I will defer to Parker on this, I know that they have done testing to determine the best way to seal fittings.
This is what they state for
O-ring Boss. R4
Inspect components to ensure that male and female port threads and sealing surfaces are free of burrs, nicks, and scratches, or any foreign material.
2. If O-ring or seal is not pre-installed to fitting male port end, install proper size O-ring or seal, taking care not to damage it.
3. Lubricate O-ring with light coating of system fluid or a compatible lubricant to help the O-ring slide past the port entrance corner and avoid damaging it.
4. Screw fitting into port and tighten to proper torque from the appropriate table located on pages R5 - R6
Below is for JIC R26
Torque Method
With proper tube fl are alignment with the nose of the fitting, tighten the nut to appropriate torque value in Table R23. This method is fast and accurate when preset torque wrenches are used. Consistent component selection is recommended so that the effects of dissimilar plating is not an adverse factor in joint integrity. This makes it desirable for high production assembly lines. However, a joint assembled using the torque method
can only be checked for proper tightening by torquing it again.
Note: This method should not be used if the type of plating on the fitting and mating parts (sleeve + nut or hose swivel) is not known. The torque method should not be used for lubricated or oily parts as improper clamping forces may result. Over-tightening and fitting damage may occur as a result
All straight thread fittings have this note.
Assembly Torque: Torque values are for unlubricated carbon steel components and properly lubricated stainless steel components. All stainless steel Triple-Lok tube nuts have an anti-seize lubricant to prevent galling during assembly.
No additional lubricant is needed unless the tube nuts are washed or heated above 150ºF. Stainless steel fittings use the upper limit of torque range
Pipe Thread R7
The proper method of assembling tapered threaded connectors is to assemble them finger tight and then wrench tighten further to the specified number of turns from finger tight (T.F.F.T.) given in Table R5. The following assembly procedure is recommended to minimize the risk of leakage and/or damage to components.
1. Inspect components to ensure that male and female port threads and sealing surfaces are free of burrs, nicks, scratches, or any foreign material.
2. Apply sealant/lubricant to male pipe threads if not pre- applied. For stainless steel fittings, the use of Parker Threadmate sealant/lubricant is strongly recommended.
(Pre-applied dry sealants are preferred over other sealants). With any sealant, the first one to two threads should be left uncovered to avoid system contamination.
If PTFE tape is used it should be wrapped 1-1/2 to 2 turns in clockwise direction when viewed from the pipe thread end.
Caution: More than two turns of tape may cause distortion or cracking of the port.
3. Screw the connector into the port to the finger tight position.
4. Wrench tighten the connector to the appropriate T.F.F.T. values shown in Table R5, making sure that the tube end of a shaped connector is aligned to receive the incoming tube or hose assembly. Never back off (loosen) pipe threaded connectors to achieve alignment.
5. If leakage persists after following the above steps, check for damaged threads and total number of threads engaged.
I was surprised about the comment for tape so I looked for another reference.
Rhino Ag in reference to installing hoses on a loader.
Apply sealant only to all tapered threads unless coupled with swivel adapters. When using Teflon tape, wrap tape clockwise (as viewed from end) and wrap only twice. Keep sealant away from first two threads of tapered end to prevent contamination of hydraulic fluid. Do not use sealant on O-ring or flare adapter threads.
Based off what the manufactures state we should be assembling straight thread fittings dry and using pipe dope or tape on tapered threads. I was surprised that tape is an approved method of sealing. The folks at parker know more about sealing threads than almost anyone on the forum and have spent thousands testing the best methods. Feel free to link to reliable sources that state otherwise. The tape for tapered threads was new to me and I have been advising clients that tape was evil for years....
