How do I calculate the maximum flow rate?

[TSN79]

A building has a water inlet and outlet. The static water pressure at the buildings water intake is 5 bar. I'm trying to determine how much water this outlet will deliver when its valve is fully open. In that state, the pipe size and length will result in a certain head loss that I can calculate for a spesific flow. But how can I determine what the maximum flow rate will be?

 

[anorlunda]

There are numerous online calculators for piping losses. One of them might be able to help you.

 

[TSN79]

There are numerous online calculators for piping losses. One of them might be able to help you.

Calculating the losses isn't really the issue. It's understanding what happens once the inlet pressure starts to drop due to the high flow rate. Will maximum flow rate be achieved once the inlet gauge pressure falls to zero? Or does the gauge pressure during flow need to be at least equal to the head loss through the pipe in order to overcome this?

 

[anorlunda]

the inlet pressure starts to drop due to the high flow rate

That's how losses are defined.

 

[boneh3ad]

Calculating the losses isn't really the issue. It's understanding what happens once the inlet pressure starts to drop due to the high flow rate. Will maximum flow rate be achieved once the inlet gauge pressure falls to zero? Or does the gauge pressure during flow need to be at least equal to the head loss through the pipe in order to overcome this?

Translation: "Calculating the losses isn't really the issue. It's calculating the losses and their effect on flow rate."

 

[jrmichler]

Calculating the losses isn't really the issue. It's understanding what happens once the inlet pressure starts to drop due to the high flow rate. Will maximum flow rate be achieved once the inlet gauge pressure falls to zero? Or does the gauge pressure during flow need to be at least equal to the head loss through the pipe in order to overcome this?

When the valve is fully open, the pressure at the outlet is zero (gauge pressure). The pressure at some point upstream is 5 bar. The head loss in between is (5 - 0) = 5 bar. You only need to calculate the flow rate at which this is the case. If the pressure at the building inlet drops, then you need to calculate farther upstream.