Hi all, I'm just curious to how a dump valve works. I'm under the impression the hose going from the top of the dump valve goes to the inlet manifold infront of the throttle body and the boost pipe is attatched to the bottom end of the dump valve.

When boosting the pressure in the inlet manifold going to the top of the valve is equal to the pressure in the boost pipe witch causes the valve not to leak. however when the throttle is closed the pressure in the inlet manifold is reduced and the pressure in the pipe is still there causing the valve to open as there isnt equal forces on each side of the valve.

Am I correct?

Cheers.

Dump valves are fitted to the engines of (usually older) turbo charged cars and sit between the turbo outlet and the throttle body. When transitioning from a boosted state to a closed throttle state (as in between shifts), due to inertia, the turbo continues to pressurize air, but the closed throttle prevents the compressed air from entering the engine. In this case the pressure exceeds the preset spring pressure in the dump valve and the excess pressure is bled off to atmosphere.

Even with a dump valve the compressed air acts as a brake on the turbo (slowing it down), because the pressure on the backside of the turbo is at a higher pressure than on the front side (and the air actually wants to flow through the turbo backwards).
A blowoff valve is a more elegant solution to this problem by allowing the turbo to "freewheel" when the throttle is closed (equalizing the pressure on both sides of the turbo). Unlike a dump valve a blow off valve can be used at multiple boost settings without reconfiguration.

Blow off valves (which may cause offence) are sometimes incorrectly called dump valves because they serve a similar function, however they are very different solutions to the same problem.

So the one I was explaining is a blow off valve? such as a hks ssqv.

Quote from ToyotaSupraUK :

So the one I was explaining is a blow off valve? such as a hks ssqv.

HKS call it a Blow Off Valve - http://www.hksusa.com/products/?id=792