Some Advice for Direct Water Distribution 2

[Chandika5]

I am an Engineer attached to National Water Supply & Drainage Board of Sri Lanka, and in general, we distribute potable water utilizing elevated water towers/reservoirs.

With the increase of demand some part of the existing distribution network of our main city does not get the required water pressure (8m) throughout the day and hence it is proposed to isolate the area and boost the pressure using in line booster pumps

The booster pump house is proposed to be constructed adjacent to the main distribution reservoir which is in a higher elevation.

The daily demand variation from off peak to peak is analyzed to be from 450 m3/h up to 1600 m3/h. It is expected to boost the pressure by around 6m using pumps (Or maintain a pressure of around 10m at pump delivery side).

Since the demand range is huge, we expect to install a series of parallel pumps and also expect to utilize Speed Control with VSDs

We do not have much previous experience on such Direct Water Distribution Systems.

Can anyone please give me some advice to proceed?

Thank you very much.

 

[ashtree]

There are many manufacturers who supply pressure booster sets for this exact purpose and they would be able to advise you directly.
What you are proposing is fairly common and straightforward. As you suggest it would be expected that a number of parallel variable speed pumps would be used. These would be controlled by the system pressure.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Review the online document:

https://www.usfa.fema.gov/downloads/pdf/publications/water_supply_systems_volume_i.pdf

Chapter 4 has some water distribution system design concepts.

 

[Chandika5]

Thank you very much ashtree and bimr

Bimr – I read that Chapter but still I have some doubts.

The area we are expecting to feed using new booster pumps was fed earlier through gravity. When the demand is high and/or when the reservoir water level is low, some areas of the network did not receive the required water pressure. Now a Booster pumping station has been proposed to construct adjacent to the elevated ground reservoir to provide the required additional pressure.

Since we are aware about the maximum and minimum flow requirement (450 m3/h – 1600 m3/h), we expect to get a pumping system that can create an additional pressure of 5-10m throughout the whole flow range.

Distribution piping network is so complex and hence, we expect to select pumps as above without much detail analysis on the distribution network.

What do you think about this method of pump selection? Do we need any further analysis?

 

[ashtree]

A network analysis would obviously be ideal, but if its very complex it will take a lot of resources and time to do properly.

If you selected pumps that could give the required flow range and provided 10m of extra system pressure at the pump station, the system will obviously work better than it did before at least for some customers. Just the fact that you are adding extra pressure that you did not have before will make some improvements. But it may not solve the problems that you have.

If the low pressure areas are serviced by pipework that is too small for the flow , or perhaps there is a blockage or restriction, or maybe out on the end of a long network, those problems will still exist. There may be a small increase in pressure but that same increase in pressure may deliver more flow in the network elsewhere which causes greater system losses etc, and you may end up no better off.

If you have maps of your network and you can plot out the areas where the problems are known you may be able to see any obvious causes. Its not a network analysis but its better than doing nothing. For example an area may be fed by only a single main and not a loop main. Likewise if you look at the layout of the larger sized trunk mains, this might also indicate why an area has low pressure. It may also help to work out whether an increase in pressure using a booster pump would actually improve the service.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[Chandika5]

Thank you ashtree

 

[cvg]

ashtree has valid points. suggest not spending a lot of money on a pump system which may not improve things much. you might need a new transmission main, another reservoir or both. You will need to do some sort of engineering analysis to find out what is causing the problem. From what little you have already stated, it sounds like insufficient capacity in the pipes.