Update: Golf Ball Piston-Valved Hybrid (LRCH-200)

[mark.f]

It looks like your sealing method could work... if it doesn't though, you could go with o-rings easily enough... take a look at the piston here... I've used the method for smaller pistons, it's just two different sized washers, sandwiched together to make a "groove". There's some extra work getting them centered on the bolt/threaded rod and correctly sizing the groove, but it works in the end.

[Binder17]

I did some tests on the rubber for the sealing face by repeatedly compressing against the metal face. The test pressure was 200 lbs, double what I intend to subject it to. The rubber had a very small groove cut into it but it did not cut any deeper even after several more tests. I plan to round off the edges of the metal face to prevent this from happening.

[MrCrowley]

Sounds okay in that case. The only killer will be piston bounce. You could build a sealing face and piston to withstand piston bounce on the off chance that it occurs and you need to troubleshoot it or you can build something less robust and do your best to minimise the chances of piston bounce occurring.

[Binder17]

A few more updates. I am only a few steps from test phase. I just need to connect pilot to the injector, and then I can begin pressure testing to make sure the piston seals(I'm sure it won't the first go around) and to check for leaks and function. Then the spark rod (Multi-Spark Gap Electrode) will be installed. At this point I may do the first ignition test here in Texas, if I make it this far in time. Otherwise it will be in Louisiana, over Christmas, where I have access to more land, tools, and second opinions.
I acquired a Cam and Groove coupling set the other day. All I need now is the aluminum barrel. This will be one of the cheaper specialty barrels I have made, mainly because I was able to get the materials at local wholesale suppliers.

[mark.f]

PIston looks beefy enough. Looking forward to seeing it working.

[wyz2285]

Why doesn't the piston has o-rings...? Should't the rear section of the piston be airtight and isolated from the chamber?

[Fnord]

You'll most likely need orings in the final design, but you can try it without them first.
I've never had reliable firing from a plain rubber plug. Expect it to burp and honk, possibly destroying your sealing face in the process (Make that part easy to replace).

That large rear washer might also get deformed depending on how it slams back, be prepared to winch the piston out if that happens.

It's also worth noting, a while back I managed to blow the seals out of a 1/4" brass ballvalve @10x. Doesn't seem to be too common, but don't count on them to protect any sensitive gauges.

[MrCrowley]

It's also worth noting, a while back I managed to blow the seals out of a 1/4" brass ballvalve @10x. Doesn't seem to be too common, but don't count on them to protect any sensitive gauges.

I blew the seals on a 3/8" ball valve not too long ago after the burst disks failed to burst on my small hybrid. Would be a good idea to make the meter detachable with a simple quick connect fitting.

I pretty much agree with what Fnord has said here, I think what is required to make the rubber washers act as o-rings (i.e. a tight fit, perhaps with some compression from air pressure) will also cause them to fail when the piston valve opens. O-ring grooves aren't too difficult to do with the ol' nut-and-washer trick, you just need to spend a bit of time figuring out the diameters and thickness of the washers and o-rings. Tip: use teflon tape under the o-ring and over the inner washer (the washer that has an outside diameter nearly equivalent to the inside diameter of the o-ring) to help with sealing if the o-rings don't initially seal.

[Labtecpower]

I would try machining a conical sealing face on your lathe, made from something like HDPE it should be able to seal well. (as long as the sealing face of the barrel is very smooth)

Edit: Wen's old profile pic, you probably don't have a lathe

[Binder17]

So it has been awhile. The LRCH-100 project went stagnant back in December after the failure of the functional test. This test was a pressure test, and piston function test. Piston function was good but pointless since it leaked. The LP-1 piston design was therefore scrapped. So it sat for 6 months while I worked higher priorities.

July 2015:
Boredom kicked in, and new ideas began to flow. I decided to roll the LRCH-100 frame into the LRCH-200. That was the easy part. Then I began brainstorming new piston designs short of having an aluminum one made on a lathe. I am now on the 4th iteration of my idea (LP-4). The LP-3 passed a "design potential" test yesterday, so it is pushing me forward with the design, but with improvements.

The LP-4 piston will consist of hard rubber caster wheels with O-ring grooves cut into them with a makeshift lathe. That's the hard part. The rest pretty much follows my original design.

The cannon itself will include some safety and performance upgrades. Pictures to come.

[ToasT]

Sounding good. Are you an engineer by any chance? The naming and lingo would suggest so .

[Binder17]

Unfortunately not an engineer...yet.

LP-4 piston is making progress. LRCH 200 is slated for operational testing this weekend at the proving grounds.

Lurch Piston 4th Iteration

LP-4.png (8.15 KiB) Viewed 5805 times

Modified Caster Wheel

[Binder17]

Functional Testing commenced September 5th at Simalusa Creek in Louisiana. Initial results were good, until I got to higher pressures. Note that functional tests are pneumatic only, no fuel. After a few cycles, leaking was detected. I concluded that:
A. The sealing compound for the piston components was not fully cured.
B. The seam in the piston housing is still recessed too low.

Solution: wait for piston to fully cure and eliminate the seam in the housing.

The next window for testing is in October. I will make my corrections and be ready again. Hopefully I will have a video of live fire then.

In the meantime, here is the LRCH with barrel affixed.

[ToasT]

October isn't so far away at least. Given the speed at which my projects come along at, this is nowhere near enough time to do anything. I'll blame work...
What pressure were you testing too?

[Binder17]

Work is my main constraint. I also have other projects that take priority. Like putting together the baby nursery for example.

I went up to 100PSI. It started leaking at 65PSI. I used Ultra black gasket sealant to seal all the piston components. The sealing face has a void in it that I filled with the sealant. Since it still wasn't cured after 48 hrs, the higher pressure caused it to ooze past the nut and washer holding the sealing face on. It has since been upgraded with a larger diameter washer and allowed ample time to cure. Might do a low pressure test this weekend. All I have in Texas is a bicycle pump. I know, what kind of spudder does not have an air compressor.

Update: Mount and Painting Complete