Handling air in metered potable water connections

[Kanyembo]

I work for a water company in Zambia and we have recently been directed to meter all our clients. However, this directive does not take into account the technical issues in the operation of meters which rrequire that the pipelines are always full of water. Our current operations in water supply are intermittent causing crazy meter readings due to the presence of air which must be expelled through the meter and obviously invites the wrath of the customers.

Is there anyway in which this problem could be sorted out?

Are there may be valves which can release the air in the pipe to improve meter performance?

Regards

Kanyembo

 

[BobPE]

Kenyembo:

I just want to clarify one thing you said, air is in the lines because of service problems. I take this to mean the you intermittently stop supporting the system gradient by the shutting down of water flow from your sources? If this is the case, air release will always be a problem. If the air is there and the system is consistantly pressurized, then air release valves may be a potential solution.

Start with your top 10 customers because chances are they will represent 50 percent of your accounted for demand. Look at ways to stabilize pressure to them and incorporate air release into their service connection design. It would be a good start for what seems to be a huge problem you have to solve.

BobPE

 

[Kanyembo]

BobPE

Thanx for the reply. To clarify the issue, yes you are right in asserting that the air is introduced because we do shut down the water supply every now and again.

So it looks like there is very little we can do is lessening the problem then?

Kanyembo

 

[bhwtam]

You did not give us an information about your distribution pipework. Is your supply directly pumped to the customers or it is through a service reservoir at high level?

I'll assume that you have a service reservoir at high level and supply by gravity.

In this case, when you stopped your supply, air will enters the distribution pipework from the service reservoir or the taps of your customers (when they open their taps for water).

To minimise the problem, I think you need to modify your distribution pipework so that:

1. the air will not be escaping through the meter, and
2. air will not be entering your system.


As I don't know exactly how your distribution network is like, I just brainstorm a few suggestions for your consideration:

1. Provide air relief valves along the distribution main.

2. Install check valves to sub-branches, so that water will not be drained out the branches when you stop your supply. (i.e. minimise air sucked into the pipeline through the taps and also minimise the air flow into the pipe when you start your supply again since the air will not be able to open the check valve with the back pressure on the other side)

3. Install the water meter at a local "low level". (i.e. arrange the pipework like a 'U' trap)
and install air relief valve at the local "high level" before the meter.

I am not sure whether these crazy ideas will help or not. If you can give more information on your system, may be we can give you more specific answers.

 

[BobPE]

Kenyembo:

I have worked on intermitttent water system like yours and air is always the problem mostly from leaks and holes in the distribution mains ans customer service connection venting.

Look at your top customers and try to modify the services to reduce the air. Managing the air in you system should be a long term goal, which air release valves should be a part of, but I would focus the short range plan on maintaining full time water service in the first place. Isolating the system with check valves probably should not be done since looping of systems like yours is so critical to reduce velocities when the system is working.

Long range planning is about the only thing you can do that would be effective for all the customers.

BobPE

 

[Kanyembo]

bhwtam & BobPe

Thanx again for those tips, I will be discussing with my operations engineers the suggestions offered.

Kanyembo

 

[keyardee]

Hi Kanyembo
Your problem is that the air is also routed through the meters and that causes unrealistic readings.Introduce a surge vessel before the meter, depending upon the service line and provide a vent point from highest point on the vessel with an air valve.Size and positioning may vary from customer to customer.Try with one of them and standardise on the practice.I hope this solves your problem.