Oil system layouts

[murpia]

I've realised recently, that the typical oil system layout goes:

Oil pump -> Pressure relief valve -> Oil filter -> Engine

Not sure why, but I always assumed (incorrectly it seems) that the Pressure relief valve (PRV) came after the filter. Seemed to me that the filter pressure drop may vary depending on the contamination level, therefore oil pressure itself could vary. I know some filters have a bypass to help this? Anyway, what's the advantage to having the PRV before the filter? And what could go wrong with the alternative, PRV after the filter?

Thanks, Ian

 

[patprimmer]

You could break oil pump drive shafts or gears.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

You could also blow up filter canisters.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CarlosReis]

Don't forget that there is another pressure relief on the filter itself that bypass the filter when it is clogged or the oil is too thick due to aging or cold weather!

Carlos Reis

 

[murpia]

Thanks guys,

Regarding the pressure drop across the filter then, I assume this will increase with contamination effects, until it becomes sufficient to open the filter bypass valve?

Engine oil pressure will therefore drop slightly from a new filter down to the filter bypass opening, and remain constant thereafter?

Thanks, Ian

 

[patprimmer]

You should change filters well before there is risk of it bypassing any significant amounts of oil.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.