Sizing maindistribution line and transmisionline pipe 2

[marBz]

Im designing a domestic water system for a 1400 population, i want to know how to obtain the size of the maindistribution line, trasmission line, and pipe used inside the house??

I want to obtain this sizes economically.. we have a limited budget...tnx a lot.

 

[bimr]

Modern water systems have minimum 8-inch water mains (for fire protection purposes) and 3/4 to 1 1/2-inch house service connections. Water mains are sized for 3-5 ft/sec flow velocity.

 

[marBz]

tnx u for the answer, but what is the best pipe material will be use?? economically?

 

[bimr]

PVC, HDPE, Ductile Iron are most commonly used.

 

[marBz]

heres my layout.. is this ryt? i will use 8inch for watermain line, what about the submain distribution line? i will use 1 inch for the house service connection..

 

[marBz]

sory, heres the layout

 

[cvg]

a little more information would be useful

what country is your project in?
do you need to satisfy a fire marshal?
what about insurance companies?

your figure does not show a water source, what about that?

not sure why you have two lines on each street

line size must be based on hydraulics, you can't just pick a size. pressure requirements and topography have a large impact on the design

service lines are based on desired flow rates, again you can't just pick a size

for 1400 people, I am sure you will need some lines larger than 8 inch

Suggest you define your design criteria and thenset up a water network model to design this.

 

[marBz]

im from the philippines.. i consider this design that have two pipes per street because it is one of the existing design here, but this is an old design with no consideration of fire flow. I thought i can use this also in insisting a fire hydrant.

 

[marBz]

the water source is at the tank.. i sure submersible pump for my water source and flow directly to the tank

 

[cvg]

no reason to have two mains in each street, just doubles the length of pipe that needs to be maintained and reduces the amount of usable space in the right of way for other things like sewers, storm drain, gas line, telephone, electric, cable tv

 

[marBz]

ahh i see.. but in my layout is it right to use 8" for the mainline and 4" for the subline? im a mechanical engr and i dont have any exp for this..my boss!! grr

 

[bimr]

Where are you in the Philippines? You can probably get by with less than 8-inch water mains because your residences are of concrete construction.

You should check with the local fire brigade to determine the water needs for fire fighting.

 

[cvg]

you cannot establish the sizes without a hydraulic analysis. you must establish minimum pressures and water demands and run the hydraulics to get the answers you want.

 

[marBz]

yes ur right about the concrete construction... I already consider the fireflow + peak demand pr day.. i have also the flow rate on each loop and the tank capacity.. how do i get the right pipe size?

8 inches are arent applicable??

 

[bimr]

Residential construction here is mostly of wood construction and you would expect higher water flows are required by the insurance services who determine these water requirememts. Of course, this is offset somewhat because the residences are usually farther apart.

That is why you should check with the local fire brigade. The water mains are sized to transport the fire water, not for daily usage.

 

[marBz]

sir bimr, sad to say that in our city there is no fire hydrant been installed i cant check that out.. thats why i cant use this old existing designs because i consider a firehydrant..Old designs, sizing of the pipe was based in daily usage considering peak demand.

 

[bimr]

Well anyway, the fire water requiements are set by the insurance underwriters. You might want to check into that a little further.

 

[cvg]

trying to save money on watermains by going to a slightly smaller size could be foolhardy. The primary cost of your water system is to install and maintain the lines, not in procurement costs for the pipe. The incremental cost to upgrade from 6 inch to 8 inch pipe or 8 inch to 12 inch pipe is small. The corresponding increase in capacity is large. Or to put it another way, it is very expensive to dig up and replace a line later on because it is too small to deliver adequate flow or pressure.

 

[marBz]

tnx a lot for the info sirs.. is it ok to use the same sizes to all my pipes sir?

 

[cvg]

it's better