Tanks, Valves, Regulators et al. for Amateur Rocketry

[jt8d]

Hello Amateur Rocketeers,



I am one of possibly many lurkers who follow the great work that Britishrockets, Stevep and Johansson have done and documented here. Thank you.



I myself as a past time have been reading SP-125, Rocket Propulsion Elements and of course, How to Design, Build and Test Small Liquid Fuel Rocket Engines.


That said it is quite difficult to find information regarding regulators, cylinders, lines and valves for use in amateur rocketry. I have no background in machining or shop work so it’s hard to learn the basics regarding pressurized systems and their components.


So for an amateur, how are you pressurizing your systems? Where are you finding regulators? Are all regulators created equal? From what I’ve read, high flow regulators are quite expensive and difficult to source. Would you concur? Can you use only one regulator to pressurize both the fuel and oxidizer?


What type of fittings are you using for your cylinders? Are there commercial fittings that allow the pressurization of a cylinder with an inert gas, while drawing a liquid out? Or are you drilling and taping another outlet in the cylinder?  


I see that many people dedicate a great deal of time to developing their own valves using RC servos.   Are NOS solenoid valves the only off-the-shelf type out there for remote operation? Or are they ill suited for proper ignition?  

Argon, CO2, Nitrogen and Helium seem to all be in the running.  Helium is expensive. Argon seems cheap and plentiful but are there any draw backs?  Why Argon over Nitrogen?  How about CO2? I would assume it would suffer the same problem with constant output as Nitrous Oxide does in high flow situations when self pressurizing.  

I guess my basic question is, can you purchase all the require components of a pressurization feed system without touching a mill, lathe or welder? 

That’s quite a lot of questions but it would be wonderful if we could concentrate all of your knowledge on pressurized systems!


Barry

[stevep]

Hi and welcome Barry,

You sound like you're at the usual starting place--so many options and not a clear path to a decision. Been there, done that :-)

If you never intend to fly the beast you build, then bulk and mass of regulators and pressure tanks aren't an issue, but cost (I assume) will be. If you *do* want to fly, then that can start to limit your choices.

Taking your questions in somewhat random order, I believe it is possible to use a tank with only one opening and by using a concentric arrangement of tubes (one within the other), withdraw liquid and add pressurant simultaneously. I don't know if such tubing arrangements are available off the shelf. I dimly recall commenting on something like that to Anders, so you might re-read the latter portions of his thread if you want to pursue that avenue.

Otherwise you need tanks with two openings. I don't know if you can find off the shelf items for that or not. Sometimes at metal scrap yards you can find odds and ends that can be repurposed, but you will have to pressure test them, etc.

This is where Nitrous is nice since *that* tank only needs the one opening (and the pressure is low enough that you don't need a separate regulator). My fuel tank (with two openings) is one that I make myself, but I have a lathe.

You *might* be able to do the plumbing without a mill, lathe, welder. However, that's only part of your problem because
without a lathe, you'll have problems making the combustion chamber and injector. Don't know where you're located but there may be a "techshop" (google it) or a "hackerspace" near you where you could sign up to use some machine tools to get you going. Else you'll need to find a friend who does have a lathe to help you out (or be willing to pay someone).

Nitrous solenoids meant for cars have two problems: small orifices and they are only meant to be on for a few seconds. Normally "a few seconds" would be enough for amateur rocketry *except* if you're filling a big flight tank by remote control. Then they burn out, so "solenoid saver circuits" were developed to avoid that problem. However, Doug Pratt at pratt-hobbies.com sells a solenoid with a bigger orifice and windings that won't burn out. However, you wouldn't want to fly that sort of thing.

Pressurized (as opposed to self-pressurized) is, as you've gathered, somewhat harder to solve since you need high(er) pressure regulators. Valves (downstream) can be lower pressure (and thus cheaper). One company that has less expensive regulators is www.aquaenvironmentinc.com They have one for about $100 IIRC. In general, you are correct that high pressure + high flow = expensive.

Fittings seem to be of the AN variety--I get good aluminum ones at a decent price from AircraftSpruce.com

You can pressurize both the oxidizer and fuel with the same pressurant (and the same regulator) assuming the pressurant is chemically compatible with both the fuel and oxidizer--you then either use valves or orifice restriction to control the flow of oxidizer and fuel such that you get the proper flows (and thus, proper ox/fuel ratio). If you want to throttle, then, of course, you need valves rather than orifice restrictors.

I think you have it about right on the pressurant options. I don't have an opinion on Nitrogen vs. Argon, although there is an issue with the dissolvability of the gas in the oxidizer and/or fuel. CO2 does indeed have the same issue as Nitrous in terms of flow vs. pressure, but whether that's an actual problem for you depends on the size of motor you're planning to build. My motor is relatively small because I plan to use it in a small (by amateur liquid standards) rocket. Anders was planning to move a rather larger/heavier object and would accordingly need higher flow. Ditto for other folks who need motors of of several hundred pounds of thrust for more than a few seconds.

However, note that in a flight vehicle you generally only need high thrust (and therefore high flow) for the first few (< 5) seconds to get off the pad and up to some sort of decent flight speed--after that you can throttle back to maintain the speed. The question then becomes whether the Nitrous (or CO2) can respond *quickly enough* (rather than for how long) to the initial request for flow. Over at www.aspirespace.org.uk/ there are some papers (and software listings) that model nitrous flow that could help with that calculation.

I don't mean to discourage you, but, frankly, the more I play with this stuff, the gladder I am that I have some machining skills and a lathe, decent programming skills to help with the calculations, and a decent electronics background. I'd love to also have a mill and be able to weld. Barring being a jack of all trades like I am, you kinda get to the point where you need a team to do stuff like this in a serious way. You can get some help on calcs from online forums like this one and you *can* make flames without much in the way of electronics, but basic machining is pretty hard to live without.

Sorry that this wasn't a more organized presentation--ask more questions if you have them or if anything I said wasn't clear.
--Steve

[jt8d]

Thank you Steve!

What wonderful information. Further, thank you for opening my eyes to hackerspaces. They look to be an excellent avenue for learning the basics. It will take a fews days to digest all the info provided.

Out of curiosity, what are your projections for the weight of your motor and feed system in your flight weight rocket?

Barry

[stevep]

Hey Barry,

Glad my comments were helpful and aren't discouraging you....

My mass budget so far looks like this:

Motor (injector, chamber, nozzle, nuts/bolts to hold it together): about 500g
Valves, tubing, fittings, motors, gears, mount(s), battery: about 550g
Propellant tank (nitrous with bladder containing fuel), carbon fiber: 300g (big enough for 2 lb propellant)
Fuselage (including electronics and chute: 300 g

Total: about 1650 g = 3.6+ lbs.

So far I'm pretty close on the Motor and Valves. I will probably go with an aluminum tank to start with rather than a carbon fiber tank, just for ease of fabrication, although I am already set up to do CF stuff, and I may use a separate tank for fuel rather than the bladder approach to start with as well (crawl, walk, run, etc.). The fuselage is from existing solid fuel work so I know I'm in pretty good shape there. I'll probably overshoot the total budget a little, but I'm OK with that--anything up to about 5 lbs will probably get off the pad pretty quickly with 50lb thrust (10:1 T/W).

--Steve