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Discussion Starter · #1 ·
Ok, so I will be putting in the turbo on my C900 relatively soon (wednesday I hope) but I am a bit confuesd with the placement of the dump valve. On the newer T5 and T7 cars, it seems to be placed in opposite way than the way it is placed in a C900. I am not shure 100 % how it goes in a C900 because it is hidden under the intake pipe and I haven't been able to have a look in person on a turbo c900.

So, the way I thought it's suposed to work:

from the intake manifold to turbo inlet>> when pressure gets excessive in the intake manifold. it pushes up on the diaphram to open the valve then air flows to the turbo inlet. (what is the vacuum line at the top for?I put my mouth on the top part to see if it held pressure but I can blow right through the vacuum line fitting at the top so it doesn't seem to have a purpose..... maybe just for monitoring of the opening and closing for APC?)

The way it is displayed when you open the hood on a T-5 or T-7 car:

The valve seems to be placed the other way around as if there was air that would push the diaphram and flow the other way into the intake manifold from the turbo inlet pipe, wich is contradictory to the whole concept.

Have I missed something? Please, someone correct me on this one!

Wich way is it actualy supposed to go in a C900?
 

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Is this a brand new valve? I only ask because I'm pretty sure you shouldn't be able to blow through the vacuum port. Never actually tried that but does it hold vacuum when you suck on it?

The valve will work either way round. It is the pressure difference across the diaphragm caused by lifting off the throttle that overcomes the spring pressure and allows it to open. The vacuum port therefore needs to be connected to the inlet anywhere on the engine side of the throttle body. Remember that you don't just have boost pressure on one side, pushing against the spring. During boost, you also have it at the vacuum port, so there is no pressure differential and the net effect is that the spring holds the valve closed. When you let off the throttle during boost, the inlet system between turbo and throttle body is still at "boost pressure" but there is now vacuum after the throttle body. The pressure difference across the diaphragm overcomes the spring pressure and the valve opens and stays open until the pressure difference is less than the pressure exerted by the spring. The spring is just there to hold the valve closed during idle and at part throttle when there is a small pressure difference that would otherwise open the valve.

OK - just popped out for a quick look at my T16S and the port opposite the vacuum port is connected to the intercooler side of the throttle body while the "right-angle" port is connected near the turbo inlet. As I say, it should work either way round but that looks like the best fit in the tight space available.
 

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Discussion Starter · #3 ·
I know what you are saying and it all makes sense.....

untill I see this setup..... have a look at the placement of the dump valve and see that it's setup OPPOSITE from what you are saying..... this pic is telling me that there is boost in the turbo inlet being re-routed into the intake under high boost...... that doesn't make sense...... se what I mean? that's why I am confused...
 

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If there is excessive boost in the intake on this picture, where does it go? It goes in the dump valve and hits the diaphram on the same side as the spring and holds it shut even tighter and no air goes anywhere...... ????????? doesn't make sense![/b]
the purpose of the dumpvalve is to vent, or recirculate pressurized intake piping, between the turbo and the throttle body. the valve is designed to be open only when there is vacuum at the intake manifold, such as when shifting or quickly letting off the throttle.

the small bore vacuum hose will always have to be connected after the throttle body because, in theory, this is the only part of a turbo-charged vehicles intake system that will be subject to vacuum (and in theory, so long as your engine is running, your turbo will be turning and thus, the intake piping and intercooler located betweeen the turbo and the throttle body will be under pressure).

the dumpvalve needs to be located so that one end is connected to the intake piping before the turbo (if you are mounting yours to recirculate air rather than vent it atmospherically). and the other side will be connected to any part of the aforementioned 'pressurized' part of the intake system.

as can be seen in the picture above, the dumpvalve is positioned so that the pressurized air will push against the side of the valve's piston so as to prevent leakage of pressurized air.

'excessive' boost is vented through opening of the wastegate, which is essentially another valve, but located on the exhaust side of the turbo. when this valve is open, pressurized exhaust gasses are allowed to flow pst the compressor turbines, essentially cutting off 'power' to the turbo.

i hope that makes some sense
 

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Originally posted by drioux15:
[qb]If there is excessive boost in the intake on this picture, where does it go? It goes in the dump valve and hits the diaphram on the same side as the spring and holds it shut even tighter and no air goes anywhere...... ????????? doesn't make sense!      [/qb][/b]
The flaw in your reasoning is that both the inlet and outlet ports are on the same side of the diaphragm (which is why it doesn't matter which is connected to inlet and which to outlet). The spring and vacuum port are on the other side.

Forget about the spring for the moment - it does not regulate boost pressure. As xassh says, that function is performed by regulating the "drive" to the turbo by means of the wastegate.

Under boost, the inlet port and vacuum port are both at roughly the same pressure and therefore will both exert the same force on either side of the diaphragm, which means there is no net force on it. In fact, the vacuum port will probably be holding it closed because the pressure on that side has access to a larger area of the diaphragm. Add the spring just to make sure and the valve is definitely closed under boost.

Lift off the throttle and while the turbo keeps spinning through inertia, the air can't get past the throttle plate and very soon the engine creates a vacuum in the plenum chamber. there is now a vacuum on the spring side of the diaphragm and boost pressure on the other side so the net force is pushing against the spring which opens the valve. The valve stays open until vacuum plus spring pressure equals the pressure in the intake.

The spring is only there to ensure that when the valve's state would otherwise be indeterminate, it defaults to being closed.
 

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Discussion Starter · #7 ·
I understand the concept and the purpose of the valve...... just confusion on the way it is hooked up in some cars. The way I had noticed when I looked at the valve is that you can see that the diaphram is closed shut (by the spring) if you look at the port opposite from the vacuum niple.

If I look in the port that is 90-degrees to the other 2 ports, I can see the spring.

This leads me to believe that pressurized air in this port would only assist in keeping the valve shut. If the pressure builds-up because throttle is closed, this will only put more pressure on the same side as the spring and keep it closed even more.

I have a hard time understanding how the (very small) vacuum hose and pressure that would be in that hose could exerpt greater force to counteract the spring AND the pressurized air that is keeping the valve closed.

On top of that, If I put my mouth on the nipple and suck (simulating vacuum) air seeps right through (presumably from the same port that I can see the spring from) and nothing happens.


The only way I can see this making sense is hooking it up like you showed in your picture...... where excess pressure would force the diphram open once the pressure is greater than the force of the spring.

Thanks for all your help in making me understand this though! I'll eventualy see the light
 

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Originally posted by drioux15:
[qb]On top of that, If I put my mouth on the nipple and suck (simulating vacuum) air seeps right through (presumably from the same port that I can see the spring from) and nothing happens.


[/qb][/b]
If you simulate vacuum on the small nipple, you should feel the diaphragm open against the spring pressure. The spring itself is quite strong. Once you've got vacuum, quickly putting your finger over the nipple should hold the spring open; if you release the vacuum the spring snaps shut. Careful, you can nip your finger!


From what you've said above, the BPV (bypass valve) probably has a ruptured diaphragm. Sounds like you'll need a replacement.

BillJ is correct in saying that it will work either way around. In many cases, when people go for an aftermarket BPV (or dump valve), they look to see which side holds the pressure better, and keep this side pointed to the pressurised pipe.


The purpose of the dump valve is literally to 'dump' the turbo pressure in the line if you suddenly lift your throttle during hard acceleration.

If the BPV is not there, the back pressure exerts a shock wave on the turbo (remember you've lifted your foot off the throttle, so it's not spooling any more) and causes the turbo to stall. You can even damage the blades.

When you lift your foot off the throttle, the engine now has vacuum. This vacuum acts on the small nipple of the BPV, opening it and letting this 'excess' boost recirculate to the intake, preventing that shock wave and potential damage to the turbo.

Not all systems can be adapted for a dump valve that vents to the atmosphere.
 

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Discussion Starter · #9 ·
Yep! I know that because of the air mass meeter, using an atmospheric dv will cause a shortage of air in the ECU's calculations and cause higher fuel consumption.


I was also thinking what you wer saying, that I have a ruptured diaphram.... that's probably the case....

I have been thinking from the start that it may be busted
 

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I agree with Vincent. You shouldn't be able to see the spring. Sounds like the valve is bu66ered. I'd have bought a new one anyway, given that they're pretty cheap and too tight a fit for me to want to risk having to do the job twice.

Originally posted by drioux15:
[qb]I have a hard time understanding how the (very small) vacuum hose and pressure that would be in that hose[/qb][/b]
The small diameter of the pipe is a restriction to flow, but not to pressure.
 

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Discussion Starter · #11 ·
Ok, I had a closer look at it yesterday and you guys are right...... I cannot see the spring (i probably thought I could) Also, the fact that air was going through when I sucked on the **nipple** was caused by the lack of a proper seal between my mouth and the port. I tried different methods and held it open while sealing the vac port with my finger and it holds no problem. I can see now why they would want to install the other way on T5 and 7 cars.

It must have been the night where I had a fiew drinks while polishing and removing grease from all the parts that I was inspecting the valve and probably had *blurred* vision..... LOL I'm such an idiot!

Thanks guys!

BTW, I installed the turbo oil cooler on the C900 N/A last night (with the oil filter bracket) and boy does it ever make a difference in maintaining cooler engine temps while sitting in smoldering heat in stop and go trafic!


If anyone is looking for a way to bring down the heat on an N/A car, this is definately the way to do it! (mine won't be N/A much longer)
 
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