Has anyone actually tested the two methods out. I agree a relay with a boosting pumper at the hydrant would have greatly assisted this operation. I feel that had a significant impact on the supplying pumper as well. I still feel the 2 discharges would be a great benefit to the aerial than the one. I am impressed with the interest and the knowledge being shared. Still looking for a definative answer though. I don't have the ablity to test the flow on another station's truck and I am not sure they want to test their own...just saying.
You can test the flow without using an aerial. Set up this test a deluge gun with whatever size tip you use on the aerial. Lay out the hose as you would to supply the aerial and feed the deluge that way. Use 2 - 2 1/2's into the five and then the 5 into the gun. Then set it up with the 5 with an adapter to the discharge and see which one works better. Use a pitot gauge to check the deluge guns nozzle pressure for accuracy.
The friction loss up the ladderand through the ladder pipe or mounted nozzle will be the same regardless of what system you use to feed aerial. What your concern is, if I am reading you correctly is which hose methode would more efficiently move the water. Frankly, unless the difference is massive, say, 30 pound or more, the speed of hoking up the single 5 inch would still make it more viable to me.
Remember to hook the 5 inch to the discharge that comes straight off the pump for the most efficiency.
So, no 5" at all. Two 100' lengths of 2-1/2"?
Originally Posted by mebmikec
I would suggest 3" coupled 2-1/2". The difference in friction loss vs. 2-1/2" will take a load off the engine. Still, the 5" coupling directly on a main pump manifold discharge and the 5" hose will be most efficient hydraulically. Operationally, it all comes down to what is fastest, easiest and safest with what you have to work with.
Just to be able to show the work so to speak, what is at the tip of the aerial and at what elevation? Or better yet, the known psi at the base of the aerial to accomplish the goal GPM? (done through testing your aerial)
If we're using the same pumper and aren't able to factor the individual discharge piping as Kuh Shise noted, then it appears the question is:
which is better: (2) 100 ft. 2.5" lines supplying the aerial or (1) 5" LDH at 100 ft? The difference being the single 2.5" discharge into the 5" vs. two 2.5 discharges into 100 ft. of 2.5" hose then into a siamese 2.5" to 5" intake on the aerial?
mebmikec: 100 ft. of 2 1/2 at 500 gpm has a loss of around 62 psi per 100 ft. From experience (35 yrs teaching pumps at the local level in Pa.) most 2 1/2" discharges have about 20 psi loss at 500 gpm (full flow 2 1/2" valves). So the dual 2 1/2" hook-up to the aerial should require the following... 20 psi in the pump house + 62 psi hose loss + 20 psi residual at the aerial = 102 psi engine pressure. Using a single outlet adapted to 100 ft. of 5" needs... 80 psi in the pump house (Fl varies with the square of the flow .. so doubling the flow to 1,000 gpm out a single discharge raises the pump house loss by 4X) + 6 psi hose loss + 20 psi residual = 106 psi engine pressure. Not much difference. However, if the valve was a 2 1/2 with a 2" waterway the losses in the pump house would rise to about 200 psi using a single valve. Hazen Williams formula had the pipe diameter in the bottom of the formula. It varies with the diameter to the 4.87 power (almost 5th) 2 to the 5th = 32 while 2.5 to the 5th is 93 or about 3 times more loss using the smaller waterway.