Sealing of 2" threads in hydraulic suction-line.

[hydraulicseal]

I have serious proplems in sealing large BSP threads 2", on stainless steel tupes, in hydraulic suction-line. Today i have tried with loctite 542 or omnifit seal 46M and activator VT2200, with no succeed. after a short while i have a leak!

 

[hydromech]

Odd one this...

I have used 542 to seal threads loads of times with no problems.

Obivious questions are...

1) Are both threads BSP tapered..?

A tapered pipe thread can be used in a parallel hole, but a parallel pipe thread in a tapered hole will have very little thread contact.

2) The fitting will have to be whacked up really tight to activate the thread sealant. Are you making the joint really tight. You should only see a couple of threads when the fitting is fully tight.

You will need to careful though as the stainless tube is not a forgiving as nominal bore steel tube. It might crack the pump body if you go too tight.

It is unusal to find hydraulic pumps with 2" inlet port threads. Could it be that the pump has an SAE flange port?

If it is SAE port, can you use a flange with a parallel thread?

Better still...can you explain what type the pump is and what the wall thickness of the tube is.

Regards

Adrian

 

[hydraulicseal]

I use not only 2" thread but also 1" 5/4" and 1½", but,
not bigger than 2". Maybe i should try to explain, a litle
more about the system.
1)From the hydralic tank i go directly to a 2" ballvalve with 2" parallel threads, here i have the first 2 threads wich might be leaking(not allways). therefrom i go to 2 variable rexrothpump type: a10vo 71 ccm/rev with sae flange and 2" parallel thread. between i have off cause a Tee and som 2" hose, but no problems with those parts.
It is very important to have large capasity because we run the system in very cold conditions (until -30C)
Our tubes(2"iso) have allways outside tappered threads.
2) I cannot allways make a tight fitting because I'm using
fittings with different bends, wich must be positioned in fixed angle and sometime i have to turn the fitting for istant 180 degree backward. and this gives me offcause some problems.
I thought that there might exist some sealing tape wich could take the clearance in the thread.
finally i can say that it is all mounted on a truck wich generate a lot off vibrations.
I hope those informations are telling more about the system and my problems.
Best Regards
LARS

 

[hydromech]

The sealing tape that you are looking for is called PTFE tape.

It is ideal for sealing tube fittings and it is easy to use and very cheap.

The problem with it is that when the pipe is installed small pieces of the tape can get pulled into the pump.

It is not recommended for use on hydraulic pump suction lines, although many people do use it.

It's upto you Lars, they are your pumps. If you want to risk it go ahead.

If the tape gets into the pump, there is a risk that it could get trapped between the port plate and the piston block, tipping the block and wrecking the pump.

Good Luck

Adrian

 

[MikeHalloran]

It sounds like a natural application for a Tru-Seal(r) nut, but I couldn't find them in metric/BSP sizes.



Mike Halloran
Pembroke Pines, FL, USA

 

[IceStationZebra]

Reading the issues hydromech listed about PTFE tape makes me wonder if "pipe dope" would work better. I'm not sure what the correct name is, but it is a viscous white sealant that comes in tubes and works much like the tape - but it is messier and you won't have bits floating in the oil. Several places I have worked for frowned upon tape but gave a thumbs-up for the pipe dope just because of the contamination issue with pumps and valves. My concern with pipe dope is that I have no experience with it on stainless. Anyone else have experience?

Regarding Loctite 542:
- It's not clear if you are using Loctite 542 with activator VT2200, but if not the "tightness" requirement hydromech mentions is acurate. It is anaerobic so it won't cure in the presence of oxygen. Been there.
- Another component is cure time. According to the data sheet you need at least a 24hr cure time with stainless to get full strength. It will be even longer with bigger gaps and cooler temperatures.
- And even when fully cured you only have ~35% the strength with steel.

When I checked the Loctite application assistant it said 567, which sounds a lot like the pipe dope I described above but I'm not sure. It also doesn't give a cure time for stainless.

Permatex recommends Permatex® Maximum Temperature Thread Sealant #567. [Could it be coincidence that they both have the same number? ;-) ]

One other question - have you checked that you don't have an excessive inlet restriction? Maybe you are sucking the sealant out before it is cured allowing drips after it shuts down. I had a problem where the inlet strainer support tube was restricting oil flow with cold temps.

ISZ

 

[hydromech]

One issue here is the orientation, Lars stated that he may want to realign the elbows and adjust the fittings by upto 180 degrees. If an anaerobic sealant is used and allowed to cure, when the joint is moved the seal will be lost as the sealant will break up.

With PTFE tape it would be possible to leave enough slack in the tube to tighten it by 1/4 a turn if required.

But here again there is a risk that the tape will be pushed into tube and when the tube is all assembled there is no way to remove the excess tape.

There is a risk of killing two pumps if it is not done correctly. It might be worth having a look at starting again and doing it another way.

Regards

Adrian

 

[kcj]

I think Loctite and Permatex are now both part of Henckel.One was the indutstrial side, one marketed to the auto market.

One caution also, teflon tape reduces thread friction considerably, allowing much tighter joint with the same wrench torques. The good side, it makes tighter threads, and seals better. The bad, it can create so much forces in teh tapered threads that the wedging action cracks castings.

Did I misunderstand, or is one part of the joint parallel thread and one part tapered? In US we don't have an equivalent straight thread like BSPP, but it seems that both halves should be tapered thread to work right?

kcj

 

[hydraulicseal]

I Know about PTFE tape, but we never use that because it is not save if you have to adjust the joint a litle bit.
Anyway I ordered a sample of ptfe tape 0.2 mmm thick special for large threads up to 2½" (normal thicknes is 0.05mm). but this is only for testing i'm still looking for something better.
for instant we use standard pipe sealing for water and other liguieds, in Denmark that is products from Unipak.
It is a 2 step solution. 1) you wrap Unigarn flax/hemp
around the pipe. 2) then grease it with Unipak jointing compound. this gives an unique joint wich are both leakfree
and adjustable. but this is not recomanded for hydralics.
But I hope there might be other products suitable for this
purpose.
Yes in Denmark we use mostly inside parallel threads and outside tappered threads, i'm not sure why because teoreticly it's a bad solution, but i think it gives better
possibility to adjust the to parts.
I'm sure the loctite is ready for use, because we use the activator, and we assambly the system long time before we fill oil in and start it up.
the oil tank level is 1 m above the pumps so i dont think i have problems with suction in the joints.
regards Lars

 

[MikeHalloran]

I also understood that he is using mismatched fittings ... and wishing for satisfactory performance anyway.



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

Here is a compund that I've used very sucessfully on troublesome thread connections. It is a variation on a magnisium oxychloride cement.

http://www.xpando.com/pjc.html

 

[vettepiper]

Forget teflon tape; if it were up to me it would be outlawed. It not only contaminates the system, it is always liquid and even if you tighten a joint it will be loose later(no good)!! First, you need matched tapered threads. With hydraulics, if you have pipe threads you are going to have leaks... But if you have to have them use a good anorobic pipe dope and lots of muscle; better than that is to use a thing called TRU-Seal. These absolutey work to stop leaks. But if you are loosening them often to get different degree, they will shortly wear out and need replacement. I would recommend to stick with o-ring, flare or gasket seals. In the case of having to move the thread often to a different direction I would recommend a swivel(which has an internal o-ring) or a flare which you can loosen and set desired direction.

 

[RBedi]

BSP parallel thread always use dowty seals. Only npt or nptf use sealant. Just stay with this principle & there would be no problem !

Cheers, Rajan