Teflon tape on hydraulic fittings

[ericm979]

You shouldn’t have to use any kind of sealant if you are connecting them properly.

That is true of most types of fittings used for hydraulics but not NPT.

NPT fittings seal by deforming the threads. Most other fittings used for hydraulics seal with O rings or dedicated sealing surfaces like the tapered seal on JIC fittings. NPT was designed for low pressure stuff like home water systems, under 100 psi. In order to get NPT fittings to seal under tractor hydraulic system pressures (2400 psi or so), I find they need sealant. Teflon dope is a lubricant but not much of a sealant and does not work in my experience. Teflon tape can seal but it can also get dislodged, go into the hydraulic system and plug passages. Loctite 545 which is are made specifically for sealing hydraulic system NPT threads has worked the best for me.

 

[CJONE]

Been working with Hydraulics for 40+ years and building systems for 30. After having a few leaks on every system we built starting out, I had my guys and myself use both TEF pipe dope and high quality TEF tape and had very few leaks if any afterward. Now this is on NPT and BSTP. Use no sealant on actual hydraulic fittings like JIC, BSPP, SAE and the like, just a good quality lube or antiseize. With tapered fittings as was said leave the 1st thread exposed so no teflon tape gets in the system. And yes I have cleaned reliefs out with teflon packed in them. From less than careful people assembling them. A good example of no tape leaks was a few years ago I built a 450HP hydrostatic drive system for a top drive oil drilling rig. The company needed the drive by the weekend so they sent 2 of their tool pushers help me assemble it. I was laying fittings out and building hoses and they were assembling. I told them to use BOTH tape and dope but they said the owner always said not to use tape. I warned them again it would leak but they said no tape. OK. I assembled the high pressure filters [with both tape and dope with them fussing]and then on friday we were ready to test. Once I figured out they had the kill and the throttle hooked up backwards on the Cat diesel, we fired it up and let it warm up as I was bleeding the high pressure side of the system. Once we had full charge pressure at 290psi the leaks were very apparent. Even their connections on the return coolers were leaking! Then I smiled at them and began testing the high pressure side. Once I got it to 4000psi the leaks were the size of pencils running out of the fittings except for the high pressure filters. I could not even get to the 5500psi relief setting but for a quick second just to check that they worked. The system really started leaking once it warmed up. They looked at me and ask what we were going to do? I told them THEY were going to pull all the leakers apart and tape and dope them and I was going home for the weekend AND shutting my phone off, so don't mess any of the lines up! I am sure they had a fun weekend. CJ

 

[Will S]

Quote:

That is true of most types of fittings used for hydraulics but not NPT.

NPT fittings seal by deforming the threads. Most other fittings used for hydraulics seal with O rings or dedicated sealing surfaces like the tapered seal on JIC fittings. NPT was designed for low pressure stuff like home water systems, under 100 psi. In order to get NPT fittings to seal under tractor hydraulic system pressures (2400 psi or so), I find they need sealant. Teflon dope is a lubricant but not much of a sealant and does not work in my experience. Teflon tape can seal but it can also get dislodged, go into the hydraulic system and plug passages. Loctite 545 which is are made specifically for sealing hydraulic system NPT threads has worked the best for me.

So much bad information;

"Parker Hydraulic Fittings and Adapters:
NPT-to-NPT steel hydraulic hose adapters provide good strength, conductivity, and durability in high-pressure hydraulic applications. They connect compatible hydraulic hoses to pipe or equipment that has different thread sizes. These adapters have an NPT (National Pipe Taper) connection on both ends of the fitting. Compare this product..."

Block Brand Thread Sealant
Hercules Block Sealant

KEY FEATURES

• An all-purpose, high-performance pipe joint and gasket sealing compound
• Quickly Provides leak-proof resistance to high-pressure, temperature, expansion, contraction and extreme vibration
• Forms a tough, flexible and leak-resistant seal
• Use for joints, threads, valves, flanges, gaskets, pumps and tanks
• Performs over a range of -90 through 450 degrees Fahrenheit on steel pipe
• Can be used with hydraulic pressure up to 12,000 psi and gas pressure up to 2,600 psi

Oatey PTFE white thread sealant:

• Lubricates and seals all threaded joints
• White, non-hardening, non-separating, non-toxic paste
• For use with water, steam, caustics or diluted acid lines
• Withstands up to 3,000 psi on gases from -50°F to 400°F, and 10,000 psi on liquids from -50°F to 500°F
• Can be used with plastic and metal threads

 

[Little Red Tractor]

My experience with the tape has always been good. I did plumbing/heating work *back in the day* and never had a problem. HOWEVER, never, NEVER, put it on the first or second thread.

 

[droy]

You shouldn’t have to use any kind of sealant if you are connecting them properly.

Especially with stainless, I often use either t-tape or a paste with PTFE as a thread lubricant, the sealant property is a plus.

 

[jdmeth]

Teflon tape is for sealing tapered threads.
Hydraulic fitting's don't seal via the threads.
If you're using teflon tape on hydraulic fittings, you're either trying to patch something in the field to hold on till you can get it to the shop and properly fixed OR you don't know what you're doing.

Or you have an older John Deere (3020 or simular) ) that uses John Deere's proprietary bevelved end fittings that use a locking lever to hold them in. Those will leak unless you use Teflon tape. I farmed for over 25 years with those tractors and replaced dozens of the fittings. Any time I couldn't find any tape and just slapped them on the hose they leaked. The newer ISO types used on newer JDs usually didn't leak but I put tape on those too. Never had any trouble but JD uses a fine mesh screen on its hydraulic pump suction intakes.

 

[ericm979]

The teflon pipe dope I tried (one that was recommended here) was a non hardening type. It might have lubricated the threads but did not seal them, and they leaked. They can claim 3000 psi but that's not the results I gott.

A sealant that hardens is the way to go. Loctite 545 works well for me but I'm sure there are others.

 

[Hilbilly]

According the information I found, the Locktite requires 24 hrs to fully cure, which could be an issue when your in a hurry. But then you will know there is no chance of tape bits getting into the system. One thing I really don't like about Locktite is the ridiculous price, at least where I am.

 

[/pine]

A few thoughts and stuff from the untold number of previous threads on the same topic...!

tapered threads are only meant to be used once...
...Teflon tape is primarily a lubricant to allow a tighter seal...If the original installation does not have any tape etc...tape or other lubricants.sealers will allow deeper thread purchase if being reused...(FWIW...I've seen tractors and all kinds of equipment sitting on dealers lots with visible tape on hose, valve and other NTP etc. fittings..)
...Even the liquid type sealants/lubricants will harden and leave flakes of plastic like substance...
...If a NTP fitting is loosened care should be taken to remove all "sealant" debris from both the male and female ends...

 

[Smokeydog]

Just built a hydraulic chainsaw for the tractor. All taper to taper NPT threads used Loctite 545. All swivel NPT to taper NPT used no sealant. These allow easy assembly and service of component parts. No leaks.