# Speedaire 3Z495 tube from crankcase to cylinder head, what is it for?



## Tundrawolf

Hello, I have a Speedaire 3Z495 air compressor. It had a line coming from the head cut and crimped and a line from the crankcase that was capped. So I reconnected the line, but I need to know what it does. Does it need a check valve? What does it do? Thank you!


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## jbtvt

More familiar with 4 cycles, but going by your position description alone, I'd assume you'd want a PCV valve there.


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## Tundrawolf

If you look at where the line connects to the crankcase, you will see the crankcase vent pipe.


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## tractornut

i believe that it hooks to an internal unloader valve on the pump side to help with starting and stopping of the compressor. and welcome to PEF


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## 89yt12

tractornut said:


> i believe that it hooks to an internal unloader valve on the pump side to help with starting and stopping of the compressor. and welcome to PEF


 
ditto on that one, my craftsman has a pipe just like that for that reason


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## Tundrawolf

Thanks guys. When I changed the oil I took the crankcase cover off and it looked like there was some sort of weighted centrifugal assembly of some kind on that end. So it pretty much has nothing to do with oil, which is good!


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## Roadlizard7

Yes, that is a centrifugal unloader to allow unloaded starts.


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## Chendler

Thank you*informed me.


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