Poly-Flo T Fitting for Brakes

[Battson]

I recall you mentioning that you had issues with the reservoir leaking. I certainly wouldn't want 5056 spraying in the cabin or engine bay. I'll be using ATF myself.

https://m.aircraftspruce.com/catalog...?clickkey=5672

Above is the matco reservoir I have. For now I'll start with it in the cabin and half full, see how it works. Overflow tube will be plan B, and relocating to the engine bay plan C.

The Matco one is different, worth a try. I tried running it half empty but no joy. Maybe I just need a better bung.

I think the leaking is caused by heavy turbulence, but I have no conclusive proof. I definitely think they SHOULD not leak. But I haven't been able to fix it.

[Archer39J]

So I got my Poly-Flo fittings. First, I notice the stud inside the fitting that the Nylaflow fits around is quite small compared to the ID of the tube. I wonder if this will cause resistance when pressing the brakes as it restricts fluid flow. Battson have you had any issues with this?

Second, when ordering these fittings from ACS note that even though the description says the fittings come with brass nuts AND sleeves the fittings I got had nuts with plastic (I presume nylon) inserts. I'm talking with ACS about a resolution and they say they'll update their website.

[S Lathrop]

Just a lesson learned from auto racing: I had trouble with brake fluid coming out the vents in the caps on the master cylinder reservoirs. This problem became a real issue when I redesigned the chassis and increased the rigidity of the chassis. The problem leaking of the brake fluid also led to the degradation of brake performance.

The problem was aeration of the fluid from the harmonics produced by the engine vibrations. The track side solution was to get a cover on top of the fluid to prevent air getting to the brake fluid (think male contraception device). About that time master cylinders were being made with a diaphragm that covered the top of the fluid. Plastic reservoirs that could be remote mounted were also a solution and the one I have used for several decades. In short a reservoir that will be free of hi frequency vibration.

Maybe this is the leaky brake fluid problem.

[Battson]

Just a lesson learned from auto racing: I had trouble with brake fluid coming out the vents in the caps on the master cylinder reservoirs. This problem became a real issue when I redesigned the chassis and increased the rigidity of the chassis. The problem leaking of the brake fluid also led to the degradation of brake performance.

The problem was aeration of the fluid from the harmonics produced by the engine vibrations. The track side solution was to get a cover on top of the fluid to prevent air getting to the brake fluid (think male contraception device). About that time master cylinders were being made with a diaphragm that covered the top of the fluid. Plastic reservoirs that could be remote mounted were also a solution and the one I have used for several decades. In short a reservoir that will be free of hi frequency vibration.

Maybe this is the leaky brake fluid problem

This is insightful and probably the cause of the problem. My reservoir is certainly able to vibrate a lot, being mounted on an unsupported area of firewall. Thanks very much for this excellent information!

[Battson]

So I got my Poly-Flo fittings. First, I notice the stud inside the fitting that the Nylaflow fits around is quite small compared to the ID of the tube. I wonder if this will cause resistance when pressing the brakes as it restricts fluid flow. Battson have you had any issues with this?

Second, when ordering these fittings from ACS note that even though the description says the fittings come with brass nuts AND sleeves the fittings I got had nuts with plastic (I presume nylon) inserts. I'm talking with ACS about a resolution and they say they'll update their website.

Certainly no issues for me. The fluid doesn't really flow, it just transfers pressure, and that is basically instantaneous. The Nylaflow tube comes in two wall thicknesses, so I guess the small stud suits the thicker-walled tube.

The nylon inserts have been standard for a long time, I think they grip the nylon tube a lot better than the brass ones.

[Archer39J]

With greatest respect, maybe you're over thinking it? The fluid doesn't really flow, it just transfers pressure, and that is basically instantaneous. The Nylaflow tube comes in two wall thicknesses, so I guess the small stud suits the thicker-walled tube.

The nylon inserts have been standard for a long time, I think they grip the nylon tube a lot better than the brass ones.

Except the piston moves right? Ergo fluid is flowing, but looking at other components (parking brake) there are fine little channels inside, if you don't have a problem then there isn't an issue. Thanks for the confirmation.

[Battson]

Except the piston moves right? Ergo fluid is flowing, but looking at other components (parking brake) there are fine little channels inside, if you don't have a problem then there isn't an issue. Thanks for the confirmation.

Yep there is definitely some movement, but from a fluid dynamics point of view the orifice isn't an issue because the flow is so small and short-lived. Yes it will result in a small pressure drop while the fluid is in motion, but that pressure equalises very quickly once the fluid stops moving.

[Archer39J]

Yep there is definitely some movement, but from a fluid dynamics point of view the orifice isn't an issue because the flow is so small and short-lived. Yes it will result in a small pressure drop while the fluid is in motion, but that pressure equalises very quickly once the fluid stops moving.

Right, and if they were pinholes there would be a damping action when you pressed on the brakes. That was my concern, images of me standing on the brakes while I slip off a cliff/runway/into a river came to mind so I wanted to be double sure it wasn't an issue

[Battson]

Right, and if they were pinholes there would be a damping action when you pressed on the brakes. That was my concern, images of me standing on the brakes while I slip off a cliff/runway/into a river came to mind so I wanted to be double sure it wasn't an issue

Yes that is right, the overall size of the orifice is what controls the flow most of all. The orifice shape is important in some applications, but in this case I can't picture it being a problem. We did a lot of calcs for this kind of stuff in the University years, so I am just basing my judgement on memory of that. I am not aware of anyone having issues with the Polyflow fittings for brakes.

[Mark Goldberg]

Just to chime in again that I have personally seen two planes (one a Patrol) have a brake failure because of the PolyFlow lines. The Patrol had a rubbing issue, and another plane had the brake caliper heat up so much from braking while taxying in a cross wind that it melted the PolyFlow tube. I use them from the reservoir to the master cyls. But not on the high pressure side. Mark

[Battson]

For avoidance of doubt:

Polyflow Fittings
brasspoly.jpg

Nylaflow tube (Polyflow can be similar):
10-Nylon-Nylaflow-Tubing-Tube-5-32-Type.jpg

[tailwind]

Mark has a valid point about the possibility of heat presenting a problem by melting Nylaflow brake line. Nylaflow is nylon tube. It is sometimes used as a bearing in some applications so the wear issue I do not see as a problem inherent in the use of nylaflow, I see that as more of a maintenance issue. The same problem could occur when using metal or rubber hose. I chose to use DOT approved push fittings. MSC J & L Industrial part number 01469055. With this part number the lines can be disassembled and re assembled without tools. I chose part numbers with swivels so that movement can occur without stressing the system.

[Archer39J]

Just to close this out. After priming the brake lines and seeing how they operate, there is considerable fluid movement when the brakes are actuated. You absolutely wouldn't want to restrict this by narrowing or kinking the passage. I haven't noticed any delay or damping when quickly cycling the brakes with these fitting though.

[Battson]

Update on Polyflow PTFE lines vs stainless steel braided PTFE lines:

• Stainless braided lines are much firmer on the pedals.
• Brake pedal travel is reduced for a given braking force, with SS PTFE lines. The brakes are more responsive, almost twitchy, but this is no problem with large tires.
• Maximum action on the calipers is slightly stronger with the SS lines.

I replaced the lines from the pilot's master cylinders to the solid lines which connect the calipers. The rest of the lines are Polyflow PLFE, and suffer no pressure during operation. I like being able to see fluid in there before I commit to landing.