems is to install a sight glass just downstream of the trap. These are relatively inexpensive and permit quick visual observation of trap operation without interfering with normal production.

Another approach to steam trap testing is to observe the sound of the trap during operation. Table 6.14 describes the sounds made by various types of traps

Steam line i-1

Condensate return line

Fig. 6.16 Visual observation of steam trap operation in closed systems.

Condensate return line

Fig. 6.16 Visual observation of steam trap operation in closed systems.

during normal and abnormal operation. This method is most effective with disk-type traps, although it can be used to some extent with the other types as well. An industrial stethoscope can be used to listen to the trap, although under many conditions, the characteristic sound will be masked by noises transmitted from other parts of the system. Ultrasonic detectors may be used effectively in such cases; these devices are, in effect, electronic stethoscopes with acoustic filtering to make them sensitive to sound and vibration only in the very high frequency range. Steam blowing through a trap emits a very high-pitched sound, produced by intense turbulence at the trap orifice, as contrasted with the lower-pitched and lower-intensity sound of liquid flowing through. Ultrasonic methods can, therefore, give a more reliable measure of steam trap performance than conventional "listening" devices.

A third approach to steam trap testing makes use of the drop in saturation temperature associated pressure drop across the trap. Condensate tends to cool rapidly in contact with uninsulated portions of the return line, accentuating the temperature difference. If the temperature on each side of the trap is measured, a sharp temperature drop should be evident. Table 6.15 shows typical temperatures that can be expected on the condensate side for various condensate pressures. In practice, the temperature drop method can be rather uncertain, because of the range of temperatures the condensate may exhibit and because, in blowing through a stuck-open trap, live steam will, itself, undergo some temperature drop. For example, 85-psig saturated steam blowing through an orifice to 15 psig will drop from 328°F to about 300°F, and may then cool further by radiation and convection from uninsulated surfaces. From Table 6.15, the expected condensate-side temperature is about 215 to 238°F for this pressure. Thus although the difference is still substantial, misinterpretation is possible, particularly if accurate measurements of the steam and condensate pressures on each side of the trap are not available.

The most successful programs of steam trap diagnosis utilize a combination of these methods, coupled with a regular maintenance program, to assure that traps are kept in proper operating condition.

This section has discussed the reasons why good steam trap performance can be crucial to successful energy conservation in steam systems. Traps must be properly selected and installed for the given service and appropriately sized to assure efficient removal of condensate and gases. Once in service, expenditures for regular monitoring and maintenance easily pay for themselves in fuel savings.

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