NH3LVR
02-10-2010, 06:24 PM
I am not directly involved with this compressor now, but was asked by my former boss about it.
The machine is a Vilter 440, 12 cylinder, two stage. 8 cylinders low stage, 4 cylinders high stage. It is not internally compounded, but has a external intercooler.
The refrigerant is NH3. Settings were at: Suction 2lbs (.1BAR) Discharge 135 lbs (9BAR) the last time I saw this machine. I do not recall where the intermediate operated.
It services freezer and cooler loads in Alaska. On occasion the high stage is not big enough and a high stage screw is used to maintain suction pressure. Condenser is adequate year around.
I did some work on it years ago.I set it up to unload 1/2 the low stage on a pressure switch. The high side remained loaded at all times.
This machine was inspected and the valves replaced a few months ago. The mechanic is a competent service person. (Yes, I said something nice about you Danny)
This machine has ran for years under these conditions.
One thing changed. The operator felt that the unloader was not working. He apparently replaced the unloader control with a manual switch and would leave it the cylinders not pumping overnight.
Now I am aware that some manufacturers do not like machines to run unloaded for long periods of time. This has never been a problem for me with machines running for hours at light loads. I do remember that Vilter will allow a compressor to run fully unloaded for up to 20 minutes in some applications.
A few days ago the compressor was heard to be making noises. A serviceman flew up to determine the problem. The four cylinders that were capable of unloading were found to have gotten hot enough to deform. The cylinders that were loaded are fine. The crankshaft was also damaged because of a failed rod.
My former employer talked to Vilter. The Rep works mostly with screws, but said you could unload 4 cylinders for up to six hours.
This seems strange, as I feel to see why 6 hours would be a magic number. If it was going to get hot I think it would do so sooner than that.
Comments or suggestions?
The machine is a Vilter 440, 12 cylinder, two stage. 8 cylinders low stage, 4 cylinders high stage. It is not internally compounded, but has a external intercooler.
The refrigerant is NH3. Settings were at: Suction 2lbs (.1BAR) Discharge 135 lbs (9BAR) the last time I saw this machine. I do not recall where the intermediate operated.
It services freezer and cooler loads in Alaska. On occasion the high stage is not big enough and a high stage screw is used to maintain suction pressure. Condenser is adequate year around.
I did some work on it years ago.I set it up to unload 1/2 the low stage on a pressure switch. The high side remained loaded at all times.
This machine was inspected and the valves replaced a few months ago. The mechanic is a competent service person. (Yes, I said something nice about you Danny)
This machine has ran for years under these conditions.
One thing changed. The operator felt that the unloader was not working. He apparently replaced the unloader control with a manual switch and would leave it the cylinders not pumping overnight.
Now I am aware that some manufacturers do not like machines to run unloaded for long periods of time. This has never been a problem for me with machines running for hours at light loads. I do remember that Vilter will allow a compressor to run fully unloaded for up to 20 minutes in some applications.
A few days ago the compressor was heard to be making noises. A serviceman flew up to determine the problem. The four cylinders that were capable of unloading were found to have gotten hot enough to deform. The cylinders that were loaded are fine. The crankshaft was also damaged because of a failed rod.
My former employer talked to Vilter. The Rep works mostly with screws, but said you could unload 4 cylinders for up to six hours.
This seems strange, as I feel to see why 6 hours would be a magic number. If it was going to get hot I think it would do so sooner than that.
Comments or suggestions?