Diesel filter - sealing

[clayjay]

I've just purchased a large Diesel filter for my supply line - the type with the large glass bowl at the bottom for filtering out water. I've also had to purchase the brass tails for the fuel lines to plug onto on the inlet and outlet.
My question is what compound, if any, do I use to seal them ?
With domestic plumbing you use PTFE tape on threads to make them watertight, is there something for use in these situations that is diesel resistant ?

[RichH]

The threads of such fittings dont do any of the 'sealing' ... either with a compression fitting (most common) the brass 'ferrule' makes a 'ring seal' (metal to metal) with the tubing end; a flared or double flared (preferred) also are 'metal - to - metal' seals.

PTFE tape is resistant and chemically compatible with Diesel Oil .... but if the threads of such a connector are leaking you have a BAD connector and should replace it with new -- if the threads are leaking it means that the metal to metal seal in the connector is not working.

Compression fittings (the cheapest and commonest fittings on boat fuel lines) are usually a 'one time only' seal as the 'ferrule' will compress the copper tube to the point of not being useable in subsequent 'tightenings' ... although most DIY'ers will re-tighten them again and again ... and wind up with 'mysterious' air suction leaks galore in the future.

[sailingdog]

Go to the store and ask them for some diesel fuel line pipe thread dope or sealant. This is one possible compound you could use. Here is another. Generally, teflon tape isn't recommended for diesel fuel lines, especially if they are downstream of the fuel filter, since the teflon tape can shred and the bits can foul the fuel injectors.

BTW, RichH, I think he is talking about the lines going into a big Racor-type fuel/water separator filter. These are generally connected using fuel hose, not copper pipe, and as such, the threads are what seal the connection... since it is just a hose nipple that he is screwing into the side of the filter housing. Compression fittings and flared fittings are generally only used with copper pipe fuel lines, and last I checked, it wasn't generally common to find copper pipes in use on a sailboat diesel fuel system for most of the runs. Copper pipe is a poor material on a boat, as it tends to fatigue from the motion and vibration of a boat.

[clayjay]

Thanks guy's. Yes it is the Racor type filter and the fittings screw into the body. They are brass and have a 45degree seat which corresponds quite well with the seat in the body. I just want to cover all bases as it would be sods law to fit it all, turn on the fuel tap and then watch the Diesel start to drip out from the threads.

[sailingdog]

Clayjay-

Get a small can of the non-hardening rectorseal. It'll last you a long time...and it's good stuff to have aboard. You can use it for propane fittings, water lines, diesel lines...basically any thing you need to have not leak that has threaded fittings.