Capacity Calculator
Vacuum tube lifter capacity calculator: tube size, porosity and altitude
This vacuum lifter capacity calculator estimates what a lifting tube of a given diameter can lift at a given working vacuum, derates the figure for a porous load and for altitude, and checks the pad area the tube needs. It is a plausibility check for a quotation, not a rating: it does not deduct the weight of the pad and tube, it ignores leaks, and the manufacturer's rating and the sample test decide. Our own vacuum tube lifter range is rated for airtight loads per the catalogue; porous loads are tested with samples.
Inputs: tube diameter, working vacuum, porosity, altitude
Four inputs; the defaults are a Ø160 mm tube at 40 kPa, a semi-porous load and sea level, taken from the tables below. Add your load weight if you want the sea-level rating the load needs.
Limits of the estimate
The theoretical mass does not deduct the weight of the pad, the tube and the handle, and it ignores leaks, so a rating is always below it; how far below is the maker's call, and ratings for the same tube diameter differ by up to about 40% between makers. The porosity shares are planning estimates, the altitude factor assumes a standard atmosphere, and neither replaces the manufacturer's rating or the sample test. Loads above 200 kg are outside this site's range.
send the load, the heights and the site altitude; porous loads go to a sample test before the quotation.
Cowest Machinery designs and manufactures vacuum tube lifters at its factory in Qingyuan, Guangdong, China.
Result
Up to five lines come back: the theoretical lifting mass of the tube at that vacuum, before any deduction; the altitude factor; the theoretical mass after derating for the porosity class and the altitude, still before any deduction, so a lifter's rating sits below it; if you entered a load, the sea-level airtight rating a lifter needs to lift it there; and the minimum pad area. A rating that sits near the 30–40 kPa result is plausible; a rating that needs 50 kPa of continuous working vacuum before deducting the pad weight is optimistic and deserves a test report.
Next step: take the figures to the selection guide to size the model, or send the load and the site and we size it; porous loads go to a sample test first.
the load, the heights and the site altitude are enough to start.
Formula
Lifting force equals the pressure difference across the tube wall times the tube's cross-section; divided by gravity it gives the theoretical lifting mass:
F (N) = Δp (Pa) × A (m²); m (kg) = F / g, with g = 9.80665 m/s², about 9.81; A = π × D² / 4, with D the tube's inside diameter in metres
Δp is the working vacuum inside the tube relative to the air outside. The UK HSE describes an average pressure difference of about 55 kPa for vacuum tube lifters; the ratings published by makers sit nearer the 30–40 kPa columns of the table below, because a rating leaves room for the pad and tube weight, leaks and a safety margin.
| Tube diameter | 30 kPa | 40 kPa | 50 kPa | 55 kPa | Typical brand rating |
|---|---|---|---|---|---|
| 100 mm | 24 | 32 | 40 | 44 | — |
| 120 mm | 35 | 46 | 58 | 63 | 35–50 kg |
| 140 mm | 47 | 63 | 78 | 86 | 45–60 kg |
| 160 mm | 62 | 82 | 103 | 113 | 60–70 kg |
| 180 mm | 78 | 104 | 130 | 143 | about 85 kg |
| 200 mm | 96 | 128 | 160 | 176 | 110–120 kg |
| 230 mm | 127 | 169 | 212 | 233 | about 140 kg |
| 250 mm | 150 | 200 | 250 | 275 | about 200 kg |
| 300 mm | 216 | 288 | 360 | 396 | about 300 kg |
Condition: our catalogue ratings are for airtight loads and are confirmed with a sample test for porous loads; the calculator checks a rating for plausibility, it does not re-rate a model.
Derating for porosity
A porous load leaks air through its surface; the generator has to make up the leak while holding the pressure difference, so the usable capacity is a share of the airtight rating. The calculator applies the same shares to the theoretical mass, which is still before any deduction; they are planning estimates, and a sample test replaces them.
| Class | Typical loads | Share of the airtight rating |
|---|---|---|
| Airtight | PE film bags, plastic and steel drums, laminated boards | 100% |
| Semi-porous | Plain cartons, paper sacks with a PE liner, laminated woven sacks | 75–90% |
| Porous | Unlined multi-wall paper sacks, chipboard | 50–80% |
| Highly porous | Uncoated woven sacks, jute, cloth bags | Often not on vacuum alone; the calculator gives no figure |
Rule: porous loads are sample-tested before a quotation, and the quotation states which load class the rating applies to. For porous loads the vacuum source matters more than the tube size: flow replaces the leaking air, a larger tube does not. Next step: how pads and blower flow are chosen for porous paper and woven sacks.
Altitude correction
Air pressure falls with altitude, the pressure difference a generator can produce falls with it, and so does capacity. The calculator uses the standard atmosphere:
p(h) = 101.325 × (1 − 2.25577 × 10⁻⁵ × h)^5.25588 kPa, with h the altitude in metres; capacity factor ≈ p(h) / 101.325
| Altitude | Air pressure | Capacity factor |
|---|---|---|
| 0 m | 101.3 kPa | 100% |
| 500 m | 95.5 kPa | 94% |
| 1,000 m | 89.9 kPa | 89% |
| 1,500 m | 84.6 kPa | 83% |
| 2,000 m | 79.5 kPa | 78% |
| 2,500 m | 74.7 kPa | 74% |
| 3,000 m | 70.1 kPa | 69% |
| 4,000 m | 61.6 kPa | 61% |
The formula agrees with the altitude table published by one US maker of vacuum lifters: about 83% at 1,524 m and about 69% at 3,048 m. Correct for altitude above about 1,000 m; above 1,500 m, ask for the quotation to state the derated capacity. Worked example (example figures): a plant at about 2,240 m lifting a 40 kg airtight load, such as a PE film bag, needs a sea-level rating of at least 40 / 0.76, about 53 kg, before any margin.
Pad area check
The pad must hold the load as firmly as the tube lifts it: holding force is the pressure difference times the pad's effective sealing area, and the practice of several makers is an effective pad area of at least twice the tube's cross-section, some makers asking for 2.5 times, so that holding force exceeds lifting force with a margin. The calculator reports that minimum area and the square or round pad it corresponds to.
Minimum pad effective area ≈ 2 × π × D² / 4. Example: a Ø160 mm tube has a cross-section of about 0.020 m², so the pad needs about 0.040 m² of effective area, about a 200 × 200 mm square or a Ø226 mm circle
If the load's flat face is smaller than that area, the pad cannot seal on it: a smaller tube or a different gripping method is needed. Next step: pad types by load are in step 5 of the selection guide.