Rocket Team is requalifying a standard, consumer off-the-shelf, pneumatic tie rod air cylinder for use with pyrotechnics. The component was purchased from McMaster-Carr with part number 6491K254.
Piston Testing
Testing Procedure
Note: The modified 1/4 NPT plug is a standard stainless steel plug with a 1/4-20 hole drilled and tapped through the middle.
Materials: Piston, 1/4 NPT Tee Adapter, Modified 1/4 NPT Plug, FireBolt, nitrile gloves, safety goggles
Steps:
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- Apply one drop at a time, gently jiggling the tee fitting after each drop. Use a flashlight to ensure that you are gradually saturating the black powder.
- If you are only using a small amount of powder, it may be easier to seal from the end of the tee fitting opposite to the end in contact with the powder.
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Testing Schedule
The piston was tested several times as a discrete component. Following the first successful test on November 7, 2017, the piston was ground test as part of the Flight Test 1 campaign.
| Date | Result |
|---|---|
| October 28, 2017 | Firebolt e-match blew out of epoxy |
| November 7, 2017 | First successful test |
| January 27, 2018 | Poor data acquisition, successful test |
Disassembly, Cleaning, and Reassembly
Details on disassembly, seal replacement, and reassembly can be found using the manufacturer's specification sheet: Piston Specifications.pdf
Disassembling the piston was is surprisingly difficult. When it was finally disassembled, we noticed that After use, the black powder residue didndoesn't extend very far up into the bore. We theorize that this is because the reaction occurred occurs faster than the piston rod could move up the bore. An alternative theory is that the reaction just naturally doesn't travel far up the bore.
To clean the piston, we use Ajax soap, and towels wetted with isopropanol. When replacing the seals, we use silicone-based lubricant white lithium grease (per the manufacturer's recommendation) to avoid damage to the O-rings.