I have a question regarding a system containing a water source, with two pipes connected using a T. There are two different states of the system; one being where both pipes are open and water is flowing, the other being that one pipe is closed.

Is it possible to have a constant flow out of each pipe, in both situations? If so, what device is needed to keep the constant flow?


Pipe 1 and 2 is open. 15 L/min is flowing out of both pipes. Pipe 1 is closed, but 15 L/min is still flowing from pipe 2. Image related.


The two things I have come up with are:

  • Flow control valves at the start of each pipe, ensuring no flowrate higher than what is set
  • A pressure reducing valve, ensuring that the pressure is constant on the valve-side.

This has led me to two things; firstly that adding a flow control valve would be costly when expanding the system, and secondly that I do not know enough about fluid dynamics to understand how a pressure reducing valve could work in relation to mass flow rate.

Thanks for the help.

  • 1
    $\begingroup$ What are you using as the pressure reservoir - a pressurized tank? If you want to control flow, you should use a flow control device and not a pressure control device. How about using orifices instead of control valves? An orifice would be a cheaper option upfront if you have only 1 flow rate you are trying to maintain in each branch. $\endgroup$
    – J. Ari
    Jan 5, 2022 at 20:50

1 Answer 1


First of all, having the same flow in both pipes without flow control valves on both is set by the characteristics of the dwnstream piping in each. Unless they are mirrors of each other, all valves open will likely not have the same flow in both. You could throttle one if desired to make them the same if that is a goal.

Second, you could control flow through one or the other when one is shut off via a throttle with specific settings (your "device to control flow"). You could determine the settings via experimenting, the setting might be different with Pipe 1 closed versus 2. This assumes that the valves for Pipes 1 & 2 are either open or shut.

If you want a specific flow rate, then flow controllers on each pipe with control valves is really the only way to go.

Also, I'm not sure what the "pressure reservoir" is for, water doesn't really need this.

  • $\begingroup$ Thank you for your answer. The "pressure reservoir" looks like this on the inside; communityenvironment.unl.edu/articles/… The pump activates at 1 bar and pumps the water reservoir up to ~4 bar, then stops. $\endgroup$
    – user36433
    Jan 5, 2022 at 22:15
  • $\begingroup$ @user36433 everything will be harder if you have an off-on system. Just size the pump for the flow rate. $\endgroup$
    – Tiger Guy
    Jan 5, 2022 at 23:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.