Hi Folks, I am trying to understand the exact function of the changeover valve that is part of the diverter valve assembly.

as far as I can see the feed from the manifold goes via the one way valve that lets only positive pressure into the changeover valve top inlet, then the changeover valve allows positive pressure to apply to the top of the DV's to help the DV's to open at higher pressure via how I am connected via the bottom outlet, as far as I can see the DV's open about 5-7 psi without assitsance, the added pressure from the manifold holds them shut until much later.

Then some signal from the DME tells the changeover valve to switch between positive pressure from the top inlet valve of the changeov DV's to the side inlet where I assume there is vacuum to allow the DV's to vent boost after acceleration shutdown.

Reason for the question after pressure testing my DV assembly, for some reason my they seem to open at stock DV pressure so I am opening at 5-7 psi and draining boost.

I am trying to work out the logic of how the assembly works so I can track down the problem, I have already replaced F hose U hose and both diverter valves.

Hope my question and assumptions make sense?

ta
mike

 

Hi Mike,

I've been reading here a lot and learned quite some stuff, so I am happy now to give something back:

The diverter valves operate as you wrote. On their inlet (F-Hose connected to the Y-Pipe) you have the boost pressure. A spring is holding down the valves, but this spring alone doesn't hold much and it doesn't have to, because on the control side you have the same pressure as on the input side.

The spring alone hold the valves shut and once the ECU switches the valves, their control side is now a vacuum and this vaccum together with the spring do open the valves.

I built myself a test rig and made some tests. A f-hose was used to mount two diverter valves and the input was plugged in order to being able to pressurize it. The output of the diverter valves vent to atmosphere.

I have attached a picture of that test rig.

These are the control pressure rates and the resulting capability of the stock diverter valves to hold against a boost pressure:


0 PSI/ 0 bar control pressure
Diverter valves hold virtually no pressure.

5 PSI / 0,35 bar control pressure
Diverter valves do not hold the pressure that the compressor delivers, but they shut at 0.9 bar once I stop delivering more air.

10 PSI / 0,7 bar control pressure
Resultung pressure that the diverter valves can hold: 1.4 bar

12 PSI / 0,83 bar control pressure
Resultung pressure that the diverter valves can hold: 1.6 bar

15 PSI / 1,0 bar control pressure
Resultung pressure that the diverter valves can hold: 1.9 bar

20 PSI / 1,38 bar control pressure
Resultung pressure that the diverter valves can hold: 2.4 bar

This test was done to see what the relation between control pressure and the resulting boost pressure is. One could provide manifold independent control pressure in order to shut down the valves very quickly and keep them shut firm without playing with different springs (an option that not all diverter valves do support). This is something I have planned to do, but had no time yet.

So, why did I do al this? My nice and shiny FVD diverter valves have leaked and after looking at how they are built I decided to used the stock ones instead and made sure that they operate as they should.

Andreas

 

Thanks GT996, so that's leaves me two thoughts why I am leaking boost at DV spring pressure levels.
1. I have a faulty changeover valve which is not allowing control pressure to the DVs
2. The connections to the changeover valve are incorrectly routed, can you confirm if the bottom outlet of the changeover valve goes to the DVs, the middle outlet to the four way connector?

Thanks
Mike

 

I wonder if that help?

 

Hi Mike,

the top inlet pressurizes the DVs thru the check valve. DVs are connected to the mid connector. Bottom is connected to the 4-way connector = vacuum.

The mid port = DVs control port is switched between manifold pressure and vaccum.

The 90 degrees rubber hoses pretty much point towards the required connection.

Andreas

 

Many thanks Andreas this is my problem wrong routing of the control vacuum pipes, thanks for taking your time to share with me.
Rgds
Mike

 

jpflip, thank you for your image.

 

Just a question there, is there any interest to disconnect and unplug the top change-over valve piping ?
I found mine disconnected and plugged away, on purpose.

 

Anyone ever made/saw this mod ?
To my understantding of the system, this is removing the positive boost pressure to assist springs and keep the valves closed...

 

It could be that the last owner bypassed the N249 valve and has the diverter valves connected directly to the intake manifold boost/vacuum source.

So basically they would have removed the check valve and connected that hose to the hose that splits and goes to the top of the diverter valves.

Kind of like this where the red lines represent where the hose is disconnected/plugged and the blue lines are the new flow path directly from the intake manifold to the diverter valves circumventing the N249 valve.