3 Bottle Wrocket Hydrostatic Testing

We decided to add another “robinson coupled” bottle to H2 to make a 3 bottle wrocket and hydrostatic test it.  We were interested to see how this coupling would go and whether we would see the drip leaks we encountered on the 2 bottle hydrostatic test.

Adding the third bottle used the same technique as joining the first two bottles, which was surprisingly fast when you know what you are doing (well have done it more than once…. :) ). I also created an additional fairing for the third bottle using the “low tech” hotplate technique.

Additional Safety Precautions

I decided that even though we are not burst testing these bottles, there is still significant energy inside the bottles at 125psi, so I will be using my safety goggles on these hydrostatic tests.

Safety Goggles

Safety Goggles

Hydrostatic Test

I took Georges advise and filled the hose leading to the pump with water, but it only filled back to the 10mm section and wouldn’t take anymore (air locked possibly). Evidently this turned out to be not enough as it stated out fine and no air was being pumped into the bottle,  but as the pressure rose the air just went around the water in the hose and got in. I will have to find a way around this problem for future tests.

You can see here the amount of air that made its way into the first bottle

air in first bottle - 3 bottle test

air in first bottle - 3 bottle test

The test itself went well. The bottles held pressure well, all the way up to the maximum on the pump gauge, which was 125psi. The first to second bottle still had the drip leak (about 3 drips every 2 seconds) but the second to third showed no leaks. This pressure was held for about 3 minutes.

125psi - hydrostatic test

125psi - hydrostatic test

here is a pic of the bottles at 125psi (you may need to click on the pic for the full size to see detail)

3 bottles at 125psi

3 bottles at 125psi

Just out of interest I weighted the 3 bottle assembly, including the 3 x 1.25L bottles, 2 x robinson couplings, 2 x fairings and nozzel. It weighs in at 193grams

Final Thoughts

Our next launch is to test the parachute deployment, so we will probably go back to 2 bottles – most likey take off the first one with the dripping connection. Once we have the parachute system working properly we will add the third again and go for some height :)

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