My team is working on designing a T-shirt cannon while we’re all stuck at home, and we had a question regarding using scuba tanks as the main air storage.
Then have it go into a custom machined buffer tank at 100 psi (holding slightly more air than what is needed for one shot) using 1/4" ID tubing (not exactly decided yet, just a rough diameter). The buffer tank will be attached to a 1" Solenoid (1'' inch 12V DC Electric Brass Solenoid Valve 110-Volts) that finally goes into the shooter barrel through some hose.
Right now, there are some missing parts. Firstly, I am not sure how to have the scuba tank interface with tubing, and secondly, I have not decided on a scuba regulator to use yet between the scuba and buffer tank.
I would greatly appreciate help with figuring out how to attach a scuba tank to the shooter and also what scuba regulator to use. Additionally any other suggestions or tips regarding T-shirt cannons are welcome. Thanks!
From the sounds of it, what you’re trying to build is pretty similar to what we built a few years back.
Our T-Shirt cannon uses a Scuba tank connected with a short hose (which I assumed was specific to Scuba equipment) directly to a regulator. The regulator outputs down to around 150 PSI and we use standard FRC Pneumatic fittings to adapt the output to 1/4" tubing, which then connects to a standard FRC regulator for more precise control of the output pressure, and then into a custom made “1-shot” holding tank.
Unfortunately I don’t remember the specifics of the Scuba regulator (other than it’s a type used by fire departments, apparently), but I’ll try to reach out to some of the other mentors that worked on the project to see if they remember.
I will say though, depending on the diameter of the barrel you’re using, you may want a larger solenoid valve. We used 1-1/4" valves and we wish we had gone to 1-1/2" (we may still at some point) for our 3" barrel. Flow rate is far more important than PSI.
Also, make sure to get any custom pressure vessels professionally tested before using them (we found a local company that was able to do this for us for free), you don’t want to accidentally build a pipe bomb. Incidentally, the same company that tested our custom tank was also able to get us a few cheap/free used Scuba tanks that they were able to revalidate for us, so that might be something worth exploring as well.
How quickly does the 1/4" tubing fill the 1-shot tank? One of my worries there was that the 1/4" tubing provide very little flow rate meaning that we would have to wait a good amount of time between each shot.
Let’s just say, it takes FAR longer to reload the T-Shirt than it does to refill the shot tank. In fact we actually put a flow control on it to slow down the air loss from the Scuba tank during the second or so that the 1-1/4" valve is open.
(Technically, you could also avoid this issue by having a solenoid on the 1/4" tubing to cut off the flow during firing, but our setup wasn’t that elaborate)
Another thing to remember is to secure that scuba tank well inside the frame. The scuba retaining method should make a good FRC battery tie down look like a joke.
3946 could put toss T-shirts over the bleachers and onto Ninth street with a 1" solenoid valve and about 70 or 80 psi; we usually ran about 55psi in our holding tank.
Ehh, in that case, IMO you should still be fine with an unrestricted 1/4" tubing, it won’t set any records for speed, but should be adequate for general use (it’s not like you’re likely to ever be firing as fast as the revolver can rotate anyways, you probably fire one, reposition slightly, and fire again). I’d estimate our tank would be filled in under 15 seconds if we removed the flow restrictor.
Keep in mind though that there are a number of variables that affect this, such as the size of the shot tank and the operating pressure of the system.
IMO, the Solenoid you linked above is a good one, we have the 1-1/4" version of that same one from that same website.
The important thing is the size of the barrel in relation to the solenoid. The larger the barrel, the larger the solenoid you need. Smaller barrel means you can use a smaller solenoid and/or lower pressure.
For my team we used a hose that converted the YOKE valve on the scuba tank to a 1/4 npt fitting through a air hose. Getting a hose adapter like that is great because you don’t have to buy a scuba tank, for events you can rent full charged ones based off if you have a scuba licence. That 1/4 npt fitting was connected to a nitrogen regulator (https://www.amazon.ca/dp/B071FFJ38X/?coliid=IUAVL07N2RXIR&colid=1LAXUM87PGFS8&psc=0&ref_=lv_ov_lig_dp_it) this regulator is good for up to 4000 psi so it will withstand a full charged scuba tank and give you a adjustable outlet from 0-800 psi.
You will need a adapter on the high side of the regulator that connects the 1/4" npt fitting from your scuba tank to you nitrogen regulator. This part is really hard to come by you can get them custom made by welding shop or a local machine shop. This is a example of one that I could find (https://www.rmiorder.com/product/SE/CGA-58012/CGA-580-NitrogenArgonHelium-Outlet-Adapter-to-Male-12-NPT-3000-PSIG) then you would use a male to male connector to attach your hose to the adapter which you can find on McMastercarr.
With this setup feeding a 80 cu ft at 3000 psi into second 80 cu ft tank at 150 psi we got about 200+ shots per tank.
edit: I have a full parts list if you are interested for what we used.
So to follow-up from my original post, I was able to find out what regulator we used from one of our other mentors. The regulator is an Air Systems International RG-5000. We connect it to the Scuba tank with a 6in long flexible hose (not sure the spec) which allows us to mount the regulator rigidly to the chassis (using a custom 3D printed mounting bracket) and still be able to connect and disconnect it without issue.
This includes all the parts that my team for both high pressure and low pressure sides. It also includes general requirements for 2 custom high pressure parts one of which we got made by a scuba shop the other by welding/tool repair shop don’t attempt to make either of those parts yourself as the pressure rating required for them is extremely high making them very dangerous if they fail.