By entrainment - the high-velocity jet drags surrounding air along with it.

Compressed air leaves the nozzle through precisely formed slots or an annular gap at very high velocity. A fast-moving stream of air creates a low-pressure region around itself, and atmospheric air is drawn into that region and accelerated along with the jet.

The result is a total airflow at the target considerably larger than the compressed air supplied - the ambient air is doing much of the work and it costs nothing.

The nozzle's geometry is what makes this efficient: the shape of the outlet, the entrainment openings and the profile of the surrounding surface all determine how much ambient air is drawn in and how well the combined stream stays coherent.

That is why an engineered nozzle and a drilled hole delivering the same compressed air do not produce remotely the same result - the hole simply expels air, while the nozzle recruits more of it.

A substantial proportion - frequently the majority of the consumption for the same blowing force.

An open pipe or drilled fitting passes compressed air continuously with no entrainment and no shaping. Almost all of the flow is compressed air that the compressor had to produce, and much of its energy goes into noise and turbulence rather than into directed force.

An engineered nozzle achieves comparable or greater force at the target while consuming considerably less compressed air, because a large part of the stream is entrained ambient air.

Since blow-off applications typically run continuously through a shift and there are often many of them, the saving compounds - and compressed air is one of the most expensive utilities in a plant.

The payback on replacing open pipes is usually short enough that it is among the first measures recommended in any compressed air audit. Manufacturers publish consumption figures at stated pressures, which makes the comparison straightforward to calculate for a specific installation.

Because the noise comes from turbulence and shear at high velocity, and entrainment reduces both.

An open pipe discharges compressed air directly into still atmosphere at very high velocity. The violent shear between the fast jet and the stationary air around it generates intense broadband noise - which is why an open blow-off pipe is one of the loudest things in many factories.

An engineered nozzle mixes the compressed air with entrained ambient air progressively, so the final stream is a larger volume moving more slowly. Lower velocity and gentler shear mean far less noise for the same effect.

Reductions of many decibels are typical, and because the decibel scale is logarithmic that represents a large change in perceived loudness and in exposure.

That matters for compliance as well as comfort: continuous blow-off noise frequently contributes significantly to a plant's noise exposure assessment, and reducing it at source is more effective and cheaper than hearing protection or enclosure.

Limits on dead-end pressure and on noise exposure, both of which safety nozzles are designed to satisfy.

The dead-end hazard is the serious one. If an open pipe at full system pressure is pressed against skin, air can be forced through the skin into the tissue - an injection injury that is disproportionately dangerous relative to how minor it looks. Many jurisdictions limit the pressure that may be dead-ended against a person for exactly this reason.

Safety nozzles are constructed so they cannot be fully blocked: relief openings ensure that if the outlet is covered, air escapes elsewhere and the dead-end pressure stays below the limit.

Noise is the second requirement, and engineered nozzles address it inherently.

Where a blow gun or nozzle can be handled by an operator or reached by a person, a safety nozzle should be treated as a requirement rather than an upgrade - and open pipe blow-offs in accessible positions are a common and readily correctable finding.

Concentrated, flat, wide-area and adjustable patterns, chosen by the shape of what is being blown.

A concentrated or pinpoint nozzle produces a narrow, forceful stream for clearing a small area, blowing out a hole, or dislodging something specific.

A flat or fan pattern spreads the stream into a sheet, which suits drying or clearing along a line - the edge of a strip, a conveyor, a moving web.

Wide-area and cluster nozzles cover a larger footprint for drying or cooling a broad surface.

Adjustable and swivel mountings allow the pattern to be aimed precisely, which matters more than it sounds - a nozzle pointed approximately at the target wastes most of its effect.

Where the area is wide and continuous, an air knife is the appropriate product rather than a row of nozzles, since it produces a uniform sheet across its length.

Match the pattern to the task, and mount so the nozzle can be aimed and then locked.

Often lower than people assume - and reducing it is one of the easiest savings available.

Blow-off applications are frequently connected to full system pressure because that is what is available, when the task requires far less. Air consumption rises with pressure, so running a nozzle at full pressure when half would clear the part wastes air continuously.

The practical approach is to fit a regulator on the blow-off line and reduce the pressure until the application just stops working reliably, then set it modestly above that. The saving is often substantial and costs only a regulator.

Turning the air off when it is not needed is the other obvious measure and is frequently neglected - a solenoid valve triggered by a sensor, so the nozzle blows only when a part is present, eliminates consumption between parts entirely.

Between reduced pressure, intermittent operation and engineered nozzles, blow-off consumption on a typical plant can usually be cut dramatically.

Blow-off, drying, cooling, cleaning and part ejection - anywhere a directed air stream does work.

Common applications are clearing swarf, dust and debris from parts and machine beds; drying components after washing or before coating; cooling hot parts, welds or tools to shorten cycle times; ejecting parts from a machine or diverting them on a conveyor; clearing conveyor belts; and blowing chips clear at a cutting tool.

They are also used to clear packaging lines, open bags, separate stacked items and remove water before labelling or printing.

What those share is a continuous or frequent demand, which is exactly why efficiency matters - a nozzle running through a shift consumes far more than its size suggests.

Where the requirement is a wide uniform sheet rather than a spot, air knives are the correct product; where it is a large volume of moving air rather than force, air amplifiers are more suitable.