Vacuum blowers for holding and handling

Leakage-dominated duties: why flow matters more than vacuum level

Vacuum holding works by creating a pressure difference across the workpiece. The holding force is roughly that pressure difference multiplied by the effective sealed area. On a perfectly sealed, non-porous part, such as glass or sheet metal on a good suction cup, very little flow is needed once the air is evacuated, and a small high-vacuum pump or ejector is enough.

Many industrial jobs are different:

• CNC router tables holding MDF, plywood or particle board, which are porous.
• Bag, sack and carton handling, where paper or woven fabric leaks air.
• Printing, paper and packaging machines with perforated beds and belts.
• Foam, textile and leather cutting tables.
• Pick-and-place of irregular or rough castings and concrete products.
• Large tables where only part of the area is covered by the workpiece.

On these duties, air leaks continuously through the material and around the edges. The machine must remove that leakage while still holding a useful pressure difference. A pump that reaches deep vacuum at no flow but collapses to near atmospheric pressure under heavy leakage is the wrong choice. A blower that holds a moderate vacuum, often in the range of about 150–500 mbar below atmosphere, while moving a large volume, is usually the right one.

How to read the blower curve against the leakage curve

Every vacuum machine has a curve of suction flow against vacuum level. As vacuum deepens, flow falls. The workpiece and fixture also have a curve: leakage flow rises as vacuum deepens, because a bigger pressure difference pushes more air through the leaks. The operating point is where the two curves cross.

1. Obtain the blower curve at the actual speed and supply frequency (50 Hz in India), showing inlet flow against vacuum.
2. Estimate or measure leakage for the worst workpiece and the best workpiece, at two or three vacuum levels.
3. Add pipe, hose, filter and valve losses between the blower and the point of use; these reduce the vacuum that actually reaches the part.
4. Plot both curves; the crossing point gives the working vacuum at the table.
5. Multiply the working pressure difference by the effective area to estimate holding force, and compare it with the cutting, acceleration or lifting force with an appropriate margin set by the machine designer.
6. Repeat for every combination of zones that can be open at the same time.

Leakage can be measured on a trial fixture using a flow meter in the vacuum line, or estimated from a test with a known blower by reading vacuum level and using the blower’s own curve as the flow meter.

Worked comparison: two workpiece conditions

Consider a router table with a 2.5 × 1.25 m bed, holding sheet material. This is an illustration of method, not a design figure.

The lesson is that the same table can be a sealed duty one day and a leakage-dominated duty the next. Size for the worst realistic condition, and design zoning and masking so operators can improve sealing.

Choosing the machine type

Compressed-air ejectors are convenient but expensive on porous work: every litre of vacuum flow costs several litres of compressed air, and compressed air is one of the costliest utilities in a plant. On large porous duties, a dedicated blower nearly always uses less energy.

Line resistance, filters and zoning

• Pipe and hose sizing: on high-flow, low-vacuum duties, line losses are a large share of the available pressure difference. Undersized hoses waste vacuum. Keep runs short and diameters generous.
• Filters: wood dust, paper fibre and fabric lint will destroy a blower. Fit an inlet filter or cyclone sized for the flow, and monitor its pressure drop. A blocked filter looks exactly like a weak blower.
• Relief valve: a vacuum relief valve protects side-channel and Roots blowers from overheating when the table is fully sealed or the line is closed.
• Zoning: divide large tables into zones with valves, so only covered zones are under vacuum.
• Concurrency: where several tables or pickup heads share one blower, size for the number that can be open at once, not the average.
• Altitude and weather: holding force depends on the pressure difference against local atmosphere, so very high sites have slightly less available force.

Controls, continuity and loss of grip

Loss of vacuum during handling can drop a part or let it shift under the cutter. The machine builder decides the safety functions; from the vacuum side the practical measures are:

• A vacuum switch or transducer at the point of use, not only at the blower, interlocked so the machine stops or does not start when vacuum is low.
• Non-return valves or a small reservoir to slow vacuum decay on a power dip, where the duty allows.
• A VFD on the blower to hold a set vacuum, reducing energy and heat on sealed jobs while giving full flow on leaky ones.
• Standby or rental blowers for critical lines, so a failure does not stop production.

Testing and acceptance at site

1. Record barometric pressure and blower inlet temperature.
2. Measure vacuum at the blower and at the point of use with the worst and best workpiece, and with all zones open that can be open together.
3. Check blower current and discharge temperature at each condition.
4. Confirm the relief valve opens at its set point and the low-vacuum interlock works.
5. Record filter pressure drop when clean, to set a change limit.
6. Run a production trial with real parts and cutting or handling cycles.

How Reddy Compressors helps

Reddy Compressors sells new and used/refurbished blowers, rents them, services them and supplies their spares, covering Roots, screw, centrifugal and side-channel types of many makes, and does the same for vacuum pumps. We are an independent multi-brand specialist, not an authorised dealer, working from Tarnaka, Secunderabad since 2002, with more than 20 service engineers and technicians covering all of Telangana and Andhra Pradesh and supply across India. We have tie-ups with all major and reputed brands.

• Selecting a side-channel or Roots blower against your measured leakage, not the open-inlet figure.
• Site vacuum checks at the blower and at the table to separate blower, line and leakage problems.
• Service and overhaul of blowers, with spares such as filters, bearings, seals, relief valves and impellers identified from the nameplate and old part.
• Rental blowers to keep a line running during repair or to trial a larger size before buying.
• Advice on whether replacing ejectors with a blower would reduce your compressed-air demand.

What to send us

• Application: table size, workpiece material and how much of the area is usually covered.
• Vacuum level and flow you need, or readings from your current system.
• Existing blower or pump: make, model, serial number and nameplate photo.
• Hose and pipe sizes and lengths; filter type.
• Number of tables or pickup heads sharing the system and whether they run together.
• Site location and power supply.

Frequently asked questions

Why does my CNC vacuum table not hold MDF properly?

Raw MDF is porous, so air leaks through the board face as well as around the edges. If the blower cannot move that leakage flow, the vacuum at the table falls and holding force drops. Check vacuum at the table, not just at the blower, clean the filter, mask uncovered areas, use zoning and confirm the blower has enough flow for porous work.

Is a side-channel blower or vacuum pump better for a router table?

For porous sheet materials and large tables, a side-channel or Roots blower is usually better because it delivers high flow at moderate vacuum, which handles leakage. A rotary vane pump reaches deeper vacuum but with less flow, so it suits well-sealed, non-porous work. Many shops that cut both types use a larger blower with zoning, or a combination system.

How do I calculate the holding force of a vacuum table?

Holding force is approximately the pressure difference at the table multiplied by the effective sealed area. For example, a pressure difference of 0.2 bar acts as about 2 tonnes-force per square metre. Use the measured vacuum at the part, not the blower rating, and let the machine designer apply the safety margin against cutting and acceleration forces.

Why does my vacuum blower overheat when the table is fully covered?

When the table seals completely, flow through the blower falls and the vacuum deepens. Side-channel and Roots blowers rely on through-flow to carry heat away, so temperature rises quickly. A correctly set vacuum relief valve admits air to keep minimum flow, and a VFD can reduce speed on sealed jobs. Check that the relief valve is fitted and working.

Are compressed-air vacuum ejectors expensive to run?

On small, well-sealed suction cups they are economical and simple. On porous or leaky work they are expensive, because the ejector needs a large compressed-air flow to generate each unit of vacuum flow, and the compressor must run to supply it. For large porous holding duties, a dedicated electric blower usually uses considerably less energy.

How often should a vacuum blower filter be cleaned?

Set the interval by the filter’s pressure drop rather than the calendar, because dust load varies widely with material and season. Record the clean pressure drop at commissioning and clean or replace when it rises to the maker’s limit. On wood dust and paper fibre duties, daily or weekly checks are common, and a cyclone ahead of the filter extends its life.

Related pages

• Side-channel blowers
• Industrial vacuum pick-and-place systems
• Vacuum grippers and ejector air consumption
• Vacuum pump-down and vessel sizing
• Central vacuum energy and load management
• Vacuum and blower performance acceptance