Taper port question

[nickjk]

I know that it is common to use a taper external (male) thread with a parallel internal (female) thread for a hydraulic joint.
Is it possible to use the reverse, a parallel external (male) thread with a taper internal (female) thread.
More specific, would it be possible to create special taper tap so I can use a small standard 4mm metric set screw as a plug.

Thanks in advance

Nickjk

 

[hydtools]

It is not common to mix straight and tapered threads, in my experience.

Ted

 

[nickjk]

Ted,

From:

http://en.wikipedia.org/wiki/British_standard_pipe_thread

<<<<Jointing threads: These are pipe threads where pressure-tightness is made through the mating of two threads together. They always use a taper male thread, but can have either parallel or taper female threads. (In Europe, taper female pipe threads are not commonly used.)>>>>


From:

http://www.ring-plug-thread-gages.com/ti-bs-21-ISO-7-Dry-Seal.htm

<<<<Now we are back to the use of the male external Rp parallel British Standard Pipe "Taper" (BSPT) screw thread with the female internal R tapered British Standard Pipe Taper (BSPT) screw thread to concentrate the pressure at one point and create a mashed together thread and a dry seal.>>>>

This is what I want to do but I have not found the parrallel male and taper female anywhere else during my research and not sure if it was an error.


Thanks

Nickjk

 

[hydtools]

Just use straight thread and epoxy the set screw in place.

Ted

 

[MikeHalloran]

I have seen a joint made up with BSP taper male into parallel female. It took a lot of Loctite PST to stop it from leaking seawater at a few psi. It may be common, but it's stupid.

Parallel male into taper female has less chance of working.
Use parallel/parallel and PST.




Mike Halloran
Pembroke Pines, FL, USA

 

[nickjk]

Mike
I need to come up with a miniature way to plug an hydraulic passage.
The plug needs to be easily removable and fit inside a port.
The smallest 1/16 R is too large, need something around 4.5mm.

Mike I am quite surprised by your response. Just because you do not agree with something does not make it stupid. This is not a method I have ever used but I am trying to keep an open mind to research found.
Nickjk

 

[MikeHalloran]

The particular joint I referenced, BSPT into BSPP, was on a boat that cost upward of 80 million USD. The joint had already shaken loose from engine vibration. I was not impressed.
Offended by 'stupid'?
Okay, it's lazy; saves a trip to the local Swagelok dealer to get a proper adapter.

The only US application of tapered male into straight female of which I'm aware is grease fittings with 1/4-28 threads. Small hex plugs and grease nipples are available.

Not quite common in the US, but available and just a little bigger than 4.5mm, is 10-32 straight threads. They're traditionally sealed with a flat gasket, but PST works better. The common plug for this series looks like a cheese head screw, and is usually the diameter of a pan head.

As to your original idea of using a straight thread setscrew into a tapered thread hole, I wouldn't do that, because you're basically trying to make a seal against the end of a thread, where the shape is not specifically controlled. I might be tempted to use a cone tip setscrew run into a straight thread hole with a countersink at the bottom, or maybe a flat bottom. ... but I'd be more comfortable using a headed screw and sealing on the flat face under that.

Above a couple hundred PSI, I wouldn't do any of the above. I'd probably use a Lee Plug in a reamed hole.

But you haven't specified a working pressure, or a fluid, or a body material so far...





Mike Halloran
Pembroke Pines, FL, USA