Vehicle & Technical > Defender

dump valves

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tonycougar:
Heard a bit about these, and as a little knowledge is a dangerous thing (Especially where I am concerned) thought I'd better ask what they do on here.

Xtremeteam:
now.....

would that be dump valves that go tish?

or the dump valves that landrover refer to in the bottom of the airbox?

If its the first one they can be fitted to a diesel but due to them being an exces air device landrovers in particular dont have a throttle butterfly,
on a petrol turbo when the throttle closes it causes a positive pressure to build & can stall the turbo or shatter the turbine blades,

as a diesel doesnt have a butterfly this doesnt happen

But you can fit a dumpvalve to a diesel to give the tish noise,Involves a micro switch & a solenoid,

tonycougar:
No don't fancy the tish noise, obviously thought it was something else.
Thanks

sas pinkie:
they release the presurised air to atmosphere when the throttle butterfly is closed to prevent the turbo impeller blades from stalling. very handy on a high boost racing car as it reduces lag, of no practical use to you on a Land Rover (or on boyed up turbo cars), it wil make a woosh, which will become very annoying after a while.....

Porny:
From one of my older postings…  :wink:

You will never, ever get a vacuum on a diesel (excluding some early Series 3's before we get someone being clever - but we'll exclude them for the time being)....

A quick explanation (sorry if this is really basic)

You won't get a vacuum on a diesel because you do not have a throttle blade,

On a petrol engine, the vacuum is created when you shut the throttle (i.e. lift of the accelerator pedal) as the engine is still trying to suck in air, but as the throttle blade is closed, there is only a small amount of air available. The engine is basically trying to get more air than is available so creates a vacuum in the inlet manifold.

A diesel though, does not have a throttle blade – a diesel basically runs WOT [Wide Open Throttle] all the time and all the accelerator pedal does is add or remove diesel.

So you will not see a vacuum even in the inlet manifold, as it can not physically create one. Hence why you have a vacuum pump on the side of the engine to supply a vacuum to the brake servo.


In terms of dump valves:
A dump valve is mainly used with high boost applications, the back pressure caused by lifting off the accelerator can cause the compressor within the turbo to stall. In extreme cases, the compressor can actually shatter.

This back pressure occurs because when you lift off the accelerator, the throttle blade closes... and as the turbo is still producing boost pressure this pressure builds up behind the turbo has no where to go - which as mentioned - in extreme cases can cause the compressor wheel within the turbo to go bang!!! - not good.

The dump valve is simply a release for this pressure... which also reduces turbo lag as the turbo is pressuring into a now empty intake manifold - which will also have a slight depression/vacuum acting on it.

A diesel though, does not have a throttle blade and as such will never see this build up of 'back' pressure.... (as mentioned a diesel basically runs WOT all the time and all the accelerator pedal does is add or remove diesel - in simple terms)

Which also means connecting a dump valve to a diesel is a little more complicated. Because it doesn't have a throttle blade, there is no-where to tap into to connect the dump valve - which relies on the pressure difference before and after the throttle blade to work.

The only vacuum created on a diesel is for the brake servo.... a diesel dump valve gets plumbed in to the vacuum circuit and is controlled by a solenoid valve that is activated when you lift off the accelerator pedal. However.... this set up will work ok on a 200Tdi or 300Tdi but is not really ideal for a TD5.

Whilst a dump valve can be made to work on a diesel, the only benefit would be that of noise…. i.e. you get a clatter, clatter, clatter, woosh, clatter, clatter noise… rather than just clatter, clatter,clatter, clatter.

Unlike a petrol, you will see no reduction in turbo lag, or turbo lifespan.... the biggest killer of turbo is not allowing them to warm up or cool correctly - i.e. thrashing the car from cold or turning it straight off after a high speed thrash. Worst still is when people rev the engine and then turn it straight off.


Ian

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