What's a dump valve?
Discussion
Ok a dump valve sits just in front of the throttle plate.
It works by allowing compressed air from the turbo to bypass the throttle plate, usually being diverted back to the intake of the turbo.
The idea is that as you mash the throttle to go into "hoonerdrive", the turbo spins up as usual.
But when you loose the throttle, the turbo is still inducing air, compressing it and forcing it up against the throttle plates. This can be quite bad as in severe cases impellers can be sheared off as the air surges back up the intake.
The dump valve simple allows the compressed air to escape, protecting the turbo from damage.
Incidentally, all these boy racers whose dump valves keep whooshing at low revs in every gear have got it set up wrong as its usual to set them up to dump at max boost on throttle closure.
HTH.
It works by allowing compressed air from the turbo to bypass the throttle plate, usually being diverted back to the intake of the turbo.
The idea is that as you mash the throttle to go into "hoonerdrive", the turbo spins up as usual.
But when you loose the throttle, the turbo is still inducing air, compressing it and forcing it up against the throttle plates. This can be quite bad as in severe cases impellers can be sheared off as the air surges back up the intake.
The dump valve simple allows the compressed air to escape, protecting the turbo from damage.
Incidentally, all these boy racers whose dump valves keep whooshing at low revs in every gear have got it set up wrong as its usual to set them up to dump at max boost on throttle closure.
HTH.
donatien said:
Thanks chaps - got a clearer view now.
Is it then fair so say that most turbo cars have one? I had a Renault 5GT Turbo and a Saab 9-3 Turbo. Would they both have one?
The Saab was one of the "full on turbos" (i.e. not the low pressure variety)
The Saab will have a Bosch Recirculating DV as standard. The 5 GTT won't have anything.
Matt
Incidentally, a dump valve is different to a wastegate - The two are often confused. Whereas the dump valve is on the 'fresh air' side of the tubocharger, the wastgate is on the exhaust side and allows excess boost pressure to be vented to atmosphere. Just though I'd add that. I'll be on my way then... :whistles:
The waste gate is a valve in the exhaust turbine of the turbocharger, it regulates the amount of exhaust gas passing over the turbine itself and controls the velocity of the turbocharger and therefore the amount of boost generated.
As far as i remember a dump valve is there as a part of when you lift off the throttle in high boost cars to dump the excess boost pressure to prevent overun (to allow engine revs to drop quicker) and to prevent damage to the throttle butterfly and inlet valves.
As far as i remember a dump valve is there as a part of when you lift off the throttle in high boost cars to dump the excess boost pressure to prevent overun (to allow engine revs to drop quicker) and to prevent damage to the throttle butterfly and inlet valves.
steve_D said:
That chirping sound you hear when a manic rally car comes charging up to a corner is the dump valve working overtime.
Steve
the chirping could also be the wastgate chatter.... this can be as loud as a dump valve.
I removed the dump valve off my old cossie (turbo not large enough to NEED it) and the wastegate chatter when charging around was a very loud chirping.
Sounded much better than the dump valve as well.
Personnely after 7 years of driving around with a group A dump valve, I got fed up with the bloody noise and wouldn't fint one unless I had to.....
also the old theory that helps throttle response also seems to be changing..... I know on my car the throttle response was better when we took it off and re-mapped the ecu accordingly.
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