# Nozzle pressure vs GPM ?

• 04-29-2011, 09:13 AM
wnyf76
Nozzle pressure vs GPM ?
I had a chart for this once but I can't find it.

What I am trying to figure out is If you pump a standard 100psi combination nozzle at less then 100psi nozzle pressure what Is your gpm flow at the nozzle
for every lets say 5psi less then the rated 100psi.

In other words what if you have only 80psi or 75psi,etc at the nozzle what would I be flowing.

We are not doing this, someone asked me to find out for them.

Thanks
• 04-29-2011, 11:16 AM
donethat
Quote:

Originally Posted by wnyf76
I had a chart for this once but I can't find it.

What I am trying to figure out is If you pump a standard 100psi combination nozzle at less then 100psi nozzle pressure what Is your gpm flow at the nozzle
for every lets say 5psi less then the rated 100psi.

In other words what if you have only 80psi or 75psi,etc at the nozzle what would I be flowing.

We are not doing this, someone asked me to find out for them.

Thanks

See if this helps
• 04-29-2011, 01:50 PM
kuh shise
Wnyf76: You need to use the nozzle flow equation and work it backwards to find the equivalent solid bore nozzle size. Nozzle Diameter, once known can be used to calculate the flow for that nozzle at any pressure. If we use a standard 125 gpm constant gallonage nozzle and put the nozzle pressure at 100 psi then by solving for diameter: 125= 30 x d x d x Sq. Rt. Of 100 we get d = 0.645 inches. Substituting back into the equation for a nozzle pressure of 81 psi the flow will be 112.5 gpm. At 70 psi the flow would be 104.6 gpm. Assuming the original nozzle pressure is 100 psi, then divide the flow setting by 10 and multiply by the square root of the new pressure. 12.5 x Sq. Rt. Of 50 psi is 88.4 gpm. Using a 200 gpm fog nozzle at 100 psi and dropping the discharge to 75 psi results in a flow of 173.2 gpm. Over pumping can be calculated in the same way. A 250 gpm fog nozzle pumped at 130 psi will flow 285 gpm. Play with the math and it will be easy using a hand calculator.
• 04-29-2011, 03:06 PM
FyredUp
Or just buy an Akron FireCalc.

Or the Akron Fire Stream Calculator plastic slide calculator.
• 04-29-2011, 10:12 PM
Nozzle nut 22
Or buy/borrow/beg a flowmeter and try it out for yourself with YOUR hose and YOUR nozzles. Then you can make a pump chart for each preconnect, etc.

Hook the flowmeter up to an intake line, then you won't have to change it over for every line or discharge. Then you can play with different discharge pressures all you want.

Who needs to deal with complicated equations at 3 in the am, with fire blowing out the windows, and hysterical parents screaming at you??