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Pro-Seal vs. RTV sealant for firewall fittings

bobhope2505

Active Member
I didn't have any Pro-Seal available when installing the fuel line fittings in the firewall, so I used RTV sealant. I've now seen posts from two others hinting they did the same. My adviser suggested that I redo it because standard RTV sealant will burn away when exposed directly to flame and compromise the firewall. (It really wasn't a "suggestion.")

He did, however, suggest an alternative to avoid dealing with Pro-Seal--3M Fire Barrier Silicone Sealant. There may be other options, but I didn't check. It proved to be very useful when I wanted to tweak the angle of the elbow in the fuel line.
 
I used 3M Fire barrier Sealant and it has held up well. Of course I have not "tested" it in an actual fire and hope never to do that.
 
Just out of curiosity, what did he think would happen to proseal in a fire, if you'd used that? (Might help evaluate his 'advice'...)
 
I didn't have any Pro-Seal available when installing the fuel line fittings in the firewall, so I used RTV sealant. I've now seen posts from two others hinting they did the same. My adviser suggested that I redo it because standard RTV sealant will burn away when exposed directly to flame and compromise the firewall. (It really wasn't a "suggestion.")

He did, however, suggest an alternative to avoid dealing with Pro-Seal--3M Fire Barrier Silicone Sealant. There may be other options, but I didn't check. It proved to be very useful when I wanted to tweak the angle of the elbow in the fuel line.

Perhaps I don't understand. If you are using a bulkhead fitting for the fuel line, why do you think sealant is required with the fitting?

Carl
 
Just out of curiosity, what did he think would happen to proseal in a fire, if you'd used that? (Might help evaluate his 'advice'...)

He said it swells when exposed directly to flame to maintain the seal instead of converting to ash and reducing in volume.
 
He said it swells when exposed directly to flame to maintain the seal instead of converting to ash and reducing in volume.

No he didn't.

Intumescent sealants swell to close gaps and openings. The usual ingredient is vermiculite, and required "swell temperature" is about 600F. There are also other ingredients in use. 3M FireBarrier 2000 appears to be intumescent. In addition, many products form a char on their surface, which is an insulator, and thus desirable. Some firestop products depend entirely on char-based protection. Char alone is a poor protection for an airplane firewall. The chars are fragile, and firewalls vibrate while being blasted by cooling air at high velocity.

Proseal is a polysulfide sealant. It was not included in the burn test earlier in this thread. I'm sure it would be a fine gas sealant when enclosed between the fay surfaces of a sheet metal joint, but I would not allow any to be exposed inside the cabin, as outgas, flame, and smoke results are unknown.
 
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