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View Full Version : Installing a hydraulic gauge to read it easily?



Jaakko Fagerlund
04-24-2013, 09:47 AM
Hello

I've recently purchased a glycerine filled hydraulic gauge that has 1/4" BSP thread, it looks like this item from eBay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=251253214244&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en

In my application the part where this is supposed to go already has 1/4" BSP thread, but if I screw the gauge to full depth, the face points away from the user. Is there some clever thing to not tighten it fully but still have it seal properly? The pressures are high, up to 350 bar but for very short durations (not shock load though).

Is it okay to just make a spacer or drop an O-ring inside the threaded hole or what?

Weston Bye
04-24-2013, 10:00 AM
Parallel or Tapered threads? BSP comes in both.

If parallel, there should be a locknut and o-ring that makes the seal. You don't have to turn to full engagement, but can back off the half-turn you need and then tighten the nut and o-ring.

If tapered, you have to tighten to the interference point of the threads.

MaxHeadRoom
04-24-2013, 10:02 AM
If it is the same as the gauge shown it has a parallel thread fitting, these usually allow the gauge to turn in the fitting in order to position correctly?
It sounds like the gauge you have is all one piece?
Solid fitting usually has the BSP taper to it.
You could drop an accurate spacer in if needed, depending on the type of mating surface.
Max.

Bill McLeod
04-24-2013, 10:27 AM
sometimes you can file or otherwise remove some of the material around the hole it is screwing into, or make an adapter 1/4 male to 1/4 female and make it so as to give you the right depth.

Jaakko Fagerlund
04-24-2013, 10:35 AM
Thanks guys, confirmed what I was thinking earlier :) Yes, it has BSP parallel threads and I think I'll just make a spacer, as it is easy to tighten the thing, look how much of a turn it needs adjustment and make one based on the thread pitch.

camdigger
04-25-2013, 10:42 AM
When we run up against this, we back the gage out and use additional thread compound or Teflon tape (if the application allows). Sometimes on the second installation, the issues goes away....

NPT threads are surprising in that a little extra torque will almost always bring the gage face around to where it is convenient to read and still have the threads be pressure tight. Dunno about BSP. No-one in my industry uses that thread standard.

And yes, on pressures up to and exceeding 350 Bar with gas, oil, mud, and water.

Jaakko Fagerlund
04-25-2013, 12:26 PM
camdigger, unfortunately both of the threads are BSP, so there is no taper. I wish the gauge would have had a BSPT, as that is easy to just tighten a little more to get it where it is supposed to be :)

And teflon tape was tried first, but it didn't want to work and tended to leak no matter what. I dunno why, as I have used it in 700 bar applications just fine, but then there has been tapered threads.

Anyway, got the thing installed just fine with a proper thickness O-ring dropped under the gauge. Took a try or two to find suitable thickness so that it tightens properly.

Paul Alciatore
04-25-2013, 01:17 PM
If it leaks with teflon tape, it sounds to me like one thread is straight and the other is tapered. You need to get or make a proper adapter with the correct threads on each end.

If both are straight threads and the teflon tape did not seal it, then you would definitely need some kind of adapter.

Or just buy a gauge that fits.

As for using an O-ring, I would not recommend it unless the hole AND gauge threads are specifically made for it. It may initially work, but also may then fail over time.