Hi,

I have a pretty specific question about friction loss.

When you have multiple lines of different diameter from a hydrant to an engine, (Say: two 2 1/2" lines and and one 4" line each into the engine using separate intakes for each line), how do you know the GPM flowing through each of the lines?

Presumably all of the lines are under the same hydrant pressure, and for arguments sake they are all the same length and the total flow from the engine is 1000 GPM. How could I compare the friction loss in my supply hoses?

Essentially, how could I determine what would be gained by going from a set up where I only have one 4" line from the hydrant supplying my engine to a set up where I have two 2 1/2" lines and one 4" line from the hydrant?

Related (but not exactly what I am looking for) info I have found suggests that:

"Siamesed Hoselines

When two or more hoselines are used to supply water to a desired point or appliance, calculations are simplified by calculating the friction loss in the average length of the siamesed hoselines. Each hoseline will deliver its equal share of water because the pressure applied by the fire pump will equalize in the hoselines. Discharge rate will be divided by the number of siamesed hoselines when determining gpm for each hoseline."

The problem with this info is that all of the lines are the same diameter and they are feeding a siamese appliance.

I have also found charts with coefficients like:

Two 2 1/2" lines and One 3" line friction loss coefficient = 0.16

How do they come up with these numbers?

I have a good understanding of calculating friction loss in general. I am just missing some explanation in this area so don't hesitate giving a complex response.

Thanks for your time,

Rob

I have a pretty specific question about friction loss.

When you have multiple lines of different diameter from a hydrant to an engine, (Say: two 2 1/2" lines and and one 4" line each into the engine using separate intakes for each line), how do you know the GPM flowing through each of the lines?

Presumably all of the lines are under the same hydrant pressure, and for arguments sake they are all the same length and the total flow from the engine is 1000 GPM. How could I compare the friction loss in my supply hoses?

Essentially, how could I determine what would be gained by going from a set up where I only have one 4" line from the hydrant supplying my engine to a set up where I have two 2 1/2" lines and one 4" line from the hydrant?

Related (but not exactly what I am looking for) info I have found suggests that:

"Siamesed Hoselines

When two or more hoselines are used to supply water to a desired point or appliance, calculations are simplified by calculating the friction loss in the average length of the siamesed hoselines. Each hoseline will deliver its equal share of water because the pressure applied by the fire pump will equalize in the hoselines. Discharge rate will be divided by the number of siamesed hoselines when determining gpm for each hoseline."

The problem with this info is that all of the lines are the same diameter and they are feeding a siamese appliance.

I have also found charts with coefficients like:

Two 2 1/2" lines and One 3" line friction loss coefficient = 0.16

How do they come up with these numbers?

I have a good understanding of calculating friction loss in general. I am just missing some explanation in this area so don't hesitate giving a complex response.

Thanks for your time,

Rob

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