Frick compressor slide valve and stop drifting 1

[pubu]

hi there,

i am currently experiencing an issue out on site that I would appreciate some advice on. I am commissioning four natural gas wellhead compressors that have Frick 1913 screw compressors mated to a CAT engine.
these compressors have both automated Vi and side valve control
the problem I have is that both these items are drifting around without the hydraulic solenoids being actuated at all.
the slide operates and controls nicely up to 50%, but beyond this, it just keeps increasing by itself.. even when the unload solenoid is on 100% of the time.

as i understand, when load is selected, oil pressure is applied to one side while the opposite side is vented back to suction. so technically, the slide shouldnt move around by itself if the actuators are not activated?
this is a brand new compressor so i doubt the seals are leaking.
does anyone have any experience with kind of issue.

i put both PID loops for the Vi and slide valve on manual and just put a set point for the unit to maintain.. it cant even do that
also seems that the slide and vi blocks sometimes stick to one another.. they both simultaneously change.

any advice would be great.
thanks
pubs

 

[zdas04]

I have seen this exact scenario when we put gas to the actuators instead of oil. Once we changed to using oil the problem stopped and we never saw it again. I have never seen this problem when driving the cylinders with oil. Any chance they connected the cylinders to the gas stream instead of the oil stream?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist