Reference Manual

15−4
Figure 15-7. Thin Stock System
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
Figure 15-8. Fan Pump
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.
Thin Stock Process
This section will describe the thin stock processes
of cleaning, screening, and diluting to
papermaking consistency (figure 15-7). The thick
slurry in the machine chest is pumped to the
suction-side of a fan pump and is diluted to 1% or
less with white water drained from the sheet
forming process into a stuffbox (figure 15-8).
Stuffbox
The stuffbox is located high in the air, near the
wet-end of the paper machine, and ensures the
basis weight valve has enough, and constant
pressure so the stock flow can be accurately
controlled to the paper machine (figure 15-9).
Stuffboxes are frequently replaced with variable
speed pumps that supply the basis weight valve
directly.
Basis Weight Valve
The stock from the stuffbox flows by gravity
through a pipe leading down into the basis weight
Figure 15-9. Stuffbox
Drawing is from
TAPPI’s Making
Pulp and Paper Series
and is used with
permission.
valve (figure 15-10). It influences moisture, caliper,
brightness, opacity, draws, strength, machine
stability, and product uniformity. If it is not within
acceptable limits, machine performance and
product quality will suffer. Most paper machines
use a precision basis weight valve to control the
amount of stock going to the fan pump. Basis
weight is the key variable in paper quality control.
Typical Specification
D Fisher Vee-Ball V150 with either a 2052
actuator or SKF actuator.
D FIELDVUE DVC6200 digital valve controller
with Performance Diagnostics
White Water
The water used to dilute thick stock in preparation
for forming the paper sheet comes from the