Vacuum Pump Usage Introduction in the Paper Industry

For many people, the paper industry feels both familiar and distant. We all use paper products daily—newspapers, cardboard boxes, printing paper, tissue—but the manufacturing process remains largely hidden from public view. What is well known, however, is that papermaking relies heavily on Vacuum Pump technology. From dewatering wet pulp to transferring delicate paper webs, vacuum systems are the unsung heroes of every paper machine. Yet, a common confusion persists: which types of Vacuum Pumps are suitable for which paper machines? And why do different sections of a paper mill require different Vacuum Pump configurations?

In this article, we will provide a comprehensive introduction to Vacuum Pump applications in the paper industry. We will focus on the two most vacuum-intensive sections of a paper machine—the forming section and the press section—and explain how Vacuum Pump selection impacts energy consumption, reliability, and paper quality. Additionally, we will compare wet Roots-type Vacuum Pumps with water ring Vacuum Pumps, offering practical recommendations based on field experience. Our company manufactures a diverse range of products, including Roots vacuum pumps, water ring vacuum pumps, and liquid ring pumps, each with distinct advantages. By the end of this guide, paper mill operators and maintenance engineers will have a clear understanding of how to optimize their Vacuum Pump systems for maximum efficiency and longevity.

Part 1: Why Vacuum Pumps Are Indispensable in Papermaking

The papermaking process begins with a slurry of water and fibers (approximately 99% water and 1% fiber) that is spread onto a moving mesh screen called the forming fabric. At this stage, the sheet is so wet that it has no structural strength. Removing water quickly and uniformly is critical to forming a stable paper web. This is where Vacuum Pump technology enters the picture. By applying suction beneath the forming fabric, Vacuum Pumps pull water through the mesh, leaving a mat of fibers that gradually gains enough integrity to move forward.

Later, after the sheet leaves the forming section, it enters the press section, where mechanical pressure squeezes out more water. Here again, Vacuum Pumps play a vital role—not directly on the sheet, but on the rolls and felts that transport and dewater the paper. Without reliable Vacuum Pump systems, a paper machine would simply produce wet, weak, unusable paper.

The paper industry uses many types of Vacuum Pumps, including water ring, liquid ring, and rotary vane designs. Among these, the Roots-type Vacuum Pump (both dry and wet configurations) has gained significant traction due to its energy efficiency and stable operation. However, selecting the wrong Vacuum Pump for a specific application can lead to high energy bills, frequent maintenance, and unscheduled downtime. Therefore, understanding the distinct requirements of the forming and press sections is the first step toward optimal Vacuum Pump selection.

Part 2: The Forming Section – Dewatering and Web Formation

The forming section, also known as the wet end, is where the paper sheet is born. A headbox discharges the fiber-water mixture onto a moving forming fabric (wire). Beneath the fabric, a series of Vacuum Pump-driven suction boxes (also called uhle boxes) remove water by creating a pressure differential. The goal is to increase the dry solids content of the sheet from around 1% to approximately 15–20% by the time it leaves the forming section.

Typical vacuum levels in the forming section:
Forming section vacuum requirements are relatively moderate, typically ranging from 15 to 50 kPa (approximately 110 to 375 Torr) depending on the paper grade and machine speed. For example, tissue machines may use lower vacuum to preserve bulk, while linerboard machines need higher vacuum to achieve rapid dewatering.

Which Vacuum Pump works best here?
Historically, water ring Vacuum Pumps have been widely used in forming sections because they are simple, rugged, and can tolerate small amounts of water carryover. However, water ring Vacuum Pumps are inherently less energy-efficient due to the energy lost in circulating the seal water. More recently, many paper mills have begun replacing water ring units with wet-type Roots Vacuum Pumps in the forming section. Why? Because a properly selected Roots Vacuum Pump can deliver the same dewatering capacity while consuming 20–35% less electricity. Additionally, wet Roots designs can handle the humid, mist-laden air extracted from the forming boxes without reliability issues.

Practical advice for forming section Vacuum Pump selection:

• For low vacuum levels (below 50 kPa), a wet Roots Vacuum Pump is highly recommended. It offers stable operation, low energy consumption, and long service life compared to water ring pumps.

• Avoid installing inlet silencers or seal water connections unless absolutely necessary, as these add complexity and potential leak points.

• Air-cooled oil tanks are generally not required for forming section applications because the gas temperature is relatively low.

Part 3: The Press Section – Higher Vacuum for Transfer and Dewatering

The press section is where the paper web, now about 15–20% dry, is transferred from the forming fabric onto a series of press felts and rolls. Here, vacuum is used for two primary purposes:

1. Web transfer: A suction pickup roll (vacuum transfer roll) uses suction to lift the wet paper web off the forming fabric and onto the press felt. This requires a clean, stable Vacuum Pump system capable of providing continuous suction at the roll’s surface.

2. Press roll dewatering: Suction press rolls have a perforated shell and internal stationary suction boxes. As the roll rotates, the suction pulls water out of the paper web and into the roll’s interior, where it is evacuated. This significantly increases sheet dryness (from ~20% to 40–50%) before the paper enters the dryer section.

3. Felt conditioning: After the felt carries the paper through the press nip, the felt itself becomes saturated with water. Felt suction boxes (uhle boxes) use Vacuum Pumps to remove water from the felt, restoring its absorbency. Felt conditioning also includes cleaning and vacuum dewatering to prevent filling and blinding.

Typical vacuum levels in the press section:
Press section vacuum requirements are noticeably higher than those in the forming section. Suction pickup rolls typically operate at 30–50 kPa, while suction press rolls and felt uhle boxes may require 50–70 kPa (up to 500 Torr). The higher vacuum is necessary to overcome the resistance of the thicker, denser paper web and the press felts.

Which Vacuum Pump works best here?
Because the press section often handles more water and higher vacuum levels, the choice of Vacuum Pump becomes even more critical. Water ring Vacuum Pumps have traditionally been used, but they suffer from the same energy inefficiency as in the forming section. Wet Roots Vacuum Pumps, on the other hand, can handle these higher vacuum levels while maintaining stable performance. However, it is essential to ensure that the Vacuum Pump selected for the press section is specifically designed for wet gas streams. A standard dry Roots pump would quickly fail due to corrosion and water ingress, but a wet-type Roots Vacuum Pump (with appropriate materials and clearances) will thrive.

Part 4: Comparing Wet Roots Vacuum Pumps with Water Ring Vacuum Pumps

Given that both wet Roots and water ring Vacuum Pumps are used in paper mills, it is useful to compare them directly across several key parameters:

The data clearly shows that wet Roots Vacuum Pumps offer superior energy efficiency and lower operating costs. However, water ring Vacuum Pumps remain popular in some mills because they are extremely tolerant to liquid slugs and require less sophisticated control systems. For new installations or retrofits, the trend is strongly shifting toward wet Roots technology.

Part 5: Special Recommendations for Roots Vacuum Pump Selection in Paper Machines

Based on years of field experience and direct feedback from paper mill engineers, we offer the following practical recommendations when selecting a Roots-type Vacuum Pump for paper machine applications:

1. Always choose a wet-type Roots vacuum pump.
Paper machine vacuum streams contain fine water droplets, steam, and sometimes fiber particles. A dry Vacuum Pump (intended for clean, dry gases) will suffer from corrosion, rotor imbalance, and seal failure within months. Wet Roots designs use materials and clearances that tolerate moisture, and they often include drain ports to remove accumulated liquids.

2. Do not configure an inlet silencer.
Inlet silencers add flow resistance and create potential collection points for condensed water. In many cases, a well-designed wet Roots Vacuum Pump running at moderate speeds produces acceptable noise levels without a silencer. If noise reduction is absolutely required, choose a silencer with automatic drain traps.

3. Avoid installing a seal water connection.
Some operators mistakenly add a water injection port to “cool” the pump or “seal” the rotors. For wet Roots Vacuum Pumps designed for paper applications, this is unnecessary and can actually cause hydraulic hammer or wash away lubricant films. Follow the manufacturer’s guidance—if the pump is rated for wet gas, no additional seal water is needed.

4. Air-cooled oil tanks are optional (and often unnecessary).
Unlike dry Roots pumps used in high-compression applications, wet Roots Vacuum Pumps in paper mills typically see moderate temperature rises because the water vapor absorbs heat. An air-cooled oil tank adds cost and complexity. For most paper machine applications, a standard oil sump with adequate surface area is sufficient.

5. Minimize on-site piping.
Every additional pipe, elbow, flange, and valve introduces pressure drop and potential leak points. Keep the Vacuum Pump as close as possible to the suction source (uhle box or suction roll). Use the shortest, straightest piping configuration feasible. This not only improves Vacuum Pump performance but also reduces installation and maintenance costs.

6. At low vacuum levels, prioritize recommending wet Roots pumps.
When the required vacuum is below 50 kPa (typical for many forming sections and some press section applications), a wet Roots Vacuum Pump offers the greatest energy savings compared to water ring pumps. The lower the vacuum, the more pronounced the efficiency advantage becomes. For example, at 30 kPa, a wet Roots Vacuum Pump can consume 40% less power than a water ring unit of equivalent capacity. Over a year of continuous operation, the electricity savings alone can pay for the pump multiple times over.

Part 6: Energy Efficiency – A Decisive Advantage

Energy costs represent a significant portion of a paper mill’s operating budget. Vacuum Pump systems, particularly those serving large paper machines with multiple uhle boxes and suction rolls, can consume hundreds of kilowatts continuously. Therefore, even a modest improvement in Vacuum Pump efficiency translates into substantial annual savings.

Consider a typical 5-meter-wide paper machine producing 400 tons per day. The forming and press sections might require a total installed Vacuum Pump capacity of 500–800 m³/min. If the existing water ring Vacuum Pumps consume 600 kW, switching to wet Roots Vacuum Pumps (with 30% lower power consumption) would reduce the load to 420 kW—a saving of 180 kW. At an electricity cost of $0.08 per kWh and 8,000 operating hours per year, the annual saving exceeds $115,000. Over the 10-year life of the pumps, the total saving approaches $1.2 million. This is why forward-thinking paper mills are increasingly retrofitting their Vacuum Pump systems with wet Roots technology.

Part 7: Operational Stability and Longevity

Beyond energy savings, wet Roots Vacuum Pumps offer superior operational stability. Because the rotors do not contact each other or the housing, there is no wear mechanism that gradually reduces performance. The only wearing parts are the bearings and shaft seals, both of which have long service intervals. In contrast, water ring Vacuum Pumps suffer from impeller erosion, port plate wear, and seal water contamination, all of which cause gradual capacity loss. Many paper mills report that after 5–6 years, water ring pumps need rebuilding or replacement, while wet Roots Vacuum Pumps continue to run smoothly for a decade or more with routine oil changes and seal inspections.

Furthermore, wet Roots Vacuum Pumps are less sensitive to variations in water quality. Water ring pumps require clean, cool seal water; if the water contains scale-forming minerals or debris, the pump’s performance degrades rapidly. Roots pumps, having no seal water, eliminate this vulnerability entirely.

Part 8: Common Misconceptions About Vacuum Pump Selection in Paper Mills

To help readers avoid costly mistakes, let us address several persistent myths:

• Myth 1: “Water ring pumps are the only pumps that can handle wet paper machine air.”
  Fact: Wet Roots Vacuum Pumps are specifically designed for such environments. They have been successfully used in hundreds of paper mills worldwide.

• Myth 2: “Roots pumps are too noisy for paper mills.”
  Fact: When operated at appropriate speeds and without unnecessary silencers, modern wet Roots Vacuum Pumps produce noise levels comparable to water ring pumps. Some models are quieter.

• Myth 3: “I need a liquid ring pump if there is any risk of liquid carryover.”
  Fact: Wet Roots Vacuum Pumps can handle mist and droplets. Only for gross liquid slugs (e.g., a burst pipe) would a liquid ring pump be preferable, but such events are rare and can be mitigated with a knockout pot.

• Myth 4: “Retrofitting from water ring to Roots is complicated and expensive.”
  Fact: While there is an upfront investment, the payback period is typically 12–24 months due to energy savings. Many manufacturers offer direct replacement frames that fit existing foundations.

Part 9: Our Company’s Product Range

As a manufacturer serving the paper industry for many years, we produce a complete portfolio of Vacuum Pump solutions tailored to paper machine requirements. Our product line includes:

• Roots Vacuum Pumps – Available in both dry and wet configurations. Our wet Roots Vacuum Pumps are specifically optimized for paper forming and press sections, featuring corrosion-resistant rotors, heavy-duty bearings, and integrated moisture drains.

• Water Ring Vacuum Pumps – For customers who prefer this technology or have applications with extreme liquid carryover, we offer single and two-stage water ring pumps with various seal water options.

• Liquid Ring Vacuum Pumps – A subset of water ring pumps, our liquid ring Vacuum Pumps can use different seal liquids (oil, solvent, or water) for specialized chemical pulping processes.

Each Vacuum Pump in our catalog is backed by comprehensive technical support, including sizing assistance, piping recommendations, and on-site commissioning. We understand that every paper machine is unique, and we work closely with mill engineers to ensure optimal Vacuum Pump selection.

Part 10: Practical Installation Tips for Wet Roots Vacuum Pumps

If you decide to proceed with wet Roots Vacuum Pumps for your paper machine, follow these installation guidelines:

1. Mount the pump on a rigid, level baseplate to maintain rotor alignment.

2. Install a knockout pot (separator) upstream of the pump to remove large water droplets and fibers. A simple vertical vessel with a drain at the bottom is sufficient.

3. Use flexible connections between the piping and the pump inlet/outlet to isolate vibration.

4. Provide adequate ventilation around the pump to dissipate heat. While wet Roots pumps run cooler than dry types, they still require airflow.

5. Set the bypass valve (if equipped) to open at a differential pressure of 30–40 kPa to protect the pump during startup or upset conditions.

6. Test the system under operating conditions and record baseline parameters (power draw, temperature, vacuum level) for future comparison.

Part 11: Future Trends – Toward Higher Efficiency and Digital Monitoring

The paper industry is under continuous pressure to reduce energy consumption and improve sustainability. Vacuum Pump technology is evolving to meet these demands. Variable frequency drives (VFDs) are increasingly used with wet Roots Vacuum Pumps to match pump speed to actual demand, saving additional energy during part-load operation. Digital monitoring systems that track Vacuum Pump vibration, temperature, and power draw can predict failures before they occur, minimizing unplanned downtime.

Some mills are also exploring hybrid systems where a Vacuum Pump controller automatically switches between multiple pumps (e.g., large Roots for high demand, small Roots for low demand) to optimize efficiency across the entire operating range. These smart Vacuum Pump systems are expected to become standard in new paper machine installations.

Conclusion: Making the Right Vacuum Pump Choice

The paper industry’s reliance on Vacuum Pump technology is unlikely to diminish. As paper grades diversify and machine speeds increase, the demands on vacuum systems will only grow. By understanding the distinct roles of the forming section (moderate vacuum, high gas flow) and the press section (higher vacuum, wet gas), mill operators can select Vacuum Pumps that deliver reliable, energy-efficient performance.

Our strong recommendation, based on field data and customer feedback, is to choose wet Roots Vacuum Pumps for both forming and press sections in most paper applications. Compared to water ring Vacuum Pumps, they offer lower energy consumption, longer service life, and more stable operation. When selecting a wet Roots Vacuum Pump, avoid adding unnecessary components like inlet silencers or seal water connections, minimize field piping, and consider air-cooled oil tanks only if justified by specific thermal conditions.

We hope this introduction has clarified the practical aspects of Vacuum Pump usage in paper mills. For further assistance in sizing, selecting, or retrofitting Vacuum Pump systems, please consult our technical team. With the right Vacuum Pump in place, your paper machine will produce higher quality paper at lower cost—and that is a benefit everyone can appreciate.