fire hydrant flow tests

[cdafd]

scenario

1. static a fire hydrant
2. go to the next one and flow both 2 1/2's very little drop in pressure
3. sorry no pitot reading, gage gave up. but good flow from both 2 1/2's.

next one, same static fire hydrant

1. fire truck is set on the same static fire hydrant and starts flowing water

2. truck gets around 1800-2000 gpm. intake pressure on truck goes down to around 20 ish psi.

what is going on here?????? why is the truck taking the pressure down so low, versus flowing the 2 1/2's?

 

[DavidCR]

If I got the idea....

First case. The flow is not that big. And the water source is big and does not suffer a drop on distant "static" hydrant.

Second case. The flow and speed is big. The gage reading sould not be taken on the same hydrant the truck is connected it may suffer from turbulence/venturi effect.

 

[cdafd]

but with the second scenario, that is real life.

Fire truck pulls up to an fire hydrant, connects , shots the water, and they are told to not drop below 20 psi.

So the 1800 gpm is all the truck can take from the fire hydrant, if they follow the 20 psi rule.

I do follow your thinking though, and thought of staticing another hydrant while the truck pumps, but still they can only get so much water from the hydrant.

 

[chicopee]

What may seem a lot of water coming out of hydrant #2 may not be so particularly if Hydrant #2 was at a higher elevation that hydrant #1( your static hydrant).