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  #1  
Old 12-01-2019, 02:14 PM
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rv8ch rv8ch is online now
 
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Default RV-8 low pressure plastic brake lines

I have not been able to fix this leak for some reason. Left leaks, right does not. Tried both the plastic insert and the brass. Cut the hose to ensure a straight connection. Made sure it's clean. Very strange.



I've read lots of threads where people write "no problem with mine leaking" or "I replaced them with real hose."

I think I will replace them. Seems like it would be better to "Y" them just under the panel, and only bring one hose to the reservoir - anyone see an issue with that?

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Old 12-01-2019, 02:57 PM
lr172 lr172 is online now
 
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You sure it's not the NPT threads on the fitting? These need to be tighter than most are willing to do and require a good sealant. I have one that leaks a drop every month or so. Keep putting it off, as I don't want to bleed again.

Larry
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Old 12-01-2019, 03:37 PM
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bjdecker bjdecker is offline
 
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Default Better stuff...

I wasn't a fan of the brass ferrule stuff that Van's puts in the kits. For my second RV-7 I used Parker Hannifin Prestolok PLP Push-to-Connect fittings for the low-pressure brake connections.

Parker Hannifin W368PLP-4-2 "Male Y Connector", 1/8" NPT to 1/4" dual tube, at the Firewall/Reservoir (Qty 1).

Parker Hannifin W369PLP-4-2 "Male Elbow Swivel", 1/8" NPT to 1/4" tube at the master cylinder "input" side (low pressure) (Qty 2).

Good luck!
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Old 12-01-2019, 03:43 PM
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Default not the npt threads

Quote:
Originally Posted by lr172 View Post
You sure it's not the NPT threads on the fitting? ...
I thought the same thing at first, but unfortunately it's leaking just between the plastic tube and the brass nut. The fluid collects on the top of the nut. Hard to see the fluid with this picture, but you can see where I'm talking about I believe.



I think before replacing the hoses I'll take the whole assembly out and look at it closely to see if I'm not missing something silly. I just drained the fluid so should be pretty quick.
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Old 12-01-2019, 03:46 PM
lr172 lr172 is online now
 
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Quote:
Originally Posted by rv8ch View Post
I thought the same thing at first, but unfortunately it's leaking just between the plastic tube and the brass nut. The fluid collects on the top of the nut. Hard to see the fluid with this picture, but you can see where I'm talking about I believe.



I think before replacing the hoses I'll take the whole assembly out and look at it closely to see if I'm not missing something silly. I just drained the fluid so should be pretty quick.
Ok. Make sure you are getting those tight enough as well. When done properly, the ferrule will compress around the tubing and this operation is critical for preventing leaks. These also need to be tighter than those are used to tightening 3/16" bolts. It takes a decent amount or torque to compress that ferrule.

When you take them off, check the ferrule. If you can't see that it created a slight indentation into the tubing, you are not getting them tight enough. Pretty much every refrigerator in america has this style fittings for the ice maker. They are very reliable when assembled correctly.
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Last edited by lr172 : 12-01-2019 at 03:49 PM.
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  #6  
Old 12-01-2019, 04:13 PM
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Pics worth 1000 words...

https://x3x0pg.by.files.1drv.com/y4m...&cropmode=none

https://xnx0pg.by.files.1drv.com/y4m...&cropmode=none
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Old 12-01-2019, 05:49 PM
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FWIW, I used the brass Parker 63PT inserts rather than the plastic. Never had a leak. On the pipe threads I used Pneumatic/Hydraulic sealant (like Permatex 54540). I figured if it was good enough for Caterpillar tractors, it was good enough for my airplane.
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Last edited by snopercod : 12-01-2019 at 05:54 PM.
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Old 12-01-2019, 09:01 PM
Norman CYYJ Norman CYYJ is offline
 
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Make the bend in the plastic less aggressive coming out of the fitting, it might help.
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  #9  
Old 12-02-2019, 07:06 PM
Scott Hersha Scott Hersha is offline
 
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I also have had trouble getting these low pressure lines to keep from leaking - slowly. I have come to the conclusion that there are two types of low pressure plastic lines terminating in brass compression fittings: those that leak, like mine always did, and those that don’t leak now - but will pretty soon.... This is (of course) untrue, but I believe these type fittings take a certain amount of expertise to install correctly, and I was never able to get it right. It’s very important to have a smooth straight cut on the tubing, use the correct tubing insert, and make sure you hold the assembly fully inserted tightly in the fitting, and straight before tightening the nut. Otherwise the brass double tapered ferrell will get slightly crooked/tilted and will either leak now, or leak later, but it will always leak if not installed correctly. I needed a more fool proof design. I found the nylo-seal all plastic fittings and lines to be fool proof and also the push on fittings from safe-air with their nylon tubing- low pressure only. Never had a leak with either of these. For the high pressure side of brake lines, I only use AN fittings with #3 or #4 braided hose and aluminum hard line - never nylon.
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Last edited by Scott Hersha : 12-02-2019 at 07:09 PM.
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Old 12-03-2019, 02:43 PM
TS Flightlines TS Flightlines is offline
 
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Back in the industrial days, only brass or stainless inserts used on airbrake tubing---like those used by Vans. THe compression action of the nut against the ferulle will try and distort the hose it there isnt something there to support the ID of the hose.

OH----and when we use teflon for the reservoir application like Mickey posted, we use a 45* hose end on the 'run' side of the tee--the port that comes straight out, we use a 90* hose end on the branch side. Both hoses converge together near the longeron, and route to the master cylinders.

Tom
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