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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old June 3rd, 2002, 18:35   #1
Boundless
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Join Date: Jan 2001
Default Air Box & Spring Loaded Door Function

There has been some discussion on the function of the spring loaded door in the VW airfilter box.

First, there is no way the panel filter will affect the function of the door. Paper, foam or cotton ainít gonna make a difference. No matter how free flowing or clogged, the panel filter will not affect the function of the spring loaded door. The function of the door depends on the pressure across the door which is the same as the pressure in front of the filter panel, therefore the filter has nothing to do with it. The pressure in front of the filter panel is primarily controlled by the impedance of the main inlet path/snorkel. The spring loaded door has a bleed through flow path with a foam washer filter. This is a small flow path, usually to prevent the door from chattering upon opening.

I did a test. I took a piece of yarn and put it in the secondary air horn. If the door opens, the yarn will be brought into the main air box. Well, I put the yarn in the air horn and then went out for a drive and tested the RPM limit function that is built into the control system. Yep, it limits the engine to 5100 RPM. Still plenty of pedal travel after the engine hits the limiting RPM in 3rd gear. Came back, opened the air box and no yarn. The yarn was still in the air horn. Stock air system all the way. Screen in place. My CAI disabled, stock primary inlet snorkel. So the door didnít open. The impedance of the stock system did not cause the door to open. Even with the stock diffuser snorkel.

What could possibly cause the door to open? A large pressure drop. What could cause that large pressure drop? A large impedance in the primary inlet path. What could cause a large impedance in the primary inlet path? The clogging of the screen or water ingestion.

It may well be both, but Iím leaning towards protection against water ingestion is the primary reason.

Okay, letís say the spring loaded door doesnít exist. There is only the main inlet. As the screen gets clogged, the compressor pressure head gets larger and larger as the screen loads up. Not good. This can lead to surge due to higher compressor head pressure. Now letís say the spring loaded door is thereÖ it can like act an air make up path intended to protect the turbo from surge. But you have to realize a clogged screen will only affect the upper RPM regime where the high air flows are. Not low RPMs and commensurate low air flows. A clogged screen will be more noticeable at high RPM. And realize, we are talking about the detection of the onset of this restricted screen and it occurs slowly, very slowly making it less observable. An air induction system is designed for max flow conditions. But big deal, a loaded filter panel will produce the same effect and there is no elaborate contingency measure in place for that scenario. So why bother with the spring loaded door to protect against a constricted screen?

The other functional option of the spring loaded door is protection from water ingestion. Letís say the spring loaded door isnít there. Also, note the flow path of the primary snorkel is a diffuser. If the snorkel inlet is in the vicinity of high water, the water will readily be inhaled. The engine might hiccup, but itís over. Now if the spring loaded door was there, something else will happen. The viscosity of water is much greater than air. Therefore, as water is pulled into the small diameter inlet of the snorkel diffuser and increases the pressure drop, that pressure drop will open the spring loaded door to Ďclampí the pressure drop and dramatically reduce the possibility of water being ingested past the filter panel. This is not a long term steady state solution. It appears to be intended for the spurious water ingestion event, limited by the water capacity of the air box volume below the filter panel.

If the rubber thingy in front of the primary inlet nozzle does as presented at TDIClub over a year ago where I first learned of it, even better. I havenít the interest to confirm if the rubber thingy in front of the inlet nozzle does as was posted, but it is a plausible explanation for all the effort that went into putting that spring loaded door in there. Even if it doesnít, the diffuser shape does, particularly the small area inlet opening.

A paper filter will obviously present a far greater barrier to water than foam or cotton. The paper fibers will allow far superior capillary forces to trap and impede water flow through the media. The foam Ďporesí are huge compared to paper and capillary forces will be virtually non-existent. The cotton media also has huge Ďporesí as compared to paper.
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Old June 3rd, 2002, 18:54   #2
valois
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Join Date: Jan 2000
Default Re: Air Box & Spring Loaded Door Function

Tell it to the TDI Rally boys Boundy.
http://forums.tdiclub.com/NonCGI/ult...;f=38;t=000062
First we had to set you straight about water in the exhaust, now it's cncerning water in the intake, what is it with you and water Boundless? Given the link above and this statement by you, you really look foolish.
Quote:
Originally posted by Boundless:
PaulB, saabguru,

The stock airbox with the inlet snorkle and flapper door leading to an alternate higher inlet snorkle are for protection against inhaling water if the vehicle is operated in deep water.

The stock snorkel (at least mine anyways) has yet another flapper (molded rubber) in front of the inlet opening of the snorkle. When submerged in water, the higher viscosity of the water and the flow of the water will shut this rubber flapper across the inlet of the primary inlet snorkle causing the spring loaded air flapper door to open, allowing the engine to breathe air from the secondary snorkle that is higher and than the normal inlet snorkle.

It is actually quite appropriate that these things are called "snorkels".

.
<font size="2" face="Verdana, Helvetica, sans-serif">Boundless, a properly oiled foam filter is impervious to water, it sheds it off like a duck's back. It is waterproof. Ask PeterV, on the way to last years fest we went through a torential rainstorm, I had my Viper inlet at the lower grill, I do not recommend this location, but that is where I chose to locate it. We stopped and I removed the Viper and POURED about a quart of water out of it. THe outlet side of the Viper was dry, Peter felt it. With the new oil I have for the Pipercross filters, I did a test, held the filter under the tap at full flow, and watched the water roll off the sides, never went through boundy old buddy, you and your paper filters are all washed up. [img]images/icons/smile.gif[/img]
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Old June 3rd, 2002, 19:05   #3
valois
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Join Date: Jan 2000
Default Re: Air Box & Spring Loaded Door Function

water in exhaust ees normal , we no lika water in intake , submarina quit working when water in intake , we use toilet flapper to seal em up intake when we go underwater, we then run exhaust to toilets so we have water for long trip, no good to drink, but flush toilet allright. [img]images/icons/smile.gif[/img] Captain Nemo is human so he's 2/3 water, so this means he is only 1/3 full of sheet. Maybe only 20 full of sheet and then 10 percent captain morgan, cause he drink allot too much. [img]images/icons/smile.gif[/img]
Onward to learning Boundless! Onward to learning!
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Old June 3rd, 2002, 19:06   #4
msauve
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Join Date: Nov 1999
Location: Hamburg, MI
Default Re: Air Box & Spring Loaded Door Function

Yeah, right.

There's maybe 2 feet of head between the airbox and the lowest point of the intake snorkel. For water, that's less than 1 psi of suction required to suck water at the bottom of the snorkel up into the airbox. (atmospheric pressure is about 33 feet of water)

I'll wager that it takes more than 1 psi to open the flapper door.
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Old June 3rd, 2002, 19:17   #5
valois
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Default Re: Air Box & Spring Loaded Door Function

Quote:
Originally posted by Boundless:


If the rubber thingy in front of the primary inlet nozzle does as presented at TDIClub over a year ago where I first learned of it, even better. I havenít the interest to confirm if the rubber thingy in front of the inlet nozzle does as was posted, but it is a plausible explanation for all the effort that went into putting that spring loaded door in there.
<font size="2" face="Verdana, Helvetica, sans-serif">But only if the domahingy is in place and the widgit has a firm grasp of the fulcrum on the thingamabob. [img]images/icons/grin.gif[/img] I cannot believe you had this knowledge for a full year and chose not to disclose this important finding. It well may affect hundreds if not thousands of thingamajigs! [img]images/icons/shocked.gif[/img]
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Old June 3rd, 2002, 19:24   #6
valois
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Default Re: Air Box & Spring Loaded Door Function

Boundless you are on to something big here, for the sake of science you need to prove your theory, spray water directly into the main snorkel while you have someone run the car in neutral at 5000 RPMS, and monitor the secondary snorkel to determine when it opens. Please let us know the results of your test. [img]images/icons/grin.gif[/img]
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Old June 3rd, 2002, 19:25   #7
Drivbiwire
Zehntes Jahr der Veteran
 
Join Date: Oct 1998
Location: Boise, Idaho
Default Re: Air Box & Spring Loaded Door Function

Rene are you trying to say that water will not pass THROUGH a foam filter? Are you also telling us that having a foam filter will make it impossible for water to pass through even if the intake is submerged under water? Please do tell...

Honest question I just want to hear you explain how this is possible.

DB
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Old June 3rd, 2002, 19:35   #8
valois
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Join Date: Jan 2000
Default Re: Air Box & Spring Loaded Door Function

Pete, you decided to join the little discussion cause your little buddy boundy is taking all the credit for this tremendous idea, well pete, lets spread the credit around where it's due. Here are some of your quotes.:
[QUOTE] Originally posted by Drivbiwire
posted December 11,
2001 15:03

Remove the snorkel and
forget about the compression check. If you
submerged the front end of the car in a lake and
the engine
was snuffed out on
water that's one thing. The bottom line is the
paper filter did it's job and absorbe the water
before it got drawn
into the intake system.
[QUOTE]

[QUOTE]Originally posted by Drivbiwire:

I have yet to see
a stock box have a single drop of water. If you
use the stock air box this will never
happen to begin
with. That is why VW designed the snow screen into
the intake along with an
"updraft" style
filter. The snow screen is there to decrease or
stop larger particles and in the vent
the screen plugs
there is a bypaass door that is sucked open by the
intake system. When the air
enters the stock
air box causing all relatively "heavy" particles
and water to drop to the bottom and
drain via the
water drain port. This wet air filter only applies
if you "modify" the stock box.
[QUOTE]

Here is another Pete quote:
[QUOTE]Originally posted by Drivbiwire:
The only time
water will get to the filter is if you remove the
factory screen. The screen in the intake is there
to stop
the large water
droplets and get them to drop out of the airstream
going into the box. As long as that screen is
intact water will
not make it to the filter. If this plugs up there
is a diverter valve that will open and reroute the
air
around the screen.

Leave the factory
intake alone as it was designed and you will have
the least amount of issues with your car.

DB
[QUOTE]
Now review this thread:
http://forums.tdiclub.com/NonCGI/ult...;f=38;t=000062
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Old June 3rd, 2002, 19:35   #9
SkyPup
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Default Re: Air Box & Spring Loaded Door Function

I keep a pair of SCUBA tanks stored in the trunk for deep river crossings in our two TDI swamp buggies.

I hook the regulator up to the ECU so that no matter what depth we get to, everything is kosher.

And since I tossed that crappy flappy airbox thingamajiggy the first day I ever saw it, we've never had any problems whatsoever.

Works great for both our TDIs! [img]images/icons/grin.gif[/img]

 
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