Nozzle selection

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Permalink Reply by Larry Lasich on September 15, 2010 at 11:24am

Fire pumps (that are rated in the USA) are rated in Gallons per Minute of draft at sea level. Therefore a 1250 GPM pump will lift 1250 GPM of water, somewhere between 22 to 33 feet at sea level. If you are drawing water from a pressurized hydrant, you are getting what ever the hydrant can send you. If you are getting your water from a water carrier, it will be somewhere in the middle.

To answer your question, we need to know what your water supply situation is.
Larry

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Permalink Reply by Girish Raj on September 15, 2010 at 11:46am

Thanks for you response. As per the pump curve we should be able to achieve 4000lpm (1057 gpm) @ 10 bar (145psi) at a 3 meter lift. when I performed testing, Im not able to achieve this pressure. Looks like my nozzle selection is wrong. In fact Im not sure about what size nozzles are to be used. Was just performing some trial and error. Would very much appreciate if you could provide some info on how to calculate the required nozzle size for the above or similar. Thanks!

Larry Lasich said:

Fire pumps (that are rated in the USA) are rated in Gallons per Minute of draft at sea level. Therefore a 1250 GPM pump will lift 1250 GPM of water, somewhere between 22 to 33 feet at sea level. If you are drawing water from a pressurized hydrant, you are getting what ever the hydrant can send you. If you are getting your water from a water carrier, it will be somewhere in the middle.

To answer your question, we need to know what your water supply situation is.
Larry

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Permalink Reply by William Hoehn on September 17, 2010 at 9:14am

Girish Raj:

There are three variables that must be met when testing fire pumps. First, is the lift. As you have indicated you are drafting at a 3 meter (about 10 ft.) which is the correct set-up for a fire pump in the U.S. Second, you must reach the 10 Bar (150 psi) discharge pressure. Lastly, you must discharge the correct volume from the nozzle or nozzles. Since we are discussing a 4,000 lpm pump it is possible to use a single 50mm (2”) diameter nozzle. A 2” (50 mm) nozzle at 79 psi (5.37 bar) nozzle pressure will flow 1057 gpm. You must use a pitot tube to measure the nozzle discharge through the 50 mm tip.
The discharge volume and the pump pressure are inter-related because the nozzle pressure is not the same as the pump pressure, and by simple math, we find that we must loose 71 psi between the pump and the nozzle opening. This is accomplished by the “friction loss” found in appliances, hose, pump piping and by throttling back the discharge valves on the pump.
Most U.S. pumps are designed to flow 250 gpm (1,000 lpm) per discharge, although the piping may be capable of 500 gpm or more, so let us assume you are feeding this 2” nozzle with two (2) – 6.3 cm lines (2 ½”) hoses, each 15 meters (50 ft.) long.
Procedure: Get your pump primed and begin flowing water through the 2” nozzle. Be certain to have this securely tied to a stationary object, as the reaction force when fully supplied will be about 500 lbs. Have an assistant monitor the pitot at the nozzle and throttle up until you achieve the correct flow when the pitot reads 5.37 bar. Check your engine pressure which should now be between 115 psi (7.8 bar) and 140 psi (9.5 bar). Alternately bump the discharge valves slightly toward the closed position. The pitot pressure will drop slightly, so raise the engine pressure slightly to bring the nozzle pitot back to the desired 79 psi. Continue this until the engine pressure is at 150 psi and the nozzle pitot is at 79 psi. Record the engine rpm and hold the system stable for the specified time to prove that the cooling system and motor are capable of meeting the specification.
If, as you indicate, you wish to use all 5 discharges, attach a 1” (25 cm) nozzle to each outlet and use the pitot to set each nozzle at 50 psi (3.4 bar) hold the engine at 10 bar and close the discharges until the nozzles all read 50 psi on the pitot gauge. (211 gpm per nozzle)

Bill

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Permalink Reply by Girish Raj on September 18, 2010 at 11:16pm

Hi William,
Thanks a lot for the information and for your time.

Would very much appreciate if you could provide some more info on what you have mentioned,

1. A 2” (50 mm) nozzle at 79 psi (5.37 bar) nozzle pressure will flow 1057 gpm. I have a chart from Akron Brass which provides this information. But could you provide some details or some links to where I can find information on how this is calculated?

2. Also, as you said, If I am using 5 deliveries,
"attach a 1” (25 cm) nozzle to each outlet and use the pitot to set each nozzle at 50 psi (3.4 bar)".
If I am using a 2" nozzle, I get 1057gpm @ 79psi nozzle pressure. How is it 1" nozzle if I am using 5 outlets?

3. Is it mandatory that we have to use a pitot tube for measuring nozzle pressure? or can I also use a pressure gauge to directly measure from the line just before the nozzle?

Please bear with me if my queries sound too rudimentary. Im a bit new to this. Thanks


William Hoehn said:

Girish Raj:

There are three variables that must be met when testing fire pumps. First, is the lift. As you have indicated you are drafting at a 3 meter (about 10 ft.) which is the correct set-up for a fire pump in the U.S. Second, you must reach the 10 Bar (150 psi) discharge pressure. Lastly, you must discharge the correct volume from the nozzle or nozzles. Since we are discussing a 4,000 lpm pump it is possible to use a single 50mm (2”) diameter nozzle. A 2” (50 mm) nozzle at 79 psi (5.37 bar) nozzle pressure will flow 1057 gpm. You must use a pitot tube to measure the nozzle discharge through the 50 mm tip.
The discharge volume and the pump pressure are inter-related because the nozzle pressure is not the same as the pump pressure, and by simple math, we find that we must loose 71 psi between the pump and the nozzle opening. This is accomplished by the “friction loss” found in appliances, hose, pump piping and by throttling back the discharge valves on the pump.
Most U.S. pumps are designed to flow 250 gpm (1,000 lpm) per discharge, although the piping may be capable of 500 gpm or more, so let us assume you are feeding this 2” nozzle with two (2) – 6.3 cm lines (2 ½”) hoses, each 15 meters (50 ft.) long.
Procedure: Get your pump primed and begin flowing water through the 2” nozzle. Be certain to have this securely tied to a stationary object, as the reaction force when fully supplied will be about 500 lbs. Have an assistant monitor the pitot at the nozzle and throttle up until you achieve the correct flow when the pitot reads 5.37 bar. Check your engine pressure which should now be between 115 psi (7.8 bar) and 140 psi (9.5 bar). Alternately bump the discharge valves slightly toward the closed position. The pitot pressure will drop slightly, so raise the engine pressure slightly to bring the nozzle pitot back to the desired 79 psi. Continue this until the engine pressure is at 150 psi and the nozzle pitot is at 79 psi. Record the engine rpm and hold the system stable for the specified time to prove that the cooling system and motor are capable of meeting the specification.
If, as you indicate, you wish to use all 5 discharges, attach a 1” (25 cm) nozzle to each outlet and use the pitot to set each nozzle at 50 psi (3.4 bar) hold the engine at 10 bar and close the discharges until the nozzles all read 50 psi on the pitot gauge. (211 gpm per nozzle)

Bill

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Permalink Reply by William Hoehn on September 19, 2010 at 10:15am

Girish Raj:

Please do not apologize for not totally understanding the physics involved with operating and testing fire pumps. I have been doing this for 40 years and still find things that I do not fully understand. I will try to take your questions in reverse order.

With fluids the total energy in the system is the product of both the pressure and the velocity. Therefore when water is flowing in a conduit the energy at the exit is totally changed to velocity, but we can get a measure of energy in the nozzle stream by stopping the velocity (opening of the pitot gauge) and applying it to a gauge. ( The area directly in front of the pitot opening has zero velocity and the water is stationary even though the rest of the stream is flying past the blade of the pitot.) The problem with measuring the pressure directly behind the nozzle is you are not measuring the velocity component in the hose coming into the nozzle, but only the pressure component at the base of the nozzle. This error can be minimized by using a large hose diameter and a relatively small nozzle diameter.
The Engilsh system equation for discharge from a smooth bore round nozzle is:
Q = 29.87 * d * d * Sq Rt of Np
Where: Q is the flow from the nozzle in Gallons Per Minute
d is the nozzle opening in inches.
Np is the pressure on a pitot inserted in the stream about 1" from the nozzle.
The 29.87 is a constant that compensates for converting inches, pressure and nozzle efficiency into an approximate value of GPM.
When I suggested using a 1" nozzle on each one of the 5 outlets, you would need to flow all five simultaneously. Using the above equation or using your Akron Brass table for a 1" nozzle should yield a flow of 211 gpm. Supplying all five outlets will require a flow of 1055 gpm or the required test volume for your engine.

The real purpose of conducting pump tests is to compare the pump performance from year to year or month to month in order to ensure that nothing has occurred to the engine or pump that drastically affects performance or reliability of the equipment.

I reread your post where you wish to use all six (6) outlets to perform the test. You could use six nozzles of 7/8" diameter at 59 psi to achieve the desired total flow of 1057 gpm.

Bill

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