Breaking an airlock

[jamieled]

We have ~300m of 25mm mdpe pipe from the burn to our raw water tank, probably around 10m head in total. The last 100m or so is pretty flat, a few minor undulations (<0.5m). Even so, we appear to have an airlock in the pipe somewhere although difficult to determine exactly where.

 

Over time I will stick in some air release valves at the most likely places.

In the meantime, any practical suggestions for dealing with the current airlock? Any recommended pumps (electrical supply not easy to get to the majority of the pipeline)? 

[Nickfromwales]

Have you fitted a non return valve ? 

[tommyt]

How is the air getting into the pipeline?

[ProDave]

I would have thought a 10M head would push any air lock through. I would be more concerned you have a blockage?

[Nickfromwales]

Is the suction side fed from a dip-pipe? If the water level gets low enough when the pump is at full wallop there is a risk of sucking in air and water not just water. 
Even so, if the pump is at the source then this should not be problematic as water will eventually get through. 
Is the pump ‘man enough’?

 

FYI Air admittance valves AAV’s will let air in as well as out, so could add to your problems instead of curing them. 

[Ed Davies]

AAV: air admittance valve: lets air (and any other fluids to hand) in. Also…

AAV: automatic air vent: lets air (but not water) out.

 

If @jamieled wanted either it'd be the second but they wrote “air release valves” which could be AAV(2) or could just be a manual valve opened to let air out until water comes out too.

[jamieled]

Thanks all. To clarify:

 

-No pump exists at the moment, just an idea to solve the airlock but I'm looking for ideas as to what type of pump to get.

-It airlocked after a very cold period, most likely due to it freezing. This happened on our old supply.

@ProDave, it could be a blockage  but it air locked before and it is well filtered at the intake.

@Ed Davies, yep, I was thinking of the second definition.

 

This pipe does not run all the time at the moment, only when the tank ball valve opens to allow water in.

[Stewpot]

Is the problem that you are drawing air into the pipe as it draws water from the burn? Can you make some sort of catch pool in the burn, so that the pickup of the pipe is deeper under water? I would guess in a natural flow of water, it will always be getting pretty aerated. You could perhaps try adding an additional length of vertical pipe at the highest part of the pipe run, which would give the air somewhere to collect. Ideally you'd put a bleed valve at the top of it - if a manual one, you'd have to periodically open it to let the air out.

[ProDave]

5 minutes ago, jamieled said:

Thanks all. To clarify:

 

-No pump exists at the moment, just an idea to solve the airlock but I'm looking for ideas as to what type of pump to get.

-It airlocked after a very cold period, most likely due to it freezing. This happened on our old supply.

@ProDave, it could be a blockage  but it air locked before and it is well filtered at the intake.

@Ed Davies, yep, I was thinking of the second definition.

 

This pipe does not run all the time at the moment, only when the tank ball valve opens to allow water in.

I have an outside tap (in a shed) that stopped working after it froze one year. I have never bothered to investigate yet why.  I refuse to believe it is an air lock that the mains water pressure cannot push through so I am assuming something has broken within the tap in my case. (I just get a dribble when I open the tap)

 

I will be interested in any other phenomena that can stop water flow when it freezes that won't re start when it thaws. 

 

Tip for the future.  If freezing is likely, leave the water running through the pipe (and overflowing somewhere safe)

[jamieled]

I'm not sure on the exact phenomena, but in our case the freezing (on our old supply) created an airlock on a few occasions. We have also broken a tap through freezing it in the past as well though. Once we're up and running properly I plan to continually circulate water through the system so hopefully this problem should reduce.

 

@Stewpot, thanks for that. I'd forgotten a bit about the intake - it's in a highly aerated pool, so perhaps a bit of work at that end might reduce the problem.

[Ed Davies]

11 hours ago, jamieled said:

I'm not sure on the exact phenomena, but in our case the freezing (on our old supply) created an airlock on a few occasions.

 

Normally gasses come out of solution in water when the water is warmed (i.e., warmer water holds less gas). However, I suspect they come out on freezing as well. Salt (partially) comes out of solution on freezing; sea ice is a lot less salty than the water below it.