Could a snort pump recharge an onboard airsupply for blowing the tank?

[Slats]

David,
I know the gas storage copper bottles on board the SDs are designed to house liquid propel, but was wondering if they could be reconfigured to house a small amount of air where by the air was drawn via a Caswell snort pump?

If so the SD could consist of a free flood tank with a snort pump to clear it at PD, and small air charge that could be utilised for blowing the tank and charged via another snort type pump either on the surface or at PD.

Of course if this was possible, the risk with this is having a failure in the charging of the air supply and diving the boat deep there after and having no tank clearing blow available.

J

[Subculture]

Those little pumps, which are diaphragm based are really only capable of pumping to about 12-14psi above atmospheric pressure. Even then the flow rate drops off a cliff face once you begin to push more than single figures in pressure.

Therein lies the rub using these for pressurizing air for storage- low pressure will only blow your tank at moderate depths, and will need a huge reservoir.
You could use the dive module/cylinder as a storage vessel, but it would need modification- you would need to tie the endcaps together to stop them popping out etc. Another disadvantage would be extra condensation forming on cylinder walls owing to humid air warmed up by compression, condensing on the cold cylinder walls.

Really the only viable design for pressurising air is a piston based compressor, using a separate tank, and using higher pressures to keep the volume of that tank within manageable limits.

Unfortunately, high quality miniature compressors are tricky to find. The Valeo compressors that the German modellers use on their 'pressluft' boats are much too big for our size of boats.

The alternative is to make your own, or convert a small glow plug engine. Either route requires decent machining skills.

A company called Craycraft used to make compressed air dive modules using small custom made single and twin cylinder compressors, based on the recirculating air principle. You could buy all the bits separately as spares, or to enable construction of your own dive module. Although these dive modules used low pressures (6-12psi), the compressors were capable of much higher pressures.

Unfortunately no longer available.

[He Who Shall Not Be Named]

Andy's spot on with his observations.

Only thing I might add, John, is that you're idea is viable -- and is indeed how most the 'real' boats do it, either snorkeling or surfacing to grab air and bang up the HP air flasks from the on-board air compressor(s).

My SubDriver on-board gas bottles are way, way too small of volume to hold a meaningful amount of compressed air, and even then, a fair sized bottle would have to be rated at about 200-300 psi to give you expanded air volume adequate to blow the tank twice (safety margin). The small peristaltic pump Mike is looking at now: we'll see what it's high-end is as to pressure and CFM's; might be just the thing for this type ballast sub-system (I assume the weak-link in that pump will be the burst/fail pressure of the squishy tube).

And using a mechanical (float) valve atop the snorkel/main induction will keep water out of the system -- It's OK to pump a dead header with a peristaltic pump without fear of damage. What the ... I'm starting to get into this (damn, you, John!). But the low CFM peristaltic pump would take forever to bang up the on-board bottle.

And I hate the thought of being stuck on the surface, wallowing in the swells (my old diesel boat days on the TRUTTA still stick in the mind, while we banged up the air-flasks and toped off the batteries).

I'm sure we could get Kevin McLeod to produce a circuit that would command a blow if the on-board bottle pressure dropped below 75 psi and would not re-set till the pressure was back up to 150 or so.

You PEOPLE! .... stop this! I have enough stuff on my plate; you're making me and Mike crazy!

David,