I have a client in the beginning stages of site developement for building a house.
The rural water district says it would supply a 1″ meter and the owner would then run a 1″ gasketed PVC line 800 ft back to the house site. I feel that the 1″ is too small for the distance.
What I need is to be able to calculate the pressure drop, and then suggest the best size to install. Elevation change from the tap to the site is 20ft uphill. The 150ft tall water tower is about 2 miles away and its base is 20 feet higher that the site.
The water district workman’s response my inquiry about the water pressure was…”Thar’s plenty!”. No quantitative numbers provided! No mention of a pressure reducer, either.
I have been to the www.engineeringtoolbox.com site and found too much information that I know too little about. Lots of formulas without clear definitions of what the results really mean.
I would appreciate some help with this problem.
Thanks……………Iron Helix
Replies
You need to get the pressure at the meter. ( And not just assumed pressure based on the tank location etc.) And you need the flow required at the house, usually based on fixture units. Then, you can size the pipe.
H
You need the pressure and flow rate at the output of the meter. Not hard to measure, but the meter has to be installed first.
Try this page http://www.the-engineering-page.com/nav/dp.html.
I'm in the same boat - I ran 2" & haven't regretted it.
Water company provided a 5/8" meter (but with 1" tubing).
They said if I ever had water volume issues, they'd upsize the meter, but I've had no problems so far.
I contacted the water company office and asked for pipe size, flow, and pressure. The technician is to call back on Friday or Monday. I'll plug in his numbers on line and see what emerges. Results to follow.
Thanks for the responses & direction..........Iron Helix
In most applications where a significant water demand is expected and the service is sized accordingly, you need to determine the demand. In most houses, the demand, even for "garage majals" is no more than a 1" can supply. The loss can be determined based on fixture supply units (FSU), obtainable from most plumbing codes appendicies or tables in the code, and the total equivalent length of the pipe and fittings. This is independent of the supply pressure.
A 1" copper pipe, 800 (eq) ft long, moving 7.5 gpm (3 concurrent showers) will have a pressure drop of 36 ft or 15.6 psi. If the supply pressure is 40 psi, this is bad. If the supply pressure is 80 psi, its ok.
I heard that explained to me by the general manager of light and water here .
It was a big math problem.
From my experience as a building inspector I know we would have reccomended a 2 inch meter. Actually fire code would have forced it .
I dont know the math to the problem .
Tim
You lose 1 psi every two feet you rise up to the house.
Have a good day
Cliffy
In todays discussions with the client, he expressed a need/desire to have enough volume and pressure to service a 1" firehose for fire protection since the site is remote and in the woods. Distance to closest fire department (volunteer) is about 8 miles and the closest manned department is 10+.
He feels he can use it for woods fires, and possibly have enough effect to allow the F.D. to arrive to fight the fire. Hope the volunteer F.D. has a tanker truck!
I'm not sure this is a realistic point of view when it comes to structure fires. Residential sprinkler might be better. This changes the parameters!
I also believe the water service tap will be at the end of a 4" main at a flush valve. I'm given to understand end of line taps may also lower the flow/pressure.
More as it unfolds.............Iron Helix
"I'm given to understand end of line taps may also lower the flow/pressure."Not necesarily.It gets back to the same thing. What is the static pressure (elevation difference from the tower) and what is the demand (flow rate) in that pipe.You can have an end of line that is just a tap of the main trunk to serve a side road and it might only be a 1/2 mile from the tank and only a couple of houses.
Another urban myth shot in the head.....thanks Bill.
......................IH
Why worry about formulas when ya can just punch in the numbers.
head_loss_calculator
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Nice set up! Sure takes away the math manipulations. When I have numbers I will plug them in!
Thanks...................Iron Helix
Tables are sometimes easier... here's one.
in a similar situation...
We are installing a line now - 300' 1" line from my house to my neighbors new house (sharing our well) our plan is to add a booster pump, check valve, then a pressure tank, both on his end of the line.
I am thinking with the pressure tank we won't need to do any loss calcs - right?
Any thing else we should be considering?
Treat every person you meet like you will know them the rest of your life - you just might!
300' is not a big deal with 1" line. I go 750'. Elevation rise is. That's what accounts for almost all of my 50 psi drop. System still works fine, just have to tweak it.PAHS Designer/Builder- Bury it!
I finally caught up with the water district tech....only one on the payroll.
He estimated the pressure at 65# and had no flow numbers for that trunk of the system, but it might be 1500 gpm on the 4"line.
He also mentioned that the owner had already called to request to a 2" water meter. The tech noted that the meter would be set about 125 feet from the main line and the system requires 2" copper from the main to the meter...materials costs at $18.50 per foot plus fittings.............Ouch$$$$$.
End of search.....now to find a residental type fire hydrant.........
Thanks for all the info.................Iron Helix
Thanks for the update!! 2" meter is a monster. Wow. Cu pipe, big $$$$$.
I guess you don't have to worry water pressure anymore.
H