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:
- Obtain all required materials and inspect parts for defects.
- Insert and screw a modified 1/4 NPT plug into one of the two female ends of the 1/4 NPT tee adapter.
- Pack the black powder in a "pillow" using Blue Tape and tape it around the Firebolt E-match head. Make sure that the E-match is shorted. you can use some clay to seal it.
- Insert and screw the FireBolt into the modified 1/4 NPT plug using Teflon tape, only applying the tape above the slot in the FireBolt. Be sure that the E-match is shorted.
- Repeat steps 2 and 3 for the other female end of the 1/4 NPT tee adapter.
- From here on, use appropriate PPE of nitrile gloves and goggles.
- Measure out the required amount of black powder on a scale.
- Insert and screw the entire assembly into the air inlet hole of the piston. Use Teflon tape to ensure a good fit.
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.