Why Screw Compressors need Deferential Pressure

It is really important for screw compressors to maintain minimum pressure differentials. 

This does affect the bearing stacks running smoother but it has more to do with maintaining oil flow.

Modern screw compressors don't use oil pumps to move the oil through the system. 

They are using the pressure difference between discharge and suction to flow the oil as needed. 

This is why the oil is part of the high pressure side and the bearings are all in the low pressure zone. 

One area screw compressors have been getting pushed harder into is their unloading capabilities to fit more flexibility and efficiency into the same machines. 

Have you heard about some of the most recent models coming out having oil stacking and oil flow issues at low loads? 

This is largely due to manufacturers trying to push the boundaries of these minimum requirements for smooth operation. 

I don't personally see this as a problem but we need to understand how these things work.

By understanding we can help tune the system in a way that allows the chiller to perform smoothly at it's extreme states. 

There are things that can help with this like periodically loading the compressor to encourage oil return. 

Even if the system has an eductor it still requires the DP to get the needed draw through the oil return. 

This is something to ponder on as we are moving into our lower load times of the year. 

I'm in Texas so winter hasn't hit yet....

MTT

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