Mystery lead off Compressor

[petermrw]

Hello All,

We are abit stuck - we have a railway locomotive powered by a Perkins 104.19 diesel engine.

To provide air for the train, we have a Leyland Compressor 02301 as seen in attached photo, which is attached via two rubber couplings on a drive shaft

However we have been unable to identify the lead (circled in red) that is on the side of the compressor and where this fits on the engine.

Any ideas what it might be. Oil Feed?!

Please see attached photos

Any help appreciated

Peter

[cedgo]

Tough one.
Oil reservoir or oil cooler?

[tractornut]

i'm thinking that it is for an unloader valve so that the compressor shuts off at the correct pressure and cuts back in when it drops too low

[stevecorio]

crankcase breather?

[pawon]

I think it's a crankcase breather.
Probably connects to the crankcase breating system of the diesel engine.