Power take-off
9
D = 0.05 x A
A = Distance between pulleys in mm.
D = Deflection in mm.
Belt tension
The correct tension must be applied to any PTO belt
driving arrangement, as insufficient installation ten-
sion could cause belt slippage at high powers and
high speeds, reducing belt life etc.
With a PTO drive from the crankshaft, excessive belt
tension will result in higher side loads than neces-
sary, which could result in crankshaft failure.
A practical way of estimating the fan belt tension is by
applying pressure in the centre of the longest run of
belt between any two pulleys, and adjusting the ten-
sion until the belt deflects by a given amount. (See
figure).
In multi-belt installations, where two or more belts are
used between two pulleys, belts matched in length
must be used to ensure correct load sharing and best
possible life.
Idler pulleys
Idler pulleys used for tensioning the V-belts should be
on the slack side of the belt, and not smaller than the
minimum diameter recommended by the manufac-
turer for a particular belt.
The use of too small a pulley will severely reduce belt
life.
A suitable spring loaded pulley is preferable to one
that is adjusted and clamped, as it can enable the
correct installation tension to be used. This is increas-
ingly more important with larger PTO values, as more
installation tension is required to avoid slippage, re-
sulting in a higher side loading/bending moment on
the crankshaft.
NOTE! A spring loaded idler pulley is also very im-
portant where there could be relative movement
between a flexibly mounted engine and driven equip-
ment mounted on a separate chassis.
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