Free 3D model · STL · GLB · AR
By Parth Parmar, mechanical design engineer · 61 pieces, 43 parts · Updated
A reciprocating air compressor squeezes air with a piston in a cylinder. On the downstroke the piston draws air in through a suction valve; on the upstroke it compresses the air until the delivery valve opens and pushes it into a storage tank. Two-stage machines compress in two cylinders and cool the air in between.
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Live 3D: drag to turn it, pinch to zoom, explode it, cut it open, X‑ray it and watch it run. Free, in your browser, no app. Open it full screen →
Single parts: scroll to the parts list. These are learning models, not a print kit: some parts touch or overlap and there are no fit tolerances.
Free for personal and educational use under CC BY-NC 4.0. Credit “Engine-X by Parth Parmar (engx3d.com)” when you share or remix it. Don’t sell the files or prints. For commercial use, get in touch. Every file carries the Engine-X mark and a hidden digital fingerprint that identifies it.
| Machine | Two-stage V-twin · 12 bar (175 psi) · 3.7 kW |
|---|---|
| Parts modeled | 61 named parts in 7 systems (43 different parts to download) |
| Model size | 1162 × 865 × 755 mm (real scale) |
| Formats | GLB (glTF 2.0) 4.2 MB, STL 3.0 MB, USDZ for iPhone AR, ZIP of part STLs 0.7 MB |
| Live 3D | Engine‑X atlas: true motion, explode, section, X‑ray |
| License | CC BY-NC 4.0, free with credit |
| Crank train | 8 parts: Crankshaft, main bearings, two connecting rods, pistons and pins. |
|---|---|
| Cylinders & valves | 13 parts: Crankcase, finned LP and HP barrels, valve plates, reed valves, heads and oil. |
| Air path | 4 parts: Intake filter, intercooler, discharge tube and check valve. |
| Motor & belt drive | 5 parts: Motor, motor pulley, V-belt, flywheel fan pulley and belt guard. |
| Air receiver | 3 parts: Tank, saddle plate and feet. |
| Controls & safety | 6 parts: Pressure switch with unloader, gauge, safety valve, service valve and drain. |
| Hardware | 4 parts: Head bolts and mounting bolts. |
Every part with a picture, what it does and its own STL file: crankshaft, main bearing, lp piston (ø100 mm), lp piston pin, lp connecting rod, hp piston (ø53 mm), hp piston pin, hp connecting rod and more. Open any part in the live 3D atlas to see where it sits and how it moves. A part used several times (valves, bolts) is shown once with its count.
↓ Download all parts · ZIP · 0.7 MB
Crankshaft, main bearings, two connecting rods, pistons and pins.
The crankshaft turns the motor's rotation into the pistons' up-and-down strokes. One crankpin carries both connecting rods side by side, so the two cylinders, set 90° apart, take their strokes a quarter turn apart. It turns at about 900 rpm, 3.2 times slower than the motor.
The counterweight opposite the crankpin balances the rotating mass of the pin and the rod big ends.
A main bearing: a ball bearing in the crankcase wall that carries the crankshaft. Splash oil from the sump keeps it lubricated.
The low-pressure (first-stage) piston, 100 mm across. On its downstroke it draws in outside air through the filter; on its upstroke it squeezes that air to about 2.6 bar and pushes it into the intercooler.
Two compression rings seal the air above; the lower oil ring scrapes oil back down the wall so little reaches the air.
A piston pin (gudgeon pin) joins the piston to the connecting rod and lets the rod swing as the crank turns.
A connecting rod, 140 mm between centres, links the crankpin to a piston. It turns the crankpin's circle into the piston's straight up-and-down stroke. Both rods share one crankpin.
The high-pressure (second-stage) piston, only 53 mm across. It takes the already-compressed, cooled air from the intercooler and squeezes it again, up to 12 bar (175 psi), for the tank.
With equal strokes, the bore ratio follows the stage pressure ratio: 53 ÷ 100 ≈ 1 ÷ √3.6.
A piston pin (gudgeon pin) joins the piston to the connecting rod and lets the rod swing as the crank turns.
A connecting rod, 140 mm between centres, links the crankpin to a piston. It turns the crankpin's circle into the piston's straight up-and-down stroke. Both rods share one crankpin.
Crankcase, finned LP and HP barrels, valve plates, reed valves, heads and oil.
The low-pressure cylinder barrel, 100 mm bore. Deep cooling fins carry the heat of compression out to the air blast from the flywheel fan.
The valve plate, clamped between barrel and head. It carries the two reed valves for its cylinder: suction on the cylinder side, delivery on the head side.
The low-pressure cylinder head, with its inlet chamber (fed by the air filter) and outlet chamber (feeding the intercooler) kept apart by a partition.
The suction (inlet) reed valve: a thin spring-steel flap. When the piston moves down and the cylinder pressure falls below the inlet pressure, the flap bends open and air rushes in; it snaps shut as soon as the piston turns round.
It opens a little after the stroke begins, because the air trapped in the clearance space must first re-expand.
The lift is exaggerated in the model so you can see it move.
The delivery (discharge) reed valve lets compressed air out of the cylinder. It stays shut while the piston compresses the air and only opens late in the upstroke, once the cylinder pressure beats the pressure waiting beyond it.
Worn or leaking reeds cut the air the compressor delivers; they are a routine replacement part.
The high-pressure cylinder barrel, 53 mm bore. It is smaller because the air reaching it has already been squeezed to about a quarter of its volume.
The valve plate, clamped between barrel and head. It carries the two reed valves for its cylinder: suction on the cylinder side, delivery on the head side.
The high-pressure cylinder head closes the top of the small second-stage cylinder. Its inlet comes from the intercooler and its outlet goes to the discharge tube and the tank.
The suction (inlet) reed valve: a thin spring-steel flap. When the piston moves down and the cylinder pressure falls below the inlet pressure, the flap bends open and air rushes in; it snaps shut as soon as the piston turns round.
It opens a little after the stroke begins, because the air trapped in the clearance space must first re-expand.
The lift is exaggerated in the model so you can see it move.
The delivery (discharge) reed valve lets compressed air out of the cylinder. It stays shut while the piston compresses the air and only opens late in the upstroke, once the cylinder pressure beats the pressure waiting beyond it.
Worn or leaking reeds cut the air the compressor delivers; they are a routine replacement part.
The crankcase, the cast-iron body of the pump. It carries the main bearings, the two cylinders and the oil sump, and its fins and mass soak up heat.
Drawn see-through so the crank, rods and pistons stay visible.
The crankcase breather and oil-fill cap lets the crankcase breathe and is where oil is topped up. It lets air in and out as the pistons move, so the crankcase does not pump itself up and push oil past the rings.
The crankcase oil drain plug, at the bottom of the crankcase, is removed to drain the old oil at an oil change.
Intake filter, intercooler, discharge tube and check valve.
The intake air filter cleans the air before it enters the first-stage cylinder. All the air the compressor will ever deliver enters here, so a clogged element cuts output and raises the temperature; a missing one lets dust wear the cylinder.
The intercooler: a finned copper tube from the LP head to the HP head, right in the flywheel fan's air blast. It cools the first-stage air before the second stage, so the HP cylinder has less work to do and the air stays cooler.
Without intercooling, two stages would save little: the gain of two-stage compression comes from removing heat between the stages.
The discharge tube (aftercooler line) from the HP head down to the tank. The hot compressed air cools a little on the way, so some of its water vapour condenses in the tank instead of in the air lines.
The check (non-return) valve where the discharge tube enters the tank. It lets air into the tank but never back out, so the tank stays full when the pump stops.
Motor, motor pulley, V-belt, flywheel fan pulley and belt guard.
The flywheel pulley, Ø320 mm pitch diameter. Its heavy rim smooths out the uneven torque of the two strokes, and its spokes are shaped as fan blades that blow cooling air over the cylinders and the intercooler.
The motor pulley, Ø100 mm pitch diameter. Belt speed is the same at both pulleys, so the pump turns 320 ÷ 100 = 3.2 times slower than the motor.
The V-belt carries power from the motor pulley to the compressor flywheel. A loose belt slips and squeals at start-up; an over-tight one wears the bearings.
The driver: a 3.7 kW (5 hp) two-pole induction motor turning at about 2880 rpm on a 50 Hz supply. The pressure switch starts and stops it to keep the tank between its two set pressures.
The belt guard covers the flywheel and V-belt to protect the operator. A spinning flywheel and belt are an entanglement hazard, so every real compressor has one; it is drawn see-through here. Its mesh face still lets the fan pull air through.
Tank, saddle plate and feet.
The air receiver (tank) stores compressed air so the compressor can stop and start instead of running all the time, evens out pressure pulses, and lets water and oil settle out.
Pressure vessels like this are built and stamped to a code (e.g. ASME), and must be drained regularly.
The saddle plate is welded on top of the tank and carries the pump and motor. The pump and motor bolt to it, which keeps the belt in line.
A tank foot supports the air receiver on the floor. Anti-vibration pads go under the feet; a compressor bolted rigidly to the floor shakes the tank welds.
Pressure switch with unloader, gauge, safety valve, service valve and drain.
The pressure switch starts and stops the motor automatically. It stops the motor when the tank reaches its cut-out pressure and starts it again when pressure falls to the cut-in setting. Its built-in unloader vents the discharge line each time the motor stops, so the motor can restart without pushing against full pressure.
The tank pressure gauge shows how much air pressure is stored in the receiver. Watching how fast it climbs after a start is the simplest test of a worn compressor.
The unloader tube, from the check valve to the pressure switch. When the motor stops, the air trapped between the pump and the check valve escapes through it with a short hiss.
The safety (pressure relief) valve protects the tank from over-pressure. If the pressure switch ever fails to stop the motor, this spring-loaded valve pops open before the tank can be over-pressurised.
Never plug or tie down a safety valve; pull its ring now and then to check it is not stuck.
The service (outlet) valve, where the air line connects. Keep it shut when the compressor is left unattended.
The drain valve at the lowest point of the tank. Compressing air also concentrates its water vapour; the water collects here and must be drained, or it rusts the tank from inside.
Head bolts and mounting bolts.
A cylinder head bolt clamps the head to the cylinder. Four per head clamp the head, valve plate and gaskets to the barrel against full delivery pressure.
A cylinder head bolt clamps the head to the cylinder. Four per head clamp the head, valve plate and gaskets to the barrel against full delivery pressure.
A hex mounting bolt that fixes the pump or motor to the saddle plate.
A hex mounting bolt that fixes the pump or motor to the saddle plate.
How does it work? Read the step-by-step guide, with key facts and common questions.
How a reciprocating air compressor works →Yes. The reciprocating air compressor 3D model is free for personal and educational use under CC BY-NC 4.0: credit "Engine-X by Parth Parmar (engx3d.com)". Selling the files or prints, or other commercial use, needs written permission.
GLB (glTF 2.0) with colours and named parts, STL in millimetres (Z-up) for CAD, slicers and 3D printing, USDZ for AR on iPhone, and a ZIP with all 43 parts as separate STL files.
61 named pieces in 7 systems (crank train, cylinders & valves, air path, motor & belt drive, air receiver, controls & safety, hardware). Repeated pieces such as bolts are folded together, which leaves 43 different parts, each one downloadable on its own.
Yes, download the STL (whole machine or single parts) and open it in your slicer. It is a learning model at real scale, not a print kit: some parts touch or overlap and there are no fit tolerances, so scale it and print parts one by one.
Tap "View in your room" on this page. Android opens Google Scene Viewer and iPhone opens AR Quick Look, both without an app, and you can place the model at real size on the floor or a table.
Yes. Tap "Play live 3D here" or open the Engine-X atlas (engx3d.com/atlas#m=aircomp): it runs in the browser with true motion, and you can explode it, cut it open and X-ray it.
Credit line: Reciprocating air compressor 3D model, Engine-X by Parth Parmar (engx3d.com)
Citation: Parmar, P. (2026). Reciprocating air compressor 3D model [3D model, CC BY-NC 4.0]. Engine-X. https://engx3d.com/3d-models/reciprocating-air-compressor
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