2 Bottle Wrocket Hydrostatic Testing

During our Launch day 6 to test the nosecone and parachute deployment we suffered a leak in our H2 rocket which limited launch pressure to 70psi. So we spent this weekend doing hydrostatic testing of the bottles including the robinson coupling where it was leaking.

As is usual with leaks it looks like it was the washers, so we made a new set of 3 washers and fitted them. We stripped the wrocket back to only the pressure bottles. This is the benefit of a modular design, the nosecone and the removable fin assembly just came off (so as not to damage them) and the 2 bottles and nozzle were left to test with.

With the 2 bottles totally full of water it weighs in at around 2.75kg, way to heavy to balance on the launcher. We used our gardena quick release and just connected that straight to the wrocket nozzle in a horizontal position.

2 bottle hydrostatic testing

2 bottle hydrostatic testing

We found that there was a leak in the one way valve coming from a molded join section at around 90psi. I fear the pressure may have been too much for the plastic valve, so we removed it. We will have to look for a brass one to use instead.

We had a few small leaks in the tubing connections which were tightened then we pressurized until around 120psi and left it there for a few minutes. There was a small leak between the cap and the bottle on the robinson coupling, but not enough to stop a launch, I think this was from the bottles swelling in this area. Here is a pic at 120psi

120psi - bottles swelling

120psi - bottles swelling

just on 120psi

just on 120psi

We are happy that we have a pressure body thats ready for launch, we just need to reassemble the rocket and do some timing tests on the nosecone and we are ready to fly. Hopefully with good weather this week we will get a late afternoon mid week launch  :)

Things we learned

  • Dont try to use a launcher for a hydrostatic test … the wrocket is too heavy
  • At 120psi full of water the wrocket is too heavy to go more than 10cm using a manual release.
  • Always check for leaks :)
  • We are probably going to have to look for a new pump soon :)
  • When fully filling a 2 bottle wrocket for hydrostatic testing the water tends to stay in the top bottle instead of making its way into the bottom bottle. The way to get the water into the bottom bottle is to gently squeezing the air out of the bottom bottle. This forces the air into the top bottle and water down into the bottom bottle. Careful not to squeeze too hard so you dont put a crease the bottle


This entry was posted on Monday, September 15th, 2008 at 2:03 am and is filed under Development. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.


2 Responses to “2 Bottle Wrocket Hydrostatic Testing”

  1. George Says:

    Nice work Todd. :) I noticed that your lower bottle has quite a bit of air in it during the pressure test. If you want to get rid off most of it, fill your entire air inlet hose with water. As the bottles expand the water from the hose will be pushed in to fill the void.

    I look forward to your next launch report.

  2. todd Says:

    thanks for the great advise George. I will give that a try :)