Air compressor

How it works

A motor or engine turns a pump that draws in air and squeezes it into a smaller volume, raising its pressure. In the reciprocating (piston) compressor, which the Compressed Air & Gas Institute’s maintenance guidance covers, a piston in a cylinder compresses the air; valves admit air on the intake stroke and release it to the receiver on the compression stroke. The compressed air is stored in a receiver, which evens out the pump’s delivery and supplies the bursts of air a nailer or impact wrench uses.

A pressure switch starts and stops the pump to hold the receiver between a set pressure range, and a regulator on the outlet reduces the stored pressure to the setting each tool needs. OSHA’s air receiver rule requires an indicating pressure gauge, one or more spring-loaded safety valves, and a drain at the lowest point of every air receiver.

The output is rated in volume of air delivered at a stated pressure. The Compressed Air & Gas Institute and PNEUROP define standard air as air at 14.5 psia, 68 degrees Fahrenheit and zero percent relative humidity, so that a standard cubic foot per minute (scfm) is comparable between machines. A tool’s demand is given in the same unit: Senco’s manual lists 10 scfm for one framing nailer at 60 cycles per minute.

Anatomy

Pump (compressor head): The cylinder, piston and valves that compress the air. CAGI’s maintenance guidance for reciprocating machines covers valves, intercooler and aftercooler cooling surfaces, and the crankcase lubricant.
Motor or engine: Electric or gasoline. CAGI’s maintenance guide pictures a roofer using a nail gun from a small gasoline or electric compressor.
Receiver (tank): The pressure vessel that stores the air. OSHA requires an indicating pressure gauge, spring-loaded safety valves and a drain at the lowest point.
Safety (relief) valve: Spring-loaded; OSHA requires relieving capacity that prevents the pressure from exceeding the maximum allowable working pressure by more than 10 percent, and no valve between the receiver and its safety valve.
Pressure switch and regulator: The switch cycles the pump; the regulator sets the delivery pressure to the tool. CAGI’s checklist includes annual inspection of the pressure switch diaphragm and contacts.
Intake filter: CAGI’s checklist says to clean or replace the air intake filter quarterly, more often in humid or dirty conditions.
Drain valve: A valve at the lowest point of the receiver to remove accumulated oil and water.

Variants

Reciprocating (piston) compressor: The common job-site type; CAGI’s maintenance guidance covers it.
Centrifugal compressor: A large industrial type that CAGI’s resource library covers, outside the scope of portable tools.
Hydraulic or water-piston compressor: Hiscox describes water used as the compressing piston; the Science Museum Group holds Riche’s water-piston compressor of 1875 and Hiscox places Sommeiller’s water compressor at the Mont Cenis tunnel.
Steam-driven and engine-driven industrial compressors: The Science Museum Group holds drawings of steam-driven compressors and of Ingersoll-Rand machines; the 1873 print shows a compressor used at the St Gothard tunnel.
Portable gasoline or electric compressor for tools: Shown in CAGI’s maintenance guidance as the air source for a pneumatic nail gun on a roof.

Specifications

Free air delivery · scfm at a stated pressure: The figure to match to tool demand. CAGI defines standard cfm as free air converted to 14.5 psia, 68 °F and 0% relative humidity. A framing nailer in one maker’s manual uses 10 to 11 scfm at 60 cycles per minute; no typical compressor delivery has been sourced.
Delivery pressure · psi: 70–120 for a framing nailer (Senco manual)The pressure the tool requires, set at the regulator.
Receiver relief capacity · % over maximum allowable working pressure: No more than 10OSHA 1910.169(b)(3)(i).

Made to

ASME BPVC-VIII-1
CAGI B19.1
ISO 8573-1
OSHA 29-CFR-1910-169
OSHA 29-CFR-1926-302

Safety and care

Safety

OSHA 29 CFR 1910.169 requires every air receiver to have a pressure gauge, spring-loaded safety valves tested frequently, and a drain; no valve may be placed between the receiver and its safety valve, and a receiver may not be buried or placed where it is inaccessible.
OSHA 29 CFR 1910.242(b) and 1926.302(b)(4) prohibit using compressed air for cleaning except where reduced to less than 30 psi and then only with effective chip guarding and personal protective equipment.
OSHA 1926.302(b)(7) requires hoses exceeding 1/2 inch inside diameter to have a safety device at the source of supply or branch line to reduce pressure in case of hose failure.
CAGI advises that if rust, cracks or leaks are found on pressurized components, use of the equipment should stop immediately and system pressure be relieved.
Senco’s safety program says to connect air tools only to clean, dry, regulated compressed air, never to exceed the tool’s maximum air pressure, and never to use bottled gas.

Care

CAGI’s sample checklist, daily: maintain the lubricant level (checking several minutes after the compressor has run), drain the receiver, drop legs and traps, inspect the machine for leaks, rust, noise and vibration, and confirm the guards are in place.
Weekly: operate the pressure relief valves by hand, clean the cooling surfaces, check for air leaks, and inspect the lubricant for contamination.
Monthly: check belt tension. Quarterly: change the oil, inspect valves for rust, wear and carbon, and clean or replace the intake filter. Annually: inspect the pressure switch diaphragm and the motor starter contacts (CAGI).
CAGI notes that manufacturers generally recommend an oil change quarterly or more often with heavier use, and that some offer long-life synthetic lubricants rated at about one year or 2,000 hours.

Tips

Match the compressor to the tool in scfm
A compressor’s rating is the free air it delivers at a stated pressure, and a tool’s demand is stated the same way. Senco’s manual gives 10 scfm at 60 cycles per minute for a framing nailer of the 701XP class. CAGI defines standard air so that ratings can be compared on one basis.1 2
Compare ratings on the standard-air basis
CAGI and PNEUROP define standard air as 14.5 psia, 68 °F and dry. CAGI also runs a voluntary Performance Verification Program in which participating manufacturers publish performance on standard data sheets.1
Find leaks with soapy water
CAGI’s weekly checklist says to squirt soapy water around joints while the compressor operates and watch for bubbles.1
Check oil after the pump has rested a few minutes
CAGI says to check the lubricant level several minutes after the compressor has run, so that oil has drained back to the sump.1
Secure the machine to stop vibration damage
CAGI names vibration from an unsecured compressor as a common cause of failure, because it loosens components and wears bearings. It advises tightly securing the unit on a flat surface and using vibration pads.1
Set the regulator low and rate the hose high
Senco says to run tools at the minimum pressure that sets the fastener, which minimizes noise, wear and energy use. It requires an air hose with a working pressure rating of at least 150 psig or 150 percent of the system’s maximum pressure, whichever is higher.1

History

Earliest documented

about 120 BCE (inferred) for a compressing air pump, per Hiscox

Alexandria, Egypt

Hiscox, writing in 1901, says the condensing air pump or compressor “must have been used” in charging the wind guns of Ctesibius of Alexandria, about 120 B.C., as described by Vitruvius, and that Heron of Alexandria appears to have been the first to invent or describe a pressure air pump for pressures greater than the forge blast. Hiscox presents this as an inference from the surviving writings; this entry has not read Vitruvius or Heron.1

Compressed air as a source of power is older than the machines that use it today. Hiscox attributes the earliest compressing pump to the wind guns of Ctesibius around 120 B.C. and dates the first trial of transmitting power by compressed air to Papin in 1653. He reports a patent by Wilkinson in 1757 for compressing air with a column of water and Medhurst’s 1799 storage of air at 15 atmospheres in a mine. None of these was a portable machine, and Hiscox treats them as the forerunners of the industrial systems that followed.

The industrial compressor grew up in tunnels and mines. Hiscox credits the improvement of rock-boring machinery by Burleigh, Ingersoll, Sergeant, Rand, Clayton and others, and names Sommeiller’s water compressor at the Mont Cenis tunnel. The Science Museum Group holds an 1873 print of a compressor at the St Gothard tunnel, an 1875 compressor with a water piston by Riche, and a drawing of an Ingersoll-Rand machine. In these installations the compressor was a fixed plant and the air was piped to the work.

The tool changed what a compressor had to be. Hiscox wrote in 1901 that portable pneumatic tools had been in use for some time but were appreciated only in the last few years, and that some earlier tools were unsatisfactory. Ingersoll-Rand’s catalog of 1940 lists impact wrenches that run on shop air at a stated pressure. The nail gun then put the compressor on the job site: in Carlson’s history portable nailers developed from the mid-1950s, and the Compressed Air & Gas Institute’s maintenance guide now shows a roofer using a nail gun from a small gasoline or electric compressor.

Safety rules followed the stored energy. OSHA’s 1974 air receiver rule requires receivers to be built to the ASME Boiler and Pressure Vessel Code, Section VIII, to carry a gauge, safety valves and a drain, and to be drained frequently; the construction rule limits the use of air for cleaning to less than 30 psi. The Institute’s B19.1 safety standard for compressor systems supersedes ASME B19.1-1995, according to its resource library.

The compressor displaced the muscle and the engine at the point of use. Hiscox introduces the pneumatic tools chapter of his book as a relief to the weary muscle of the mechanic. The power now sits in a receiver and a hose rather than in the operator’s arm, and the user’s concerns are volume of air, pressure and moisture, the quantities the Institute’s standard-air definition and the tool maker’s scfm rating are written to settle.

Timeline

about 120 BCE
A compressing air pump “must have been used” to charge the wind guns of Ctesibius of Alexandria, according to Hiscox.1
1653
Denys Papin makes the first trial of transmitting power to a distance by compressed air, according to Hiscox.1
1757
Wilkinson in England patents a method of compressing air by a column of water, according to Hiscox.1
1799
Medhurst, a Danish engineer in England, compresses air to 15 atmospheres (210 pounds), stores it and transmits it to a motor in a mine, according to Hiscox.1
1873
A print from Engineering of 1873 shows an air compressor used at the St Gothard tunnel; the Science Museum Group holds it.1
1875
Riche’s air compressor with a water piston is made in this year, in the Science Museum Group collection.1
1886
The Science Museum Group holds a sectional drawing, made in 1928, of Atkinson’s air compressor of 1886.1
1901
Hiscox reports that portable pneumatic tools are of comparatively recent application and that some of the earlier tools were unsatisfactory.1
1940
Ingersoll-Rand’s Air Tools catalog lists pneumatic impact wrenches and other air tools for shop use.1
1974
OSHA publishes 29 CFR 1910.169 on air receivers on 27 June (39 FR 23502), requiring new receivers installed after the effective date to be built to the 1968 ASME Boiler and Pressure Vessel Code, Section VIII.1
2023
CAGI refreshes its reciprocating compressor maintenance guidance with a daily-to-annual checklist.1

Gaps in the record (6)

Hiscox’s history is a 1901 secondary account; Vitruvius, Heron, Papin, Wilkinson and Medhurst have not been traced to primary sources, and Hiscox’s date for the Mont Cenis installation has not been checked.
The origin of the portable tank-and-wheels job-site compressor, and its first maker, has not been found in a primary source.
The Science Museum Group records read give only titles, dates and object numbers, not descriptions of the compressors.
ASME BPVC Section VIII, CAGI B19.1, ISO 1217 and ISO 8573-1 have not been read; the standard slugs are inferred. The CAGI B19.1 note comes from the resource library page.
No independent test of delivery, noise or durability has been sourced, so buying is null.
No typical compressor delivery rating is sourced for the specs table.