Flange Jack Screws

The settlement of the piping system after fabrication could squeeze the wafers so tightly that it would be nearly impossible to remove it. Jack bolts provide a means to spread the flanges. Jack bolts can also be used with components that are mounted between flanges such as wafer check valves, spectacle blinds and orifice plates. A machine bolt with a heavy hex nut which is mounted in a hole drilled on the flange center line used as a jack screw.

ASME B16.36, which standardized orifice flanges, recommended installation of one jack screw per flange and position them in 180 deg apart. It should be 90 degree far from pressure tap of orifice flanges.

Although that is possible to thread the holes in the field, where threading in field is expensive, jack screws to be purchased with flanges which is drilled and threaded by vendor. Orifice flanges are purchased with flange taps and jack screws.

Jack screws also are 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, jack screws threaded into one surface and jacking against the other surface in order to make disassembly much easier. In fact, it would be nearly impossible to disassemble some parts on rotating machinery if not for jack screws because they are so tight.

As a normal practice the manway cover will be standard blind flanges with additional threaded hole for jack screw.

Since jack screws are convenience feature and not always needed to separate flanges, so it is not required to consider a permanent access for them.