Nice idea, but I'll be very surprised if it works. Durifort is fairly heavy guage, similar to the tubing regularly used for hydraulic systems. Assuming a wall thickness of about .035 inches(.5mm is about .020), we would have figured an operating pressure of somewhere around 2000 psi. The safety factor we used was most often 4:1, so the burst pressure would be roughly 8000 psi. These were conservative ratings, since systems were often pushed beyond the stated limits. Over pressurised tubing usually swells along it's entire length, and dosen't usually push out a dent.
With a setup like this, the rubber plug will usually push out first, at a surprisingly low pressure. There are test stands with this sort of connection, but all the pieces are held in place so no part can move. Just wear safety glasses, and maybe put something solid like plywood between you and the bike just in case. There shouldn't be anything much worse than a messy leak that starts with a popping sound, but it's better to overdo the safety stuff. Air trapped in the system can cause dangerous things to happen, but it's not common.
I can give more details if needed, but off-list, since I've strayed pretty far already.
Steve Birmingham Lowell,Ma USA
Subject: [CR]Dented Tube Repair
There are severaI possible methods of repairing dents in frame tubes, depending on location, severity, wallet, and imagination. I have a Durifort Bertin that's a nice bike except for a shallow though large (1/4" deep x 1" circ) dent right on top of the toptube. Since the original paint is not damaged, I've been considering my options.
I've settled on trying the hydraulic method using a porta-power (a hand-operated hydraulic pump capable of 6,500 psi). The toptube is closed at the head-tube and has a small hole at the seat-tube. I'm going to rig a rubber plug with fittings and expander-bolt that will fit into seat-tube and allow attachment of the hydraulic line. I will fill the top-tube and fittings with hydraulic
oil, attach pump and pump dent away. I believe the thin-wall tubing (at the
dent) will be the first to pop. Pics before and after will be available next week (if successful). If unsuccessful and you don't hear from me again, this method is not advised.
Jack Romans
Sacramento, Calif