FED-STD-791D
value obtained on the last eight determinations, i.e., when two new
determiations are made, the two oldest determinations of the eight
determinations used in determining the previous reference oil rating are
dropped, the two new ratings replacing them and a new reference oil average
rating 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 item l, 6.9).
NOTE 10: Maximum and minimum acceptable average ratings for the reference oil
are 5780 N/cm (3300 lb/in) and 4030 N/cm (2300 lb/in), respectively.
Rigs which do not give an average reference oil rating within these limits
shall not be considered as being satisfactory. Faulty maintenance
practices, improper test procedures, and/or the need for major overhaul
can be indicated if the average on the reference oil does not fall within
these limits.
4. Determinations, as necessary, shall be made on the oil under test and an average
obtained. Should the high and low values of these determinations differ by more
than 1400 N/cm (800 lb/in) additional determinations should be made to
establish an acceptable average.
7. CALCULATIONS
7.1 Calculate the effective tooth width (cm, in)
W 2 = W 1* R
where:
W2 = effective tooth width in cm or in.
W1 = measured gross tooth width in cm or in.
R = W2/W1 = estimated ratio.
7.2 Calculate load carrying ability by the following formula:
KL
P=
W2
where:
P = load carrying ability (or scuff limited load) of the lubricant, N/cm (lb/in).
K = Ryder gear machine constant (4.1.1).
L = Load oil pressure, gage Pa (psig).
W2 = effective tooth width, cm (in).
7.3 Calculate the percent relative rating using the following formula:
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