Designing a Shorter Vertical Leg for Sanitary Steam Traps - - BioPharm International


Designing a Shorter Vertical Leg for Sanitary Steam Traps

BioPharm International
Volume 19, Issue 9

Figure 6. Close-up view of back-up leg
Condensate backup tests were conducted from 20 to 35 psig, which represent the practical minimum and maximum values for SIP pressures. Various condensate loads were generated by changing the cooling water load. Condensate backup was measured in inches above the trap's inlet tri-clamp connection. The weight of condensate for these 5-min tests was recorded by the scale shown at the bottom of Figure 5. The trap cycled many times during this 5-min period.

Table 3. Test data runs with the CDS trap
Temperatures were recorded throughout the test. The difference between the highest temperature measurement and the lowest temperature measurement for a given cycle was designated as the test sub-cool. The test pressure, condensate load, maximum backup, minimum temperature, maximum temperature and sub-cool are shown in Table 3.


Loads indicated in Table 3 are the average flow rate over the five-minute test period. Care was taken in the test set-up to ensure that condensate could not settle in low points in the piping. If this occurred, this puddled condensate was periodically pushed to the trap in slugs. The maximum backup reported in Table 3 includes slugs of condensate. Sanitary steam piping is always sloped to be free draining and steam legs are taken from the top of steam headers to prevent condensate buildup in the lines.

The highest temperatures were recorded when the trap was open and the thermocouple was exposed to live steam. The trap closed when higher levels of condensate reached the bellows. When this occurred, condensate backed up and the temperature dropped.

Figure 7. An illustration of the data from Table 3
As expected, condensate backup depends on the condensate load, steam pressure, and steam trap sensitivity. Backup is higher for higher condensate loads. Backup decreases with increasing pressure. This is the result of the sub-cool decreasing with increasing pressure. Backup is lower for the more sensitive Nicholson B bellows. The backup for the B bellows never exceeded 6 in. in all of the tests in the pressure and flow ranges of interest. (Figure 7 summarizes the results of these tests).

Inspection of critical SIP steam trap subassembly installed on a 500-L bioreactor at Dakota Systems Inc.
During the five-minute tests the steam trap typically had smaller temperature variations with more cycles at low loads than with high loads. For low, steady condensate loads, the bellows may be "throttling" as the bellows moves slightly to small temperature changes. At other times a slug of condensate reached the trap. When this occurred the condensate quickly backed up and then discharged completely, all within a few seconds, as the trap opened fully. The backup sometimes dropped off with increasing loads as the trap moved from on/off mode to throttling mode.

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