# Valve open to air

• Fellps

#### Fellps

I have a centrifugal pump 50 m above a vessel, I’m pumping water in at 4 bar gauge into this vessel. I then close a valve to cease pumping ensuring no air enters the system.​

My question is, if I now open that same valve to atmospheric air this time, will the water exit from the pipe through the valve at a 4 bar pressure differential. Or will it, the water, go down the pipe to 40 m from its originally closed valve position of 50 m.

I have a centrifugal pump 50 m above a vessel, I’m pumping water in at 4 bar gauge into this vessel.​
Is the 4bar measured at the valve/pump or in the tank?

Is the 4bar measured at the valve/pump or in the tank?
At the tank

At the tank
Then the pressure at the valve is roughly 0 absolute and opening the valve to atmosphere will cause the water level to fall. How much it falls will depend on how the tank is being pressurized. If there is compressed air at the top of the tank, the water level will drop about 10m. If there is no air in the tank and it is just solid water, it will only drop a little and the tank pressure will increase to 5 bar gauge since water is incompressible.

...of course, that begs the question: why do you need a pump to begin with? Why couldn't you just let gravity fill the tank?

Then the pressure at the valve is roughly 0 absolute and opening the valve to atmosphere will cause the water level to fall. How much it falls will depend on how the tank is being pressurized. If there is compressed air at the top of the tank, the water level will drop about 10m. If there is no air in the tank and it is just solid water, it will only drop a little and the tank pressure will increase to 5 bar gauge since water is incompressible.

...of course, that begs the question: why do you need a pump to begin with? Why couldn't you just let gravity fill the tank?
Thank you very much, the need for the pump comes from the need for control. The vessel must be remotley flooded at a controlled rate.

The vessel will contain compressed air. Should a dewatering process be required, further compressed air will be pumped into the vessel to 'push' the water the extra 10 m and induce a flow rate