# Thread: Maximum flow in supply hose?

1. ## Maximum flow in supply hose?

I know the friction loss formula, but is there a ceiling maximum flow for supply hose? A hydraulics buff tells me that 3" hose cannot flow more than 750 gpm at any time. Anyone care to dispute?

2. I was taught 700 gpm max. At that flow rate you have 40 psi friction loss. After that you risk bursting the hose.

3. Originally Posted by firemonkey311
I was taught 700 gpm max. At that flow rate you have 40 psi friction loss. After that you risk bursting the hose.
unless I got it wrong it can't burst a hose. Think about it if you are trying to maintain 100 psi in the flow, Friction loss is dependant on several factors such as length and/or elevation and GPM trying to achieve. Service test on a annual test is at 250 psi. Also, if you are supplying another pumper on 3" you generally without question lay two lines and the most a "average" GPM one would be supplying is 1500.

4. Originally Posted by Lieutenant387
unless I got it wrong it can't burst a hose. Think about it if you are trying to maintain 100 psi in the flow, Friction loss is dependant on several factors such as length and/or elevation and GPM trying to achieve. Service test on a annual test is at 250 psi. Also, if you are supplying another pumper on 3" you generally without question lay two lines and the most a "average" GPM one would be supplying is 1500.
Good point.

5. We use 500 gpm as the max for one 3 inch line. Anything above that either requires dual 3 inches or 5 inch.

6. ## It Depends!

The maximum flow is dependent on several factors including the working pressure of the hose, the length of lay, and application.

Attack rated hose has a maximum working pressure of 275 (even though you would be unlikely to pump at that pressure). Supply rated hose (like some large diameter hose) has a maximum working pressure of 185 psi.

Length of lay is also significant in that friction loss is directly proportional to the length of the hoseline. If lays are short, you can move more water through a given size line.

Application has a significant impact in that in a relay, you only need to have 20 psi residual pressure at the end while supplying a master stream may require 80 or 100 psi nozzle pressure, and an elevated master stream adds in substantially more pressure for the appliance loss and elevation (adding to the line pressure required and moving you closer to the maximum working pressure). This is generally a greater concern with supply rated hose.

Cheers,

7. Basically, its whatever the burst point is. However, when you go above 36psi in friction loss of the line, you are losing more flow due to turbulence and it is important to switch to a larger size, smaller tip, or pull another line.

8. Originally Posted by firedrewski03
Basically, its whatever the burst point is. However, when you go above 36psi in friction loss of the line, you are losing more flow due to turbulence and it is important to switch to a larger size, smaller tip, or pull another line.
I'm not disputing this, but it is the first time I've heard of a magic number. Can you tell us where you found or heard this?

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