Cutting a hole in the tunnel?

[mlh1936]

I need to run my vent pipe from one side of the bay to the other. There is not room to fit between the top of the tank and the tunnel. Is it feasible to cut a 2 inch hole near the bottom of the side walls of the tunnel? Then I could run the vent pipe through the tunnel. At present I have the vent pipe crossing the bay below the top of the tank. This is no good because when I accidentally let the tank fill completely the liquid runs into the crossover vent pipe stopping it up. Another piece to the puzzle is that I can't get to the bottom cover of the tunnel to see what is in there near the bottom. I am hoping that I could use a metal cutting hole saw and not harm anything inside. Thanks.

[Singing Land Cruiser]

Looks like we have the same bus. Let me know where you want to make the hole and I will have a look see on mine. I would never cut blind on the tunnel. M&C

[Brian Diehl]

NO!  Do not cut a hole in the bottom of the tunnel.  All your air lines, power steering lines, freon, and wires run in the lower half of the tunnel.  However, the upper half of the tunnel is an option.  I did exactly what you are wanting to do with my setup.  The top half of  the tunnel is the return air duct for the HVAC system for return air from the back of the bus.  The upper half of the tunnel is actually double walled.  There is a couple of inches of insulation between the outer layer of sheet metal and the inner layer of sheet metal.  A good hole saw and VERY CAREFUL measurements will  allow you to cut a hole in each side of the tunnel tightly enough to just fit your pvc pipe through.  You want to make the whole very tight since you will get  air leakage out of the tunnel and into the tunnel from the bay once you drill those holes.

I have a couple of pictures that show where I put the pipes at the bottom of this page:
http://home.earthlink.net/~diehls0792/BusSection6.html

Let me know if you have any questions or want more pictures.  I'm sure I could track some down on my hard drive to show you closer to what you want to see.

[artvonne]

  Even without knowing the Bus, its doubtful you could run anything that large through it. If you could, you'ld think they would have made the tunnel 2 inches thinner. But ya never know.

 Have you considered a flatened pipe that could pass through with clearance yet offer the same cross section area?

[mlh1936]

Thanks folks, I would like to cut the holes in the tunnel in the rear bay about 3 feet aft of the forward bulkhead. I no longer need the air ducts in it since I use roof air. It sounds like the walls nearest the top would be ok. Any further advice would be appreciated.
Thanks.
MaL

[Sean]

Have you considered a flatened pipe that could pass through with clearance yet offer the same cross section area?

Vent plumbing must consist of approved and listed DWV fittings and pipe.  I've never seen one that was anything but round.

Also, when talking about crossing a bay with a "horizontal" vent line, you still need to slope the vent just as if it was a drain.  The RV code is a bit more lenient here than residential code; you need 1/8" per foot.  So a pipe that crosses an entire bay (8') must be a full inch higher on the stack side than on the tank side.

I'm not familiar with the tunnel on an MCI, but I am guessing it's about 18" wide.  That means the hole you cut on the downhill side must be 3/16" lower that the one on the uphill side.  Remember to factor this in to your calculations when assessing the feasibility of running the pipe through the tunnel above anything else already in there.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[Paul]

We installed three 1 1/2  PVC pipes front to rear and five over them side to side over water bay.  Some pic at www.incredibus.com
Hop this helps.
Paul

[Rick 74 MC-8]

I know it prob in not up to code but why can't you use the tank itself as a vent and just vent one side. As long as the tank is not full there is plenty of air space at the top of the tank for the gasses to flow. Just a suggestion not trying to lead anyone in the wrong direction. My feelings are if you know the code and can accomplish  its desired effects no harm no foul. let the flames begin Sorry

                                                                                         Rick 74 MC-8

[Sean]

.. why can't you use the tank itself as a vent ...

I don't follow you.  All tanks need to be vented to atmosphere.  If there is no vent at all in the tank, several bad things can happen, including traps sucked dry when the tank is emptied; the tank itself collapsing completely when it is emptied; sewer gas pushing back past traps either when liquid is dropped to the tank at another fixture, or bacterial action in the tank creating gas; etc. etc.

Besides which, "probably not up to code" ought to be reason enough not to do something -- every provision of the code has at least one and usually many good reasons behind it.

... and just vent one side. As long as the tank is not full there is plenty of air space at the top of the tank for the gasses to flow....

Just to be clear, the tank only requires a single vent.  It must exit at the highest point in the tank.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[Rick 74 MC-8]

Sean

        That is what I was trying to say. If the tank if vented to the roof with a proper size pipe. Could the drains on the other side of the bus not be vented to the top of the tank. The gasses would flow Thur the open space on top the tank and vent Thur the vent stack.  If I understand his problem he wants to connect the vent on one side on the bus to the vent stack on the other side. The


                                                                                 Rick 74 MC-8

[Tony LEE]

I've cut several holes in the side wall of the return air tunnel - one 3" diameter. I assume that like the rest of the bus, the tunnel does supply some part of the structural strength so I keep them as small as possible and space them apart as well

[Sean]

... Could the drains on the other side of the bus not be vented to the top of the tank. ...

Again, the tank itself only needs a single vent.

That said, all fixture drains must also be vented.  So the main waste pipe from any set of fixture drains will also thus be vented and will provide additional venting for the tank.  In fact, it is common for the entire gray waste drain system in an RV to be the "wet vented" type wherein there is only a single waste/vent pipe going to the tank.

...  If I understand his problem he wants to connect the vent on one side on the bus to the vent stack on the other side ...

I understood the question only to be that the existing vent (and/or waste) is on one side of the bus, and the opening in the tank is on the other.  That could be because the tank does not extend all the way across the bay, or simply that's where the threaded fittings have already been located.

There is no reason why an opening could not be installed in the tank closer to the existing or planned vent/waste location if that's easier than running the pipe across the bay.

There are lots of reasons why wastes or vents may need to be run horizontally in a bay.  On my coach, for example, the waste tanks are below the living room, and there is a long run of glass on both sides directly above the tank locations.  The vents (and wastes) are a good five to six feet aft of the tanks, across the fuel bay.  My waste and vent pipes have to run "horizontally" (with proper slope) across the top of the fuel tank, then halfway across the waste tank bay before turning downwards into the tanks.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[artvonne]

  While im sure the RV Code people mean well, I cant see anything that critical in running the vent line horizontal (with clean out caps on either end). When your driving down the highway there is always a crown, so the Bus is always leaning. Slope the pipe the wrong way and it will will have one heck of a slope in the wrong direction. Even if you were parked long term, I just cant see that being an issue. Its not a house that your going to be sitting stationary in and living in indefinetly, which many RV Campers, 5th wheels and the like become. Its a motorhome, made for bouncing and swinging and rolling down the highway. Once in a while anyway.

  Flat or oval pipe can be found, or you could make it if need be. But in afterthought it wont work. The low hanging loop would fill with condensation and you would be plugged.

  You could run a vent off the other end of the tank to serve the other side of the Bus. They dont all have to be interconnected. You just have to vent the tank and the sources. Its not critical to fumes as long as everything has traps, but it is critical to getting water to flow. And in reality, if your just running a sink into the tank, as long as the tanks vented on the other side, and the sink has a trap, it shouldnt pose a problem. I certainly wouldnt hack a hole through the tunnel unless it was a real issue. A real issue would be a sink that gurgled and spit and was slow to drain. You could also run a stand pipe up and vent it out the roof on that side as well.

[JackConrad]

Mal,
  If you look at the side of the tunnel, you will see a seam about 2-3" up from the bottom. Below this seam is all your air lines, water lines, electric wires, shift linkage etc. Above the seam is the air return. Unless you, or Fred, added something in this space, it should be empty.  I would stay at least 1" above the seam to avoid drilling through the thicker metal near the bottom of the air return wall.  Are ya'll going to Palmetto Cove?  Hope to see ya'll there.  Jack

[mlh1936]

Thanks folks, I think I have an idea of what to do now.
Mal