Shallow dive gear
- Thread starter Tiger Rag
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Jaguar 25
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More problematic is that you're asking your lungs to expand outwards against a pressure differential of 100 millibars per metre of depth and most people's intercostal muscles are not up to this. Even hanging vertically in the water with a standard snorkel is noticeably harder work - any deeper and you can't breathe in at all.
If that is the case, how do scuba divers manage to breathe?
If that is the case, how do scuba divers manage to breathe?
prv
Well-Known Member
Because the regulator supplies air at exactly the same pressure as the surrounding water.
At ten metres below the surface, a diving regulator will feed you air at two bar absolute. A pipe to the surface would contain air at only one bar, the same as at the surface.
This also means that you will use up your air twice as fast at ten metres - and four times as fast at thirty - because each breath contains twice as many molecules squeezed into the same space. That's (partly) why technical deep wreck divers go down festooned with bottles, and why professional divers (like Rob on the mobo forum) doing an 8-hour shift at 100 metres cannot possibly carry enough air and need to be supplied via an umbilical hose. The pros carry a pair of cylinders on their back for emergency use, but at their depths it only gives them a very few minutes to get to another source of supply.
Pete
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nigelmercier
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The UK agents for the Thomas 907CDC18 Pump (and others) are:
Gardner Denver Ltd
Waterbrook Estate, Waterbrook Road, Alton, Hampshire, GU34 2UD
Tel: +44 (0)1420 544184 DDI: +44 (0)1420 567437 Mobile: +44 (0)7775 701574 Fax: +44 (0)1420 544183
http://www.gd-alton.co.uk
Don't tell them what you want it for though, they refused to sell me one. If anyone gets a price out of them I may be interested.
prv
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John Barry
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lw395
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John Barry's numbers look reasonable to me.
58 litres a minute gives some margin over his minimum 45, which in itself includes a 'worst case' factor in the depth.
I would say that doing something not very physical, it sounds fine while you stay relaxed, but if you were to get tangled and panic you could get in trouble.
Bearing in mind that working under a boat you may have to use ropes to hold you in place, otherwise instead of turning the spanner you simply turn the diver.
From my own experience, cleaning a hull in a drysuit is pretty physical, trying to move a scrubbing brush quickly through water is hard work and awkward.
If you are unfit and inexperienced you can use more air.
As John says, the peak demand in a moment of crisis might be more than the pump can deliver.
I would always advocate doing a diving course. Because it's fun.
58 litres a minute gives some margin over his minimum 45, which in itself includes a 'worst case' factor in the depth.
I would say that doing something not very physical, it sounds fine while you stay relaxed, but if you were to get tangled and panic you could get in trouble.
Bearing in mind that working under a boat you may have to use ropes to hold you in place, otherwise instead of turning the spanner you simply turn the diver.
From my own experience, cleaning a hull in a drysuit is pretty physical, trying to move a scrubbing brush quickly through water is hard work and awkward.
If you are unfit and inexperienced you can use more air.
As John says, the peak demand in a moment of crisis might be more than the pump can deliver.
I would always advocate doing a diving course. Because it's fun.
nigelmercier
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Irrelevant. The usage at depth has already been factored in to the calculation by his statement (in #37) about a 12 litre tank lasting about an hour at shallow depths. This is why his calculations end up with a similar result to yours: 40 litres cf. 35 to 50 litres.
Based on my previous calculations, I wouldn't be happy with much less than 100 litres per minute to give a factor of two safety margin.
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lw395
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From 2m underwater, I'd be happy with an assured route to the surface, a second air supply, or a buddy with a spare reg.
It depends whether you view it as an alternative to scuba, or as one up from ducking under the boat with a snorkel.
It sounds fine, used within its limitations.
But anything running off a battery I would be using it on the basis that it may stop working at any point.
Might be an idea to practice drills for that.
Same as you do for scuba.
fishermantwo
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Any idea what a plausible non-diving use might be, for cover purposes?
Pete
They are made for laboratories, hospital and ambulance breathing equipment. You can also use other diaphragm pumps like those used to inflate dinghies etc. Piston pumps can also be used as long as they are oil less. Just ensure they have 100% run time. Its volume you need and not pressure so much.
If you have 240volts available you can use diaphragm pumps like the SIP Hobby Air 210. These are very cheap. With these you can use a standard second stage regulator un modded. They are high pressure and high volume but you will need a cooling hose for the first metre or so before it connects to the hookah hose. The high pressure creates a lot of heat and normal hose will blow off the fitting. I paid $40 for mine off eBay. Standard regs are common and cheap. Which ever way you go, 12v or 240v, the critical component of hookah gear is the hose. It has to be rated as a hookah hose and made from food grade plastics, the sunlight can not pass through it. The cooling hose also has to be rated for hookah use.
fishermantwo
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One more thing I should mention. If you use a petrol driven pump, ensure the exhaust is well clear of the pumps air intake. For electric pumps as well as petrol pumps have a filter over the intake. I use a couple of layers of pantyhose to keep the flies out!
nigelmercier
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Yes, lab equipment is a good cover.
I wonder if you can buy springs to mod the stage 2 regulator.
prv
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Exactly.
Last summer I cleaned a thick coating of barnacles off my prop just with mask and snorkel, holding my breath. So I wouldn't be worried about the air supply stopping - if it did I'd just pop to the surface.
I imagine you'd get at least a breath out of the hose anyway after the pump dies, maybe more.
Pete
slipknot
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This type of equipment, whilst very basic, does seem to be used very successfully for short spells just under the surface to inspect and scrub off. I also attempt to do this just using a mask and snorkel, and a little help from a assisted air supply isn't going to present any greater risk. I'd be keen to make a unit but need to identify the most suitable diaphragm compressor, both in terms of output and availability. There have been several mentioned in this thread with various outputs ranging from 50l/min to 160l/min. The 50l/min is being used successfully and surely the 160l/min would produce too much and require a regulator. I wouldn't want to get it wrong and waste my money.
fishermantwo
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You always need a regulator although there is a system sold on eBay that uses an aquarium pump and a length of hose to the end of a normal snorkel with an exhaust valve. I would stick with the normal hookah arrangement.
Motor driven compressor hookahs are in wide use by abalone divers in this country and they spend hours on the bottom in their wire cages. The cages are powered by the compressed air as well. In the USA hookahs are used in the gold prospecting industry and their web sites are a good source for parts as well.
bikedaft
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Remember not to hold your breath... (Ok i'm sure you know, but maybe not everyone reading that etc)
Tho you may be ok from such a minimal ascent, fair chance you could be completely isolated should you collapse a lung...
slipknot
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Fishermantwo, your posts are really helpful. The fact that you see so many units in use where you are, and have already put together a home made kit which you use successfully, counters the view here in the uk that you will instantly die the moment your head goes below the water.
My point re the regulator was related to regulating the operation of the compressor (not your mouthpiece regulator) If you have a compressor which delivers more than you need, what happens to the excess. For this application would you need a compressor that cuts in and out on a pressure trip. If you size the compressor too low you have a completely different set of problems.
Fisherman two, I understand that the mouthpiece regulator will deliver air to you at the appropriate rate. I'm still not sure how the same design of system deals with the difference in capacity between the compressor you use which delivers 50l/min and other 'homemade' units like the eBay one delivers 160l/min. Once I get that I would be more comfortable sizing the compressor and sourcing one locally.
nigelmercier
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It pressurises the hose, which is what you need.
mjcoon
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Cannot there be a simple pressure release valve that bleeds off the excess? Like a pressure cooker or lots of other devices (engine oil etc)?
Mike.
slipknot
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I see that it would pressurise the hose, and the hose would act as an accumulator. But if the compressor keeps running what would stop something bursting?
Is there a pressure that the system should maintain, and how should it do that?
Is there a pressure that the system should maintain, and how should it do that?
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