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Hoists, Chain, Hand-Operated, Hook and Trolley Suspension
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Geared trolley



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MIL-H-904J
4.73 Efficiency test. Efficiency tests shall be performed as specified in 4.7.3.1 through 4.7.3.3.
4.7.3.1 Hand chain operated hoists. The hoists shall be loaded to rated capacity and operated
to raise the load through any conveniently measured distance. The number of feet of hand chain
passed by a reference mark in raising the load to the selected height and the tension in the hand
chain, measured with an accurate spring balance for attached weights, shall be recorded. The
mechanical efficiency of the hoist shall be determined from the formula specified in 4.7.3.3.
Failure of hoists to conform to specified minimum mechanical efficiency shall constitute failure of,
this test.
4.7.3.2 Type H hoist, lever operated. The hoist shall be loaded to rated capacity and operated
to raise the load through any conveniently measured distance. A spring balance shall be connected
not more than 2 inches from the end of the operating lever of the hoist. The mean force required
to operate the lever through one operating stroke shall be determined by measuring the force at
five equidistant positions over the operating stroke. Measurement shall be made with the spring
balance always at a right angle to the level and for at least six successive operating strokes. The
total distance through which the operating force acts and the distance through which the load is
lifted shall be noted. The mechanical efficiency of the sample hoist shall be determined from the
formula specified in 4.7.3.3.
4.7.3.3 Efficiency formula. The efficiency formula shall be as follows:
C x L x 1OO
E=
PxT
where:
=
E
Mechanical efficiency in percent of 100
=
Rated capacity of hoists in pounds
C
=
L
Distance lifted (feet)
=
P
Mean operating force in pounds
Number of feet of hand chain to raise load, or total distance through which "P" acts
T
=
for lever operated hoists.
4.7.4 Track clamp. When a trolley hoist is fitted with a track clamp, the clamp shall be tested
with hoist loaded to its rated load; by subjecting the trolley to a pull in either direction, parallel
to the track equal to one-third of the hoist rated load. Failure of the hoist to remain stationary
during the test shall constitute failure of this test.
4.7.5 Plain trolley. The pull required to move the hoist loaded to its rated load (plain trolley
suspension) along a straight portion of track shall be determined by attaching a cable or cord to
the trolley, passing the cable or cord over a sheave suspended from the track at a reasonable
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