What are Jack Screws 1

[alebenco]

I am working on a project where the client is asking for Jack Screws on some flanges.
What are Jack Screws and what is their application?

 

[JLSeagull]

Jack screws permit spreading flanges. See the excerpt from B16.36 orifice flanges:

Each flange shail have a machine bolt mounted in a hole drilled on the flange center line at 90 deg. from the pressure taps, for use as a jack screw. Machine bolt shall be regular with one heavy hex nut.

A slot shall be provided in the flange 0.06 in. wider than the width across flats of the nut. The depth of the slot shall admit the nut so that there is no interference with the joining of the flanges when bolted together without orifice plate.

 

[JJPellin]

Jack screws are much more common on mounting flanges for various parts of rotating machinery. Since the rabbett fit may be fairly tight, and the surfaces may pull up metal-to-metal with no gap to allow for a flange spreader, it is very common to use jack screws threaded into one surface and jacking against the other surface in order to make disassmbly much easier. In fact, some parts on rotating machinery are so tight and configured in such a way that it would be nearly impossible to disassemble the machine if not for jack screws. With that said, I have never seen jack screws on piping flanges. There is usually a gap where you can easily place a flange spreader or drive in a bananna wedge.

 

[vzeos]

alebenco: flange jack screws are usually used on orifice flanges to facilitate the removal of the orifice plate. There should be one jack screw per flange and when the flanges are installed, the jack screws should be 180 deg apart. Orifice flanges are purchased with flange taps and jack screws. See attached pdf.

http://www.emersonprocess.com/rosemount/document/drawings/01497-1003.pdf