How much air to fill tank?

[Drewsaid]

I need to determine the flow rate of air into a tank which is to be pressurised, pushing water out of an inclined pipe. The incoming pressure is 6bar before the regulator, and the desired tank pressure is 12kpa the change in volume of the tank due to the pushing out of water is 5 litres

 

[quark]

Your question is not very clear, particularly the last sentence. If you want to know how much air pressure you require, just calculate the frictional losses in the piping at the required flow rate and add the height of the pipe exit from nozzle of the tank. Convert the head in meters to bar and this is the pressure you have to maintain in the tank.