Air knives and blow-off nozzles · compressed-air knives that entrain ambient air, blower-fed knives, replacing open blowing with engineered nozzles, the 30 psi limit for cleaning, chip guarding, and the energy cost of compressed air
An air knife is a slotted nozzle that blows a thin, wide sheet of air across a surface or web to dry, clean, cool or separate material; compressed-air knives use plant air and entrain surrounding air, while blower-fed knives use a dedicated fan or blower. Ask three things first: what force and coverage the job needs, whether compressed air or a blower should supply it, and how operators are protected and air consumption is controlled.
Compressed-air knives, blower-fed air knives and engineered blow-off nozzles for drying, cleaning, cooling and product separation on lines and conveyors. Spray nozzles for liquids (a separate product page), ionising air knives sold for static control, hand-held blowguns and vacuum venturis are outside this page except where compared.
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EXAIR, an air knife maker, describes its compressed-air Super Air Knife as delivering a uniform, laminar sheet of airflow across its full length with an air amplification ratio of 40:1, entraining ambient air to reduce compressed air use and noise compared with other blow-offs, in stock lengths up to 108 in.; its range also includes standard and full-flow air knives, air nozzles, air jets and air wipes. [1] The US Department of Energy's compressed air sourcebook lists open blowing (an open, unregulated tube, hose or pipe used for cooling, drying, clean-up, draining lines or clearing jams) as a potentially inappropriate use of compressed air, and gives alternatives including brushes, dust collection, blowers, blowers with knives, electric fans and nozzles. [2]
Editorial note: ask the supplier to compare compressed-air and blower-fed options on running cost for your duty cycle, since the sourcebook treats blowers as an alternative to compressed air for blowing tasks.
Give the supplier the task (drying, cleaning, cooling, separating), product or web width and speed, distance from knife to surface, required force or air velocity, water or debris to remove, available air supply (pressure, flow, quality) or electrical supply for a blower, noise limits, material (aluminium or stainless) and food or hygiene needs, mounting, and controls (solenoid valve, flow control).
02
OSHA's general industry rule on hand and portable powered tools requires that compressed air not be used for cleaning unless reduced to less than 30 psi, and then only with effective chip guarding and personal protective equipment. [3] The DOE sourcebook adds that hand-held blowguns must have no more than 30 psig discharge nozzle pressure, a nozzle that relieves backpressure if blocked and a spring-operated throttle that shuts off when dropped; it warns that personnel cooling with compressed air is dangerous because it can shoot particulates into the skin, and that a 1/4-inch tube blowing on an operator can consume 15 to 25 brake horsepower of compressed air, where a fractional-horsepower fan of 1/4 bhp or less would do. [2]
Editorial calculation: 20 bhp of compressed air is about 20 × 0.746 ≈ 14.9 kW at the compressor; over 2,000 operating hours a year that is about 30,000 kWh for a single open tube. The horsepower is a mid-range value from the sourcebook and the hours are an assumed example; measure flow before and after replacing open blowing with an engineered knife or nozzle.
03
Paxton Products, which makes blower-fed air knife drying systems, lists its knives in aluminium or 304 stainless steel, the stainless version for washdown areas with harsh detergents, with a continuous air slot set as standard to a gap of 0.055 in. Its performance table gives air flow per inch of knife length at the supply pressure from the blower: 9.5 cfm at 40 in. of water, 10.5 cfm at 50, 11.3 cfm at 60 and 12.2 cfm at 70; in metric, 6.3 m³/h per cm at 100 mbar, 7.0 at 125, 7.6 at 150 and 8.1 at 175 mbar. Paxton pairs the knives with its centrifugal blowers and describes food-plant cases where compressed air was replaced. [4]
Editorial calculation: a 24-in knife at 50 in. of water needs about 24 × 10.5 = 252 cfm (about 428 m³/h) from the blower; 50 in. of water is about 1.8 psi, far below the compressed-air pressures used by compressed-air knives and below the 30 psi cleaning limit in the OSHA rule above. The 0.055 in gap is about 1.4 mm. Ask a blower-knife supplier for blower power at your flow and pressure, and a compressed-air knife supplier for air consumption at your pressure, then compare annual energy as in the calculation above. [4] [3] [2]
04
Devices include compressed-air knives that entrain ambient air, standard and full-flow knives, air nozzles and jets, air wipes, and blower-fed knives as an alternative to compressed air. [1] [2]
05
EXAIR supplies a filter separator and pressure regulator in its knife kits, so ask whether a quotation includes them or expects plant air to be treated upstream. [1]
| Part | Role | Fix in the order |
|---|---|---|
| Knife body and slot | Forms the air sheet. [1] | Length; material; gap. |
| Air supply | Compressed air or blower. [1] [2] | Pressure; flow. |
| Filter and regulator | Clean, set pressure. [1] | Kit contents. |
| Control valve | Switches air on demand. | Solenoid; flow control. |
| Mounting | Positions knife to surface. | Bracket; angle. |
06
Only the cleaning-pressure row is a legal limit; the length, entrainment and blower-flow figures are maker examples from EXAIR and Paxton. [3] [1] [4]
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Length | Example: up to 108 in. [1] | Length for your width. |
| Entrainment | Example: 40:1 amplification. [1] | Air consumption at pressure. |
| Supply | Compressed air or blower; e.g. 9.5–12.2 cfm per inch at 40–70 in. H₂O. [2] [4] | Running cost comparison. |
| Cleaning pressure | < 30 psi with guarding and PPE (OSHA). [3] | Nozzle pressure. |
| Noise | Lower than other blow-offs (maker claim). [1] | dBA at distance. |
| Material | Aluminium or 304 stainless (washdown). [4] | Material; hygiene. |
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Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Task: [dry; clean; cool; separate] Product: [width; speed; distance] Removal: [water; dust; chips] Supply: [compressed air psi/scfm; or blower power] Limits: [noise; safety; hygiene] Controls: [valve; flow control]
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EXAIR says its Super Air Knife entrains ambient air at 40:1, reducing compressed air use and noise compared with other blow-offs. [1]
OSHA allows it only below 30 psi and with effective chip guarding and personal protective equipment. [3]
DOE lists alternatives including blowers, blowers with knives, electric fans and nozzles. [2]
One maker lists 9.5 to 12.2 cfm per inch of knife length at 40 to 70 inches of water from the blower, with a standard 0.055 in slot gap. [4]
Sources checked 2026-10-12. EXAIR is an air knife maker describing its own products; the DOE compressed air sourcebook (cited from an Internet Archive copy) and OSHA 29 CFR 1910.242 are US government documents.
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