The International Cessna^® 170 Association

Are there legal alternatives to the metal oil pressure guage line (the section from the engine to the firewall)? I've heard stories of it breaking right in the vibration loop. I'm thinking braided flexible high pressure hose...Russ Farris

Russ

You can use an Aeroquip 306-2 hose with 471-2D fittings but then you've also got a life limited hose. I still like it better than copper behind the firewall. They can be made up without a mandrel tool but you should get instructions or a lesson from your local mechanic. In my conversion/restoration project I've replaced all the 1/8th copper forward of the firewall with new. It's amazing how hard it gets. I also have a fuel pressure gauge and Manifold pressure gauge that use the 306 hose behind the firewall. (the man pres is a -4)

If you get the chance to check it the fitting on the case for the oil pressure is a special restricted steel fitting so that if you do break a hose the oil will puke out slower. I've seen a number of these replaced with standard non-restricted fittings. Worse yet with aluminum.

GOOD question! I had never thought of this changeover possibility. I think the aeroquip hoses would be much better. Once again, the automotive industry is far ahead of us in this respect...as metal capillary hoses are just not seen. I am not aware of a life limit for the aeroquip hoses, but they do deteriorate over time. My experience with them is that they fail slowly, developing a slow leak that can be detected and disaster averted. The copper lines tend to fail in a spectacular manner, spraying oil all over the place. I am not aware that copper lines or any metal capillary lines in flexible service ever give a warning of impending failure. My aircraft goes in for annual next month and I'll specify the changeover! Thanks for the idea!

George

The Stratoflex equivalent is 193 hose which on their website states it as Buna-N ...oil resistant..."Beech, Cessna, Piper used for fuel, oil, and hydraulic drains. Also in some aircraft it's used for engine fuel pressure and oil pressure instruments."

The Aeroquip website really sucks and my research so far shows them not mentioning 306 hose to be used with fuel or oil. But no real cautions against it.

I've used it for oil pressure leads before and it held up fine for the 195 for ten years before I sold it. The problem is of course that all the pressure gauges are set up for -2 size and the 306/193 are the only hoses that comes in that size. So to use 303 or something else one would need to adapt to -3 fittings somehow. You've got me concerned though as I was about to make up these hoses for behind the firewall on the 180 conversion for both fuel and oil pressures. I need to get this figured out or look for some -2 to -3 bulkhead fittings which might be hard to find. Or maybe I'll just go back to copper for now and solve it later because I'm getting pretty close to running it. Just rambling on.....Thanks for listening.

Aeroquip and Stratoflex are different mfr's who make various products, not all of which are directly interchangeable. The Aeroquip hose meets Mil spec (H-55903) for air. Statoflex does not specify which Mil specs are met by their 193 hose in the catalog.

Another option is to replace it with an electric unit. Install the sending unit and run a few wires to the instrument. The restrictor is not to impeed the flow of oil in case of a failure; it is to remove the wiggle from the gauge that can be seen occasionally. If you had an engine with a diaphragm pump it would be a common thing to stake the hole to close it up even more to remove all wiggle.

Kelly

In an oil pressure line, the restrictor is to reduce oil loss in case of line failure. In a manifold pressure gauge system, the restrictor is to reduce "wiggle" of the needle (however most modern gauges already have a dampner already incorporated.) (Russ, the gauge you have selected is already dampened....you do not need a restrictor.)