FED-STD-791D
6.3.5.1 Determination of load-carrying capacity. Using semi-log paper (Figure
10), plot the average percent of tooth area scuffed for the narrow test gear versus the
load-oil pressure. Determine from the plotted curve the load-oil pressure at which the
average percent of tooth area scuffed is 22.5%. Calculate load-carrying capacity, see 7.2.
6.4 Relative rating procedure. This procedure consists of reporting the load-
carrying capacity of an oil under test as a percentage of the load-carrying capacity of a
standard reference oil obtained using the same test apparatus. Details of this relative
rating procedure are given in the following paragraphs:
6.4.1 Determination of reference oil average rating.
NOTE 10: All load-carrying capacity tests on the standard reference oil are conducted
with Test #6517, using AMS 6260 steel test gears at 165F test
temperature conditions.
6.4.1.1 For a new rig, at least eight determinations (four gears) shall be conducted
on the standard reference oil. If the high and low values obtained do not differ by more
than 140 N/m (800 lb/in), the average is taken as the reference oil rating. If the high low
values differ by more than 140 N/m (800 lb/in), four additional determinations (two
gears) shall be conducted and the aver-age of the 12 determinations taken as the reference
oil rating.
6.4.1.2 After a major overhaul to a rig such as a bearing or shaft replacement,
four determinations (two gears) shall be conducted on the standard reference oil. If the
average of these ratings does not differ from the average obtained prior to the overhaul by
more than 52.56 N/m (300 lb/in), and the high and low valves obtained do not differ by
more than 140 N/m (800 lb/in), this average will be taken as the reference oil rating. If
the ratings obtained do not meet the above criteria, four additional determinations (two
gears) shall be conducted and the average of all eight determinations taken as the
reference oil rating.
6.4.1.3 At least two determinations (one gear) shall be conducted on the standard
reference oil for each 20 determinations made on oils under test. The reference oil rating
is a progressive rating in that it consists of the average value obtained on the last eight
determinations, i.e., when two new determinations are conducted, the two oldest
determinations of the eight determinations used in determining the previous reference oil
rating are dropped, the two new ratings replace them and a new reference oil rating are
dropped, the two new ratings replace them and a new reference oil average rating is
obtained. The sole exception to the above is where it is necessary to run 12
determinations to establish an average on a new rig. (See 6.4.1.1)
NOTE 11: Maximum and minimum acceptable average ratings for the reference oil
are 578.1 N/m (3300 lb/in) and 438 N/m (2500 lb/in), respectively. Rigs
which do not give an average reference oil rating within these limits shall
377
For Parts Inquires call Parts Hangar, Inc (727) 493-0744
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business