Originally Posted by Electric-Mayhem
I watched some fire fighters try to use one of their high pressure oxygen tanks that they use to breath in fires (similiar to a scuba tank) to inflate their raft on the Salt this year and it didn't work very well since its similar to the inflator. Works great for relative small things that need to get up to high pressures but doesn't fill large low pressure spaces very well.
Those SCBA cylinders that firefighters use are quite a bit smaller than SCUBA cylinders. SCBA stands for self-contained breathing apparatus. The U in SCUBA is for underwater. The SCBA cylinders are typically fitted with DIN valves, and that lets them operate at higher pressure and thus have a bit more air stuffed in them. And it's just compressed air, not oxygen. Carrying pure O2 into a fire would not be a great idea.
At a rated pressure of 3000 PSI, the "standard" 80 cubic foot aluminum SCUBA cylinder holds about enough air to fill a phone booth, but actually less than 80 cubic feet. High pressure steel cylinders are becoming more popular. With a yoke valve, they typically can hold 3442 PSI, and the rated capacity is what's in the bottle at the rated pressure (an HP 100 holds 100 cubic feet).
I never thought to figure out how much air a raft holds. For grins -- 20" tubes have a radius of 10" or 0.83 feet. That gives a cross sectional area of the tube about 2.18 feet. Ignoring the bow and stern and just considering the main side tubes, a 15' raft has 30 feet of tubes which would mean an internal volume of 65 cubic feet. The aluminum "80" holds 77 cubic feet of air. That air bottle would just barely be enough to fill the boat to atmospheric pressure. The firefighting SCBA cylinder probably holds less, but I'm not certain.
I have an adapter I can put on my SCUBA regulator to fill the tires on my truck if needed. Just to top off uses hardly any air, and even to fill from flat shouldn't take that much since the volume inside the tire isn't that much. I sure will never try it with a bicycle pump again, though.
I can totally see using a SCUBA or SCBA bottle to top off a raft, but it's just not convenient. I'd rather use that air to go diving. You would probably want to leave the bottle in the truck, and then it can be exposed to high temperatures and rupture the burst disc or worse.
I have one of the NRS clip-on pumps. Works great, but since my raft is on a trailer, the wires won't reach. I have a deep cycle battery I often would carry to run the thing, or else trade off using another vehicle battery, but that deep cycle was heavy and awkward. It also had died. I'm looking for a much smaller gel cell that can run the pump to fill one to three rafts to 1 psi and then top off with a K-pump. I went to the battery shop, but they weren't any help. They said I would need to know the amperage. I contacted NRS, and all they could tell me is that it draws 29 amps. TWENTY NINE AMPS!!!
That means, yeah, it takes a HUGE battery, but I can run the pump for a really long time with the big battery. Anyone have any success running these pumps on smaller gel cell 12-volt batteries? Because I don't want to own a leaf blower