Static vs Residual on a rural waterline extension

[HELLA21]

Readings at two local fire hydrants on a 4" line, so we are a ways from the reservior, but what else might cause the vast difference in static vs residual psi at the main line.

Static 190 psi
Residual 20 psi
Flow rate 100gpn

Re-ran the test and got the same results. I need to serve 6 homes the farthest being 800 feet away and 100' higher than the connection point. Does someone have a recommendation on what type of booster pump to use/cost of it?

Thanks in adv.

 

[bimr]

The difference could be serveral things. The simplest item that would cause this may be a closed valve. You may also have a scaled water main.

Your should ascertain the root of the problem prior to use of the water main.

 

[jgailla]

That static pressure is awfully high.

 

[cvg]

if you are 6 or 7 miles from the reservoir, than it sounds about right for normal head loss. If you have additional demands between your hydrant and the reservoir, than the main is handling additional flow. Did you do your test at dinner time? (or supper time if you are from the midwest?) Is the main supplied by a gravity tank or by a pump?

 

[HELLA21]

I'm not sure to tell you the truth, I wasn't the one who performed the test, it was done by the Rural Water Authority and these were the pressure readings I received.

I havn't done a lot of water line extensions, but have never seen a residual pressure test vary so much from the static prssure...

 

[coloeng]

I would ask them to redo the flow test and see if there was a problem with the first test.

 

[cvg]

before doing that, a little review of the system might be prudent. Determine:

length of the watermain from the water source to your hydrant
size of the watermain
any other waterlines parallel to your main?
is the source a tank or a pump?
if a pump, see what the capacity is
how old is the waterline and what type of pipe?
how many service connections between the tank and your hydrant?

The review may lead you to the conclusion that the pressure test was accurate. If not then redo the test and be there when it is done.

 

[redbridge]

I agree with cvg. These numbers would be right if you are 10 miles away from the tank. You really need their water system map so you can simulate what is going on. I agree with bimr, if the tank is fairly close to the hydrant then there is probably a valve partialy closed.

 

[cvg]

If you have additional demand on the main while it was being flow tested - say an additional 25 - 50 gpm it could have a huge effect on the total headloss in the main. Maximum length of the main from the hydrant to the tank might be reduced to only 3 or 4 miles.