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26-06-2009, 08:14 PM #1
Vilter tuning/unload and load setpoints
Hello, I've got a air seperation plant with a Vilter 456XL chilling 780,000 cu.ft/hr @ 90 deg F. to around 40 deg.F. My target suction pressure is 65 PSI. The plant installed a pressure transmitter and controlling loading and unloading with the plant computer system. I have fixed several things already: evap level float controller new needle and seat, correct spring( it was calling for liquid 100% of the time) didn't flood the evap. due to low level in the receiver, so added *****(R-22), installed a new compressor, and have been struggling with a suction pressure that goes from 60 to 74 PSI in cycles.
Come to find out they put a timer on the setpoint to load and unload for-get this- 30 seconds! It would pull down at 100%, hit the setpoint of 64.5 PSI, and not unload til 60 PSI or so. Then it would unload to 66%, then 33% and turn on the hot gas! Then the pressure would shoot up, past the load setpoint of 65 PSI, start timing, and finally load, first at 66% and finally 100% By then of course the pressure is at 70 or more, all the liquid is at a full boil, and it would take (depending on how hot it is) a long time, or never,to come back down.
I got them to let me adjust the timers(2 sec. delay to load, 5 to unload) I cannot convince them that they need to get rid of the timers( they say they need a "deadband") and set up 4 different setpoints for the loading and unloading and another one for the hot gas bypass. This would control it and give it a pressure controlled deadband rather than a time based deadband between steps. They don't think it's a problem because it's run this way for years(until I came along and started fixing stuff) It's been blowing hot gas thru the liquid add line for years due to a low receiver!
Does anybody know where I can get some data to show these guys? They just don't believe me.Last edited by US Iceman; 27-06-2009 at 07:05 PM. Reason: edit text into paragraphs - no charge!
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