# Two Tanks, One High, One Low

Hello,

I have a situation with two tanks in my model (WaterCAD, standalone).

The current set up is thus:

The model - The larger of the two tanks is at a higher elevation, as are the piping and junctions for the larger tank. The smaller of the two tanks is at a lower elevation, as are the piping and junctions for the smaller tank.

Here are the current operating parameters of the two tanks:

T-1

Elevation (ft)                   553.46

Elevation (Base) (ft)        553.46

Level (Minimum) (ft)      17

Level (Initial) (ft)              18.5

Level (Maximum) (ft)     19.5

T-2

Elevation (ft)                   550.52

Elevation (Base) (ft)        550.52

Level (Minimum) (ft)      17

Level (Initial) (ft)              18.5

Level (Maximum) (ft)     19.5

The issue - The larger of the two tanks is flowing into the smaller tank according to the model (makes sense if the system is gravity fed). I need the two tanks to run in parallel because that is the current operation.

The question - If the system is completely gravity fed, what valve or valves do I need to use to prevent the larger tank from flowing into the smaller tank, and have both run in parallel operation? I need both tanks to contribute to the system. I assumed a check valve would work to prevent the larger tank from flowing into the smaller tank, but I have no experience using them, so I am hesitant to.

Thank you for reading all of this,

Clint Taylor, EIT

Parents
• Why would you assume that the two tanks are both at 18.5 ft.? In reality flow would go from the higher HGL to the lower HGL until they both equalize.

So for a steady run or the initial condition for and EPS rum, I'd set the two HGLs equal.unless there is some very compelling reason not to.