Reliable valves permit "smoking" in space

Aug. 8, 2002
Microgravity combustion experiments conducted aboard the International Space Station will use the X-Valve from Parker Pneutronics as a key control element.

Microgravity combustion experiments conducted aboard the International Space Station will use the X-Valve from Parker Pneutronics as a key control element.

Project "Smoke" is a microgravity experiment being developed at NASA's Glenn Research Center that will take place late next year aboard the International Space Station (ISS). The experiment will burn samples of different materials commonly found aboard the ISS and Space Shuttle.

The objective is to characterize smoke particulates generated by these materials. Due to the lack of convection and gravity, materials burned in low gravity produce particulates whose size and density differ greatly from that produced by burning on Earth. If particle size and density were known, smoke detectors for the Shuttle and ISS could be "tuned" for the correct signatures of fire in microgravity.

According to Nathan Funk of Zin Technologies, Cleveland, the objective is to bring two samples of smoke from each burn back to Earth for post-flight analysis on a transelectron microscope (TEM) grid. This amounts to 48 test runs and 96 samples. Astronauts will direct the flow of smoke through a small section between a heater and a TEM grid — called a thermal precipitator. Crew time permits maintenance every sixth test run, which led to the design of a replaceable thermal precipitator containing 12 TEM grids.

Smoke can only travel over the TEM grid once, to avoid cross contamination. This requires valving that permits different flow pathways for each TEM sample, as well as isolating samples from the system when not in use. Preliminary analysis of the X-Valve, manufactured by Parker Hannifin's Pneutronics Div., Hollis, N.H., shows that it meets the extreme size, weight, and reliability demands of space flight.

The X-Valve is an ultraminiature two-way, three-position valve that handles flows to 10 lpm at 30 psi. The valve's high flow rate results from the coil and body being combined in a single unit with a unique flow-path design. Even with 12 valves mounted on the thermal precipitator, the unit is still small enough to fit through the test device's gloveports for removal.

The valves must also prevent leakage when the units are stowed. Another key feature is that the stainlesssteel plunger that directs flow in the valve has Viton elastomeric ends which tightly seal the valve port. This streamlines flow and permits close spacing of the pneumatic tubing ports.

The valve has only five parts, versus a typical miniature solenoid valve that may contain as many as 25 internal parts. This equates to fewer potential leak paths and higher reliability.

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