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3. OPERATION
3.1 Pump Startup
Before starting up the
it is important that no debris or foreign material can enter the pump head. Because of the tight clearance
between the spindles and the pump housing, any debris entering the pump housing can cause severe
damage to pump housing and spindles. After any system modification upstream occur, the piping needs
to be severely flushed. Before the pipe flushing begins, the pump suction line needs to be disconnected
from the pump face or pump housing, and directed to the floor so no debris can be flushed into the pump
housing.
3.2 Soft Starting the Pump
It is recommended to gradually ramp up the pump speed, as opposed to performing a hard start. Twin
Screw pumps are mostly used in heavy duty applications with viscous media, often with particulates, and
changing viscosity based on product properties and fluctuating temperatures. Most food products have
non-Newtonian fluid behavior and are shear thinning.
When starting up slow, the viscous product is forced into motion. Friction along the pipe walls is imparted
onto the product. The imparted friction on the shear thinning product lowers the apparent viscosity
momentarily. The lower apparent viscosity results in a lower overall pressure drop in the system. This is
especially helpful in the suction line of the pump. Lower apparent viscosity increases the NPSH available
(NPSHa).
The soft start allows the pump to ramp up speed over a period of 15 to 30 seconds in a controlled manner
while reading the motor amps from the VFD into the PLC. The shear thinning effect is sensed with the
decreasing amps indicated by the VFD.
PROCESSTEC INC. 2022
ViscoTwin 130
pump after the installation, or after system changes upstream occur,
3. OPERATION
Page 33
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