Experiment: What's the Purpose of Holding Tank Vent? - Fiberglass RV


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Old 05-16-2015, 08:04 AM   #1
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Name: Huck
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Experiment: What's the Purpose of Holding Tank Vent?

The reason I am asking is, I am trying an experiment with shade cloth.

I bought one that is knitted 70% and 12' x 20'. For my experiment, I'm just going to drape it over the trailer. It will cover all the top and part of the sides and part of windows. It will also cover my roof mounted solar panel, so I will use my portable panel during experiment.

Is the holding tank vent for smell and gas? With the shade cloth draped over it, should it still vent OK since the shade cloth allows air flow? With all the things sticking up on the roof (fan, vents, solar panel), there will be about 3" deep air space on much of the top of the trailer.

I am doing a test this week and if it looks like the shade cloth lowers the inside temperature, I will be trying it at the beach next week. When I'm at the beach, I won't have access to a ladder, so I have to be able to install the shade cloth from the ground. My plan is just to throw a light rope over the trailer and fasten to the shade cloth. I think I can just pull it over without too much trouble. I bought a 20' bungee cord with adjustable fasteners to connect under the trailer to hold the shade cloth down. If this works, I will buy a couple more of them so I can have 2 running across the width and 1 across the length of the trailer.

Longer term, if this lowers the temperature inside the trailer enough to make it worthwhile, I will try to figure out a way to do cutouts for the holding tank vent and the solar panel.

If looel covering the holding tank vent is going to prevent smells and gasses from escaping and causes them to backup into the trailer, then I need to figure out a better plan.
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Old 05-16-2015, 09:53 AM   #2
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Hmmmm... You didn't mention the color of your "Shade Cloth" but if it is a dark color one would think that laying it on the surface of the trailer would actually increase surface temp as it absorbs rather than reflects heat.

If it is lighter than your current trailer color it might reflect more light, but to get real "Shade" effect I think that you need to raise it above the surface to prevent sun from hitting the surface of the trailer and also allowing air circulation between the two surfaces to dissipate the additional absorbed heat.

Against the surface it may appear to be little more than a thin blanket with only minimal insulating value. But it will help a bit over the windows, if only to cut down transmitted energy


And Yes, the purpose of the vent stack is to vent gas/smell/pressure from the tank so that it doesn't come back into the trailer/.


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The laws of thermal dynamics can be a harsh Mistress.... lol
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Old 05-16-2015, 09:55 AM   #3
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Originally Posted by Bob Miller View Post
Hmmmm... You didn't mention the color of your "Shade Cloth" but if it is a dark color one would think that laying it on the surface of the trailer would actually increase surface temp as it absorbs rather than reflects heat.

If it is lighter than your current trailer color it might reflect more light, but to get real "Shade" effect I think that you need to raise it above the surface to prevent sun from hitting the surface of the trailer and also allowing air circulation between the two surfaces to dissipate the additional absorbed heat.

Against the surface it may appear to be little more than a thin blanket with only minimal insulating value. But it will help a bit over the windows, if only to cut down transmitted energy


Don't Shoot the Messenger
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The laws of thermal dynamics can be a harsh Mistress.... lol
It's black. I contacted the manufacturer and they thought it would work just laying on the top of the trailer.

Quote:
70% Shading rate, keep 30% sunlight out, provide a protect from overheat while you can still enjoy the sunlight needed
http://agfabric.com/product_show.asp?pid=172
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Old 05-16-2015, 10:06 AM   #4
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Agfabric

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Originally Posted by Huck View Post
It's black. I contacted the manufacturer and they thought it would work just laying on the top of the trailer.

70% 12ft Width Knitted Shade Panel, Sunblock Tarp Mesh-Agfabric
Sounds Good....Let us know how it works out.....


I see that they are just down the road from me in Vista, CA, the heart of Avocado Country.
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Old 05-16-2015, 10:08 AM   #5
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You might also look into this stuff. Aluminet Reflective Shade Cloth | Envirotech Greenhouse
It is often used to cover vehicles at dog shows- put that over open things like windows and put something else reflective (I used either reflective tarps or reflective insulation) over non-open things (like the top of the car) and it is amazing how cool it can stay inside. Much better than shade cloth.
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Old 05-16-2015, 11:06 AM   #6
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I like the Alumanet best too, although I do use the black shadecloth (NOT the knitted) that they sell at dog shows also. Kinda depends on the weather.

One show I was at, the dogs and I stayed in my parked car in a field of parked cars in August, and kept quite cool when I opened all four doors and draped the aluminet over the car and doors. I was able to sit in my "tent" and read until ringtime, and my dogs didn't even pant.

Mon
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Old 05-16-2015, 11:38 AM   #7
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Shade cloth laid directly on roof is a failure.

I pulled the cloth back a little so that on the sunny side of the trailer, there was a covered part, an uncovered part, and a small section that was shaded by the shade cloth at an angle (not directly over the section). Temp was between 5 and 10 degrees hotter directly under the shade cloth. It was only about 1 degree hotter in the shaded area compared to uncovered.

When I have time, I will try some more experiments with increasing air space between the shade cloth and what I am shading. I might try it on the hood of my car (white) as that will be easier to work with.
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Old 05-16-2015, 12:45 PM   #8
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Back to your original question - the purpose of the vent. It does vent some fumes most of the time, however its primary purpose is to let air into the tank to replace the volume of water (and "stuff") as you dump the tank. Without it, a vacuum would built in the tank as the effluent ran out, slowing down the draining of the tank. To a lesser extent, it also provides a path for displaced air when you flush the toilet.
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Old 05-16-2015, 01:05 PM   #9
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Originally Posted by Jon Vermilye View Post
Back to your original question - the purpose of the vent. It does vent some fumes most of the time, however its primary purpose is to let air into the tank to replace the volume of water (and "stuff") as you dump the tank. Without it, a vacuum would built in the tank as the effluent ran out, slowing down the draining of the tank. To a lesser extent, it also provides a path for displaced air when you flush the toilet.
Thanks. So it sounds like if the shade cloth had worked out, it wouldn't have caused any problem with the vent.
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Old 05-16-2015, 01:17 PM   #10
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Get an air conditioner.
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Old 05-16-2015, 01:31 PM   #11
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You might want to contact Pop-up Gizmos. Their solar bunk covers for pop-up campers are popular. I had a set myself and let them go with the camper. They seemed to work quite well, but I never camped without using them so I can't give a comparison.

I'm sure they would be glad to custom make something, although the initial prototype cost might be a little high. Maybe you could convince them that it would open up a whole new market (FG trailer owners) and get them at their cost in you do a review.
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Old 05-16-2015, 01:35 PM   #12
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Second the air conditioner idea.

Any black or dark color will increase the heat on the covered roof.

Find a shade tree and park under it...open a cold beer and enjoy!

Happy Camping.
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Old 05-16-2015, 02:09 PM   #13
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I have an air conditioner, but that's beside the point. There are no hookups in National Seashore campgrounds on the Outer Banks, and 3 of the 4 campgrounds have no shade. Frisco does have some shade, but mostly for tent campers who can move under the trees.

It cools down at night, but the trailer retains heat for a while. If I could keep the heat from building up during the day, it should cool down faster at night. I'm trying to find something that will give me at least a 5 degree reduction in heat.

The other thing is the Parkliner has a 5000 BTU ac. In hot temperatures it can't keep up, so anything that will lessen the heat buildup during the day is a winner.
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Old 05-16-2015, 02:20 PM   #14
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Originally Posted by gordon2 View Post
You might want to contact Pop-up Gizmos. Their solar bunk covers for pop-up campers are popular. I had a set myself and let them go with the camper. They seemed to work quite well, but I never camped without using them so I can't give a comparison.

I'm sure they would be glad to custom make something, although the initial prototype cost might be a little high. Maybe you could convince them that it would open up a whole new market (FG trailer owners) and get them at their cost in you do a review.
It sounds like they work, but I need something that lets air through so I can use my rooftop fan.
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