Dump Valves
Turbo Mini Forums

Been researching some parts for my turbo build which is about to commense shortly. There are many different types of dump valves that i have found. BOV believe these are blow off dump valves the most simple, sequential dump valves and recirc dump valves, what is the differences, advantages and disadvantages of these dump valves advise and comments please what you are running and also what else is on the market like trick jap technology that NASA probs doesnt know about8)

Where is the best place to install a dump valve, to begin with i am not planning to run a intercooler but will soon upgrade to one am planning to run with 9-10 psi

Any info will be great many thanks
chris barkas

to be honest i dont think fitting a £300 hks will give any benefit over a £30 one

First point to note is that not all dump valves will work with an SU carb.

BOV do just that, lift and release the preasure.

Sequential valves have a stepped release sequence (not used one myself so not 100% sure how it will work with our application)

Recirc valves work the same as normal BOV but recirculate the 'dumped air' into the intake so the is no "wooossshhh" on dump. Not easy to make work well with a cone type filter though but the peice and quiet can be worth it sometimes

There are several types of internals too.

Diaphram valves, single piston and twin piston valves.

Most people I know use diaphram valves on carb'd engines, luckily they are also usually the cheapest!

Don't buy a cheap valve, you will regret it later and make sure you can get a range of springs so that you can match the valve to the boost level as you upgrade the engine or transfer it to another.

Avonbar, Bailey and Forge valves all have good reps and I have never had a problem with any of them!

Every day is a school day ...........

How fast and how expensive ...... the same question...

Hi,
Fit it to the plenum chamber. The difference between std and recirc, the recirc valve has the outlet piped back to the turbo inlet, as far as I know this is just a noise reduction thing. Sequencial, not got a clue, but with 10psi your not going to give a cheap one a hard time...
I'm running a Forge Group A because it has a filter, air can go in aswell as out...
Cheers,
Gavin :)
EDIT Must type faster!

Edited by Bat on 21st Nov, 2006.

VEMs Authorised Installer / Re-seller. K head kits now available!

WB/EGT gauges. Click here for customers write-up

Visit www.doyouneedabrain.co.uk

My Mini build diary

DONT by a bailey one, it will end up going wrong on you thanks to fuel contamination with the seal

From what little i know i dont think theres much point running a dump valve with anything smaller than a t4. People say it keeps the turbo spinning but ive heard arguments that without one pickup is actually quicker between gear changes etc. I suppose if you want that typical whoooosh sound then go for it, personally id much rather hear a turbo chatter its nutts off when it stalls

How much boost were they running to snap a shaft?

Its not the boost levels that kill the compressor, its surge. Running without any sort of pressure relief IE poppet or dump valve, will force the compressor into surge. This surge generates vibrations in the shaft causing the retaining nut to come loose after prolonged time. The impellor then walks forward on the shaft and hits the shroud. At 29,000rpm this is not good. White metal swarf is ingested by the engine, which, again is not good.

Any one who says that any sort of relief is not needed does not understand the dynamics of a centrifugal compressor.

Watch this space for some real compressor failures caused by surge.

Edited by Sprocket on 21st Nov, 2006.

You say that its not boost that kills turbos but if you run higher boost doesnt the turbo spin faster? Thus the force on the shaft will be greater when the turbo stalls making failure as descibed abouve occur earlier? Bear with me im still learning

Assuming no d valve etc...

Edited by AL on 21st Nov, 2006.

surge also causes large loading on the thrust bearing in the turbocharger, again NOT good!

J

hmmmm maybe a dumpvalve then. But would have to be a recirculating one jus to keep me sane

Would like to see pics, esp as thats more than my house is worth

Have seen many turbo minis with the dump valve fitted to the plenum chamber but has any one tried different locations to mount a dump valve, eg closer to the turbo, why is it not mounted close to the turbo as i would of thought that the pressure down stream of the dump valve would also cause the turbo to stall, heard the best place to mount a dump valve is as close to the intercooler on the carb side as possible.

I thought it had to be as close to the butterfly as possible, hence in the plenum is the usual place. Not sure why thats just what i heard.

Dump valves on minis seem to make more turbo lag, i have a BOV only cos i got it cheep and want people to know the little mini behind then has a turbo, it's about all there are good for on minis.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

This is most probibly the biggest electric supercharger you will ever see!!

Comparison picture to give you an idea of the size. Thats a 1/4 drive 6" wratchet in the eye of the shroud.




This is what the impellor should look like




This is what can happen if surge goes unchecked



Notice in this picture part of the high speed shaft. Its 2" in diameter. The rest of it is still in the machine.



The whole thing including the motor weighs 5200Kg and draws over 1000 amps. Try fitting that under the bonnet!!

Ouch!!!! What is one of those used for then?

Im guessing its for some sort of air conditioning system?

If you mount a recirculating one after the intercooler and then post the air back to the turbo inlet, will the air not be cooler entering the engine? This is the princible that air conditioning systems work on?

Compress the fluid and create heat, lose the heat with a heat exchanger, then decompress the fluid dropping its temperature?

My mind may be a bit frazzled!

J

Indeed it is a centrafugal refrigerating machine.

This is the biggest 'package' machine of this type we manufacture, 'we' being the pioneering manufacturer of these machines and the worlds largest refrigeration and Air conditioning company in the world. The founder member of the company invented the centrafugal compressor way back in the 1920's and was originaly a steam driven turbine. so when you see a centrafugal compressor there is some pattent of ours involved in it somewhere, however small that may be.

London has the largest conglomerate (sp) of these machines in one place within Europe.

It makes a change working on stuff this big compared to the cramped engine bay of the Mini. This is heavy engineering.

You KNOW when one of these babys is surging, the building vibrates!!!

Edited by Sprocket on 22nd Nov, 2006.

your right you do need a dump valve on big turbos, but on any thing around are sizes or smaller there don't really help.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

come on, own up, you left that ratchet in there didnt you

Edited by Nic on 23rd Nov, 2006.

LOL brill comment!

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

http://www.mattwoodsphotography.com

ha ha yeh

It has been known!

It can be quite surprising where you find a Snapon socket. The yank that built it is still looking for it :-

well ive been needing one for the supercharger setup, and ive just got one like this for the steal of the century at £10 brand new including postage!





J