LocostBuilders - powered by XMB

Blowing up Fire hose

RickRick - 31/7/13 at 06:54 AM

For our RC car racing club, we've aquired miles of fire hose about 4" dia in various lengths, and we want to inflate it. One end is sealed. we also want to be able to inflate it fairly quickly, and we don't need it rock hard, just so it holds its shape so was thinking more along the lines of an 12v airbed pump rather than a car tyre pump. we're outside too so 12v only

snakebelly - 31/7/13 at 07:03 AM

you'll be there all day with a 12v pump, if I was you I would find a local dive shop or industrial gas supplier and invest in a gas bottle and get them to fill it for you, it doesn't need to be filled to max pressure but with some sort of regulator and a piece of hose you will be able to fill them in seconds.....instead of hours :-).
thinking about it if you have access to a proper compressor you might even be able to fill it yourself with enough air to do the job?

ashg - 31/7/13 at 07:05 AM

bouncy castle fan.

Davey D - 31/7/13 at 07:26 AM

As above, id go with a fan from a small bouncy castle.

plentywahalla - 31/7/13 at 07:44 AM

I doubt a bouncy castle fan will even inflate it, they are very low pressure.

I would agree with the plan of stored pressure. Get an old propane gas cylinder, vent all the gas out and pressurise it from a compressor.

whitestu - 31/7/13 at 07:51 AM

I was expecting an expolsion!

Bluemoon - 31/7/13 at 09:29 AM

quote:
Originally posted by whitestu
I was expecting an expolsion!

You might get one, depending on how they do it!

Compressed gas in a cylinder gets my vote (this could just be a portable compressor with a reciver of sufficient volume/pressure.

i.e. total volume of gas to fill hose = cylinder volume X preasure in bar

So long as the volume is say twice that of the hose you should get two shots at filling the hose up..

Dan

loggyboy - 31/7/13 at 10:01 AM

I doubt anything simple would create the type of pressure you would need. Could you not insert 1-2m lengths of pipe lagging that could be slid along to the desired location, then you could fold the hose at 1/2m lenghts when clearing away.

MikeRJ - 31/7/13 at 10:06 AM

You'll need a big compressed air cylinder to inflate a decent length of 4" diameter pipe. e.g. A typical scuba bottle will hold around 2300 litres of air, which is only enough to inflate about 280 meters of pipe to atmospheric pressure. You'd probably want a bit more than atmospheric pressure to make the pipe rigid as well.

Likewise using a compressor is a total non-starter as the airflow is far too low. A 240v compressor with a 3hp motor might give 11cfm, which would take 1 minute to inflate 38 meters of pipe.

High flow and low pressure is exactly what the OP needs, and this is exactly why a bouncy castle fan or similar is the best solution. The little fans used for inflating air beds would take hours, and probably burn out long before they finished.

[Edited on 31/7/13 by MikeRJ]

Bluemoon - 31/7/13 at 10:06 AM

quote:
Originally posted by loggyboy
I doubt anything simple would create the type of pressure you would need. Could you not insert 1-2m lengths of pipe lagging that could be slid along to the desired location, then you could fold the hose at 1/2m lenghts when clearing away.

What do you mean by "type of pressure", if you only need it "floppy", it will be atmospheric pressure inside puss a very small amount to hold the pipe wall up, so long as you don't have leaks it will take very little.. Also I would guess fire hose is wanted to make a compact size when packing away...

Dan

britishtrident - 31/7/13 at 10:12 AM

As Bluemoon posted the problem is more volume than pressure what will do the job is the turbine compressor from a DIY HVLP spraygun --Earlex, Bosch, B&Q Performance Power or similar. I use one of these compressors blow up an air bed in a few seconds.
They are all 240v and are rated about 500-600 watts so to convert from 12v you would would need a inverter rated at 1KW+ -- loads on ebay.

[Edited on 31/7/13 by britishtrident]

loggyboy - 31/7/13 at 10:19 AM

Im talking about the weight of the hose. These things are designed to be robust, take huge water pressures, its not like a hot air baloon!

gremlin1234 - 31/7/13 at 10:26 AM

could you fill it from a car exhaust?

Slater - 31/7/13 at 10:43 AM

quote:

could you fill it from a car exhaust?

Great idea, 2 litre engine at 2000 RPM should give 2000 litre per minute of exhaust gas, I think.

1 exhaust cycle per 2 revolutions. Is that right?

dinosaurjuice - 31/7/13 at 10:45 AM

a slightly modified vacuum cleaner motor and a 12v inverter would be way to go i think.

MikeRJ - 31/7/13 at 11:24 AM

quote:
Originally posted by Slater

quote:

could you fill it from a car exhaust?

Great idea, 2 litre engine at 2000 RPM should give 2000 litre per minute of exhaust gas, I think.

1 exhaust cycle per 2 revolutions. Is that right?

One exhaust cycle per revolution on a 4 cylinder 4 stroke engine, and you will get rather more than 500cc per exhaust stroke.

quote:
Originally posted by dinosaurjuice
a slightly modified vacuum cleaner motor and a 12v inverter would be way to go i think.

That's not a bad idea, I have an "Earlex" shop vac that you can attach the hose to the outlet for blowing.

coyoteboy - 31/7/13 at 12:08 PM

You won't need much pressure - I have kitesurfing kites that get 4-5psi in their leading edge (about 4" diameter) and they're rigid enough to use as an edge bumper (they're a plastic tube inside a fabric cavity (hold themselves rigid in 40kt gusts with me hanging from the bottom of the tips).

Bouncy castle fan might do it nicely, compressed air cyl assumes you have no leaks or it'll be flat in seconds, plus you would likely need safety certificates for it if it's an organisation.

RickRick - 31/7/13 at 12:24 PM

Wow this seems to have got you all thinking Thanks

low pressure is all we're after just enough to hold it "full" but not to make it rigid, it's also a lot lighter material than i expected it to be.

We did think about exhausts as there's always plenty of cars, but i think it'll all get a bit of a mess after a few inflates.

i like the paintgun turbine idea, could even be hacked more to run off an rc car motor/battery there getting up towards 1kw now

also the next part of the problem is how to make a sealable opening to inflate / deflate. one end will be perminantly sealed up, but i need to find/make a quick and easy seal for the other end ( or near the end and seal both ends up if needed) that will also allow a decent flow rate

britishtrident - 31/7/13 at 01:04 PM

quote:
Originally posted by loggyboy
Im talking about the weight of the hose. These things are designed to be robust, take huge water pressures, its not like a hot air baloon!

It is exactly the opposite a fire hose simply needs filled with fluid at a pressure very slightly above atmospheric to occupy the volume, with a balloon you need a positive pressure differential stretch the rubber to make the balloon take up its filled shape.

britishtrident - 31/7/13 at 01:07 PM

I have used air bag jacks filled by exhaust pressure works they were very effective but do get very mucky, however my experience was back in pre-cat thse days exhaust gas is much cleaner.

[Edited on 31/7/13 by britishtrident]

coyoteboy - 31/7/13 at 04:16 PM

Indeed, that's a great idea BT - modern exhaust should be pretty clean and easily available. Only minor issue is you may need to "overinflate" initially as it'll cool but with that sort of volume I suspect it'll be fine and cooled by the time it reaches the ends anyway, meaning the drop in volume will be minor as a percentage.

loggyboy - 31/7/13 at 04:21 PM

quote:
Originally posted by britishtrident

quote:
Originally posted by loggyboy
Im talking about the weight of the hose. These things are designed to be robust, take huge water pressures, its not like a hot air baloon!

It is exactly the opposite a fire hose simply needs filled with fluid at a pressure very slightly above atmospheric to occupy the volume, with a balloon you need a positive pressure differential stretch the rubber to make the balloon take up its filled shape.

Try blowing up a baloon with someone sat on it!

loggyboy - 31/7/13 at 04:31 PM

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]

RickRick - 31/7/13 at 04:41 PM

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

karlak - 31/7/13 at 04:48 PM

Any outside taps where you are ?

Fill it with water ? Would also have the advantage of keeping it in place with the weight - although I guess fire hose is heavy anyway. Water pressure could be an issue I suppose as well.

RickRick - 31/7/13 at 04:55 PM

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

Slimy38 - 31/7/13 at 04:57 PM

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!!

plentywahalla - 31/7/13 at 06:23 PM

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.

britishtrident - 31/7/13 at 06:33 PM

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.

gremlin1234 - 31/7/13 at 06:58 PM

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.

britishtrident - 31/7/13 at 07:09 PM

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.

nick205 - 31/7/13 at 07:46 PM

The 230v issue could be overcome with a decent 12V to mains inverter, widely available and not expensive.

plentywahalla - 31/7/13 at 08:47 PM

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!

Ninehigh - 1/8/13 at 07:39 AM

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!

richardm6994 - 1/8/13 at 10:22 AM

use an electric supercharger! They're 12v and I hear they can generate 3psi of boost on a 2ltr engine

gremlin1234 - 1/8/13 at 10:49 AM

leaf blower?

loggyboy - 1/8/13 at 11:01 AM

LOL at my maths fail....

britishtrident - 1/8/13 at 11:50 AM

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

MikeRJ - 7/8/13 at 07:23 AM

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.

richardm6994 - 7/8/13 at 08:10 AM

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!!!

mangogrooveworkshop - 31/10/13 at 03:30 PM

why not use expanding foam inject a few blobs every meter or so

coyoteboy - 31/10/13 at 06:05 PM

He wants to be able to roll it away again I think?

SteveWallace - 31/10/13 at 06:31 PM

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.