FED-STD-791D
size and axial straightness should be made by silver soldering the orifice end of the jet tube and
redrilling.
4.1.2 Test bearing. An unshielded 0.10-m straight roller bearing is mounted on the free
end of the shaft in the test oil compartment of the bearing head. The test bearing is loaded
radially by the slight downward displacement of the free end of the shaft caused by a straight
downward force from the loading piston acting on the outer race of the main support ball bearing
shown in Figure 1. The test bearing is lubricated by a single jet located at 12 o'clock which
supplies essentially a solid stream of oil midway between the I.D. of the outer race and the O.D.
of the retainer on the top or unloaded position of the test bearing.
4.1.3 Test bearing mount. The bearing mount is made with an outer race removal feature
which permits the removal of the bearing outer race for cleaning and inspection without
disturbing the aluminum oxide packing. Three spot-type thermocouples are located 120 apart
(radially around the I.D. of the bearing mount and indicate the skin temperature on the periphery
of the outer race, which is pressed into contact with these thermocouple junctions when it is
installed in the bearing mount. One of these three thermocouple leads is connected to a
differentiating type temperature controller (proportional controller) or to a suitable
autotransformer. "ON-OFF" type control is not recommended.
4.1.3.1 Three thermocouple junctions are silver-soldered to the outer-race housing. The
soldering operation should leave enough excess metal to provide good contact with the outer race
when it is pressed into the mount. Each of the three thermocouple leads are routed out directly
through the bearing housing or end cover at 120 intervals.
4.1.3.2 Thermocouple packing. Teflon or an equivalent should be used for all
thermocouple leads where they pass through the housing or end cover fitting. This also applies
to the two Calrods where they pass out through the end cover.
4.1.4 Test oil system. A schematic of the test oil system is shown in Figure 2. The test
oil cycle starts at the tank where three 1500-W, series connected heater elements (refer to 4.1.7)
maintain the desired temperature by means of a differentiating type temperature controller or a
suitable autotransformer. "ON-OFF" type control is not recommended. The test oil is then
pumped from the tank to the bearing head where it passes through a No. 60 drill size orifice and
lubricates the test bearing. The test oil is drained from the bearing head at three locations. The
front drain handles splash oil which does not pass through the test bearing, whereas the rear drain
collects only oil that has gone through the bearing. The middle drain is looped into a 360
configuration to slow oil flow and lessen air entrainment in the oil. The three drains go into a
sump from which the test oil is pumped back into the top of the tank.
4.1.4.1 The test oil system provides for the installation of a fine 100-mesh filter screen
(stainless steel, Erdco P/N 1RB 2006 S.S. for Type 1-1/2 test conditions) in the pressure line
only just ahead of the jet to collect the sludge particles circulated in the test oil system. Pressure
taps are located before and after the fine strainer in order to monitor the degree of screen
plugging.
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