Gravity Water Pressure

   / Gravity Water Pressure #21  
The conversion factor I always used for water head was 0.424 times head in feet to get psi. You can get around 5 gpm through your 1" pipe without any significant pressure drop. I have a gravity system that I sized for about 2 gpm and put in 3/4" poly pipe 800' down the hill with almost exactly 100' vertical drop. One of my tanks is a few inches above the other one. The only thing I watch is to close off the lower one in order to fill the higher one (from downspouts off the roof); no big deal, the lower one will just overflow a bit if the higher one fills up. Turns out it almost never does because that roof has a tree overhanging it that restricts the rainfall hitting the roof; whereas, the lower tank gets more rainfall on its 3 roofs without trees over them.

You might want to check out the prospects of using a ram pump if you want more pressure. I've heard of people putting them on a flowing stream to get water up higher than the stream. Think it takes a high flow under low head though. You probably can't get enough flow (no more than about 5 gpm) to get much flow out of a ram pump. They work by flowing water pressurizing an air tank and then a trip releases the pressure and pumps the water up to a tank. I've looked at some Google sites on them.

Ralph
 
   / Gravity Water Pressure #22  
Not too many years ago my town replaced an old water tank with a new one higher up. Surprise, surprise, people had fixtures blowing all over the low part of town. Town refused compensation, homeowners had to buy their own PRVs.

Harry K
 
   / Gravity Water Pressure
  • Thread Starter
#23  
I just got a new GPS and with all the snow that fell this week it will be a while before I get up to the cabin to check the actual elevation. It will be interesting. Great ideas and info from you guys. Thanks.
 
   / Gravity Water Pressure #24  
Not stupid at all. I was in construction a number of years before I knew. They skin that a couple of ways. For a sprinkler system they add what we call a jockey pump to boost pressure to upper floors. I'm familiar with DC and Balto. and DC in particular has tight height restrictions on buildings, that's somehow tied to the Wash. Monument height for buildings within a certain distance. Whole town is limited though, so most buildings don't exceed 12 stories and you can booster pump that kind of height. For real high rise situtations elsewhere they generally put a holding tank in the mechanical area on the Penthouse level or perhaps on the roof down south. Not unlike a water tower set-up where you pump it to the elevated reservior and then re-pump and/or gravity distribute it from there to the lower floors. PR valves as mentioned can be used for floors where the pressure is excessive. For example they may use the static public pressure for floors 1-6 or wherever it drops to about 40 PSI and then feed the rest of the floors above # 6 from the Penthouse reservior. You don't necessarily need a PRV at every floor above the sixth but grab a group of floors above the sixth as a range of say 40 to 60 PSI works rather well. Then another valve for the next group above that, and finally go from gravity flow to pump flow from the penthouse holding tank (reservior) on the upper floors, where there isn't adequate head to create good pressure. Sounds involved but it's simple once explained. A big city plumber may add to my comments. They and the engineers are the real experts.
 
   / Gravity Water Pressure
  • Thread Starter
#25  
I finally got up to the cabin today. Quite a bit of snow on the ground but GPS'ed the altitude difference from cabin to tank. It was 74 feet which would equate to almost 35 PSI. I'm happy with that.
 

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   / Gravity Water Pressure
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#26  
One more pic
 

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