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Compressor Seal Gas System
Why Seal gas supply pressure is less than the compressor discharge pressure

Why Seal gas supply pressure is less than the compressor discharge pressure?

In our plant we are using Hitachi compressor to compress Refrigerant Butane. Its a Dual Suction and single discharge line compressor. the primary seal gas pressure is 1.04 Barg (process gas) and Secondary is 0.3 barg (Nitrogen). Compressor operating suction pressure is 0.25 and discharge pressure is up to 7 bar. My question is:

1. i have worked in Nuovo pignone centrifugal compressors in BCL and MCL there the seal gas pressure will be always more than the discharge pressure for (Ex: Discharge pressure is 5 mean seal pressure will be 6 bar on the NDE and DE sides of seal.) But on this Hitachi compressor why the the seal gas supply pressure is less than the discharge pressure.

My name: Kishore
Email id :

Today is 6/21/2018. Hope you already get the answer since long time past.

I see your post when I am searching the other issue about the seal gas. I am not a specialist, first of all. Here is just my understanding.

In your situation, I assume there is a balance line connecting a balance piston or drum to the compressor suction side. So, even on the discharge side, the inner pressure is equal to the compressor suction pressure. Then you don't need a seal gas higher than the discharge pressure.

Forgive my poor English.