RickRick
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| posted on 31/7/13 at 04:55 PM |
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naah we're in the middle of a field, only thing close is kendal ski slope.
other clubs have used gravel, but only in short lengths to mark corners. another club a long time ago, put blocks of wood inside the hose, 2"
block every 6" or so, but they smashed cars too easily
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Slimy38
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| posted on 31/7/13 at 04:57 PM |
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quote:
Originally posted by loggyboy
Some very basic maths
4" hose = 0.008107m2. over a 20m length thats 1621m3 of air, which is 1621000 Litres. So even trying to get half that ino to the hose so its
looks slightly inflated will be a mamouth task.
[Edited on 31-7-13 by loggyboy]
I think that's wrong isn't it? 0.008107m2 by 20 m = 0.162 m3? 1000 litres per cubic metre, 162 litres.
Think about a 2 litre bottle, that's about 4 inches diameter. How many bottles could you fit end to end to get to 20 metres?
And think about the size of an average bouncy castle, they can be inflated in less than five minutes and are huuuuge!!
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plentywahalla
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| posted on 31/7/13 at 06:23 PM |
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I am not sure how the fire hose would stand up to the hot exhaust gases. They are normally synthetic rubber laminated to a woven nylon outer. On
marine engines the flexible rubber exhaust hose is a much heavier construction and cooled by the injection of water, if this water flow stops then the
rubber delaminates.
Also did the OT not say that the solution had to be portable i.e 12 volt. I thought all bouncy castle pumps are 240volt as they need to run
continuously to keep the thing inflated. Blowers are basically centrifugal pumps which are not very good when subjected to back pressure, eventually
they just stall. The problem with inflating a very long length of fire hose is that the resistance of the air moving along the hose and inflating it
as it goes means that the pressure at the inlet will need to be quite high. The outlet of the bouncy castle pump will need to be initially constricted
down to 4" anyway so I suspect that the pump would inflate the first dozen or so metres and then it will stall.
Its all to do with the internal volume V the surface area.
Rules are for the guidance of wise men ... and the obedience of fools. (anon)
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britishtrident
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| posted on 31/7/13 at 06:33 PM |
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quote:
Originally posted by RickRick
Hmm that does sound like a poo ton of air!
i think i'll bodge the roll i have at home with some blocks of wood and clamps to seal the ends and try blowing it up with the 12v airbed blower
i've got, that chucks out a reasonable amount if thats going to take half hour rather than a minute or 3 it might be that it's just not
practical
Those little pumps take a good few minutes even to blow up a an air bed , one these
Earlex Spray
centre will blow up an air bed in about 5 seconds.
Only downside is they are 230v take about 500watts and the air output is quite warm cos that where the 500 watts ends up.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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gremlin1234
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| posted on 31/7/13 at 06:58 PM |
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quote:
Originally posted by plentywahalla
I am not sure how the fire hose would stand up to the hot exhaust gases.
I would have thought a fire hose was designed to be used in hot environments.
I also found that some rescue services do inflate hoses with air (typically from scba bottles) for ice and water rescue.
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britishtrident
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| posted on 31/7/13 at 07:09 PM |
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quote:
Originally posted by plentywahalla
I am not sure how the fire hose would stand up to the hot exhaust gases. They are normally synthetic rubber laminated to a woven nylon outer. On
marine engines the flexible rubber exhaust hose is a much heavier construction and cooled by the injection of water, if this water flow stops then the
rubber delaminates.
Also did the OT not say that the solution had to be portable i.e 12 volt. I thought all bouncy castle pumps are 240volt as they need to run
continuously to keep the thing inflated. Blowers are basically centrifugal pumps which are not very good when subjected to back pressure, eventually
they just stall. The problem with inflating a very long length of fire hose is that the resistance of the air moving along the hose and inflating it
as it goes means that the pressure at the inlet will need to be quite high. The outlet of the bouncy castle pump will need to be initially constricted
down to 4" anyway so I suspect that the pump would inflate the first dozen or so metres and then it will stall.
Its all to do with the internal volume V the surface area.
I am 100% sure your wrong on that one the, any restriction due to the hose being initially flat does not reduce final equilibrium pressure only the
rate of flow and rate of pressure increase at the blanked off end.
The hose only needs a sufficient volume of fluid (air/liquid) at a tiny amount of pressure above atmospheric to inflate to its working round
cross-section (ie maximum CSA for its circumference) as the leakage should be minimal once inflated only a small volume flow rate of gas will be
required to maintain the inflation.
Fluid (gas/liquid) pressure acts equally on all internal surfaces so if the pressure is 0.25 bar at the inlet the fluid will flow along the
hose until 0.25 bar is reached at the blanked off end and equilibrium reached.
It is exactly the same a filling a fixed volume such as an air tank or car tyre from a compressor air receiver through a restriction (Throttling),
the restriction slows the rate of pressure increase but doesn’t alter the final equilibrium pressure. Think of blowing up a car tyre as the
pressure in the tyre increases the rate at which the pressure in the tyre increases slows but if you leave the airline connected long enough the tyre
will eventually reach the full pressure in the air receiver tank, I might add a few tyre fitters have been killed over the years because of this.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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nick205
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| posted on 31/7/13 at 07:46 PM |
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The 230v issue could be overcome with a decent 12V to mains inverter, widely available and not expensive.
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plentywahalla
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| posted on 31/7/13 at 08:47 PM |
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quote:
Originally posted by britishtrident
I am 100% sure your wrong on that one the, any restriction due to the hose being initially flat does not reduce final equilibrium pressure only the
rate of flow and rate of pressure increase at the blanked off end.
The hose only needs a sufficient volume of fluid (air/liquid) at a tiny amount of pressure above atmospheric to inflate to its working round
cross-section (ie maximum CSA for its circumference) as the leakage should be minimal once inflated only a small volume flow rate of gas will be
required to maintain the inflation.
Fluid (gas/liquid) pressure acts equally on all internal surfaces so if the pressure is 0.25 bar at the inlet the fluid will flow along the
hose until 0.25 bar is reached at the blanked off end and equilibrium reached.
It is exactly the same a filling a fixed volume such as an air tank or car tyre from a compressor air receiver through a restriction (Throttling),
the restriction slows the rate of pressure increase but doesn’t alter the final equilibrium pressure. Think of blowing up a car tyre as the
pressure in the tyre increases the rate at which the pressure in the tyre increases slows but if you leave the airline connected long enough the tyre
will eventually reach the full pressure in the air receiver tank, I might add a few tyre fitters have been killed over the years because of this.
You are entirely right assuming the air is delivered from a positive displacement pump such as a compressor. The pressure can rise to overcome the
frictional losses and the energy required for inflation until inflation is achieved. A centrifugal fan type pump will only achieve a pressure ratio,
inlet to outlet, of 1.1:1 to 1.2:1. that is a pressure of 1.5 to 3 psi. A back pressure above that will cause the air on the low pressure sides of the
impeller blades to cavitate and the fan will stall. A 100 metre length of 10 cm diameter hose has a length diameter ration of 1000:1 and will require
a significant pressure differential along its length as it inflates, only when it is inflated will the pressure equalise. 100 metre length of fire
hose weighs about 66 kilos and the air pressure will need to raise this into a circular form and continue to support most of this weight by
maintaining pressure at the inlet. Remember The OT was talking about inflating 'miles' of hose.
Therefore I believe I am right to say that somewhere along its length the pressure required for continued inflation will eventually overcome the
efficiency of the fan and it will stall.
Your theory and my theory are just that, and can only be proved in practice, but I am willing to bet a pint on it!
Rules are for the guidance of wise men ... and the obedience of fools. (anon)
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Ninehigh
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| posted on 1/8/13 at 07:39 AM |
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You could cut holes at intervals, stick several tyre valves to it and have a whole bunch of you using the bog standard tyre inflaters. They've
not got much airflow but 20 of them will have!
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richardm6994
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| posted on 1/8/13 at 10:22 AM |
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use an electric supercharger! They're 12v and I hear they can generate 3psi of boost on a 2ltr engine 
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gremlin1234
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| posted on 1/8/13 at 10:49 AM |
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leaf blower?
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loggyboy
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| posted on 1/8/13 at 11:01 AM |
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LOL at my maths fail....
Mistral Motorsport
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britishtrident
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| posted on 1/8/13 at 11:50 AM |
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2.5 psi is actually quite a lot of pressure, the equivalent of a 1kg bag acting on the area the size of a 10p coin.
Modern fire hoses are made from very light weight, thin and flexible material nothing like the WWII era canvas hoses.
There would need to be a decent bleed off to allow enough air flow to cool the compressor
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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MikeRJ
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| posted on 7/8/13 at 07:23 AM |
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quote:
Originally posted by plentywahalla
Blowers are basically centrifugal pumps which are not very good when subjected to back pressure, eventually they just stall.
Remember that a turbocharger is a centrifugal compressor! They manage to generate a pretty decent amount of pressure and airflow.
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richardm6994
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| posted on 7/8/13 at 08:10 AM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by plentywahalla
Blowers are basically centrifugal pumps which are not very good when subjected to back pressure, eventually they just stall.
Remember that a turbocharger is a centrifugal compressor! They manage to generate a pretty decent amount of pressure and airflow.
yeah but at what rpm!!!
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mangogrooveworkshop
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| posted on 31/10/13 at 03:30 PM |
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why not use expanding foam inject a few blobs every meter or so
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coyoteboy
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| posted on 31/10/13 at 06:05 PM |
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He wants to be able to roll it away again I think?
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SteveWallace
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| posted on 31/10/13 at 06:31 PM |
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I've used a leaf blower to inflate quite large paddling pools before. All I did was tape a thick plastic bag to the outlet of the blower and
then cut a small hole in a corner of the bag and tape an adaptor for the valve into the hole. It worked a lot better than I was expecting.
Of course, it doesn't get around the problem of needing mains electricity unless you have a petrol driven (or a rechargeable - if they exist)
blower.
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