Thursday, November 09, 2006

Valve frustration

In a large way rockets are just plumbing.
Tanks pipes, valves and showerheads.

Rockets are weight sensitive, traditional industrial plumbing is not.

It would be nice to use an off the shelf valve.
Off the shelf controllable valves are slow and heavy.
Real aerospace rocket valves cost more than the budget for this whole project.

So I've been trying to build valves.
The first attempt looked good they were reasonably light and fast.

My son and I built a whole test stand based on these valves, it was ready for a static fireing in late July The valves froze up when tested at liquid nitrogen temperatures.
In messing with these valves I now have a pile of dead hitec robot
servos. the servo is just not going to cut it in this application.

(I've been mostly working on other things in between July and now, so I have not spent 4 months playing with valves, more like a month.)

So I'm now back on to valves full time.

I'm a firm believer in the markets ability to optimize things and create cool engineering solutions at low cost if the volume is high enough.

One key is to discover these items and use them in the project.

In that light I've been looking for a tough lightweight valve actuator.
Whats lightweight, powerful and tough? Battery operated hand held tools.
After buying disassembling and destroying a large number of Home Depots finest
hand tools I've settled on a Roybi 18V P240 right angle drill, very tough well built and
not too expensive.

The first thought was to just grab the valve stem with the drill chuck and go from there.
this works when hand held as your body provides a little bit of compliance for misalignment.
When you build study brackets to tie the drill down it breaks/jams things.

The second thought was to remove the chuck and machine an adaptor that provides for some misalignment and threads on where the chuck used to go. I almost finished that assembly tonight. I'm short one hole, as the plate that mounts to the valve stem is stainless it work hardens and I broke off my last 8-32 tap drill in the bracket. I was hoping to test this tonight,
but I'll have to get some good carbide drills and redo that plate Friday.

If the ryobi drill does not work I have one more valve concept to try. I'll spend another 3 weeks on valves and if I can't make it work by then I'll bite the bullet and buy the heavy industrial valve actuators like armadillo is using. The results from this will effect my fundamental vehicle design as they are heavy and you need at least 2 per motor. I was hoping for a small 4 motor vehicle with fully differential throttling.

When I get a valve fully assembled I'll post pictures.

I need to move on to engine tests, igniter development and tanks.
I have bits and pieces ordered for all of these, most due in around the end of the month.


Lee Valentine said...

Call XCOR, they have a selection of good, lightweight rocket engine valves for sale that may be cheaper than developing your own.

Jon Goff said...

If he's trying to differentially throttle his engines, I'm not sure that XCOR has any valves in stock that will meet his needs. XCOR has some pretty sweet valves, but almost all of them are pneumatic on/off. Making your own, high-speed throttling valve for a differentially throttleable vehicle is actually a challenge. If all goes well, we'll be doing our first dynamic throttle tests today with our valves.

Basically, making a biprop vehicle with valves fast enough that you can differentially throttle it (especially if it is light) ends up being a real challenge. Especially for LOX you end up needing something that is fast, high-torque, and light, and that doesn't come cheap.

We have some ideas for a next-gen valve design now that we're wrapping up the first gen, and it should be a lot lighter, but throttle valves are a non-trivial development task.


gate valves said...

Goodluck on your projects.

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