SA Firefighter
Equipment => All Equipment discussion => Topic started by: bittenyakka on March 18, 2007, 06:05:56 PM
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As MFS use 50mm as their main working hose and i believe it is on some CFS pumpers does anyone think this type of hose has any use in CFS standard stowage on 24/34 appliances?
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MFS use 50mm hose for most jobs, with modern ff techniques such as those taught in compartment fire behaviour, we are using less and less water to supress fires, for this reason i think it would be almost silly for CFS to adopt the 50mm hose size as standard stoweage.
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We dont need 50mm :-P
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Darn tootin. No need for it.
38mm gives enough pressure/water for any internal attack.
64mm is great for water supply and large surround and drown jobs.
The very few occasions when it could be handy is not enough to go put it onto our already overflowing trucks.
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What you have to remember is that MFS appliances have true High pressure lines which put out the same amount of water as a 38mm line therefore they just use H.P lines and not 38s. They use 50mm lines purely as a working length on the end of 64mm lines to make it easier to handle. Using the 50mm hose loses very little volume and increases pressure.
So in answer to your question no they shouldn't be on any other appliance other than a pumper.
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Using the 50mm hose loses very little volume and increases pressure.
So the hose increases pressue? There I was thinking it was the pump.
Based on the fact water is incompressible the only loss in volume would occur if it had a leak.
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We carry a couple of 50mm hoses on Burnside pumper, I have used it a number of times in anger and think it's an awesome working length. I would go as far as to say that I have used in more than i have ever used 38mm lines. As previously stated i think if CFS appliances had true high pressure pumps then HP lines would be more effective and efficient and therefore used far more often compared to 38mm lines....
My thoughts only....
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I think skirkmoe's comment has merit, maybe have 50mm hoses as standard stowage on the type 2 pumpers??
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Well i dont know about you but i thought when you force 64mm worth of water into a 50mm hole the water would have to speed up therefore giving you more pressure at the tip...
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What you have to remember is that MFS appliances have true High pressure lines which put out the same amount of water as a 38mm line therefore they just use H.P lines and not 38s. They use 50mm lines purely as a working length on the end of 64mm lines to make it easier to handle. Using the 50mm hose loses very little volume and increases pressure.
So in answer to your question no they shouldn't be on any other appliance other than a pumper.
This is probaly the best comment of the thread. Unless you have actually used it then you probaly wont see a need for it.
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Tiller man is correct with the increase of pressure. The best example is a garden hose that you put your finger on the end where you get way more pressure but much less volume. or just a branch where you set the LPM to 19 and there is more pressure.
So essentially a 50mm hose is only use full on pumpers with the extra pressure. Do they require any less strength to use by your self than a 64mm?
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You put your finger over the end of a 64mm, 50mm and 38mm hose line and tell me the difference. While your at it take a photo and post it to SAFF.
Your ill informed assumption is completely wrong. Smaller hose lines do not increase pressure at the action end.
You don't need any general solution to the Navier-Stokes equations. Just a simple energy balance. Perhaps consider Bernoulli's equation.
http://en.wikipedia.org/wiki/Bernoulli%27s_equation
Its all about pump output (Pressure vs Volume relationship) and hose line impedance. While the diameter of the hose is a limiting factor in pump output volume it is completely incorrect to say that reducing hose diameter increases nozzle pressure (both of you are completely wrong).
For the same material smaller hoses do have higher bursting pressure but this is a different matter all together.
The main issue here is a trade off between internal hose friction and pump end pressure vs ease of handling (both weight and flexability).
PS If you do have for mentioned general solution to the Navier-Stokes equations please get in contact with me.
This has been another public education message from RHIT (Royal Hicksflat Institute of technology). Making saff a slightly less stupid place to be.
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**Edit - First statement was dodgy**
If we are looking at a simplistic view.
If you try and force the same volume of something into a smaller space the pressure exerted to achieve this will increase...
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Without graphics this is probably going to go over some people. Fluid dynamics is a second semester first year subject at RHIT requiring prerequisites of statics and dynamics. If you like fighting fires or watching day time TV stop here and go read some "funny" pager messages, or dig up a thread from over a year ago with a post including the phrase "I haven't heard anything lately hows that going now" or add a smiley face.
If you try and force the same volume of something into a smaller space the pressure exerted to achieve this will increase...
Correct. To obtain the same volumetric flow rate through a smaller diameter requires higher pressure PUMP end. But this does not equate to a higher pressure nozzle end for the same nozzle and volumetric flow rate (which is what they were talking about).
A particular nozzle setting and flow rate will require a particular pressure differential hose side to atmosphere side. So for the same flow rate and nozzle geometry this pressure differential across the nozzle is exactly the same regardless of hose size or type (both static and dynamic pressure).
With the pressure on the hose side of the nozzle (no matter the hose size) now fixed lets start talking about hose loss (friction) and flow energy (pressure volume) and kinetic energy from the pump to the hose side of the nozzle.
The smaller the hose the higher the pressure required to produce the velocity in response to the reduction in cross sectional area for the same volumetric flow rate.
However this is negated by our fixed nozzle outlet cross sectional area (and velocity). This is based on the fact all the flow energy (gage pressure based) will be converted to kinetic energy (the water jet basically at atmospheric pressure) no matter the hose size.
But the higher velocity required in the smaller hose to obtain the same volumetric flow rate increases friction and viscous forces. This is what increases pressure drop between the pump and the nozzle. As the hose side nozzle pressure is fixed, PUMP pressure must increase to obtain the same volumetric flow rate.
So the at the end of the day for the same flow rate and nozzle geometry the frictional loss is the key.
Slightly different story for fixed PUMP pressure and nozzle geometry
But the end result is about the same being that there is no increase in effective pressure with reduced hose diameters. Although the burst pressure may be higher depending on construction.
The comment
"i thought when you force 64mm worth of water into a 50mm hole the water would have to speed up therefore giving you more pressure at the tip..."
Partly recognises the concept but completely miss understands the application of static and dynamic pressures.
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Has anyone ever told you that you are a tool!
If you think this is such a stupid place to be then why are you here?
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it all reverts back to BFF1 :-P
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Shame they don't offer communication subjects at RHIT, where you learn not be such a prat while sharing information.
I hadn't heard of the RHIT, I thought it was the State Hicksflat Institute of Technology. (You know how much I love my acronyms....)
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Yeah well we all think your great but it would be nice if you could actually write it in lay terms so that we can all learn something...
So what you are saying is if i set my pump to 1000KPA with 2 lengths of 64mm hose coming off 1 outlet with a TFT branch on full and then replace the 64mm hose closest to the nozzle end with a 25mm hose still with the same TFT branch on full there will be no difference in pressure at the tip?
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there will be no difference in pressure at the tip?
You started talking about constant volumetric flow rate "when you force 64mm worth of water into a 50mm hole" and the nozzle pressure "therefore giving you more pressure at the tip" previous answer was based on this.
ie the situation where the flow rate remained constant and in that case yes, the nozzle end pressure is the same no matter the hose size. Ie it takes the same pressure at the NOZZLE to drive the same amount of water out of it. However the PUMP pressure will need to be much higher with the smaller hose to get the same NOZZLE end pressure and flow rate.
(layman: smaller hose, same flow rate, same nozzle pressure, higher pump pressure)
However your question NOW relates to constant PUMP pressure. Which is a different situation. In that case volumetric flow rate will change. This is because in the smaller hose the water will travel faster and result in higher frictional pressure loss. So in this case NOZZLE pressure will drop which is what most would expect. But your initial post said "loses very little volume and increases pressure" which is wrong.
(layman: smaller hose, same pump pressure, lower flow, lower nozzle pressure )
It's a simultaneous equation type problem. As the operation point of the hose system is the match between the pump output and hose line impedance. Things get even more tricky when a TFT is involved as they generally have self adjusting variable geometry.
Your statement
"water speed up therefore giving you more pressure at the tip..."
confuses static and dynamic pressures. Think about a venturi like the ones used in the direct induction foam branches. They actually use a constriction to make the water flow faster and a pressure low enough to draw the concentrate up from the drum (lower then atmospheric). So yes the greater the velocity the greater the difference between the dynamic pressure and static pressure. But smaller hoses doesn't equate to more pressure at the NOZZLE.
Anyway when Ive got a moment I may knock up some diagrams and stuff and post them somewhere on SAFF that may be a nice reference for people.
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so essentially the Pressure measured at the pump end can be different to the pressure at the Branch end.
How come certain pumps are advertised as 3800 LPM @ 1000 kPa, 750 LPM @ 4000 kPa, 380 LPM @ 6200 kPa which is saying more volume can be moved at lower pressures.
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This is all very interesting but in my time as a water squirter it never matters. If you need more pressure or volume you ask the pumpy for more - which they give you if they can. If the hose and pump configuration you are using doesn't have enough flow to overcome the heat release of the fire then add more hoses/pumps.
Let's keep it simple a fire ground is not the place for volumetric pressure this and that. I like training that is real world, practical and easily understood.
There is a place for this depth of understanding and I commend anyone that has it. Most fireys I have ever met would struggle with most of the scientific explanations above. And then they would say to me why does it matter. :-D 8-)
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Got to love common sense!!!!
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Here Here....
The main thing is they are good hoses to work with if you have the appliance to utilise it...
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How come certain pumps are advertised as 3800 LPM @ 1000 kPa, 750 LPM @ 4000 kPa, 380 LPM @ 6200 kPa which is saying more volume can be moved at lower pressures.
Its related to whats commonly known as a pump performance curve. Pumps can be optimised for different performance primarily by the shape and dimensions of the impeller, ie radius, thickness, vain spacing, vain curvature. All this results in a different pressure performance relationship, one coming at the expense of the other. Usually pumps are tuned for optimum performance/efficiency at one particular setting. While were not too fussed about efficiency its a very critical factor when your using pumps in your business to get a pump optimised to the pressure/volume required.
If you look at just about any of the pump suppliers web sites they have them (darley etc). Even domestic pumps like onga have them. Many of the performance curves just give the performance at max RPM. The pumps we use (and many modern electric industrial pumps) have variable speed so there is another dimension to the curve really making it a 3D surface. Then there are additional corrections required based on pump inlet pressure etc.
Firefighters are primarily interested in what volume they can get at hose rated pressures. So if the pump has been matched up with the correct motor/gearing it should be able to provide that particular volume at that particular pressure.
Let's keep it simple a fire ground is not the place for volumetric pressure this and that.
Many fire services think otherwise. Thats why REAL pumpers have all this instrumented and displayed on the pump panel and in some services they train members to a higher level of understanding.
While volunteers don't do it much these days its also useful for appliance design. I bet the Burnside crew have spent many an hour flicking through manuals to get the pump they think they deserve on their new appliance (lets call it 441a)
Its also a useful part of planning. Lets say you expect that there will be 5 air tractors flying in and out of a nearby airstrip, each with a 3000L load on a 6 minute turn around and your going to bomb all day long dawn to dusk. Is the current pump capacity at the field sufficient? Do you need a pump that a local farmer has offered? Do you need to ship one from Adelaide overnight? or just commit an appliance to sit there and have one less on the fire line?
On the upper end most large industrial fires would have a team of engineers calculating numbers and equations all day long. How much water is going on, how much run off will there be, how to contain it. If your putting so much water onto a ship how long till it sinks or becomes unstable etc etc. Firefighting is half art half science.
I like training that is real world, practical and easily understood
Trial and error can be an expensive and dangerous pursuit. Understanding is critical in what we do so we can adapt to the situation to optimise the outcome without having to try the other umpteen options.
In the fire service we should start off as recruits knowing how and progress to why. Most national accreditation based learning doesn't really progress beyond how as it is considered unnecessary. However failure to go beyond how results in lack of innovation as people just do things as thats the way things have always been. While not everyone has to go beyond how the majority should to some extent.
Most fireys I have ever met would struggle with most of the scientific explanations above"
Indeed but this doesn't mean they shouldn't be exposed to it from time to time even if they don't understand it fully. God forbid we should ever think and just trust that those higher up in the system are thinking for us.
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Thanks for that explanation
It is good that CFS generally won't have to combat ship fires and other fires that require huge equations but watching your runoff is important.
just a quick poll if CFS was to put a course on where you could learn all this stuff would you go? I would like to but I would probably forget it all the next day.
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Isn't it 52mm? :lol:
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Um you use it don't you> :?
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Yes the MFS use 52mm hose, the yellow ones.
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That forgetful you need to colour code the hoses?
:lol: :lol: :lol:
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I was just being facetious, devil's advocate if you will, pointing out the 2mm discrepancy :wink:
Don't say just yellow hose if you want 52mm Ath, cos I might bring you some 25mm lay flat instead :lol:
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Well you wont find any layflat on our appliances. Only on the white ones..lol.
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And the yellow ones :lol:
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Oooohh can we steal the white hose? It will match our truck!
:lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:
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It only stays white until you go to a fire :-P
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You put your finger over the end of a 64mm, 50mm and 38mm hose line and tell me the difference. While your at it take a photo and post it to SAFF.
Your finger may not do much but what about sticking a nozzle on the end of the hose and tell me what that does to the pressure brainiac!
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*Yawn* Its been discussed already. Learn to read, when you get to high school study physics, then come back to the forum with anything you don’t understand.
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I started reading it then found it to be a whole heap of dribble so didnt bother continuing.
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And anyone who uses the term "layflat" doesnt know their terminology for fire hose.Its a slang term which the fire services have adopted
Remember its either percolated or non percolated hose
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Relating to hicks flat's comments on the previous page about flow rates etc.
Re-reading the initial statement about forcing 64mm work of water through 50mm increases pressure is correct. When pumping volume, the larger the hose, the less pressure required for the same volume/flow rate, as hick correctly stated. however what the initial comment meant was that if you had fixed pump pressure and branch flow rate on a 64mm line, and you restricted the flow (ie adding a 50mm working length) the pressure inside the hose would increase if nothing else changed. Same as when you knock off a branch, the pressure inside the hose increases (except on a smaller scale as the restriction in flow is minimal)
To explain in a tangable fashion: (figures are not accurate - demo only)
A 64mm hose has a flow rate of 400GPM at 700kPa
A 50mm hose has a flow rate of 400GPM at 800kPa
A 200mm hose has a flow rate of 1500GPM at 700kPa (if the pump could do it!)
In lay terms, to achieve the same volume: the smaller the hose, the higher the pressure.
to achieve a flow rate of 400GPM in 50mm hose, Pressure would have to be 800kPa.
This is based on a branch with fixed flow rates, non adjustable etc (as in basic, hick)
I am also familiar with fluid mechanics my friend, and by over-complicating a simple issue, you have not only made your self seem like a jerk, but actually shown your stupidy in not being able comprehend the initial meaning of the statement. Brainiac...
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Re-reading the initial statement about forcing 64mm work of water through 50mm increases pressure is correct.
It increases pressure PUMP end, but the poster that kicked this all off believed it increased pressure BRANCH end which it does not. Tillerman confused static and dynamic pressure and the significance that each plays.
however what the initial comment meant was that if you had fixed pump pressure and branch flow rate on a 64mm line, and you restricted the flow (ie adding a 50mm working length) the pressure inside the hose would increase if nothing else changed. Same as when you knock off a branch, the pressure inside the hose increases (except on a smaller scale as the restriction in flow is minimal)
To maintain the flow rate with the 50mm as the second line then the PUMP pressure would need to be increased. The pressure at the end of the 64mm would increase but the pressure at the end of the 50mm (at the branch) would be the same for the same flow rate, not higher as stated by the original post.
In lay terms, to achieve the same volume: the smaller the hose, the higher the pressure.
to achieve a flow rate of 400GPM in 50mm hose, Pressure would have to be 800kPa.
This is based on a branch with fixed flow rates, non adjustable etc (as in basic, hick)
You are perfectly correct there and consistent with my previous posts being that the pressure PUMP end needs to be higher to get the same amount of water out the other end. This however does not result in higher pressure at the BRANCH end for the same volume flow.
I am also familiar with fluid mechanics my friend
Congratulations.... even though you do seem a little lost. Its covered in most science, maths and engineering courses so its not exactly difficult to come across while studying.
you have not only made your self seem like a jerk, but actually shown your stupidy in not being able comprehend the initial meaning of the statement. Brainiac...
well my initial statement was:
"So the hose increases pressure? There I was thinking it was the pump."
And that is still 100% correct. You can have all the hose you want, but the pressure/flow/energy comes from the pump (neglecting gravitational effects).
Next I quote for you what tillerman said:
Well i don't know about you but i thought when you force 64mm worth of water into a 50mm hole the water would have to speed up therefore giving you more pressure at the tip...
I didn't think you could miss comprehend that, but you are from Burnside. If you know fluid dynamics like you say you do, then you should know that statement is incorrect. Pump end pressure increases but "tip" pressure remains the same for the same flow rate.
I put it to you that you have over simplified the problem and not only made your self seem like a jerk, but you've actually shown your stupidity (not to mention miss spelling stupidity) in not being able comprehend the initial meaning of the statement.
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And anyone who uses the term "layflat" doesnt know their terminology for fire hose.Its a slang term which the fire services have adopted
Remember its either percolated or non percolated hose
Same as my gripe about the 'Hooligan' tool but everyone still says it SA Firey
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Hick
I agree with your information mate, but did not like the way it was initially delivered. I cannot speak for every one here, but i can hazard a guess to what they thought also.
The comment about the brigade I'm from is a bit unnecessary, and shows a lack of anything else to say.
Thankyou for the tip with the spelling too. I'll try harder in future. I'm still on an "A" though aren't I? :-)
No hard feelings
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NSWRFS use 52mm blue hose nice :roll:
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NSWRFS use 52mm blue hose nice :roll:
They get more money than we do Bill :lol: :-P