System head curve

Question

Hi all, 
 I am trying to make system head curve for transmission pipeline which has flow control valve and software is giving un logic curve. I think this due to the FCV. So kindly what is the sugessted solution to make system head curve? 
 
 Regards 
 Eng.Sayed Elhagar

Scott Kampa · Answer

Hello, 
 The FCV in the system can act as a sort of boundary. It limits the flow, resulting in a situation similar to the case of only having fixed demands downstream and no tank or reservoir. In other words, it acts like a closed system. The calculations start to become invalid if more flow through the FCV is greater than the FCV setting. 
 There are a couple of options. Assuming you have a tank or reservoir downstream of the pump, you can add loops around the FCV. This is typically a good idea anyway in case a modeling condition arises were the FCV is closed. With no loop around the FCV, downstream demands cannot be met. You can also change the status of the FCV to "Inactive". As long as there is a downstream tank or reservoir, the system head curve will have a more normal appearance. 
 Lastly, you can set up pressure dependent demands, similar to that suggested in your other forum post related to system head curves. The link to using pressure dependent demands with system head curves can be found here: 
 communities.bentley.com/.../15371.system-head-curves-with-no-downstream-storage-solution-500000056093.aspx 
 Regards, 
 Scott Kampa 
 Bentley Technical Support

Tom Walski · Answer

You need to consider how the FCV will behave in the real system. 
 Is this a real FCV or is it a trick to force a certain flow? If it is the latter, get rid of it. 
 Does all the flow go through it to get to the tank? If so, then the curve is only valid up to the setting on the FCV.

Tom Walski · Answer

I looked at your model and think I see what you are trying to do. 
 First, I'll assume that you have individual pumps to take water out of the tanks during irrigation times. 
 It looks as if the transmission system is one pressure zone and the area is relatively flat. 
 Flow control valves would work but they are a relatively expensive solution. There is nothing wrong with having some tanks fill faster than others as long as they all eventually fill. An altitude valve an altitude valve. This will shut off the flow when the tank is full. 
 To better model the tanks, don't have the pipes come directly in and out of the tank but place a node in front of the tank and connect that single pipe to the tank. Put a check valve on the line coming into that node unless water can flow from the tank back into the system. 
 As tanks fill and get shut off, the demand on the pumps (and the system head curve) will change. The solution is to have a larger pump that runs when all tanks are on line and some smaller pumps that run when only a few tanks are left to fill. Having more pumps will slightly increase the cost but will give you much better flexibility and reliability. It will be a small fraction of the piping and tank cost. 
 These are just suggestions. There are a lot of ways to design a system like this.