# Tank flooding time for a compartment

1. Jun 11, 2013

### arjal

Hi can someone please help me I have been asked to calculate how long it would take to flood a compartment taking into account:

Back pressure due to the air inside the tank being compressed. This will happen as the tank floods until the point when air pressure inside the tank is the same as the hydrostatic head at the inlet to the upper valve. From this point on water will continue to enter via the bottom valve as the air leaves by the upper valve.

Thanks

2. Jun 11, 2013

### SteamKing

Staff Emeritus
If the upper valve is open during flooding, then the tank will see a certain mass flow of air out of the upper valve and another mass flow of water into the lower valve. The net amount of air within the tank will govern the internal pressure as a function of time.

I assume the the tank is fully submerged, including the upper valve during this process. With the tank fully submerged, if the internal pressure is less than the hydrostatic pressure at the mouth of the upper valve, then water will want to enter through the top and bottom until the conditions within the tank cause a change in flow of the water in and air out.

The flow through the valves will also depend on the head losses through the valves and attached piping. The air pressure in the tank can be estimated using the gas equation PV = nRT.

3. Jun 11, 2013

### arjal

hi thanks

the flood valve at the bottom is 6" as is the vent valve at the top. Is it possible for you to show me an example?