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Innovative Aftermarket Products for Experimental Aircraft | |
All Stainless Steel Firewall Mounted Heater Valve
During the construction of an RV-6A quick build kit, we were confronted with the classic problem of "How do we keep hot vapors and flames out of the cockpit should a fire occur in the area of the engine/cowling?"
Aluminum is definitely not suitable for this function since aluminum loses substantial mechanical strength in the temperature range 500°F to 600°F and melts in the range of 1220°F.
Stainless type 304 exhibits good structural service at 1600°F and a nominal melting point of 2600°F.
We conducted initial high temperature studies of 304 stainless as a replacement for aluminum units currently available.
These test results were quite clear and pointed us in the direction of producing an all 304 stainless steel heater valve.
NO thin wall stainless tubing in the thickness range of 0.025" or less was found.
In fact, standard small stainless tubing starts an an O.D. of ¼" with a wall thickness O.D. of 0.035".
The final solution was to create our own thin wall 304 stainless tubes and flat sections.
The initial shapes were formed with hardwood tooling to create proof of product concept parts.
At this point a new group member Paul Bowmar, an experienced machinist and tool designer, stepped in to design in house permanent hard tooling.
Paul also initiated experimental high temperature testing of the initial 304 stainless products and previous aluminum parts using a 1200°F to 2000°F propane blowtorch impacting on a stainless firewall mockup. The test setup and results are illustrated below.
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With an all stainless heat selector box design now in hand, our attention turned to testing the unit in a simulated "real life" application. Paul built a mockup firewall and attached it to a stainless steel heat selector box and proceeded to apply flames from a propane weed burner affectionately named "Puff the Magic Dragon". "Puff" spits out 2 ft. flames in the neighborhood of 1800 to 2000°F.
Immediately the temperature sensor output signal in the firewall mockup raced past 500°F. Within two minutes the firewall temperature was over 1000 degrees and the heat selector box began glowing dull red. In about three minutes the firewall temperature stabilized just below 1400 degrees and the selector box was glowing bright red.
Some surface scaling was present but the unit did not melt. After ten minutes "Puff" was extinguished. The stainless selector box held up well as expected. What happened next caught our attention!
We attached an all aluminum heat selector box to the mockup firewall and reproduced the same flame test. Within eight seconds of flame impacting the aluminum selector box the frame changed shape and lost substantial strength. The firewall temperature at this point was approximately 400°F. Within sixteen seconds, the "flapper" valve melted, allowing test flames to enter the test cockpit area. Within one minute the selector box melted away, with only the mounting bolts remaining.
The dramatic and rapid meltdown of the aluminum box inspired concerns about the time available to shut down engine operation and cut off fuel flow.
This selector box flame test results also caused us to realize straight through firewall flame penetration via electric cables and mechanical tubes and rods is also a very serious fire hazard.
With some helpful background information from Bob Nuckolls we developed an inexpensive and very effective firewall flame penetration suppression system for the homebuilder. See 2 Stainless Steel Firewall Straight Thru Tube Seals.
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1A Stainless Steel Firewall Mounted Heater Valve $96.00
1B Stainless Steel Firewall Mounted Heater Valve $96.00
1C Stainless Steel RV-10 Vent Set $192.00
To Order This Product either click on Secure Product list on top of this page or Call (435) 826-4601
EPM.AV Corp.
160 W. 300 N. • Escalante, UT • 84726
TEL (435) 826-4601 • FAX (435) 826-4602
Phone orders encouraged. Hours 8:00 to 6:00 MST Monday through Friday
info@epm-avcorp.com
www.epm-avcorp.com
