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10-02-2010, 07:50 PM #1
TEV on long liquid line, liquid hammer
I have a case with Alco TEV's (the XWB serie) where a contractor installed a liquid line of 1/2", 25 tot 30 m (75 to 90 ft) long and where in a timespan of 1.5 tot 2 years 5 TEV's failed. Capacity 20 kW (+/- 68200 BTU)
Freezer application and evaporators going each time in pump down when defrosting or temperature reached.
HP kept at 15 bar (215 psi)
The TEV's were each time closed when erratic and only opened again after removing the thermostatic element from their housing. They apparently functioning normal after reassembling.
TEV's (external equalization not connected)where tested in a lab where the bulb was submerged in glycol from -30°C and heated to 20°C (-22°F till 60°F)
They measured needle displacement and the displacement of the erratic ones was the same as a new TEV. The new TEV was also measured as a reference.
My theory is that the TEV's encountered a serious liquid hammer when opening the SV which injured somehow the diaphragm and/or the needle assembly of the TEV. I should expect then a complete opening of the valve but they were each time completely closed.
I would appreciate any comment on this issue.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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