Forge DV007P (green spring) testing

[Markus]

I tested the pressure characteristics of my Forge DV007P bypass valve a while ago, and I thought that I should share my results with you guys.

The valve has the green (weakest) spring. All pressures mentioned are gauge pressures.


1. Vacuum applied to small connection (vacuum connection that is connected to intake manifold):

- valve no longer airtight at -0,1 bar
- valve fully open at -0,3 bar


2. Pressure applied to side connection (S2 stock installation), small connection not connected:

- max attainable pressure: 0,3 bar -> valve opens


3. Pressure applied to bottom connection (end of piston, "reversed" installation), small connection not connected:

- max attainable pressure: 0,5 bar -> valve opens


4. Same pressure applied to small connection and to either side or bottom connection (situation when under boost at WOT):

- valve stays shut for very high pressures (my pressure reg ran out at 1,7 bar) since the piston area in the vacuum chamber is larger than the piston area of the side or bottom connection. In addition to this difference in surface area, the spring will also help to keep the valve shut.


What does this mean? No matter how high boost you're running, a weak spring will not make the valve leak at WOT (unless you have a very high pressure drop between turbo outlet and the intake manifold). If it leaks, it's because there is a fault in the piston sealing or then there is a leak in the vacuum hose. The spring does however affect the characteristics of valve operation at part throttle and off boost.

What I found interesting is the fact, that most of the time when driving at steady speeds, the valve is, in fact, open. My ABY has an vacuum of over 0,5 bar in the inlet manifold when at idle and this stays about the same when driving at constant speed. This is a lot more than the 0,1 bar vacuum needed to open the valve.

Theoretically, the valve will seal "harder" when installed in reverse. Installing it the stock way around doesn't, however, mean that it would start leaking at high boost pressures under WOT. Airflow and therefore also noise levels might however vary according to installation.

Eh, pretty hard to explain everything clearly and in detail. And it might be that I've overlooked or misunderstood something, so feel free to correct me if you think I'm wrong. Prior to thinking these things over I didn't realize how the operation of such a simple gadget can be so complicated and play such an impotant role in a turbo system.

One final comment on the spring:

The spring can be changed. Forge provides the following springs (from weakest to stiffest): green, yellow, blue, red. In addition spacers can be used to fine tune the response.


EDIT: Realized that some of my comments regarding the way the valve is installed were not completely true so I edited them. It's a bit more complicated than I initially thought.

[91_S2]

Thanks for that write up. Most lazy b**tards like me, prefer to let hard working guys like you do the work and documentation and then just read

I still haven't decided on an aftermarket dump as opposed to the OEM but It is interesting with data in any case.

[Paulm]

R u using a dump to atmosphere or re-circulate type. I used a Bailey to atmo on my last S2 but it made the car hesitate. it was the double piston type so stayed shut under idle and part throttle situations.

Paul

[SteveH]

Thanks for the info Markus

[SteveH]

Paulm...There's been plenty of discussion on both types of DV in a couple of threads. Recirculating is the correct type for the S2. Dump to atmosphere DVs can cause some running problems like hesitation, due to air being 'lost' from the system.

Re-circulating

Dump to atmosphere

HTH

[jameswkr]

Markus, have you run back to back comparison on the car using standard and reversed installation? Any comments ? Cheers James.

[Markus]

Nope. In fact, the valve isn't yet installed, it still sits on the shelf waiting for me to find the time....

[Corey]

Sorry if this is a stupid question but it is the first time I have played with a DV, I am fitting one to my ur.
I have a Baliey Closed Loop type, the piston is very stiff and when pushed on it will not return to it's seat, I do not believe for one minute that this is normal, I am intending replacing the plastic piston with a metal one.
But the stiffness does concern me (no pun's please, matron!!!)

[Markus]

I'm not familiar with the Bailey valve, but it does not sound normal. Make sure that the vacuum chamber inlet is not plugged.

Basically, a simple leak test on a piston bypass valve can be done like this:

1. Push piston to the bottom
2. While keeping piston at the bottom, place finger on vacuum connection. Release piston. Piston should stay open.
3. Remove finger from vacuum connection. Piston should return to its seat.

[Corey]

I wasn't happy with the plastic piston and the fact that it didn't seem right to me, made me make a new piston out of aluminium, the new piston now slides in and out of it's chamber and it holds a vaccum now.
It does what it says on the tin.

Thanks for the help.