New Holland 850 hay baler hydraulic hose fittings

[aussieboy1000]

Hi All
Just got 4 hoses made up for the tailgate rams - the 2 hoses that fit into each ram on each side, not the tractor coupling end.
I see on the hydraulic shop invoice they used 3/8 NPTF fittings.
I cannot get them to engage more than 1 1/2 threads by hand before they get "spanner tight". I am a bit hesitant to tighten them right up in case I strip the threads. With the old fittings they hand tighten 3 threads before reaching for a spanner.
Would the old fittings be NPT? Is there that much difference between NPTF and NPT? I know when I measured with the callipers the old fittings are 1/4 of a mm smaller.
Are the new fittings going to leak with only a couple of threads engaged even if I use thread tape ( as I see the old fittings had).
TIA
Dave from Australia

 

[K5lwq]

It should be 3/8-18 NPT. NPT and NPTF is the same. I think you are good to go! :thumbsup:

 

[TX mower]

Actually NPT and NPTF are not the "same", though they share common gross O.D., taper, thread angle, and thread-count/inch specifications for any given nominal size. There are meaningful differences (though sometimes difficult to detect by casual inspection) between the two in the detail of the thread profile at the 'peak' and 'valley' of the thread.

NPT male mated with NPT female, by design, requires sealant/tape to effect a leak-free connection (the primary contact surface between the male and female threads is at the sloped face of the thread).

NPTF male mated with NPTF female, by design, is a 'dryseal' connection not requiring sealant/tape to effect a leak-free connection (the primary sealing contact surface between the male and female threads is at the 'peak' and 'valley' of the thread).

All that notwithstanding the two are generally 'compatible' though sealant/tape is most often required when mixing the two to effect a leak-free connection.

One of the issues with 'mixed connections' is the lack of published torque or 'additional turns of hex-flats after finger-tightening' specifications for effecting a proper seal - you're left with Trial-and-Error to determine how tight to make the connection to effect the seal.

The differences in the detail of the thread profile accounts for the difference in 'tightening effort vs depth of penetration' when they are mixed and may be more apparent when dealing with 'harder' fitting materials vs 'softer' fitting materials (e.g. steel vs brass).

Among many sources of info found via google that may be of interest:
BAER Toleranzen fur Schneideisen (German source in English language)
Thread Type Compatibility | Pipe and Hose

Yeah, maybe a nuanced distinction of machinist's interest, but IMHO it's sometimes useful for even non-machinists to have an accurate basic understanding of such nuances.

 

[K5lwq]

TX mower, thanks for clearing that up. I have always interchanged both without issues although I have noticed some tightened up better than others. Now I know the difference!:thumbsup:

 

[TX mower]

To the point for Dave in Australia .... given that the 'old' interface used tape and the 'new' interface is tighter, I suspect that the original ram fitting is NPT and you're just observing the expected difference mating that with the new NPTF hose fitting.

With sealant/tape and judicious tightening IMHO you should be able to effect a good 'lifetime' seal without stripping anything - you'll likely not end-up with as many total turns/depth of penetration on the fitting as you would if they were an exact thread 'match-match'.

IF this is a connection that's frequently R&R'd you might want to consider getting a proper exact thread 'match-match' .... either with a short adaptor fitting with 'proper' threads on each end or a revised end on the hose; that might make things easier to effect the seal with frequent removal/replacement and more robust over the long-haul.