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Old 02-13-2020, 07:38 AM
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The key is that a banjo bolt will tighten against the caliper, crushing the copper washers on either side of the banjo fitting. The seating area on the caliper would be machined square to the threads and there should be small annular ridges machined to cut into the copper washer between the banjo fitting and caliper.
NPT would seal by mechanical interference between the threads as it is tightened , the interference increases as the fitting is tightened. This could make clocking problems if you were to use an elbow.
There is BSPP british straight parallel pipe, I believe has the same dimensions as NPT & NPS thread, but has collar nut to tighten against the caliper after the fitting is positioned (clocked). This requires a small chamfer at the lead thread, were an o'ring is squeezed into, as the seal. If it lacks a chamfer, there are steel washers to contain the o'ring while the collar nut is locked down.
BSPP would also require that there be straight thread in the caliper and that there was a flat area around the hole. But would cure any clocking issues for an elbow.
If you dont use an elbow, then there is no clocking problem. A NPT fitting is adequate for the pressure in the system and should be fine except you would have to use a steel fitting. Brass fittings tend to crack at the base of the thread.
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