Hydraulic hose and fitting threaded connections.....

[Chuck Wintle]

at work i will need to make a few hydraulic connections for the equipment we use. is it better to use teflon tap or some of this anaerobic paste that is available? it made by 3M and it has some teflon in it. I like it because its easier to apply and connections rarely leak but what about hydraulic? Thx.

[Mark Bolton]

Worked with a friend for a while who was a parker hannifin distributor and we were constantly warned that teflon was the killer of hydraulic pumps. Tape was to be kept back 3 threads from the end and we never used any teflon paste or dope out of concern for it getting into the system.

Keep in mind too that hydraulic fittings of any kind nowadays are using rolled threads and not cut threads. These threads are much more precise and much stronger. Many of them can be assembled dry without leaking. Even taper pipe connections can be assembled with just a little bit of oil on the threads as a lubricant. Remember that pipe dope and teflon tape are actually just a lubricant. They are not there necessarily to seal imperfections in the joint. They are there to provide lubrication and prevent gauling (sp) which prevents you from getting the joint completely tight.

In days of old things like cotton wicking were used on crudely cut pipe threads to act as a sealant or gasket. This isnt the case any more with modern rolled threads.

[Tom M King]

Around here, almost any good auto supply store can make hydraulic hoses. I've always heard not to use Teflon tape.

[Lee Schierer]

Teflon tape is not a pipe sealant. You want to avoid it in a hydraulic system as it can get in the valves and cause problems. Shredded teflon is really bad in hydraulic systems. Anaerobic pipe sealants can be used with care, but keep it 1-2 threads back from the end of the threads. Most quality fittings don't require sealant.

[Myk Rian]

If you need any type of thread sealer for hydraulics, you need new fittings.

[Rich Engelhardt]

Teflon tape is not a pipe sealant

That's my understanding also. Teflon tape doesn't seal, it acts as a lubricant so the fittings can be tightened.

[Dan Hunkele]

Most all hydraulic fittings use o-ring seals or 37 degree bevels as sealing methods and should not require sealant. It still can be pipe thread, just be careful with the sealant so it doesn't get inside the system.

[Erik Loza]

I've always used teflon tape but as someone else mentioned, not near the tip. Never had a problem with it over the years.

Erik Loza
Minimax USA

[Mike Lassiter]

Most all hydraulic fittings use o-ring seals or 37 degree bevels as sealing methods and should not require sealant. It still can be pipe thread, just be careful with the sealant so it doesn't get inside the system.

As Dan said - it can still be pipe thread. Regardless of what others have said, pipe threads DO require a sealant. Male threads can be rolled instead of cut as someone noted; but as far as I am aware, all female threads are cut threads in any type of valve or housing that a fitting would be screwed into. Most are boss o ring fittings, but some are not. Teflon tape works fine if you are careful and not let it run off the end of the threads. It is also less messy if you have to get in an awkward place and try to screw a fitting in with dope on it - that ends up all over your fingers and tools.

Every pipe thread fitting I have ever saw in use had thread sealant or tape on them. Hydraulic, water, gas, fuel, oil, air systems always have pipe threads sealed. If it wasn't necessary to prevent seeps and leaks - it wouldn't be done all the time. JIC fittings and boss o ring fittings don't require sealant - except if the other ends is pipe thread.

[Mark Bolton]

Every pipe thread fitting I have ever saw in use had thread sealant or tape on them.

It's cheap insurance but with high quality threads lubricant is the only need. The taper is what's doing the sealing. The dope is there to lubricate the joint allowing you to get it fully together. Most dopes incorporate a sealant as well to cover poorly cut/made or field cut threads.

I'm not advocating not using some form of thead lubricant, just that it's not there as a sealant unless your using poor quality fittings. As has been, other than on returns pipe threads are not as common in hhydraulics any more but definitely are still used.

[Tom Welch]

Okay, if you want the down and dirty scoop, here it is. Hydraulic fittings can be, 1. Pipe thread- NPT or NPTF 2. Boss (oring sealed)
3. JIC (37º flared) 4. Autoclave - for extremely high pressure (like 10,000 psi) 5. SAE (45º flared for low pressure like 1,000 psi or less) 6. Tube fittings - like swagelock etc...

Pipe thread fittings - are either NPT or NPTF. The NPT do require some type of sealant like teflon tape or pipe dope to get a seal, as they only get a root to crest seal on the threads. NPTF (originally made for the fuel industry thus the "F") make up root to crest and cheek to cheek on the threads. these fitting are made to seal with out any sealant of any kind. A lot of companys now only make NPTF pipe thread fittings, so check with the manf and see what type you are buying.

Now concerning what type of sealant you use - Teflon tape is high cause of many of hydraulic failures, but only cause it is installed improperly, always start with the third thread when putting it on, as the fitting is tapered and the first 2 threads do not really make up real tight to get a good seal anyway. Pipe dope - Made for hydraulic systems is fine for use, the biggest mistake here, is applying too much.

Remember, just use sealant on NPT fittings. Do not put on flared fittings or oring seal fittings.

Just my 2 cents from almost 30 years in the fluid power industry.

[Mike Lassiter]

Okay, if you want the down and dirty scoop, here it is. Hydraulic fittings can be, 1. Pipe thread- NPT or NPTF 2. Boss (oring sealed)
3. JIC (37º flared) 4. Autoclave - for extremely high pressure (like 10,000 psi) 5. SAE (45º flared for low pressure like 1,000 psi or less) 6. Tube fittings - like swagelock etc...

Pipe thread fittings - are either NPT or NPTF. The NPT do require some type of sealant like teflon tape or pipe dope to get a seal, as they only get a root to crest seal on the threads. NPTF (originally made for the fuel industry thus the "F") make up root to crest and cheek to cheek on the threads. these fitting are made to seal with out any sealant of any kind. A lot of companys now only make NPTF pipe thread fittings, so check with the manf and see what type you are buying.

Now concerning what type of sealant you use - Teflon tape is high cause of many of hydraulic failures, but only cause it is installed improperly, always start with the third thread when putting it on, as the fitting is tapered and the first 2 threads do not really make up real tight to get a good seal anyway. Pipe dope - Made for hydraulic systems is fine for use, the biggest mistake here, is applying too much.

Remember, just use sealant on NPT fittings. Do not put on flared fittings or oring seal fittings.

Just my 2 cents from almost 30 years in the fluid power industry.

+1
And to add to the fittings - it you don't KNOW BOTH fittings are the NPTF style you could get a leak or seep by putting the two different styles together. Most tapered pipe fittings commonly available to "everyday people" are not the dry seal type available from plumping supply stores or Home Depot or Lowes. But the original question was about hydraulic fittings. I haven't got 30 years experience but over half that working on equipment and garbage trucks that have a little bit of hydraulic lines, tubing and valves. When you 2500+ PSI you need a good seal, and even then sometimes you get seeping. Ex-coworker was a gorilla when it came to tightening fittings. I have saw the JIC type fittings so tight that the nuts had to be heated with a torch or us a air hammer and chisel on the nut to get it to loosen. Everyone hated to come behind him on anything like that - but I have to say, he NEVER had a leak from loose fittings. Although there were a few times the fittings would crack in use and leak because of over tightening. Common sense goes a long way.

[Jim Koepke]

My experience in this kind of work is very limited.

My question is if a joint is made with tape or sealant, doesn't it risk getting into the system if the joint ever needs to be opened?

Ex-coworker was a gorilla when it came to tightening fittings. I have saw the JIC type fittings so tight that the nuts had to be heated with a torch or us a air hammer and chisel on the nut to get it to loosen.

From everything I understood about the fittings in the equipment I worked on this was a sure way to damage the fittings. Someone like this would have likely been talked to once and dismissed the next time.

Much of my experience was with Parker fittings. The instructional literature had warnings to not over tighten.

jtk

[Mark Bolton]

Okay, if you want the down and dirty scoop, here it is. Hydraulic fittings can be, 1. Pipe thread- NPT or NPTF 2. Boss (oring sealed)
3. JIC (37º flared) 4. Autoclave - for extremely high pressure (like 10,000 psi) 5. SAE (45º flared for low pressure like 1,000 psi or less) 6. Tube fittings - like swagelock etc...

Pipe thread fittings - are either NPT or NPTF. The NPT do require some type of sealant like teflon tape or pipe dope to get a seal, as they only get a root to crest seal on the threads. NPTF (originally made for the fuel industry thus the "F") make up root to crest and cheek to cheek on the threads. these fitting are made to seal with out any sealant of any kind. A lot of companys now only make NPTF pipe thread fittings, so check with the manf and see what type you are buying.

Now concerning what type of sealant you use - Teflon tape is high cause of many of hydraulic failures, but only cause it is installed improperly, always start with the third thread when putting it on, as the fitting is tapered and the first 2 threads do not really make up real tight to get a good seal anyway. Pipe dope - Made for hydraulic systems is fine for use, the biggest mistake here, is applying too much.

Remember, just use sealant on NPT fittings. Do not put on flared fittings or oring seal fittings.

Just my 2 cents from almost 30 years in the fluid power industry.

What about BSP? BSPP? ORFS? Seal-Lok? Ferrule-Lok? JIS?

[Dan Hunkele]

45 degree fittings are meant to be used for flammable liquids. Read specifications here.

http://www.parker.com/portal/site/PA...ARE%20FITTINGS