| Author | Message | ||
| Nick Morris (Nick3751)
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I thought of this on the way back from church tonight so I haven't had anytime to smooth it out any so I'll let ya'll to that. If a fella was starting from scratch could you run your gen exhaust under the coach to your wet bay then up inside and some how join a vent pipe comming out of the waste tank and then run your exhaust up inside the vent so you could put one hole in the roof and get your waste vent and gen exhaust out the top. I suppose with the heat of the exhaust pipe would create some lift of the air in the vent pipe and might creat a small amount of suction on the tank and help keep odor out of the coach if the genset was running. I don't think it would be near enough to suck out the P-traps but maybe. Also, what size pipe would you have to have to put an exhaust pipe inside a vent and have enough exhaust and vent? Any and all input on this brain cloud burst is welcome. I'm not sure how plausable this is but it's a thought that may bring up a good idea sometime. | ||
| bruce king
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sewer gases are sometimes both flammable and heavier than air. Methane comes to mind. | ||
| TWODOGS (Twodogs)
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yep...methane....not a good idea... | ||
| Marc Bourget Rating: N/A |
If you do it right, placing the exhaust pipe inside of the vent pipe, with the outlet of the exhaust just below the top of the vent pipe a type of venturi action takes place and the exhaust will act to purge the waste tank. You'll need a separate intake to permit airflow. You "tune" the draft formed by raising and lowering the exhaust relative to the vent outlet. By the time you got the exhaust that far down the line, it would be too cool to ignite any methane. This is a "takeoff" of the blast tube cooling used on T-34 Mentor's, Some Navions and other aircraft. Onward and Upward Marc Bourget | ||
| Greg Roberts (Gregeagle20)
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Do not do this. You would expose yourself to the possibility of CO poisoning. Simply not a good idea to mix systems because engineering controls can quickly loose meaning and disaster might be the end result. | ||
| Marc Bourget Rating: N/A |
I'd like an explanation of your thoughts as how an exposure to CO would occur? I didn't describe the fitting where the exhaust would insert, concentrically, into the vent pipe ,but in my approach it would be sealed. The exhaust is hot, close to the vent outlet and under considerable velocity. The separate intake would provide a one-way flow. The hot air of the exhaust would otherwise rise. If the genset was running there would not be a positive pressure in the waste tank. There are no controls to this system. It's fixed, with no movable parts. If the exhaust developed a hole, the only exposure would be during a flushing operation. I doubt the exposure would be sufficient to cause harm. (Yes, I admit CO poisoning is cumulative, but I believe it would still be low and if a leak developed the odor would give a ready clue!) What am I missing? Onward and Upward Marc Bourget | ||
| Nick Morris (Nick3751)
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Ok guys according to Ask Jeeves and the noa web site the ignigiton temp of Methane is 999F I don't think genset exhaust is that hot at the exhaust valve. Even if it is it sure won't be at the top of the stack which would be a minimum (in my case) of 10 ft. or so. Even though the pipe would warm up inside the ventI don't think it's going to reach 1000F. Not to mention the 8-10ft it's going to travel under the bus before makeing the turn to join the vent pipe (again in my case). Now I don't want anyone saying I don't want they're opionion cause I want them all so keep 'em comming. I will think about and research your thoughts as I hope you will mine when I read them and post my responces. As for the CO problem it could easily be solved but just running the exhaust out the top of the vent and putting a flapper on it. I think if it was 3 inches out or so that would stop the problem as well as give the exhaust pipe a place to attach at the top by putting a cap on the vent and having a large hole for the pipe in the center and either several small ones for the vent or slots in the pvc vent pipe itself just under the cap or both. Thanks for the feed back. | ||
| BrianMCI Rating: N/A |
Gen. exhaust in the black tank vent... Nice mental exersize. I'm not sure of its practicality though. Sounds like a lot of engineering to get it right. It could be done. Might even be safe to do it. I doubt anyone will do it though. Brian | ||
| Greg Roberts (Gregeagle20)
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A cracked exhaust pipe (yes it does happen) and a dry sink vent is all that it would take to introduce CO into the coach space. Also, heat and PVC don't mix well so the waste vent would need to be made of something other than PVC most likely. An engineering control would be to design a system that has at least two layers of pre-designed safety features. In the case of the exhaust pipe running through a people space, you would run a pipe with-in a pipe and then you would have to have two pipes break to allow exposure. Running the exhaust inside a vent does not accomplish this because of the other possible openings into the people space such as sink drains and toilet seals. The key is to control these exposures up front by engineering design. These type of things are fun to think about but in this case I would not do it. | ||
| Ed
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What comes to mind for myself is the lenght of the exhaust. If you are using a diesel gen set, as I am myself, I would be concerned about the carbon buildup at the engine. In the case of diesel the shorter most direct the better. | ||
| Gary Stadler (Boogiethecat)
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Marc, usually I like your advice and opinions on things but not this time. Consider this... when an engine is running and opens it's exhaust valve, flaming hot gasses come out and right at that point things can be ignited. So, let's say you're pooh tank has sat there bubbling away making methane which over a day or a week has found it's way thru the vent system and into the genset's pipes. Let's also say that due to some lucky circumstances the amount of air left in the pipes was just enough to cause an explosive mixture. Then you start the genset. Boom. Granted it's a longshot but I bet I could make it happen if I was hired to test the theory. And as Greg pointed out, all it would take would be a broken or leaky sewer pipe or a dry trap somewhere inside your bus and you'd be a dead, dead duck. ABSOLUTELY do not mix these two systems... it might me a neat mental win but it's a stupidly unsafe system and it's soooo simple to do it another way that it's just not worth the risk. And if that wasnt' enuff... My genset exhaust pipe runs up from the floor thru the living quarters and out on the roof. BUT I welded a 3" one-piece galvanized steel tube into the roof, sealed it into the floor, and ran the 1.5" exhaust tube thru the center of it. This gives a double walled safety net and also convection currents running up thru the big pipe keep it cool. Even at that, the big pipe gets hot enough that it's uncomfortable to touch. The inside pipe at that point is DEFINITELY too hot for an ABS sewer pipe, and this is ten feet away from the generator! This's about as close as I'd ever come to running any exhaust pipe component inside a living quarters. | ||
| Cliff (Floridacracker)
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You are also depending on the fact that the water in the traps of the sinks and shower has not evaporated and allowing CO into the coach. An interesting Idea , but I would run it seperate. Cliff | ||
| Marc Bourget Rating: N/A |
Gary, Your outer tube is open at the bottom. Try the extractor method I detailed above. John Thorp constructed an extractor cooling system for a Porche 911 that allowed him to remove the engine driven fan. It passed the 30 min idle test at 80 deg. Should be enough airflow to keep your "through" tube cool to the touch. I acknowledge your view point but if it were that much a danger we'd see sewer gas related explosions alot more frequently in the news. I don't think a properly maintained tank will get close to an explosive mixture, but I have nothing but opinion to base this on (at this point) and it's simply smarter to err on the side of caution and follow your suggestion. {giggle,giggle} Of course, your digestion may vary from mine! LOL!!! {I'm sure many have formed the opinion that I feel my ca-ca don't stink! {wish it were true!} Onward and Upward Marc Bourget | ||
| Mike (Busone)
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We should send this to the Discovery channel show "Myth Busters" and see if they could make a black tank blow up from a generator exhaust. It would be amusing to see it go. | ||
| Henry R. Bergman, Jr. (Henryofcj)
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Please do not do this. Hate to lose you due to an explosion running from the exhaust pipe of the gen set, then thru the empty portion of the black tank, then running up and eventually out the roof stack. Sewer gas is not to be messed with. Methane is very explosive. Actually used as fuel. What WILL eventually happen is that the black tank will rest for days/weeks in a nearly empty condition collecting explosive gasses that will run from the roof stack all the way back to the gen set exhaust manifold. As already said, such gases are heavier than air. Time will allow this. Then...when you start up your gen set, the exhaust gases just outside the exhaust pipe ARE QUITE hot enough to ignite the sewer gas. If not the exhaust itself, then the occasional spark of burning carbon will certainly do it. And...all it takes is for it to do it once. The result? BOOM!!!! Enough to gut out the black tank, along with enough overpressure to maybe rupture of bin of the bus, plus maybe enough left to enter the cabin of the coach. The possible resulting fire may finish off everything else. The overpressure can render individuals somewhat dazzed, then you burn alive. Yeck! Sorry to dump on your idea. Don't want to. I'm retired fire service from what once was an I.S.O. class One fire department with mulitiple fire service related college degrees. Please do not try this. Shit will happen, and always when you least expect it. Thank you. | ||
| TWODOGS (Twodogs)
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just picture....you sitting on the throne ...& BOOOM | ||
| H3 (Ace)
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Sort of like being a star in Lethal Weapon! Ace | ||
| Marc Bourget Rating: N/A |
Can't hide in a bathtub with a couple of Flack Jackets like Danny and Mel in a Bus Conversion! Lends a new mental image to "Onward and Upward" Whoopee! | ||
| Cable (Fe2_o3)
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Why not use the energy from the gen. exhaust to turn a fan to vent the tank. Safer and you can boast of a turbo charged toilet.... | ||
| Gary McFarland (Gearheadgary)
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Is there an old boot that kicks a ball somewhere in this proposed design? Gary | ||
| Tim Hoskinson (Tdh37514151)
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Gee Nick you shure stirred them up this time | ||
| Nick Morris (Nick3751)
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I did didn't I. I don't think it's something to do blind folded but I think it's worth a little more looking into, like some testing, heck maybe we need to get the mythbuster on it like someone said up the tread. | ||
| Mike (Busone)
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Actually Methane is lighter than air. Air has a molecular mass of 28.8 and methane has a molecular mass of 16. I still would not want methane to build up in the genset exhaust. It would be possible but not probable for an explosion to occur. You would have to get the right fuel to air mixture as well as reach the ignition temp. | ||
| Ron Rutledge
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Please do not do this!..take the short cut, pipe it into your engin ext. system,it will be much nice and so quite... | ||
| Marc Bourget Rating: N/A |
Pipe it into your ext. system, Exhaust or Intake? | ||
| bruce king
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Article on through-the-roof generator exhaust. http://www.rvtechstop.com/articles/rofexhok.pdf | ||
| Marc Bourget Rating: N/A |
Gary, Rethinking your comment about "flaming hot gasses" I don't think this is correct with a 4 stroke diesel or a properly injected 2 stroke. Truth is, the conditions for combustion within the chamber are such that the flame front dies when the pressure drops with the decending piston. Yes, it's hot, yes things are combusting but I'd wonder whether someone smoking while on the toilet is risking more than cancer. This doesn't attack your premise, just relates the information I've obtained on the combustion cycle of 4 stroke internal combustion engines. Onward and Upward. | ||
| Carroll Sasscer
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Given that our 150 head hog farm didn't produce enuff crap and in turn enuff methane gas to make it worthwhile to capture and use for heating of the buildings, I question what you would have to eat to make a black water tank explosive. Either that or maybe you guys need to dump your tanks a little more often. | ||
| Henry R. Bergman, Jr. (Henryofcj)
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Yeah, to make this apparent to all, what we need is further testing. Now calling for volunteers to experiment to failure the notion that certain conditions are unobtainable at all times. Easy work actually. Mostly a sit down job with nothing else really to do. A sense of adventure or risk is desirable or required plus the necessary high value life insurance policy. Ah shit!!  | ||
| Gary Stadler (Boogiethecat)
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Marc, just take the exhaust manifold off of virtually any internal combustion engine, and fire it up in the dark. Hit the throttle. Flames WILL come out. Maybe if everything was totally ideal, it was running under a constant load with perfect mixture, etc. but that's not real world. Every engine I've ever seen from lawnmowers to motorcycles, cars and my bus spit fire if you've got the manifold off and you're looking at the backside of the exhaust valve. try it And if nothing else, look at the EGT while pulling a hill. That alone is enough to light things, and it's measured many inches away from the valve... | ||
| Lin Rating: N/A |
I just don't see the point. Venting a holding tank through the roof is easy and fool proof. Done right they do not leak and will not with mere minimal preventive maintenance. Why engineer and put extra work into solving a problem that does not exist? | ||
| Gary McFarland (Gearheadgary)
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Lin, I know you're relatively new here so i'll 'splain somthing. there are actually two words in busnuts. the first one is "bus" Gary | ||
| Niles Rating: N/A |
Gary - ROTFLMMFAO - niles | ||
| Nick Morris (Nick3751)
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Lin, It's not the holding tank vent thats the issue; it's the genset exhaust. Since most places want you to run it out the roof this is a way to do that with only one hole in the roof; i.e. less holes in the roof less CHANCE of a leak. From what I read in the article posted by Bruce it was been done resonably safely. Now everyone tell me what you think of my numbers here: If I use around 1 1/4 inch exhaust pipe that will keep the temp up enough to reduce carbon in the pipe. Then a 2 inch vent pipe over that but leaving the exhaust pipe unsealed at the bottom(I'll get to why in a sec). Then run a 3 1/2 or 4 inch piece of either stove pipe or PVC over that that would be open from the top to the bottom and be sealed to both the top and bottom so hopefully if anything should leak out of the exhaust pipe and the vent pipe it will stay in the outer pipe. I could then fit a small fan in the bottom to run only when the genset is running to help keep the pipes cool reduce the risk of CO in the bus. In addition I'm already planning on putting a CO detector so I'd put near the stack so as too catch anything that may leak out of the stack and possibly another in another area to cover the P-traps. I may also put extra deep traps in to help prevent them from drying up. I think that pretty well covers all the safty concerns correct? Just in case some of you are wondering why I'd go through all this I'm trying to keep the line on my rig as clean as possible. The only thing I'm planning on having on the roof is a sat dome, solar pannels(down the center out of sight) and a few low profile vents and the waste vent. All of which I'm going to keep as close to the roof line as possible. | ||
| Greg Roberts (Gregeagle20)
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I can't help but think of Rube Goldberg when reading this thread. I would not take any risks to simply have a clean roof line. Maybe you should put the waste vent up into the underside of the sat dome assembly and vent the exhaust through an outside extension. I would hate to see anyone get hurt when one of the many weak links of a Goldberg scheme fails. | ||
| Gary McFarland (Gearheadgary)
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Greg--read about 15 posts up. Gary | ||
| Greg Roberts (Gregeagle20)
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Ahhh, the boot and the ball. Yep! That is it |