Dump valves

[Dippy]

KayGee,
I understand that it's easier to measure flow rate with water, but I don't see that it has much value. The volume of air that a DV has to shift is really quite small, that I believe (I certainly don't know), all the air will have flowed before the valve is fully open. That's one of the problems with all this 'off-car' testing - it doesn't take into account what the DV actually does on the car.

I disagree with you on the terminology. Unfortunately dump valve and diverter valve have the same acronym. But to me dump valve means the air is wasted (i.e. those which vent to atmosphere), whereas diverter valves/recirculating valves keep the air in the system.


Wak,
I'm afraid you're going into this far more technically than I want to or for that matter am competent to contribute. My comment about matched springs is that if you take a piston DV which has a weaker spring than a diaphragm DV and compare them, you may well find the piston valve responds quicker, because the difference in spring tension dominates. Only by removing the spring tension from the equation (matched springs) can you really compare the responsiveness of the two types.

Having said that, unless you have a variable tension DV, in the real world we are stuck with a limited choice of springs. Going back to my compromise statement, if you have a chipped car, then you're likely to need a stronger spring for your piston valve to avoid hesitation. This will make its response time worse than a Bosch DV. However that Bosch DV will be prone to cause hesitation.

[Wak]

Dippy,
I never wanted to get this technical either, by the way , the Forge DVRS is a variable tension piston DV as is the Optimus, a variable diaphragm.

I was given a couple to play with and found that I had DV chatter straight away and the car felt worse on the lowest setting, turning up the dial just made it laggy even more.

So in trying to understand why the latest Diaphragm Optimus was not coming up to expectations I had a play with a number of springs down Forges weekest which is used on some DV's for Japanese spec cars.

vacuum testing was the only way to test them off the car and the only way to review relative performance with the different springs.

My conclusions based on the vacuum tests it visualise differences and the seat of the pants driving fell in line with the opening vacuums having an optimum level and getting them too high with stronger springs or turning up a dial didnt make for a better DV.

There really is no substitute for being able to plumb some DV's in and go for a drive at the end of the day.

[Rees4]

Ok,im going for the 710 n's.My S4 is standard apart from a Tanoga s/s and K/N filter element.Cant be arsed paying out for the Forge type,will just take your advice and check my valves regular and keep fingers crossed.Probably an embarresing question but would i be needing 2 DV's?, sorry im a Kitchen fitter not a mechanic lol.

[MarkB]

You need two

[Dippy]

Wak,

I was interested in the DVRS so asked Forge about it and they recommended that I stick with the 007Ps. I can see why now.