Valves for approach flow system

The approach flow system is the part of a paper mill where pulps are mixed and refined with the most minimal fiber loss possible for a specific paper grade. There are almost as many different stock preparations as there are different paper machines. Stock preparation, in general, consists of raw material handling, pulping, cleaning, screening, flotation, washing and refining. The short circulation is a wet end process located between the paper machine and stock preparation in which water from the wires of a paper machine is circulated to dilute thick stock to headbox consistency.

Good controllability

In modern stock preparation and wet end operations, the focus is on controlling the flows. The basis weight of the paper needs to be strictly controlled to meet high-quality requirements. Many unit operations with different media add pressure to a cost-efficient valve selection. Also pulp consistency control can cause problems. Some additives used in papermaking cause erosion in the valve structure. Additives, too, can cause environmental problems if they leak into the environment

Precise control

The precision of V-port segment valves is recommended when flows need good controllability. To control the basis weight, nelesACE™ valves can be used. These are specially designed for even better flow control. Metso's triple eccentric disc valves are a good and cost-efficient way to handle flows with large pipe sizes and low pulp consistencies of below 2.5% in control and 4% in on-off applications. Segment and ball valves can be used for higher consistency flows. Erosion problems can be prevented by using ceramic materials in the valves.

Low cost of ownership

  • Good controllability results in lower losses and higher product quality
  • Total valve costs can be significantly reduced and fouling prevented with the right valve selection
  • Erosion lowers the valve lifespan; preventing erosion reduces maintenance demand
  • A plant's environmental impact can be reduced and safety improved with a tight shaft sealing

Basis weight control

Learn more about the short circulation, which is a part of the papermaking process in which water filtering through the wires is utilized for diluting the stock supplied to the headbox