I heard there was a way you could substitute an air compressor for the normal CO2 tank. This looks like it would be helpful, particularlly when you just want to practice at the local pond. How is this done?
Dave, I have used air compressors in place of CO2 bottles. I have a few photos, and I will write up details on it later today. Right now, I just finished lifeguarding and it's too early in the morning for me to do detailed technical writing. Expect more info in a few hours.
Considering how each air compressor draws 10A and requires 12v batteries, yeah it's power-intensive. On the other hand, batteries are then the only resource you have to worry about. If someone forgets to fill the club CO2 tank before a battle, whoop-de-doo, as long as you've got enough batteries. Just had that happen on Sunday, where someone forgot to fill the club CO2 tanks. Fortunately I was using HPA, and had a full SCUBA tank for refilling.
Another potential issue to keep in mind is that a lot of air compressors have moving parts made of steel. Once water get inside the compression chamber and/or crankcase, the water will displace much of (if not all) of the oil or grease inside, allowing it to rust. If there's an excess of moisture inside while the compressor is running, there's a risk of overloading the attached motor (from trying to compress a lot of incompressible fluid) or turning a lesser amount of moisture into steam that could cause a compressor failure. While these are, of course, much bigger issues with larger commercial/industrial compressors, they could easily still cause a small onboard compressor to fail at an inopportune moment and thus should be kept in mind. On the other hand, having more, smaller batteries instead of both batteries and a CO2 bottle might provide quite a bit better flexibility for locating everything, especially in smaller ships.
Yes, water has always been one of the biggest dangers to an air compressor. When I used one, I could manually disable it with my radio, which I planned to do if I sank. However, that would not guarantee that it wouldn't turn on later once the servos got wet and twitchy. I intended to eventually use a water sensor to disable the compressor if the water level got high enough, but I removed my compressor before I got around to it.
Sure! Let's see.... A collection of various air compressors: Air Compressor, sprayed black, in the bow of a Monitor: The entire ship: A collection of various pressure shut-off switches (air compressor's equivalent of a regulator):
What is the weight difference between the compressor vs. the CO2 bottle? Does the need for more battery power cancel it out?
Depends on what CO2 bottle you're using. It most certainly is NOT a drop-in replacement for a 3.5oz or 7oz CO2 bottle. Probably closer to a 12oz, 16oz, or 20oz, depending on how high-tech you go with your batteries. To give you an idea, I'm considering using an air compressor and Lithium-Iron batteries in a predreadnought. In my old Scharnhorst, my extra-large compressor was powered by a 12v 12Ah SLA, and the whole thing was almost exactly the same as a 20-oz CO2 bottle and two 6v 7Ah SLAs.
How much does it cost and where can you order the air compressors? I'm not too worried about weight, but I'd like to make my boat simpler by not needing a bottle of compressed gas that needs to be filled every time I go practice. It just seems like a hassle.
You can buy a cheap tire inflator 12v air compressor at bike stores, hardware stores, and often even walmart. All you need to do is rip the compressor out of the case, wire in a pressure-shutoff device, and find a way to deal with the noise and vibration. Air compressors aren't exactly silent.
The air coming out of the compressor is pretty warm. After initially charging the accumulators, you can hear it turn over a few more times as the gas cools and shrinks, lowering the pressure and turning on compressor again. Heat is another issue you need to be concerned about. The ships that I have seen didn't have any preparations made for cooling the compressor head or motor, and they seemed to be OK, but it's something you do want to keep in mind.
Yeah, I did some idealized (isentropic) math on the compession of air from atmosphere to 150 psi just to get a bound on the temperature, and estimated about 280 degrees C... now real life will be much lower than that but it will still be hot... I need to think a bit more about it to figure out how much cooling would be required... not that there is not plenty of cooling available.
I can't imagine it to be of much difficulty to come up with a simple but effective after-cooler for the air coming out the compressor by running the air through a length of hose exposed on the exterior of the bottom of the hull. What I see at work for air outlet temperature numbers from somewhat larger reciprocating compressors is between 220-310 0F while the screw compressors tend to be in the low 200s. Other than the ones that sometimes come integrated with compressors, I'd sure like to know if anybody has a good source for small and lightweight switches. I know that Clippard has some pressure switches but if memory serves me right, they only go up to about 4 or 5 bar for actuation and deactuation set-points. Other sources for presure switches that I use at work (such as here) are overkill and too heavy for our applications here.
It just occured to me that I could use one of these for testing guns in the shop rather than taking my 2 bottles back and forth to the shop. Any suggestions on that?
I do that, too. It's very handy for initial tests, and for diagnosing problems when your CO2 bottle or HPA tank has already been drained. For a cutoff switch, I use the Dwyer Series A-2 subminiature pressure switch: http://www.dwyer-inst.com.au/htdocs/pressure/SeriesA2Price.cfm It works very well, is compact, and doesn't seem to mind sinking too much. You can adjust it from 50-150 PSI, so you cannot physically exceed club safety settings, and it handles sufficient current to not melt when running a compressor.
