Drain Vent Question

[Glennman]

I'm working on the design for my solar panels. I can squeeze one additional 305 watt 39"x65" panel on the roof, but I might have to cut off one of my (2) drain vents and have it terminate under the panels. Can you guys see any disadvantages to that?

[Bus Lurker]

Glen,

When we had 25 solar panels mounted on the roof of our home in Bakersfield, the installer told us according to code, they are no longer allowed to install panels over vents.  They had to space out over the vents.  Sorry, I don't know the reason, but there must be something to it.

Mike

[Dave5Cs]

Could cut off the purpose of the vent if not enough air gets to it and might not let the sewer gases escape enough. The vent is like a pop can turned upside down and someone makes a hole in the bottom while you are drinking. It allows the liquid or in this case the gases or air to vent.

[richard5933]

Our 4108 had a single 1/2" vinyl tube serving as the vent for our combined gray/black tank. Never had an issue. If you are able to maintain adequate air flow through your vent, I don't see a big problem. With the actual function when parked.

But, if you have a vent designed to pull sewer gases out as you drive, you will likely lose any suction on the vent created by going down the road. You might actually create a wind tunnel which would serve to force airflow down the vent pushing sewer gases inside the bus, depending on how the panels are configured over the top of it.

You'll have to consider all possible scenarios on this one.

[epretot]

Perhaps an air admittance valve could replace it.

[chessie4905]

plumb a sewer vent into engine air cleaner with a solenoid to close it when engine off. Use a solar fan powered roof vent, but since sun is blocked from it, wire into house batteries instead.

[luvrbus]

2 vents 1 is for the gray water like the sink or shower to drain,like mentioned if that is the case admittance valves would work on each fixture   

[Jim Blackwood]

For best results (less stink) your waste tank vent system should actively (or better yet passively) encourage continuous air circulation through the tanks. If you can do that, breakdown will be aerobic in nature and stinky gases will not accumulate. Reconciling the actual vent outlets with the solar panels is a matter of form, function, and appearance, with the thought in mind that the more active gases could possibly cause some degradation over time.

I've not built my tanks yet and so have only considered vent system designs, however a few ideas come to mind.

A siphon type vent cap may generate suction on the purge vent line OTR or in wind. I have had very limited success with that concept and would not rely on it entirely at least not with a single vent line. A second fresh air vent line needs to let air into the tank. The more continuous that flow is, the smaller the lines can be.

A bilge fan in the purge vent line, connected to the bathroom light switch would be a very effective venting method and probably turned on often enough to allow aerobic decomposition. It would also generate a negative pressure in the tank at the time of operating the flush valve, a very valid reason for considering it.

A vent line exiting to the suction side of the radiator fan could possibly make a very unobtrusive and effective purge side configuration.

Properly designed, convection can add considerably to constant airflow. This presupposes a low and shaded fresh air inlet and a high purge exit with the vertical sections exposed to heat. How to best do that part is the tricky bit considering seasonal and heat/AC use, but the wheelwell area could be a source for cool supply air, at least when parked.

A manometer can be used for finding high and low pressure areas to terminate vent lines. This can be done both OTR and stationary, and can also be used to evaluate a convection system. The simplest form is a U shaped tube with water in it. Any rise in one leg and lowering in the other indicates a pressure differential. (acceleration must be compensated for such as by turning the device 90 degrees) Even a 1" difference is enough to create airflow.

The simplest system is often the best.

Jim

[Iceni John]

Jim, that's exactly what I've done.

My grey and poo tanks each have two 2" vents.   The poo tank's rear vent goes up to a forward-facing louver just below the roof drip rail that blows air in while driving, both tanks' front vents are inter-connected, and the grey tank's rear vent goes down to just ahead of the differential with a venturi on the end to suck air out while driving.   When driving, air is forced into the poo tank, then travels to the grey tank and is sucked out at ground level.   When parked, the airflow is reversed, with cool air drawn in from below the bus and eventually exiting high through natural convection.   This way both the tanks get a continuous flow of fresh air to allow the aerobic bacteria to do their thing, and any smells are left behind at ground level while driving.   So far, so good.

I did it this way primarily to vent the tanks well, but also because my roof is covered with solar panels and a walkway, making a conventional roof vent pipe ineffective.

John

[Glennman]

The way my venting is set up (haven't used it yet) is I have (2) 1 1/2" vents dropping into either end of the single purpose black/grey 125 gallon tank (1 vent at each end). These both go through the roof on both sides of the bus (1 on each side). Neither is an inlet or outlet, as they are both essentially the same, except being on each end of the tank. If I cut one of them off, it would still have about 3" clear above it but it would be under the solar panels, but only about 4" from the edge of the panels to the vent. It's not like it would be buried deep under them. I was hoping to install one of those units that would suck the gasses out, so I could install one on the wide open vent and the one that's cut off could work as the "inlet" side. Maybe?

[Jim Blackwood]

John, your system sounds like it would be very effective. Have you ever gotten a 'whiff' from it? Just curious if it's as good as it sounds like it ought to be.

Glen, you may have a problem with both vents going to the roof. See the thing is, sewer gasses are heavier than air. So they tend to stack up in the vent pipes and then when you flush they want to flow out through the toilet opening. Also unless one outlet is shaded and the other is in sunlight you have very little chance of getting any convection flow. A bilge blower on one line wired to the bathroom light could fix it though. I'm not sure if one of those venturi attachments would be enough.

Jim

[Glennman]

I've never seen a bilge blower. I'll have to look into that. I suppose I could leave the vents the way they are (including cutting a little height off the one), but add a lower vent with said blower. Makes sense.

[chessie4905]

they make a solar powered fan that mounts to vent pipe on the roof. Amazon.

[epretot]

Reading through this thread caused me to see the importance of having the house mechanical systems active before closing up the walls, floors and ceilings.

I knew early on I would install the ceilings and floors last just in case I needed to change or alter the mechanicals.

[Jim Blackwood]

Yes, as an example of that I have enough room in the shower space to incorporate a broom closet on the plumbing end of the shower. Perfect place to run a roof vent.

Jim