Firewall forward fire protection.

[RoarkS]

Actually posting a dayjob question for once!

G.A. Cabin air control valve. There is a cable operated stainless steel shut off valve at the firewall. However there is also a proportioning valve that's driven by a COTS electric actuator. We have certified the actuator to Part25 Appendix F (b)(4) Vertical Test "12 second vertical burn test" as usually these are put in the cabin.

I inherited the project and now, I've been asked separate the shut off and proportioning valve. Shut off valve stays stainless. proportioning valve became composite... they got picky about composites so I asked for what burn spec they are designing to and was told AC 20-135 "fire resistant". The duct no problem... but the COTS actuator is going to melt/fail/ possibly catch on fire. I've not subjected it to 2000°F for 5 minutes!

Thoughts?

 

[verymadmac]

Assuming the proportioning valve is fwd of the firewall, what are the consequences of its failure.

The shut-off valve maintains the integrity of the firewall so no problem there unless the proportioning valve penetrates the firewall or its failure would also cause the failure of the shut-off valve.

 

[Sparweb]

Like Mac says, if the SOV is still the last thing isolating the firewall from everything forward, you should have no problem. Go look at all the other flammable stuff in the engine compartment (wire bundles, hydraulic hose jackets, batteries, etc) and your proportioning valve is not too different. Almost everything's flammable when exposed to 2000F!

http://www.sparweb.ca

 

[RoarkS]

Okay that's good to hear, that's basically what they are saying. Was shocked by that AC 20-135 spec... that's pretty harsh.

 

[WKTaylor]

Hmmm... military requires added fire resistance for battle damage, ruptured fluid lines and/or ruptured high speed components [turbine disks, etc].

Quite-often fire/heat/tear-resistant sleeves or jackets, or fire-resistant enclosures are usually required for fluid hoses, wire harnesses, certain mechanical/electrical components and fuel cutoff valves in engine bays.

Any way a damaged valve [case/attaching duct etc] could allow force-fed flames into the cabin-air duct work? Air-flow surrounding engines has a pesky way of pressurizing heat/flames thru the tiniest holes into undesirable locations. I could tell You some hair-raising fire/heat penetration 'war-stories'... Naw.

BE EXCEPTIONALLY careful about any adjacent flammables or electrical power wires in fire-rated compartments.

Is there any porous insulation [etc] that could trap/retain leaking flammables... oil, grease, fuel, etc... nearby?

Also is there any urgent need for high-electrical-energy bonding/grounding of the component to the airframe??

Just saying... probably over-thinking this... it's late.

Regards, Wil Taylor
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