Differential pressure?

arctictraveller · 10-23-2020, 02:19 PM

Probably not what you think after reading the title. I'm wondering if anyone has ever done some differential pressure testing between the interior of the van and the exterior while driving. I've often noticed that there is a lot of dust ingress at the rear doors, the battery compartment vent and any penetration through the body. Clearly, there is a low pressure area around the rear doors while driving, and some how that translates to a lower pressure in the back of the van that draws in the dust somewhere. I've improved the door seals as much as I can, but I keep finding new spots dust gets in. What I don't understand is how the interior pressure ends up being lower than the exterior pressure when there is a partial vacuum at the back. If I had a DP gauge, I'd do some testing but I wondered if anyone has already done this? I'm aware that running the AC or heater drawing fresh air in should somewhat pressurize the interior, but unless your first in line, you just sucking in more dust. Clearly I just need to seal things better, but if something like just cracking a window eliminates the vacuum, I'd like to know and some testing might reveal some insight. Anyone?

ShuttlePilot · 10-23-2020, 03:42 PM

I will share what I know. In my van if I open my driver or passenger door windows or either side sliding window, hot air will rush in from the tranfercase shifter boot on the floor even at slower speeds. Enough that in hot weather it will make the shifter shafts hot to the touch and heat up the cab. Windows up and A/C on recirculate (Max) only a small amount of heat comes from the shifter boot gap. And, as one would assume if A/C is on outside air (normal) there is no heat and the metal shafts will be cool. It's pretty dramatic. So, it seems that windows up and A/C off I would agree there is a slight neg pressure in my cabin. This is what I would expect on my van as the floor of the van has a lot of wire and pipe penetrations. One example is where the city water connection is. SMB cut a 4x4" hole in the under, inner, body panel which now has no air tight barrier from under the van, through the wall to the interior wall board. One of many reasons I won't do deep water crossings in the van.

- Eric

cthayn · 10-23-2020, 04:22 PM

I have used my MaxxAir fan to pressurize the interior while on dirt roads. I did a test where I drove a 100 miles of dirt road with the fan on, and then 100 miles with the fan off. Pressurizing the fan definitely reduced the dust seepage around the rear door, which was my trouble spot. The only issue is we have an insulated cover for the fan to reduce noise while driving. That has to be removed pressurize the van.

I also use the fan in reverse to reduce the pressure in the van when lowering the pop top. This sucks the canvas sides in so I never have to walk around the van tucking the sides in as the top goes down. This makes lowering the CCV top a piece of cake.

ctb · 10-23-2020, 10:50 PM

Arctic, great post! All the places you spoke of... yes. Had SMBNorth recaulk all the drain tubes etc. last time we were there, put the plastic tubing in rubber door seals (I think that might even have been you that I learned of that trick), put/stuffed steel wool in the battery vent holes when I changed my house batteries (since they are non-vent, you know), and put the fan on high when driving down the dusty dirt/gravel...and last of all, we have drywall masks we pull out when we start 'smelling' the gravel dust...

I think I found a open spot when I was looking at my onboard compressor (for my rear bags) and saw the light of day where the hood hinge is located/hinged by firewall...It is quite puzzling all the ways it creeps in...I did notice on our last camp, I had the AC cranked (Danhard) PH top up/all zipped up, and the PHtop windows were bulging out...so weird...

again, great post...one of those when you think there has been something posted about every subject, you get one of those "oh yeah, me too" posts that make coming back t the Forum a daily must (kinda) lol

BrianW · 10-24-2020, 06:41 AM

What is the “plastic tubing in door seals” mod? Don’t recall reading about that in the past.

Twoxentrix · 10-24-2020, 06:56 AM

Quote:

Originally Posted by BrianW

What is the “plastic tubing in door seals” mod? Don’t recall reading about that in the past.

Doors seals around the doors begin to loose their playability and end out not making secure contact, so instead of replacing all the seals some have inserted tubing into the round cavity - fluffs the seal back up so it makes better contact.

BrianW · 10-24-2020, 10:52 AM

Quote:

Originally Posted by Twoxentrix

Doors seals around the doors begin to loose their playability and end out not making secure contact, so instead of replacing all the seals some have inverted tubing into the round cavity - fluffs the seal back up so it makes better contact.

Ah, that rings a bell now. Thanks. I was thinking a tube to drain the door cavity or something.