Friday, June 20, 2008

Floats as Tanks

This is a picture of hydrotesting I did on a 6" 316 Stainless steel float from McMaster-Carr (2762K49). It failed at 2150 psi. Interestingly, the failure was a tiny pinhole that opened right at the weld termination. My grease gun was not able to pump enough water fast enough to get the pressure higher higher than 2150 once the hole opened up.

I proof tested a second of these floats to 1900 psi without failure. And 3 more were tested to 1500 psi.

Tuesday, June 10, 2008

Valves (again!)

I have developed a direct drive version of the valve I've been using. It was used in my last testing which was described in the previous post.

The packaging comes out quite nicely. They have several advantages to the linkage actuated version - this will be my go forward design.

Along those lines, I have been wondering if there are people out there that might like to buy a pre-made valve like this one. It was actually more of a pain to build than I thought it would be and personally, I prefer to spend my time building rockets rather than various peripheral devices.

Here are some of the relevant details:

  • CV of 1.6 and is rated for 1.6 gpm of flow at 1 psi delta and 5.1 gpm at 10 psi
  • rated to 3000 psi
  • can throttle fairly well and has fast response (as can be seen on this blog)
  • o-ring sealed and can be compatible with most non-cryogenic propellants, including hydrocarbons and hydrogen peroxide
  • the servo would be a Hitec digital servo with titanium gears (6.0V or 7.2V input)

If you're interested in buying a valve like this, drop me an email.

Monday, June 2, 2008

Fits and Starts

Long time, no post. I wish I could say the delay was due to my making lots of progress and not having time. The truth is much closer to not having much to share.

I was able to get out and test some modifications this weekend. The good news is that the urethane o-rings seem to be working. I did a long term pressure test with N2O to see if they would remain sealed for several days. Also, after the testing this weekend they showed no signs of damage.

The main point of this weekend's testing was to test a new configuration with the propane/spark ignition with the goal of eliminating the initial pressure spikes. The new configuration seems to have reduced the tendency towards hard-starts. Unfortunately, the ignition sequence which was quite reliable before is no longer. I spent quite a bit of time just getting it to light at all and stopped testing without arriving at a reliably repeatable sequence.