Tank to Tank Pumping over high point

[TonyBr]

I am currently investigating connecting 2 existing treated water distribution systems together by laying a new pumped pipeline between 2 clear water tanks sited at the existing water treatment works.

It is intended that one of the water treatment works will be upgraded and the other decommissioned, with the upgraded one supplying both zones.
A pumping station will be built to boost the water over the hill from one tank to the other, gravitating down the hill to the other tank. The intention is to control the pumps by water level in the downstream tank, having the pumps switch on and off at min and max levels.

http://files.engineering.com/getfil...-9c6d-491918503488&file=pumping_over_hill.jpg

The issue is that when the pumps are switched off leakage within the pipeline will draw the pressure down, potentially causing ingress of ground water.

My thought is to install a small tank on top of the hill … or maybe a pressure vessel at the pumping station to keep most of the main charged to above atmospheric pressure….. the problem with this is the length of main either side of the tank may be at less that 10m when the pumps are off.

An alternate option would be to have the pumps run all the time to maintain a constant level in the downstream tank……. But this obviously has the issue of maintenance of the pumps and high energy consumption.

It is our intention to install a turbine on the downstream side of the hill, to try and recover some of the energy.

Has anyone come across similar situations, how did you prevent ingress of groundwater into your pipe line? Would you use either of the above 3 options, if so which one?

Hopefully my sketch clarifies my description above.

Thanks in advance Tony

 

[BigInch]

It would help to have some idea of the scale of this installation. It looks like your potential water ingress will be limited to only a relatively small length of pipeline at the top of a hill, uh.. where there is usually the very least amount of ground water to worry about in the whole system. Water ingress is going to be max where there is some kind of underground water table. Probably not at the top of the hill. Is it really that severe? If so, wouldn't it be better for you to use welded steel or some other pipe that DOESNT LEAK. I mean, seriously, you must be able to pay for any cost difference between leak/non-leak pipe materials by your saving in energy costs from NOT running the pumps ALL the time. It would seem that you'd be better off ditching the turbine and spending that money on NO-leak pipe. After all, You have to pay for that leakage twice, once for not having it as available water to sell, twice for not having it available to make turbine juice too.

Why not just put a pressure switch at the top of the hill and it looks like a small jockey pump would hold the little bit of + pressure you need after the main pump is shut off, rather than a pressurized tank. Tanks are better used to balance mismatched variable inputs with variable outputs. Pressure tank for < 15 psi hardly seems worth the trouble.

 

[bimr]

I also do not understand why you would not fix the water main to protect the integrity of the water system.

 

[TonyBr]

The scale is relaatively large, 25+Km of 300mm pipeline and the water table is high with plenty of flooding in winter. The area is hilly I have simplified my query to try not to complicate matters. But this may not of worked.

Unfortunately, in my experience contractors are not able to lay a pipe line which does not leak over time. We use an ecominomic level of leakage; which in its simplest form ... is based on the cost to treat the raw water and the cost to find and fix the leak. Under current legislation we are happy to have a leaking pipe as long as the volume lost does not exceed this economic level of leakage.
In terms of the length of main at risk it is the entire length, we may have a small failure at say a joint at the bottom of the hill, which over time may draw down the pressure allowing contamination of the drinking water.

 

[bimr]

Several issues:

1. It would hardly seem economical for a turbine unless you have a very high difference in elevation. Why don't you just use the energy from the water flowing down hill to lessen the work of the pump?

2. You will have to have pump controls to maintain a minimum water pressure in the water main to eliminate the possibility of inleakage.

3. You won't be able to operate the line by gravity because that would mean that you are opening the water main to atmosphere and exposing the water to potential contamination.

4. Consider locating the turbine generator at the discharge point.

 

[BigInch]

Put a nonpressurized tank on top of the hill. Pump to and gravity feed from that to anywhere you want.

Its not the contractor, its your engineering design, material, construction and testing specs and your inspectors that cause leaks.

 

[BigInch]

and lack of maintenance

 

[btrueblood]

Vacuum breaker on the hilltop. Yes, air ingress is a potential for contamination, so you need to address the air intake the same way you would for a non-pressurized tank (vent screen/filter).