Papermaking is, at its core, the process of turning a slurry that is mostly water into a dry paper web within seconds. Most of that transformation happens through vacuum-driven water removal, before mechanical pressing or steam drying ever comes into play. Liquid ring vacuum pumps are widely used in papermaking to separate water from the pulp. This article covers exactly which sections of a paper machine rely on vacuum, and what technical requirements each point brings with it.
Table Of Contents
- What Is Vacuum's General Role on a Paper Machine?
- How Do Vacuum Boxes Work in the Forming Section?
- Why Does the Couch Roll Require Vacuum?
- What Do Suction Rolls Do in the Press Section?
- What Role Does Vacuum Play in Felt Cleaning?
- Why Is Vacuum Pickup Critical in Tissue Production?
- Which Pump Series Fits a Paper Machine's Vacuum System?
- Frequently Asked Questions
What Is Vacuum's General Role on a Paper Machine?
The pulp entering a paper machine starts out as an almost entirely water-based mixture. Most of the water in that mixture is removed through direct drainage and vacuum before mechanical pressing or steam-heated cylinders take over — because pulling water out with vacuum requires far less energy than evaporating the same amount.
For that reason, a modern paper machine applies vacuum at multiple points along its production line, each handling a different water-removal task. The sections below walk through those points in order.
How Do Vacuum Boxes Work in the Forming Section?
In the first section of a paper machine — the forming section — dilute pulp is deposited onto a moving wire mesh. Foil elements and vacuum boxes (flat vacuum boxes) mounted beneath the wire pull water down through the wire, rapidly reducing the water content of the pulp. This section is one of the points on the machine with a high vacuum demand, since the amount of water that needs removing here is very large.
Vacuum boxes in the forming section are typically arranged in a series of stages, each applying slightly deeper vacuum than the last, removing water in gradual steps. This staged approach keeps the pulp forming an even layer on the wire, while preventing surface defects that can result from pulling water too quickly.
Why Does the Couch Roll Require Vacuum?
At the end of the forming section sits the couch roll, a perforated roll with an internal vacuum box. Its job is to let the wet paper web separate cleanly from the wire and transfer to the press felt.
The vacuum applied during this transfer helps the web adhere to the felt and release evenly from the wire; insufficient vacuum can cause the web to tear or transfer unevenly. This is why keeping vacuum stable and continuous at the couch roll becomes especially critical on machines running at high speed.
What Do Suction Rolls Do in the Press Section?
After the forming section, the paper web moves into the press section, where it loses more water mechanically as it's compressed between felts. Some press configurations use perforated suction rolls with an internal vacuum box; these rolls draw additional water through vacuum, on top of the mechanical pressing effect, boosting the overall dryness achieved.
Suction press rolls provide extra water-removal capacity particularly on high-speed, heavy-basis-weight machines, where mechanical pressing alone reaches its practical limits.
What Role Does Vacuum Play in Felt Cleaning?
The felts that carry the paper web through the press section gradually accumulate absorbed water, fiber fragments, and filler material; this build-up reduces felt permeability and, with it, pressing efficiency. Vacuum boxes known as "uhle boxes" are used to maintain felt performance — as the felt passes over them on each revolution, they draw water and contaminants out of the felt, cleaning and drying it.
This cleaning function can require a vacuum circuit separate from the one applied directly to the paper, because felt cleaning typically runs at a different vacuum level and on a different timing. Because of this, planning separate groups of vacuum pumps for different tasks is a common engineering practice on large paper machines.
Why Is Vacuum Pickup Critical in Tissue Production?
Machines producing tissue paper have a different vacuum requirement than standard paper machines. The wet web is taken off the forming wire and carried to a large drying cylinder (a Yankee cylinder); taking the web off the wire is done with a vacuum pickup roll or pickup shoe.
Because tissue machines typically run at very high speed, the vacuum at the pickup point needs to be both deep enough and fast-responding — otherwise the web can tear or transfer unevenly at high speed. This makes vacuum system design for tissue production considerably more demanding than for standard papermaking.
Which Pump Series Fits a Paper Machine's Vacuum System?
As covered in our article "Where Are High-Capacity Single-Stage Liquid Ring Pumps Used?", the volume of air and water vapor that needs to be drawn from a single point on a paper machine is typically very high — making high-capacity single-stage pump series a natural fit for this application. Gücüm Pompa's GMVT/GMPT series reaches capacities from 650 to 12,000 m³/h, capable of serving these high-volume points.
Given the different vacuum level and capacity needs of the machine's various sections — forming, couch roll, press, felt cleaning — general engineering practice typically favors separately sized pump groups for each section rather than a single central system. The exact system design should be determined on a project-by-project basis, according to the machine's speed, width, and the type of paper being produced.
Frequently Asked Questions
Which Section of a Paper Machine Requires the Most Vacuum?
The forming section is generally where the highest volume of water needs to be removed, making it one of the sections with the highest vacuum capacity demand. The exact distribution can vary depending on the machine's design and the type of paper being produced.
How Many Separate Vacuum Circuits Does a Paper Machine Have?
This varies with the machine's size and complexity; large machines typically plan separate vacuum circuits for the forming section, couch roll, press section, and felt cleaning. The exact number requires project-specific engineering design.
Why Does a Tissue Machine Need a Different Vacuum System Than a Standard Paper Machine?
Tissue machines need a very high-speed, precise vacuum pickup system to take the wet web off the wire and carry it to a Yankee cylinder. Standard paper machines typically don't have this kind of pickup and Yankee cylinder arrangement.
Why Is Felt-Cleaning Vacuum Kept Separate From the Vacuum Applied to the Paper?
Because felt cleaning requires different timing and typically a different vacuum level, designing it as a circuit separate from the vacuum applied directly to the paper lets both systems operate under their own optimal conditions.
