Originally Posted by
NH3LVR
About a year ago we installed two used Stal Vertical Screw Compressors in a customers NH3 plant. It is a mixed bag of parts with flooded coils in both the Freezer and Cooler. Not a very efficient design feeding both loads into a common suction.
I have not been the lead person on this job, and I got the Model Numbers from one of the other guys. Hopefully they are correct. (R-57, Generation E, MK1, R570-40C)
Bear with me in my ignorance as we do not work on Stals as a rule. But when the Customer purchased them we were bound to install and maintain them. And they had Frick Quantum 3 panels installed so we were familiar with that part of them anyway.
The original installation was with Thermosyphon. It was elected to continue this when reinstalling them. This was a problem as the plant has two Frick VSA Compressors with lubricators pumping oil into the system continuously. The Thermosyphon Vessel caught most of it and sent it to the Vertical Oil Coolers. This caused a great deal of trouble. We had difficulty running both Screws at the same time without overheating.
Both of the Units required Seal replacement. ( I realize these are designed to save space, but putting the Seal on top of the motor required a rewind) New bearings were installed in one.
Finally we had every thing going well. We went to lunch and one of the machines had shut down on temperature. The new Suction Check Valve had failed and when the machine shut off the oil disappeared up the Suction Line. (We found it in one of the Frick's.)
I have had better days.
After a lot of time spent it was decided to install Liquid Injection on one of the machines. The TX Valve hunts a bit but works well.
After a long preamble I can get to the point. We decided to find out why the Suction Check did not operate. (I felt that the machine running backwards every time it shut off was not a good thing. (Humor) We had installed Discharge Checks but it would spin backwards for 30 Seconds or so after shutting off)
The new check valve had had the plastic sealing surface slip out of the groove! One of the rivets securing the flapper had sheared and it was not landing squarely on the seal face.
Parts and support for Stal is almost nonexistent on in the U.S.
We were able to get a new Suction Check coming from Denmark. At a cost of $1000.
My questions are;
Is Check Valve failure common on these?
Are the Rivets on the Hinge loose when the are manufactured to allow movement?
Is there a better quality Suction Check available for these?
The check we removed had a 1/8 hole in the Disc. Was this a attempt to depressurize the machine slowly after shutdown?
Any other stal tips would be appreciated. As I say we are not familiar with these at all.
One other note. I called the Fine Frick Folks about with a panel question.The Controls Engineer asked me about the Software Version. Fortunately I had written it down. It seems that the old Software would shut down the Liquid Injection on the 29th of October. (Daylight Savings time), as well as stop the five second countdown in the Discharge Temperature.
The result would have been that the Liquid Injection would not have came on and the Discharge Temp Safety would not have worked.
I would have been very puzzled on the 30th of October. As well as busy taking a machine apart.
Any information or tips would be appreciated.
