A venturi vacuum lifter or handling pad uses around 50 to 200 l/min per ejector, continuously for as long as the stone slab is held, and generally needs 5 to 6 bar at the inlet. On its own, a lifter does not justify a large compressor: it is its consumption added to the polishers and the engraving that has to be covered, with an air reserve that protects the load if the pressure drops. In most stone workshops, a 7.5 or 11 kW 4-in-1 screw compressor, the K 75 or K 110, covers this need.
This article deals with vacuum handling. For every use of air in a stone workshop, see our page on the compressor for stonemasons.
How does a venturi pad create a vacuum?
A venturi ejector is a small part with no motor. Compressed air passes through a narrowing at high speed, which creates a vacuum at a side outlet. This outlet is connected to the suction pad: the air under the pad is drawn out, and atmospheric pressure presses the pad against the stone.
The advantage is simplicity: no pump, no electric cable, little maintenance, reliable operation in the dust and damp of a stone workshop. The drawback is that the ejector uses air for the whole time it holds the load, not just when it picks it up.
This principle is found in several pieces of equipment in a stone workshop:
- vacuum lifters hung from an overhead crane or a jib crane, for lifting and turning granite and quartz slabs;
- hand-held suction cups and vacuum handles, for laying a worktop or setting a headstone;
- table suction pads on some cutting and milling machines, which hold the piece during machining.
Some lifters have their own electric or battery-powered vacuum pump. In that case, they take nothing from the air network. The manual says which.
How much air does a vacuum lifter use?
Values given as a rough guide, to be checked on the ejector's or the lifter's data sheet:
| Equipment | Indicative consumption |
|---|---|
| Small ejector, hand-held cup or small piece | around 50 to 80 l/min |
| Lifter ejector for slabs | around 100 to 200 l/min |
| Lifter with two ejectors, large slab | around 200 to 400 l/min |
The surface finish matters. A polished slab seals well under the pad. A sawn, flamed or bush-hammered face, or a porous sandstone, lets air through: the ejector has to draw continuously to keep the vacuum, and the holding force falls. The lifter manufacturer states which materials and surface finishes it is designed for.
What pressure for a venturi ejector?
An ejector is designed for a precise supply pressure, often around 5 to 6 bar. Below that, the vacuum produced falls, and the holding force with it. Above it, the ejector uses more air without holding any better.
This is the safety point: the pressure at the lifter inlet must not fall below the value in the manual during handling, even if a polisher or an engraving starts at the same moment. Set the compressor to around 7 to 8 bar and check the pressure at the lifter with the tools running.
How do you secure the air supply to a lifter?
Lifting regulations and the lifter manufacturer's instructions take precedence. On the compressed air side, several common measures reduce the risk:
- A non-return valve and a small dedicated air receiver just before the lifter. If the pressure drops on the network, this reserve keeps feeding the ejector long enough to set the load down. See our air receivers.
- The lifter's vacuum reservoir and alarm, where fitted: check them before every lift.
- A protected supply hose, free of kinks, with couplings that cannot disconnect under load.
- A compressor sized with a margin, so that the pressure does not collapse when every station is running.
And the basic rule: nobody under a suspended load.
The step-by-step calculation
For a lifter, we count the ejector at 100% during handling, to be on the safe side, even though our configurator treats it as intermittent use over the day.
Example: a worktop fabrication shop. While one operator moves a slab with the lifter, another is polishing.
- Lifter with two ejectors: 2 × 120 = 240 l/min.
- Wet polisher: 650 l/min.
- Blow gun: 150 l/min × 50% = 75 l/min.
- Subtotal: 965 l/min.
- 25% safety margin: 965 × 1.25 = 1,206 l/min.
- 20% expansion margin: 1,206 × 1.2 = about 1,450 l/min (around 51 CFM).
The K 110, an 11 kW 4-in-1 unit, delivers 1.7 m³/min at 8 bar: it covers this need.
Example: a memorial masonry workshop. The lifter sets bases and headstones while a mason works with a carving hammer.
- Lifter: 240 l/min.
- Carving hammer: 250 l/min.
- Blow gun: 75 l/min.
- Subtotal: 565 l/min, which with both margins gives about 850 l/min.
The K 75, 1.1 m³/min at 8 bar, is enough. Its 420 L air receiver serves as the general reserve; the small receiver dedicated to the lifter is still recommended.
Venturi or vacuum pump - which to choose?
| Criterion | Venturi ejector | Vacuum pump |
|---|---|---|
| Compressed air consumption | continuous while holding | none |
| Maintenance | very low | pump to be serviced |
| Dust and water | copes well | needs protecting |
| Porous or rough stone | makes up for leaks by using more air | depends on the pump's capacity |
If you handle slabs only occasionally, the venturi is simple and safe. If a lifter holds slabs for much of the day, work out its consumption: it may justify a vacuum pump. Our article on the CNC router with vacuum pods makes the same comparison for a machining table.
The pitfalls to avoid
- Worn suction pads. A split or hardened lip leaks, so the ejector uses more air and holds less. Replace them as the manual specifies.
- Water in the ejector. Condensed water or polishing slurry sucked in fouls the ejector. Use dry air, with an automatic condensate drain on the air receiver, and a filter on the vacuum side if the manual calls for one.
- A single compressor for everything. If it stops, the lifter loses its air. For a workshop that does a lot of lifting, our article on the backup compressor sets out the solutions.
Enter your stations in the configurator, or send us your lifter's data sheet with a quote request.
For your trade: Compressor for stonemasons, memorial masons and worktop fabricators.