Why industries choose air hoists
Air hoists use a vane, piston or gear air motor to drive a chain or wire-rope drum. They are chosen where electric hoists struggle: hazardous areas such as refineries, paint shops, chemical and pharma plants, mines and offshore work; heavy-duty cycles where an air motor will not overheat if it runs continuously or stalls; wet and dusty environments; and applications needing very fine, smooth control of speed during positioning. In many Indian workshops, foundries, shipyards and fabrication shops, compressed air is already available, which makes air hoists convenient.
The trade-off is that an air hoist is only as capable as the air it receives. A hoist rated for a given load and speed at its nameplate pressure lifts more slowly, or not at all near full load, when the inlet pressure falls.
What the hoist needs at its inlet
Hoist makers state a rated working pressure, commonly around 6 bar (87 psig) at the inlet while running, and an air consumption at that pressure. Consumption is normally highest when lifting a rated load at full speed. Lowering, trolley travel and idle motion use less, but are not zero.
- Pressure: the maker’s rated pressure at the hoist inlet, measured while lifting the heaviest routine load.
- Flow: the maker’s consumption figure for lifting at rated load, converted to free air at the compressor’s reference conditions.
- Air quality: dry, filtered air, with lubrication as the maker specifies.
- Continuity: what happens to a suspended load if air is lost, which depends on the hoist’s brake design.
Both lifting speed and lifting capacity fall as inlet pressure falls. Never raise a hoist’s supply pressure above its rating to “get more lift”; that overloads the motor, brake and structure and invalidates the hoist’s rating.
Duty cycle: one lift or a production shift
A maintenance hoist that makes a few lifts per day and a production hoist transferring parts all shift can have identical nameplates but very different air demand. Describe the full movement: preparation, raising, positioning, lowering, release and return, plus trolley moves.
| Duty type | Typical pattern | Supply implication |
|---|---|---|
| Occasional maintenance lifts | Short bursts, long idle periods | Receiver near the hoist can supply the lift; compressor refills between lifts |
| Production transfer | Repeated lifts all shift | Compressor must cover average demand; receiver covers peaks; check dryer and filter capacity |
| Hazardous-area or continuous duty | Long runs, slow positioning | Steady high flow; distribution sized for low pressure loss over long runs |
| Temporary site lifting (shutdowns, construction) | Variable, often heavy | Portable compressor on hire, with aftercooler, separator and correctly sized hoses |
Sizing the air supply: a worked method
- Take the hoist maker’s air consumption at rated pressure for lifting at rated load.
- Estimate the share of time the hoist actually runs in a busy hour (its use factor) from the process, not a guess.
- Add the trolley motor and any other users on the same branch, each with its own use factor.
- Add an allowance for leaks and future users.
- Check that the compressor’s free air delivery at working pressure covers the average and that a receiver can supply the peak lift without the pressure at the hoist dropping below its rating.
- Calculate pressure drop from the receiver to the hoist inlet through pipe, filter, regulator, lubricator, hose and couplings at the lifting flow.
- Measure pressure at the hoist inlet during a lift with the heaviest routine load to confirm.
As an illustration, if a hoist consumes a given flow while lifting and runs a quarter of the time, average demand is about a quarter of that flow, but the hose, coupling and filter must still pass the full flow without excessive drop during each lift. That is why a hoist that “has enough compressor” can still be slow.
Hoses, couplings and pressure loss
The last few metres are where most hoist supply problems hide. Pendant-controlled hoists often hang from a long hose with a quick coupling, a filter-regulator-lubricator set and a swivel, all of which add loss.
- Use the hose bore the maker recommends, and do not reduce it to match a smaller coupling.
- Choose full-flow couplings rated for the flow; standard small quick couplings are a common restriction.
- Size the filter, regulator and lubricator for the lifting flow, not the pipe size.
- Keep the hose as short as practical and protect it from crushing, heat and abrasion.
- Fit a safety device against hose whip on supply hoses where required.
- Each extra bar raised at the compressor to overcome these losses costs roughly 7% more power, so fix the restriction first.
Air quality and lubrication
Water is the enemy of air motors and brakes. It washes away lubrication, causes corrosion, and water can freeze in the exhaust as the air expands, sticking valves and brakes. Dirt wears vanes and seals.
- Supply dried air where possible; a refrigerated dryer at a typical +3 °C pressure dew point suits most indoor plants.
- On portable or site supply, fit an aftercooler and moisture separator and drain them regularly.
- Filter ahead of the hoist with a correctly sized filter and working drain.
- Lubricate as the maker specifies: some hoists need an in-line lubricator with a specified oil, others are designed to run lubrication-free. Do not add oil to a lubrication-free design, and do not run a lubricated design dry.
- Where the exhaust is released in a clean area, consider exhaust mufflers and filtration, and check that oil mist is acceptable.
Brakes, controls and air loss
Most industrial air hoists use a spring-applied, air-released brake, so the brake holds the load when air is removed. Some designs differ. The brake’s behaviour on loss of air must be known for every hoist in service. Pendant or remote controls throttle air to the motor; sticking valves or contaminated air can cause creep or erratic control.
From the supply side, avoid sudden pressure collapses by giving hoists a reliable branch and, where several hoists share a line, enough storage. Plan compressor maintenance so lifting is not in progress when air is isolated. Brake adjustment, load tests and lifting-equipment examinations are matters for competent lifting personnel under the applicable rules, not for the air-supply design.
Common air hoist supply problems
| Symptom | Likely supply-side cause |
|---|---|
| Slow lifting at full load | Low inlet pressure under flow: small hose, coupling, blocked filter, long branch |
| Hoist stalls near rated load | Pressure at inlet well below rating while lifting |
| Erratic or jerky control | Contaminated air, water in valves, poor lubrication |
| Water spitting from exhaust | No drying or failed drains upstream |
| Motor wear or loss of power over time | Dirty air, wrong or no lubrication |
| Other machines slow when hoist runs | Shared branch undersized, no local receiver |
Hazardous areas and site work
Air hoists are often chosen for hazardous areas because the motor has no electrical ignition source. The hoist must still carry the appropriate rating for the zone, and the air supply arrangement, including any portable compressor, must be positioned and approved under the site’s own rules. On refinery and petrochemical shutdowns, the diesel compressor normally sits outside the classified area with a long supply hose, so hose sizing and pressure loss deserve extra attention.
How Reddy Compressors helps
Reddy Compressors, Tarnaka, Secunderabad, has supplied, rented and serviced compressors since 2002 as an independent multi-brand specialist. We work with ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other makes, and we are not an authorised dealer of any brand. We have tie-ups with all major and reputed brands. Our role is the air supply to your hoists:
- Sizing compressors, receivers, dryers and filters for hoist duty cycles.
- Pressure-at-inlet checks and pressure-drop audits to find why hoists are slow.
- Rental compressors from 50–2,000 cfm and 2–30 bar, diesel and electric, with hoses, aftercoolers and separators for shutdowns and site lifting.
- Service and AMC across Telangana and Andhra Pradesh by over 20 service engineers and technicians; supply of compressors and spares across India.
Hoist selection, structural checks, brake adjustment and lifting examinations remain with the hoist maker and your competent lifting personnel.
What to send us
- Hoist make, model, rated load, rated pressure and air consumption.
- Number of hoists, trolleys and other users on the same supply.
- How often each hoist lifts and for how long.
- Hose length, bore and coupling type, and the FRL set fitted.
- Existing compressor, dryer and receiver details, and measured pressures if available.
- For site work: location, duration and whether the area is hazardous.
Frequently asked questions
What size compressor do I need for an air hoist?
Start with the hoist maker’s air consumption at rated pressure while lifting rated load, multiply by how much of the time it actually lifts, and add other users and leaks. The compressor covers the average; a receiver near the hoist covers each lift. The hose, couplings and filter must still pass the full lifting flow without dropping the pressure at the inlet below the rating.
Why is my air hoist lifting slowly?
The most common cause is low pressure at the hoist inlet while it lifts, from a small hose, a restrictive quick coupling, an undersized or blocked filter-regulator-lubricator or a long branch shared with other users. Measure pressure at the inlet during a lift. Worn motor vanes from wet or dirty air and incorrect lubrication are the next things to check.
What air pressure does an air hoist need?
Many industrial air hoists are rated at around 6 bar (87 psig) at the inlet while running, but the maker’s nameplate governs. Lifting speed and capacity fall when pressure at the inlet drops. Never set the supply above the hoist’s rated pressure to gain lift, because that overloads the motor, brake and structure.
Does an air hoist need a lubricator?
It depends on the design. Many air hoists need an in-line lubricator with a specified oil to protect the air motor, while others are designed to run lubrication-free. Follow the maker’s instruction. In either case, supply dry, filtered air, because water washes away lubrication and causes corrosion in the motor and brake.
What happens to the load if the air supply fails?
Most industrial air hoists have a spring-applied, air-released brake that holds the load when air is lost, but designs differ, so confirm the behaviour of each hoist with its maker’s documentation. Plan compressor maintenance and changeovers so air is never isolated during a lift, and give critical hoists a reliable supply with local storage.
Can I rent a compressor to run air hoists during a plant shutdown?
Yes. We rent diesel and electric compressors from 50–2,000 cfm and 2–30 bar, with hoses, aftercoolers and moisture separators to deliver cool, drier air for hoists and tools. Send us the hoist models, their consumption, how many will run at once and the site details, and we will propose a suitable machine.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Compressed air demand estimate
Add up the air your tools and processes use, apply duty and simultaneity, then add leakage and growth allowances to reach a capacity to enquire about.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Unit for the air each tool uses: L/s
- Group A: number of tools: 6
- Group A: free air each (in the unit above): 4
- Group A: duty (%): 40
- Group B: number of tools: 2
- Group B: free air each (in the unit above): 15
- Group B: duty (%): 60
- Group C: number of tools: 1
- Group C: free air each (in the unit above): 40
- Group C: duty (%): 80
- Simultaneity of all tools (%): 65
- Leakage allowance (%): 15
- Growth allowance (%): 10
Result
- Connected demand: 94 L/s = 199 cfm
- Average demand (duty-weighted): 59.6 L/s = 126 cfm
- Simultaneous peak: 61.1 L/s = 129 cfm
- Design basis (higher of average and peak): 61.1 L/s = 129 cfm
- Design capacity with allowances: 77.29 L/s = 4.64 m³/min = 163.8 cfm
Method. Average demand = Σ(number × air per tool × duty). Peak = Σ(number × air per tool) × simultaneity. The peak can never be lower than the average, so the design basis is the higher of the two. Design capacity = design basis × (1 + leakage) × (1 + growth).
What to take from it. Leakage and growth allowances move the answer as much as any single tool. Where you can, replace catalogue figures with measured ones.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.
Pipe pressure drop and sizing
Check the pressure drop and air velocity in a compressed-air line, or find the smallest bore that keeps the drop within a target.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Flow (m³/min free air): 12
- Inlet pressure (bar g): 7
- Pipe length (m): 150
- Inside diameter (mm): 80
- Roughness (mm): 0.046
- Fittings allowance (% extra length): 30
- Air temperature (°C): 30
- Target pressure drop (bar): 0.1
Result
- Pressure drop: 0.059 bar (0.839% of the inlet gauge pressure)
- Air velocity: 5.22 m/s
- Reynolds number: 2,06,066
- Smallest bore for the target drop: 73 mm inside diameter
- Velocity check: Within the common rule-of-thumb range for mains (roughly up to 15–20 m/s)
Method. Darcy–Weisbach: ΔP = f × (L/D) × ρv²/2, with the friction factor f from the Swamee–Jain relation and air density taken at mean line pressure. Fittings are allowed for as extra equivalent length. Typical commercial steel roughness is about 0.046 mm.
What to take from it. Pressure drop varies roughly with the fifth power of the bore at constant flow, so a larger main is a cheap way to hold pressure.