Side Channel Blowers for CNC Vacuum Tables: Selection, Power and Connection

Anyone machining workpieces made of wood, MDF, plastic or thin aluminium sheet on a CNC gantry milling machine cannot avoid a vacuum table. But a vacuum table is only as good as its vacuum source: industrial vacuum cleaners barely manage more than 200 mbar of negative pressure and burn out under continuous load, classic rotary vane vacuum pumps are oil-lubricated, maintenance-intensive and overwhelmed as soon as leakage increases at the clamping surface. The most robust, continuous-duty and almost maintenance-free solution is the side channel blower. It reliably generates negative pressure in the range of 150 to 280 mbar at a very high volume flow, exactly the combination that vacuum tables need in CNC machining.

In this guide you will read how a side channel blower works, which power class suits your table size, how the connection to a multi-zone vacuum table is carried out properly and what holding force you can expect with MDF, plywood or dense materials. At the end you will find price ranges for orientation as well as six of the most frequent questions from our advisory practice.

How a Side Channel Blower Works

The side channel blower (also called a regenerative blower) is a non-contact, dynamic blower design. A multi-bladed impeller rotates in an annular housing channel. The air is accelerated several times by the impeller through the adjacent side channel: with every blade revolution it gains additional energy. The result: a single-stage machine reaches pressure differences of 150 to 350 mbar and volume flows of 70 to over 1000 m³/h, depending on power and size.

Unlike rotary vane vacuum pumps, a side channel blower works oil-free: there is no lubricating film that could contaminate the conveyed air. The bearings are designed as encapsulated continuous-duty bearings. The impeller does not touch the housing, so there is no mechanical wear from friction. This gives three decisive advantages for CNC use:

• Continuous-duty capable: a side channel blower is designed for 24/7 operation. A whole shift of vacuum milling is no problem.
• Low maintenance: apart from the pre-filter and an occasional visual check of the bearings, there is nothing to maintain. No oil changes, no vanes, no diaphragms.
• Dry air: the extracted air contains no lubricant residues, ideal for food, pharmaceutical or paint-shop environments.

This design has a typical character: high volume flow, medium negative pressure. While a rotary vane vacuum pump pulls down to 50 mbar absolute pressure (almost a full vacuum), the side channel blower stops at 200 to 280 mbar of negative pressure. On a CNC vacuum table, however, this is no disadvantage: on porous materials such as MDF, air escapes through the workpiece permanently anyway. What counts is not the maximum negative pressure but how much leakage the pump can compensate, and that is the domain of the side channel blower.

Suction or Blowing: Both Functions Explained

A side channel blower can be operated both as a vacuum source (suction) and as a compressed-air generator (blower), simply depending on which connection the vacuum table is attached to. In the CNC environment it is almost always used in suction mode:

• Vacuum mode (suction): the suction connection is connected to the vacuum table. The pressure connection blows off the conveyed air, usually silenced by a silencer. This mode produces the holding effect on the workpiece.
• Pressure mode (blowing): the pressure connection delivers conveyed air at up to 350 mbar of overpressure. Useful, for example, for pneumatic cleaning of the machine, blowing chips away from the workpiece or compressed-air holding fixtures. Not relevant for normal vacuum clamping, however.

Some users operate a side channel blower on the suction and pressure side at the same time, for example to work with compressed air at a second clamping fixture. It is usually more practical to implement both functions with separate devices. The scope of delivery of BZT side channel blowers for vacuum tables usually includes a pre-filter, a vacuum control valve and the necessary suction connection.

Choosing the Power: Which kW Class for Which Table Size?

Choosing the right power class is the most important decision. If it is dimensioned too small, the workpiece does not hold; if it is dimensioned too large, you burn electricity and money unnecessarily. The following table shows typical values for single-stage side channel blowers in 400 V three-phase operation. For more precise values, consult the manufacturer’s data sheet.

The most common rule of thumb: 2.5 to 3 kW of blower power per square metre of vacuum area. If you want to be on the safe side, round up. A BZT PFE 1300 with 1300 x 800 mm travel runs comfortably with a 4 kW unit. For a BZT PFU 2510 you should plan for 5.5 kW or more. An industrial BZT PFH with travel of up to 6 metres needs at least 7.5 kW, and when the table surface is fully used, more like 11 or 15 kW.

Important: with very porous materials, meaning classic MDF with high air permeability, soft plywood or open-pored solid wood, the leakage flow through the workpiece can be so high that one class larger makes sense. With dense materials such as acrylic, hard plastics or aluminium sheet, the smaller class is entirely sufficient. You will find a selection aid by material further down.

Connection to the CNC Vacuum Table

The connection is technically uncomplicated, but in a few places the care taken during installation decides whether the vacuum builds up stably. You should note the following points:

Hose Diameter

The hose between the blower and the vacuum table is the most frequent bottleneck. A hose that is too thin creates flow resistance and reduces the volume flow drastically. Rules of thumb for choosing the diameter:

• Up to 2.2 kW: NW 40 (1.5 inch) suction hose is sufficient.
• 4 to 5.5 kW: NW 50 (2 inch) is standard.
• From 7.5 kW: NW 63 or NW 75, if necessary two NW 50 in parallel.

The hose should be reinforced (with a spiral coil or steel insert) so that it does not collapse under negative pressure. Keep it as short as possible: every additional metre costs 2 to 5% of volume flow. Avoid sharp bends.

Filters and Safety Separator

A side channel blower must never draw in chips, dust or wood particles. Even the smallest quantities in the impeller mean bearing damage within minutes. An upstream filter is therefore mandatory, ideally a cyclone separator that spins out heavy particles, combined with a cartridge filter (5 µm) for fine dust. For MDF-intensive machining, an electrostatic pre-separator or a HEPA filter is recommended, because MDF fine dust is harmful to health.

Vacuum Control Valve

A vacuum control valve is mandatory, not optional. Without a control valve, the blower draws “against the wall” when the clamping surface is sealed. It heats up, the motor draws maximum current, and in extreme cases the fuse trips or the unit goes into overtemperature shutdown. The control valve sits in the suction line and opens automatically as soon as the negative pressure exceeds an adjustable value (typically 200 mbar); false air flows in and the pump can breathe. With BZT vacuum table sets, this component is always included in the scope of delivery.

Solenoid Valves for Multi-Zone Vacuum Tables

Larger vacuum tables are divided into several zones, typically 4, 6 or 8 quadrants. Each zone can be switched on or off individually so that workpieces smaller than the total table surface do not “suck through” the entire blower. The zones are switched via pneumatic solenoid valves, controlled by the CNC controller or a manual selector switch. In the G-code, the right zone can be activated directly with an M command: convenient and reproducible.

Clamping Surface Geometry and Holding Force

The theoretical holding force of a vacuum table is easy to calculate: pressure difference × effective area. At 250 mbar of negative pressure (= 25,000 Pa or 0.25 bar) and 1 cm² of contact area, 2.5 N act, that is, around 250 grams of holding force per square centimetre. At first glance that is little, but with real workpiece sizes it adds up quickly:

• 10 x 10 cm workpiece (100 cm²): approx. 25 kg holding force
• 30 x 30 cm workpiece (900 cm²): approx. 225 kg holding force
• 1 m² workpiece: approx. 2500 kg holding force

In practice you never reach these theoretical values at 100%. Three effects reduce the holding force: leakage through the material (especially with porous materials), false air at the edges (with workpieces that do not lie flat) and friction loss in the hose system. With a properly sized side channel blower, sealing cords and an MDF spoilboard, you typically achieve 60 to 80% of the theoretical value.

An important rule of thumb for machining: the cutting force at the cutter may be no more than 20 to 30% of the holding force, otherwise the workpiece slips. With a 6 mm end mill in aluminium at 0.1 mm feed per tooth, around 50 to 80 N of cutting force arises, that is, roughly 5 to 8 kg. Any vacuum table holds such values effortlessly. However, as soon as you rough over a large area or “pierce” the workpiece with holes, the vacuum is locally reduced and the holding force drops; dividing the table into zones helps here.

Workpieces of MDF/Chipboard vs. Dense Materials

Material density and porosity decide the vacuum strategy:

Porous Materials (MDF, Chipboard, Soft Plywood)

These materials let air through: the side channel blower has to compensate for leakage permanently. Advantage: you can place the workpiece directly on an MDF spoilboard, which acts as a diffuser. Disadvantage: the blower runs at a higher load, and the volume flow must be dimensioned generously. For machining 1500 x 1000 mm in MDF we recommend at least 4 kW, better 5.5 kW.

Dense Materials (Acrylic, Hard Plastics, Aluminium Sheet)

Here leakage is minimal and the blower quickly pulls a high negative pressure. A smaller power class is sufficient. Important: avoid direct contact between workpiece and table, either by clamping over vacuum grooves (CNC vacuum tables have milled channels) or over a perforated MDF spoilboard. On smooth materials, the vacuum holds extremely well.

When Is Vacuum Not Enough?

For small individual parts under 30 cm² of contact area, for very heavy roughing operations with large cutting forces or when machining solid metals such as steel or titanium, vacuum clamping is not enough. Mechanical strap clamps, chucks or vices are needed here. You will find an overview of suitable clamping solutions in our CNC accessories.

Maintenance and Service Life

Side channel blowers are among the longest-lasting components of a CNC system. A typical bearing life is 20,000 to 40,000 operating hours, which is around 10 to 20 years of use at 8 hours a day. Routine maintenance is limited to a few points:

• Check the pre-filter weekly: daily with MDF-intensive use. Clogged filters reduce the volume flow drastically.
• Replace the filter cartridge every six months: even if the filter looks clean, fine particles collect in the depth filter.
• Check the vacuum control valve: test its function annually. If the springs are clogged, the valve no longer switches.
• Listen to the bearings: listen briefly before the start of every shift. Running noises become audibly louder long before bearing damage occurs.
• Clean the motor: remove the fan cover every 6 months and extract the dust, otherwise the motor overheats in summer.

If the unit is correctly sized and operated in a low-dust environment, a bearing replacement is usually not due until after 15+ years. By comparison, a rotary vane vacuum pump needs vane replacement and an oil change every 6 to 12 months.

What does a good side channel blower cost?

Prices vary greatly with brand, power and equipment. The following guide values apply to high-quality, industrial-grade units with an accessory package (filter, vacuum control valve, suction connection). Cheap hobby units from China can be considerably below these values, but are rarely continuous-duty capable.

A well-sized side channel blower is an investment with a very long service life. Over 10 years, it is typically the lowest-maintenance and cheapest component of your CNC system, cheaper than the annual maintenance of a rotary vane vacuum pump.

Frequently Asked Questions

What is the difference between a side channel blower and a vacuum pump?

Classic vacuum pumps (e.g. rotary vane) generate deep negative pressure (down to 50 mbar absolute) at a small volume flow, ideal for tightly sealed suction plates in the packaging industry. Side channel blowers deliver medium negative pressure (150–280 mbar) at a very high volume flow, perfect for CNC vacuum tables because they compensate for leakage through porous workpieces. In CNC wood and panel machining, the side channel blower is virtually without competition.

What power do I need for a 1500 x 1000 mm table surface?

For a vacuum table with 1.5 m² of area, we recommend a side channel blower with 4 kW of motor power. For particularly porous materials such as open MDF or soft plywood, preferably 5.5 kW. A PFE 1300 with 1300 x 800 mm travel and a matching vacuum table is comfortably equipped with 4 kW. More power does no harm, but costs electricity and investment.

Can I let a side channel blower run continuously?

Yes, side channel blowers are explicitly designed for continuous operation. The bearings are continuous-duty capable, the impeller does not touch the housing, and there is no wear film. A prerequisite is a correctly set vacuum control valve, so that the blower does not work against a closed suction side. With a control valve and a clean pre-filter, 24/7 operation is unproblematic for years.

How loud is a side channel blower?

Without a silencer 80 to 90 dB(A), which is very loud, almost hammer drill level. With a connected silencer and ideally a sound-insulating hood, the level drops to 64 to 78 dB(A) depending on the power class. For workshop operation with ear protection, this is unproblematic. If you want to work quietly, install the blower in a separate plant room or a soundproof cabinet.

Which hose diameter makes sense?

Rule of thumb: NW 40 (1.5 inch) for blowers up to 2.2 kW, NW 50 (2 inch) for 4 to 5.5 kW, NW 63 or NW 75 from 7.5 kW. The hose must be reinforced (spiral coil or steel insert), otherwise it collapses under negative pressure. The shorter the hose run, the better: every additional metre of hose costs 2 to 5% of volume flow.

Does a side channel blower need maintenance?

Very little. Check the pre-filter weekly, replace the filter cartridge every six months, remove dust from the fan cover twice a year: that is essentially all. A bearing replacement is not due until after 15 to 20 years of typical use. Compared with rotary vane vacuum pumps (oil change and vane replacement every 6 to 12 months), the maintenance effort is negligible.

Advice and Finding the Right Unit

Which power class, which hose routing and which vacuum table set-up suits your CNC system depends on the material, the machining spectrum and the machine size. We will advise you personally, ideally together with the selection of the right CNC gantry milling machine. You will find an overview of all series including a travel comparison on the series comparison page. For the specific design of your vacuum solution, contact BZT advice: we will recommend the right unit from our side channel blower range, matched to spindle, table size and workpiece.