Fuel line and fittings assembly - SailNet Community
LinkBack Thread Tools
post #1 of 3 Old 07-20-2010 Thread Starter
Join Date: Mar 2007
Posts: 124
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 11
Fuel line and fittings assembly

My new fuel system has many fittings between the tank and the lift pump--filters, valves, electric pump, etc. Most of these pipe fittings are 1/4-inch brass with standard pipe threads. In all my previous plumbing experience I always used Teflon tape on the threads to prevent leaks. Some are saying that Teflon tape is not appropriate in a fuel system--pipe dope is the preferred sealant. What is the collective wisdom of this forum? Thanks.

s/v Truthsayer
I33 is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
post #2 of 3 Old 07-21-2010
Senior Member
RichH's Avatar
Join Date: Jul 2000
Location: Pennsylvania
Posts: 4,463
Thanks: 42
Thanked 249 Times in 235 Posts
Rep Power: 18
NEITHER PTFE tape nor PTFE 'dope' is appropriate for fuel system connections !!!!!

The common connection fittings on fuel system are either very inferior compression fittings or flared/double flared connectors whose mechanism of 'sealing' is by METAL TO METAL (ring-seal) CONTACT - the 'threads' of the connector only providing the necessary force to 'drive' the metal mating surfaces together and make a 'seal'. Such sealing methods are always DRY and one should NEVER use dope or tape to make them seal.

So, if a typical fuel system connector is leaking it means that the metal-to-metal seal in not 'integral' and using dope or tape will only cause the leaking fluid to be 'trapped' on the outside of the sealing surfaces.

Of the two, (and when used correctly in 'threaded' - NPT or BSB joins) PTFE tape is SUPERIOR because it will stay in place and wont generate 'particulate'. Dope isnt very strong because the 'carrier' which holds the PTFE particles together can easily 'wash away' leaving only the PTFE partices, which after the carrier migrates, so too in a short time the residual particles will also migrate.

BTW - the so-called compression fittings are the LEAST desireable for a fuel system; double flared is the choice for MANY reasons:
1. The compression fitting is considered to be a ONE-TIME-ONLY usage/tightening. If opened the tubing under the 'ferrule' should be 'trimmed back' and the ferrule should be reinstalled over 'fresh' or NON-COMPRESSED tube.
2. Compression fittings are subject to 'stress-relaxation' of the copper tube, thus leaving the connection very subject to leakage over time .... very important on 'VACUUM' motive systems.

Whenever possible one should choose 'double flared' connectors for 'surety' and 'safety'
Boat builders use compression fittings because they dont require 'special tools' - cheap
Copper tubing is REACTIVE to most diesel fuels - a 'prime' system should be with stainless steel tubing.

Last edited by RichH; 07-21-2010 at 09:03 AM.
RichH is offline  
Quote Quick Reply Share with Facebook
post #3 of 3 Old 07-23-2010
Join Date: Dec 2009
Location: North Jersey
Posts: 166
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
Gil, I just did a complete overhaul of my mech system, from prop to the fan belt new. I was at the point where I was laying out my supply and return fittings and valves, in copper. I was advised by my engine supplier, also a certified mechanic, to use coast guard approved rubber hose only, to abandon the old copper system. I installed a new ballvalve at the tank and ran I believe 7/16" approved hose for supply and return lines. I clamped everything down and it was a good deal easier than the copper also. He said it was something to do with vibration and imbedded copper in the glass. Red

Red, 77 Jeanneau Gin Fizz 38
redhead78 is offline  
Quote Quick Reply Share with Facebook

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Forum Replies Last Post
Don't need no stinkin' fuel tank! 30Irwin Gear & Maintenance 12 04-02-2010 08:13 PM
Permanent gas line fittings for outboard? BallastBoy Gear & Maintenance 2 04-08-2002 04:26 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome