Does Xantia TD have dump valve?

JohnCKL · Post by **JohnCKL** » 18 Oct 2003, 12:37

I was wondering whether my 1996 Xantia 1.9TD have a dump valve or blow off valve as stock standard? If not, which type of dump valve is suitable? Thanks.

mbunting · Post by **mbunting** » 18 Oct 2003, 12:55

I read somewhere that they were pointless on TD's anyway, because they always run with an excess of air, rather than being throttled as a petrol is.
Do a search for things like pump tuning on these forums, plenty discussed.

NiSk · Post by **NiSk** » 18 Oct 2003, 16:30

The purpose of a dump valve is to keep up turbo pressure when the (petrol) engine has it's throttle closed (as when changing gear) and to prevent the excess pressure blowing any air hoses off. As a diesel has no throttle and always runs with the intake wide open, a dump valve is absolutely useless and whould never be put to any use.
Save your money!
//NiSk

JohnCKL · Post by **JohnCKL** » 18 Oct 2003, 23:09

Thanks mbunting and nisk. I still got a lot to learn about my XTD.

KevMayer · Post by **KevMayer** » 19 Oct 2003, 02:35

A dump valve is used to relieve inlet manifold pressure when the throttle closes on a petrol engine. But it does this because if the turbo pressure is high, the trapped pressure can cause the turbo to stall or possibly damage the turbo impeller. A stalled turbo then takes time to spin back up.. so causes turbo lag for the maniac driving it. If the same hot head has upped the boost pressure, a dump valve is a good idea to protect his turbo from destruction when he repeatedly closes the throttle as he races up the gear box.
So, on a diesel turbo there is no throttle and so nothing to trap the excess boost pressure.
Having said this, I used to have an Audi 80 1.6 TurboD. It had a kind of dump valve on the inlet manifold. It was original equipment fitted by Audi in the factory when the car was manufactured.
It was more of a pressure relief valve. I had a Garret T2 turbo and the waste gate arm came loose (went faulty) so my boost pressure was unregulated (i.e. the waste gate was shut all the time). When I accelerated hard I got this sort of popping sound and the car lurched like it was misfiring. The pressure relief device was opening and relieving my boost pressure. So, some turbo diesels do have a type of dump valve.