Wichita Clutch Fluid Coupling - Manual (Page 4)

C
Mesur-Fil Fluid Couplings
P-1100-WC 1/12 Wichita Clutch 800-964-3262 157
G
Fluid Requirements
Figure 2 reveals a typical NEMA B electric
motor torque curve together with the
particular op er at ing characteristics of a
specific coupling with a designated fill
level. With no power supplied, all of the
fluid is settled at the bottom of the
coupling. Slip rate in this condition is
100% with the input free to turn. With the
motor starting and increasing in speed to
the breakdown point, torque builds in the
coupling. As torque in creas es, the
coupling begins to deliver the load to the
motor, eventually bringing the load up to
speed (refer to the load ac cel er a tion area
in Figure 2).
Figure 1 - Motor Breakdown Points
The area on the chart between
the motor torque curve and the
100% slip curve represents the
excess torque available to the
motor to start itself without also
having to start the load. It is this
op er at ing char ac ter is tic which
permits a soft start with a one-
third lower current draw on the
motor (see Figure 3). (It should
be noted that because the
coupling torque can only be de -
vel oped if the runner is turning at
a slower speed than the impeller,
an ideal small amount of slip of
3% to 5% is nec es sary).
The Mesur-Fil Fluid Coupling
provides for jam load pro tec tion
to the motor and other vital
power system components. It is
designed to allow the motor to
decelerate only to its breakdown
point (see Figure 4). The results
without the fluid coupling could
be a locked rotor con di tion,
resulting in excessive current
draw and potential motor
damage. Ad di tion al ly, the
coupling dis trib utes the shock
of an overload over a longer
time span, thus reducing the
pos si bil i ty of damage.
Delayed Fill
Mesur-Fil Fluid Couplings, sizes 15 through 34
(30 to 1500 HP), have an available delayed fill
option restricting starting torque to 140% of
full load while still ensuring low slip at full
speed. The result is a softer, more gradual
start which can be advantageous for
ap pli ca tions such as belt conveyors and
mixers.
The operating principles are simple. With the
idle coupling (see Figure 5) the purpose of the
delayed fill chamber is to isolate a portion of
the fluid from the main cou pling. As the runner
ac cel er ates (see Figure 6), the chamber
attached to the runner gradually releases fluid
into the main coupling through specially
calibrated orifices. The fill increases
proportionally with the output speed. With ac -
cel er a tion complete (see Figure 7) at the high
speed running position, almost all of the fluid
has been released from the
chamber into the cou pling,
giv ing the cou pling
high fill/low slip char -
ac ter is tics.
Figure 2 - Starting Torque
Figure 3 - Start-up Burnout Protection
Figure 4 - Jam Load Burnout Protection
Figure 5
Standstill
Figure 6
Accelerating
Figure 7
Running