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Old 02-18-2010, 01:22 PM   #1
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newb here..gravity h20 question

Hi all...I'm in the market for a bus. My mom has been working on a 69 international for 10 years making it into a 2 story with full lexan top that opens. Its a pretty amazing unit and I will post pics I'm sure it will be a famous bus. Now it's my turn to get the bug. My first question is..Why arent more people using tanks on top of their bus for water rather than using a pump? Wouldnt seem like a big deal to run a hose up to refill and I plan on using at least two 50 gallon tanks up there and painting them black. thanks.
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Old 02-18-2010, 07:28 PM   #2
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Re: newb here..gravity h20 question

pressure=gamma*h

62.4lb/ft^3*7 ft (vertical distance from tank to faucet, roughly)=436.4 lb/ft^2
436.4lb/ft^*(1 ft^2/144in^2)=3 psi

I think that explains why people don't use tanks on the roof. Now there is some velocity to factor into the equation once it starts moving, but I think that gives you a pretty good idea why people don't use tanks on the roof. You just don't get any pressure. Without the pressure you will have to make up for it with volume (like to get soap out of your hair) and we just don't have the resources to do so.

Typical bathroom type fixtures are designed to run on about 40 psi and are restricted such to deliver the proper spray pattern and strength at that pressure. If you drop below it I think you will be disappointed.

What you CAN do is something similar to what I did and just pressurize your water tank with air. My water pressure is NOT consistant as a result and varies within 1 psi of what the air pressure is in the tank, but it's silent and easy to deal with. Realistically, 15-20 psi is more than sufficient for most purposes, but you'd need to have your water tank mounted 35 feet above your bus to achieve this.
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Old 02-19-2010, 12:24 PM   #3
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Re: newb here..gravity h20 question

That's where that velocity thing comes into play. A higher velocity (which means more energy... v^2/(2*32.3ft/s^2)) means you're going to need a higher volume and that's where we run into a problem on a schoolie. I'm not saying roof tanks won't work...I just wouldn't count on them for anything more than a minimalistic shower. But...pressurize that tank even to 10 psi and I think you'd be cooking.
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