WaterCad question

[Rookie2]

Hi,
I am modeling a proposed residential subdivision for adequate fire flow. I have done this several times before, but the available flow and pressures at the connection to the existing system were based on hydrant flow tests. I then used that data to model the connection as a reservoir and pump.

On this project, the flow data at the point where we connect to the existing system is based on a model that includes improvements that aren't in the ground yet.

The information I'm given is 900gpm @ 20 psi at our connection point. How can I model this connection? Can this be done with a storage tank somehow?

TIA

 

[cuels]

I have used a reservoir and a pump to model a design flow + head in the past. It seems to work accurately, and I have checked this with Bentley on several occasions. They have always given this option to me for a constant flow situation.

However, You may be able to use a tank with a flow control valve. You would have to set your tank elevation to match the pressure head, and you would have to maintain that level throughout a time-step model.

Possibly a better model would be a reservoir set at your pressure head elevation and a flow control valve set at the given flow constraint (at the subdivision elevation). That way you maintain a constant 900 gpm through the FCV and a 20 psi pressure head with your reservoir elevation (approx. 46.2 ft of equivalent elevation head). I have never tried this, but I would be interested to find out if it models correctly. Intuitively, it should work.