Dad has a ? about new water main

[meledward23]

I think most of the replies have been right on.

I might make a few comments.

The price of the water meter is in line with what a I see on a semi regular basis. (about 6 times a year).

The dual meters is usefull if your city/county waives sewage fees on the second meter becasue /if it acts as irrigation.

 

[GaryQWA]

""....but head loss is based on velocity.". Could you explain?"

To have a head loss due to friction you have to have motion. It is a dynamic loss. If you have no flow you have no velocity and no pressure loss due to friction. In the no flow case, even a tiny 1/4" line would provide the full pressure from the main to the home. The losses happen when you try and get flow.

I know, there's no sense in having a water line unless you cause the water in it to move. lol Velocity is dependent on pressure. I've never heard of velocity being the determining factor of friction loss, you have friction loss no matter what velocity is present. Pressure and the ID of the pipe dictates/controls the velocity.

Based on the above situation, the minimum could be 3/4" IF the sprinklers were run at night. One inch provides for potential higher gpm needs.

So I say use a chart to find the correct size ID. Here we have suggestions the right size all the way up to and including 2"!! IMO going larger based on picking a number out of the air isn't the right way to do it. Here's a link from a manufacturer of PE pipe; note how they control the velocity.
http://www.oilcreek.com/supp/water/size.php

Gary
Quality Water Associates

 

[meledward23]

Gary,

"The head loss for fluid flow is directly proportional to the length of pipe, the square of the fluid velocity, and a term accounting for fluid friction called the friction factor and inversely proportional to the pipe diameter"
Head Loss = f((LV*LV)/D)

Just a little something to mull over. I dont really care to get into a debate. Just thought I would point this out.

Although I agree just using a simple chart works wonders.

NOTE there are many equations relating to this subject. I just thought I would point out the velocity is involved. You can find some differing equations if you do search due to technical needs/lack of.

 

[Highbeam]

The engineer that made that chart knows that velocity is tied directly to friction losses. It is a good chart and applies very well here.

Nowhere on that chart does 1" pipe flow 15 gpm. The jump to 1.5" pipe allows nearly triple the flow rate at any distance. A typical fixture will flow about 2.5 gpm so if your consumption is limited to two bathrooms then the 1" pipe looks fine.

I would not design a system that limited domestic flow to less than 15 gpm for my own home.

 

[BillyP]

All these charts are fine and dandy but doesn't water pressure come in there somewhere?

For example.

350' of 3/4" with a PSI of 90.
350' of 1" with a PSI of 60.

How would you determine GPM for each one?

 

[Highbeam]

The chart calls out the allowed 10 psi pressure drop so if your main is at 70, the chart allows a drop to 60 when determining the GPM for each pipe size. If you start at 70 and are willing to see less than 60 psi then you could milk more flow out of a given pipe size than the chart shows.

 

[GaryQWA]

Guys, I grant that I'm not into formulas much, I let that up to those that do that type thing and use their charts provided by the material manufacturers and my experience with replacement well pumps. My point was, or is, that the velocity is dependent on the pressure and ID and type and pressure rating of the tubing or pipe; steel, copper or plastic (all three types). IOWs, the velocity varies based on the pressure and the ID and type of material being used. Each material has its own maximum velocity and they can vary substantially.

The normal 2.5 bath house has internal 3/4" plumbing reduced to 1/2" to the second floor etc. or at least before the fixtures; currently there are millions of houses plumbed that way. If the water source is 'city' water, they probably have a 3/4" service line if the house was built more than say 20 years ago. If the source is their own well, they'll have 1" service line from the foot valve or submersible pump running 30/50 psi on the pressure switch. Many submersible pumps will be 300' plus deep and the well from the house will be from 10' to a 150' from the house. That would be a total distance of up to 450', and yes, the pump is moving water from the static water level, not the total depth to the foot valve or sub pump.

Furthermore... if there are sprinklers in the future, using a larger (1.25" or 1.5") line to/for them works on the same principle as the 3/4" meter here on up to the suggested 2" line.... not a problem due to the velocity increasing as the water flows through the ID reduction; but there is a corresponding pressure loss. All this depends on the available pressure, and if there's is insufficient pressure, add a booster pump, Cycle Stop Valve and small pressure tank. That would cost somewhat less than oversizing the pipe to start with.