Water flow and gravity

[DeeGee]

Basically we have had to install a new header tank to supply the farm by gravity. The old galvanised tanks were of 400 gallon capacity but are not now fit for purpose. The new tank is smaller but fed by a float switch activated pump which fills the tank in a matter of minutes. Admittedly the new tank about three foot lower than the old but is still more than high enough to provide gravity fed water where it is needed via 25mm alkathene pipework.

However, when the new tank is full (100 gallons approx.) and the stop taps are opened there is no water reaching most of the system. One tap nearby has a slow flow and that is about 6’ below the header tank, but more distant but lower taps are completely dry with not even a trickle of water.

It has been suggested by a physics expert that the new tank is too low and doesn’t have the head of water to reach the more distant taps say 20 meters away due to friction resistance in the pipework. But my point is that surely there would be some water flowing there by gravity, and if the new tank wasn’t high enough then it would just mean a lower pressure and slower flow of water, and not zero supply.

The fact that all outlets are below tank level and are totally dry is really baffling everyone: all ideas welcome! Please!

 

[335d]

U sure nothing has dropped into the pipe from the tank and causing a blockage, or an airlock somewhere?

 

[Rossymons]

Or a tap somewhere not opened?

 

[JWL]

Any high points in the delivery pipes to the various outlets you have could have caused an airlock. Pick one and use a suction pump to pull the water down the pipe. Think along the lines of siphoning one bottle into another, when it's flowing it's fine but until you take the air out of the siphon pipe you're flogging a dead horse

 

[br jones]

sh!t in the pipe ,you should have check valves on your tsps ,they will be blocked ,unscrew a tap to see if any water runs out

 

[renewablejohn]

You have air locks in the pipe. Start at the tank and do a section at a time until you get running water without air then go onto the next section working away from the tank and repeat again until you get water flowing without air.

 

[sulky]

Basically we have had to install a new header tank to supply the farm by gravity. The old galvanised tanks were of 400 gallon capacity but are not now fit for purpose. The new tank is smaller but fed by a float switch activated pump which fills the tank in a matter of minutes. Admittedly the new tank about three foot lower than the old but is still more than high enough to provide gravity fed water where it is needed via 25mm alkathene pipework.

However, when the new tank is full (100 gallons approx.) and the stop taps are opened there is no water reaching most of the system. One tap nearby has a slow flow and that is about 6’ below the header tank, but more distant but lower taps are completely dry with not even a trickle of water.

It has been suggested by a physics expert that the new tank is too low and doesn’t have the head of water to reach the more distant taps say 20 meters away due to friction resistance in the pipework. But my point is that surely there would be some water flowing there by gravity, and if the new tank wasn’t high enough then it would just mean a lower pressure and slower flow of water, and not zero supply.

The fact that all outlets are below tank level and are totally dry is really baffling everyone: all ideas welcome! Please!

this may sound daft but are the stop taps fitted right , flow in direction of arrow on tap body if a new tap has been fitted to tank, as been on gravity wont lift jumper in tap if its got gate valves its not as important most work in both directions

 

[DeeGee]

this may sound daft but are the stop taps fitted right , flow in direction of arrow on tap body if a new tap has been fitted to tank, as been on gravity wont lift jumper in tap if its got gate valves its not as important most work in both directions

Yes thanks the stop taps are facing the right way.

 

[DeeGee]

You have air locks in the pipe. Start at the tank and do a section at a time until you get running water without air then go onto the next section working away from the tank and repeat again until you get water flowing without air.

Yes, I think it might be air locks, but shouldn’t gravity push out the air at the taps, or not?

 

[DeeGee]

You have air locks in the pipe. Start at the tank and do a section at a time until you get running water without air then go onto the next section working away from the tank and repeat again until you get water flowing without air.

Okay, and do I always leave the end tap (furthest point) open or closed while doing this?

 

[Exfarmer]

If there is any way to connect the pump direct to the system temporarily and flood the air out.
However with this issue I rather think there is a danger you will have repeated issues unless you raise your tank to at least the old level

 

[renewablejohn]

Yes, I think it might be air locks, but shouldn’t gravity push out the air at the taps, or not?

No the water will just compress the air. Water itself is hard to compress so the aim is to get the pipe full of water without any air in it. Flowing water is the easiest way to remove air out of a pipe.

 

[caveman]

Pump water back up the pipe

 

[Frodo]

Have you upgraded anything else. We put in a meter which had a check valve, which would not work under low pressure.

 

[renewablejohn]

Okay, and do I always leave the end tap (furthest point) open or closed while doing this?

I normally leave it closed then I can do one section at a time. When you break the pipe wait for the section you want the water to go into to drain completly then reconnect when the pipe from the tank is flowing without any airlocks. Then move onto the next section. On the last section just open the tap and leave open until it flows without airlocks. Dont be tempted to turn it off until you have got rid of the air in the pipe. If you still have problems check your pipe seals are not letting air in or cuts in the pipe letting air in.

 

[sandy2210]

i have done numerous gravity fed supply's and always put the first 25 meters or so at least one or two sizes of pipe larger water always seen reluctant to go through a small pipe direct out of a tank

 

[Storeman]

sh!t in the pipe ,you should have check valves on your tsps ,they will be blocked ,unscrew a tap to see if any water runs out

How often would you need to do that?

 

[puppet]

One tap nearby has a slow flow and that is about 6’ below the header tank, but more distant but lower taps are completely dry with not even a trickle of water.

Something must have got stuck in the outlet somewhere. An air lock to a tap a short distance away seems unlikely unless there is a sharp u-bend but even then with the tap open then gravity should let water out.
My diesel tank sits 2 feet above the tractor tank and the hose might drop 2 feet below but fuel comes out quickly.
Can you undo some connections to see where water gets to or stick a hose back up in case something is lodged?

 

[owen r]

Have you got new inline stop taps? If they are the screw version can reduce flow.

 

[DeeGee]

Have you got new inline stop taps? If they are the screw version can reduce flow.

Yes new one way taps, both fitted the right way and are fully open, thanks.