So our department started making the switch from economy hose to combat hose. The decision was made rather quickly without really testing other hose for various reasons. One being that the vendor wouldn't let us demo any without purchasing it and we had no neighboring departments running the hose we could borrow it from to try. It hasn't been too bad, I noticed the kink resistance and whip is much better, but it felt harder to advance solo. I just read Dennis Legears' articles Nozzle Dreams and Hose dreams, and now I am thinking twice on the combat hose. I was thinking maybe its a sales pitch from the guy who makes Tru ID hose, but, it actually makes a lot of sense to me now. I wanted to throw this out there and see what you guys think.
If you haven't read his articles, here is the most concerning part that I read.
"The greatest reduction in friction loss in modern fire hose has been created both accidentally and later intentionally by increasing the internal diameter of charged fire hose. It started when the thicker double jackets of cotton were replaced by mold resistant thinner double jackets made of nylon and polyester. At this time the rubber liner remained, however the bowl size of the coupling remained the same leading to a slight increase in the internal diameter of charged fire hose.
Recently, with the invention of lightweight hose, the problem was amplified. Lightweight hose rapidly became the worst offender because the new thinner liners and jackets created a larger internal diameter as coupling bowl size either remained the same or were intentionally made larger in some lightweight hose designs. This gave lightweight hose a larger diameter when charged. This increase in size lowers the friction loss at a given flow and increases the volume of water in the hose. This also means it is heavier when deployed, because it is carrying more water inside of it when charged. Do not let the hose brochure or salesmen mislead you."
We currently have a 7/8" smooth bore tip that we run at 50 PSI and160 GPM on our 200' 1.75" crosslays. With the combat hose coefficient of 6.59 we run them at a PDP of 85 PSI. It appears that the ACTUAL inside dimeter of combat hose when it swells is 1.9, according to Key. This adds extra water, and thus extra weight to the hose lay. Also, I imagine that a larger diameter hose has more surface area contacting with the ground creating more friction. The entire purpose of switching the combat hose was because we thought it was a lighter, less friction loss hose. Now come to find out, I am thinking its a little misleading. Undoubtedly it has a lower friction loss coefficient, because its a larger hose! Its not a 1.75" hose, its a 1.9" hose, and its actually heavier, although their listed uncoupled dry weight appears to be light, at less than half a pound per ft, again misleading. The water weight increased the total charged hose weight from 296 pounds to 321 pounds when compared with Tru ID hose. Here we are thinking we are being efficient, and we actually have a larger hose that is providing more water and heavier to drag around while flowing the exact same GPM with our same nozzle as before. With the 7/8" the PDP would go from 85 PSI up to 130 PSI following the switch in hose from combat to tru ID. However, this is still under 150 PSI and doesn't affect the pump capacity. Unless we ever ran into the situation where we had a really long 1.75" lay that pumped up to 200 PSI PDP, then our capacity would reduce from 1500 GPM to around 1,000 GPM. It seems the combat would actually be better paired with the 15/16 tip and that may be cheaper to maximize the larger diameter hose and utilize the extra water (185 GPM) we are dragging around, as well as be substantially cheaper than replacing all this new hose. I wont bore you with all the math, and disclaimer, some of my math may be a little off. But, if you're curious on how to find the weight of the hose line; take the diameter of the hose, divide it by 2 to find the radius, then square the radius and multiple it by pie. Then, you take a 50' section and turn it into 600 inches and multiple those. This will give you cubic inches, then divide it by 231 to get from cubic inches to gallons. Then multiple that number by the weight of water, 8.34, and that will give you the weight of WATER per 50' section. Now add the weight of the hose itself, in this case 0.38 lbs per ft, and multiply by however many sections of hose you have. Clear as mud?
The change may seem negligible to some, however, I was thinking that we make the switch from combat to Tru ID before we get really invested in it anymore than we already are. As for our 2.5" lay, we currently have combat for it as well and they have an elkhart chief 4000-26 nozzle that does 250 GPM at 50 PSI. The hose actually swells to 2.6 ID, with a bowl size of 3" and has a total charged weight of 568 pounds. I was also thinking of recommending the switch to Tru ID here, but going with their 2.25" hose as this would reduce the weight to 456 pounds and better be paired with a 1 and 1/8 " tip flowing more water at 265 GPM. This would give us a lighter, thinner hose with increased GPM, although the nozzle reaction would jump from 89 to 99. The tip size of 1 and 1/8 fits perfectly to the 1/2 diameter rule, matching the 2.25" hose.
Thoughts?
If you haven't read his articles, here is the most concerning part that I read.
"The greatest reduction in friction loss in modern fire hose has been created both accidentally and later intentionally by increasing the internal diameter of charged fire hose. It started when the thicker double jackets of cotton were replaced by mold resistant thinner double jackets made of nylon and polyester. At this time the rubber liner remained, however the bowl size of the coupling remained the same leading to a slight increase in the internal diameter of charged fire hose.
Recently, with the invention of lightweight hose, the problem was amplified. Lightweight hose rapidly became the worst offender because the new thinner liners and jackets created a larger internal diameter as coupling bowl size either remained the same or were intentionally made larger in some lightweight hose designs. This gave lightweight hose a larger diameter when charged. This increase in size lowers the friction loss at a given flow and increases the volume of water in the hose. This also means it is heavier when deployed, because it is carrying more water inside of it when charged. Do not let the hose brochure or salesmen mislead you."
We currently have a 7/8" smooth bore tip that we run at 50 PSI and160 GPM on our 200' 1.75" crosslays. With the combat hose coefficient of 6.59 we run them at a PDP of 85 PSI. It appears that the ACTUAL inside dimeter of combat hose when it swells is 1.9, according to Key. This adds extra water, and thus extra weight to the hose lay. Also, I imagine that a larger diameter hose has more surface area contacting with the ground creating more friction. The entire purpose of switching the combat hose was because we thought it was a lighter, less friction loss hose. Now come to find out, I am thinking its a little misleading. Undoubtedly it has a lower friction loss coefficient, because its a larger hose! Its not a 1.75" hose, its a 1.9" hose, and its actually heavier, although their listed uncoupled dry weight appears to be light, at less than half a pound per ft, again misleading. The water weight increased the total charged hose weight from 296 pounds to 321 pounds when compared with Tru ID hose. Here we are thinking we are being efficient, and we actually have a larger hose that is providing more water and heavier to drag around while flowing the exact same GPM with our same nozzle as before. With the 7/8" the PDP would go from 85 PSI up to 130 PSI following the switch in hose from combat to tru ID. However, this is still under 150 PSI and doesn't affect the pump capacity. Unless we ever ran into the situation where we had a really long 1.75" lay that pumped up to 200 PSI PDP, then our capacity would reduce from 1500 GPM to around 1,000 GPM. It seems the combat would actually be better paired with the 15/16 tip and that may be cheaper to maximize the larger diameter hose and utilize the extra water (185 GPM) we are dragging around, as well as be substantially cheaper than replacing all this new hose. I wont bore you with all the math, and disclaimer, some of my math may be a little off. But, if you're curious on how to find the weight of the hose line; take the diameter of the hose, divide it by 2 to find the radius, then square the radius and multiple it by pie. Then, you take a 50' section and turn it into 600 inches and multiple those. This will give you cubic inches, then divide it by 231 to get from cubic inches to gallons. Then multiple that number by the weight of water, 8.34, and that will give you the weight of WATER per 50' section. Now add the weight of the hose itself, in this case 0.38 lbs per ft, and multiply by however many sections of hose you have. Clear as mud?
The change may seem negligible to some, however, I was thinking that we make the switch from combat to Tru ID before we get really invested in it anymore than we already are. As for our 2.5" lay, we currently have combat for it as well and they have an elkhart chief 4000-26 nozzle that does 250 GPM at 50 PSI. The hose actually swells to 2.6 ID, with a bowl size of 3" and has a total charged weight of 568 pounds. I was also thinking of recommending the switch to Tru ID here, but going with their 2.25" hose as this would reduce the weight to 456 pounds and better be paired with a 1 and 1/8 " tip flowing more water at 265 GPM. This would give us a lighter, thinner hose with increased GPM, although the nozzle reaction would jump from 89 to 99. The tip size of 1 and 1/8 fits perfectly to the 1/2 diameter rule, matching the 2.25" hose.
Thoughts?
Comment