Ventilation fans

[mike barnes]

Over the last 10-15 years,  CDG folk have made small oxygen re-breathers using modern DIY available kit. I was never one of these people, hence I'm still alive. Rather than scrub the air as mentioned, why not just scrub the air the digger is breathing. A small piece of drain pipe filled with scrubber. Hole to let air in, mouthpiece to breath from. Used intermittently, it could save headaches and cut down on CO2 at dig. But, it may be way to much resistance, I think the term is WOB, Work Of Breathing, to be useful. Maybe Dr Dunc or some other re-breather user could comment.

 

[khakipuce]

When I worked in tunnelling we used "air movers". Needs a compressed air supply but these things are really effective, and if you can afford enough compressor hose you can use them anywhere. They work by blowing compressed air in at the narrow point of a venturi which causes a large volume of air to move through the venturi. As some said earlier in the thread the aim in mining/tunneling is to keep the air moving and mixed rather than trying to suck the bad air out.

Air movers http://secure.thorite.co.uk/Moving-and-air-handling-equipment/HMC-Brauer-air-movers/c-1-318-764/

Remember that the same rule that says you can only "suck" water up a certain distance applies to air too. Air being less dense means that you can suck it up a lot further but your pump becomes less effective the greater the suction head. Better just to get it moving, many tunnels don't need forced ventilation as the muck removal trains running up and down push air in and out.

 

[Bit_Twisted]

Just read the thread and the first thing that came to mind was some sort f compressed air air mover... Only a little late with the idea.

The main problem seems the amount energy needed to move a fair bit of air, and hence the size of the storage media (batteries etc)
There's lots of energy stored up in a diving bottle,
Using a small directional flow of high pressure air to drive air forward down a much larger pipe should be 'relatively' simple in engineering terms,
although most experienced divers will have tales of what can co wrong, so might need a bit of thought.
Note. The Brauer units operate at a 'much' lower pressures and so would need some sort of high flow pressure regulator...
Still very interesting the use of a ring venturi probably adds a fair bit to the efficiency.

 

[Graigwen]

CO2 is a compressible gas so unfortunately no syphon is possible. you can't syphon compressible fluids since compression of the fluid will occur in the pipe rather than flow. Also the gases will just mix. 33 feet suction head of water causes it to shear (cavitation) and break the syphon. Different fluids have different density and viscosity so will shear at different suction heads. A gas will effectively shear with no suction head which means no syphon. I agree with the vacuum idea though.
James

All you need to do is remove some of the CO2 so that the air breathed does not contain more than about half a percent of CO2.

If it was just a short straight sloping passage with CO2 pooling at the face, sucking out might be done with a rag 'n' chain pump. All that would be needed at the other end would be to discharge the air where the CO2 would sink away where it would not do any harm. One problem with rag 'n' chain pumps is that the internal friction makes them much harder to pull through than you would expect even if well greased. Also anything other than a short straight run causes problems with the chain return.

On the other hand, perhaps blowing in air intermittently by bellows and a bit of fanning in the working face would be simpler and a lot less tiring.

.

 

[manrabbit]

Any one tried using an air bed pump? These are designed not just to move air but also create pressure. The one I have will pump our double air bed up with me lying on top with out any problem at all. They're cheap enough too. Run it off a few Yuasa type dry cell batteries, small enough for every one to carry one to the dig site and carry out for charging again.

http://tinyurl.com/yfgeerf

Huw

 

[estelle]

I seem to recall that the BEC used to use a domestic vacuum cleaner on the surface with a long hose, powered by a generator to remove CO2. I think they took photos and sent them to the manufacturer who sent them a n ew vacuum for free.

yeah that was me who did that as i worked for a panasonic partner at the time and when i sent panasonic the pics of us using the vacuum cleaner to remove co2 from Barrow Rake attached to a long pipe and they very kindly sent us a new vaccum cleaner for originality! LOL

 

[4bags]

Same set-up is currently in use at Gibbets Brow - a Henry vacuum on the surface, powered by a generator, and about 40m of flexible hose, which runs down 2 pitches to the dig-face. It's amazing how quickly it gets rid of CO2 and pulls fresh air in from the entrance (note: don't put the generator too close to the entrance or you could end up pulling in carbon monoxide from the generator which could be far worse than CO2! )
The suction at the end of the hose is as good as it is at the hoover end and it's even strong enough to pull small bits of mud and grit to the surface, as you can hear them rattling up the tube! Probably not an effective digging method, though!
And additional bonus is that the pipe can be used as a voice-tube to speak to the surface crew when the hoover isn't connected, or for them to speak to the diggers... i.e. when it's time for 

 

[potholer]

Removal of exhaled air seems like a more efficient use of power.
In a recent ~30degree downwards-sloping dig, dug out to ~1m square, there was a definite outward flow of air along the roof, and fresh air back down in along the floor.

Even with CO2 being denser than air, it's being exhaled along with warmed air and water vapour, (caver breath does seem to rise in cave air rather than falling).
Heat from the digger's exertions will also create some upflowing of air around them.
Collecting/removing air from roof level seems likely to take a good proportion of the exhaled air away, even at fairly low flow rates.

The sloping dig has now gone horizontal, and ventilation has become a definite issue there, so I'm watching this thread with interest.

 

[exsumper]

Suck or Blow?. When Jake and I first used the BEC Vacuum at Barrow Rake, we installed a 2 1/2 inch pipe to the bottom of the 10mtr dig and it worked very effectively. A five minute run beforehand cleared the CO2 to allow a sessions digging. The reason Suck works better than Blow is down to basic physical principles. CO2 is heavier than air, If you use a vacuum you actually remove the CO2 causing the problem from the shaft, the only thing that replaces it is fresh air entering the shaft to replace the CO2 removed. In a shaft or downward inclined dig, yes the blower supplies fresh air to the dig face, but it only displaces or dilutes the CO2, (and you have to keep it running for the whole digging session). Once you switch the blower off,  the remaining CO2 runs straight back into the dig.
Hope this helps.

 

[littletitan]

OR.....pack the dig in and find one with a draught.

 

[Maisie Syntax]

How about sub-letting the dig to the Pembertons until breakthrough point, then jump in for the glory?

 

[jarvist]

Any one tried using an air bed pump? These are designed not just to move air but also create pressure.

I think this makes the sensible 'next step'. They seem to boast around 10L/s and 0.05ATM, though these are almost certainly figures from opposite ends of the performance curve!
Will certainly be many times more effective than computer fans, which as pointed out by Nick, won't push any pressure at all.
Just a ?10 investment, runs off your current 12V setup, and a bit of duct tape to fit.

In terms of your piping setup, you're loosing almost all the pressure difference in that final section of thin 1-inch pipe.

 

[Jams]

manual air bed pump, depends on time pub closes!