--- title: "Components of reciprocating air compressor" subject: "Applied Thermodynamics" chapter: 2 key: "semester_3/applied_thermodynamics:reciprocating-compressor-components" source: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/reciprocating-compressor-components site: BCT Engineering --- # Components of reciprocating air compressor Applied Thermodynamics · Chapter 2: Air Compressors - Asked in: year not given, 6 marks - Video: [Air Compressor (Basics, Parts, Diagram, Working & Applications) Explained with Animation](https://www.youtube.com/watch?v=N6Xn4qt6ZyY) — Engineering Funda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/reciprocating-compressor-components - Whole chapter: https://www.bctengineer.com/md/semester_3/applied_thermodynamics/chapter-2 ## Question Describe the primary components of a single-stage reciprocating air compressor with a neat sketch, and explain its working. ## Short answer Primary components: cylinder with cooling, piston and rings, connecting rod-crankshaft, suction and delivery valves, cylinder head, crankcase, flywheel, filter, receiver, and safety valve. Working cycle: suction draws in air, compression raises pressure, delivery discharges to receiver; residual clearance air re‑expands before the next suction. ## Answer A **reciprocating compressor** draws air into a cylinder, compresses it by the movement of a piston, and delivers it at a higher pressure. ```text delivery valve suction valve | | +-----v-----+-----------v----+ | cylinder head | | ______________________ | cooling| |<-clearance->| | |cooling fins / | | piston |==| rings| |fins / jacket | |__________|__|_______| |jacket +---------------+------------+ | connecting rod | crank --o-- crankshaft ``` #### Primary components | Component | Function | |---|---| | Cylinder | Holds the air during compression; made of cast iron with cooling fins or a water jacket | | Piston and piston rings | Compress the air; the rings seal the gap against leakage and carry heat to the wall | | Connecting rod and crankshaft | Convert the rotary motion of the motor into the reciprocating motion of the piston | | Suction valve | Spring-loaded; opens automatically when the cylinder pressure falls below the suction pressure | | Delivery valve | Opens when the cylinder pressure exceeds the receiver pressure | | Cylinder head | Houses the valves and closes the cylinder | | Crankcase and flywheel | The crankcase supports the shaft and holds the lubricating oil; the flywheel smooths the speed | | Cooling system | Fins or a water jacket remove heat and keep the lubricant stable | | Air filter and receiver | The filter cleans the inlet air; the receiver stores air and damps pulsations | | Safety valve and unloader | Prevent over-pressure and relieve the load at starting | #### Working 1. **Suction stroke:** the piston moves away from the head, the pressure falls, the suction valve opens and air enters. 2. **Compression stroke:** both valves are closed and the air is compressed as the piston returns. 3. **Delivery:** when the pressure exceeds the receiver pressure, the delivery valve opens and air is delivered until the piston reaches the end of its stroke. The air in the clearance volume remains. 4. **Re-expansion:** at the start of the next suction stroke, the trapped clearance air expands until its pressure falls below the suction pressure and the suction valve opens again. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. When does the suction valve open? A. When cylinder pressure exceeds the receiver pressure B. When cylinder pressure falls below the suction pressure C. When the piston is at top dead centre D. Only when operated by the camshaft Answer: B. The spring-loaded suction valve opens automatically when pressure inside falls below suction pressure. (Key point: Suction valve action) 2. When does the delivery valve open? A. When the piston begins the suction stroke B. When pressure falls below atmospheric C. When the cylinder pressure exceeds the receiver pressure D. When the crank is vertical Answer: C. Air is delivered once compressed pressure exceeds the receiver pressure. (Key point: Delivery valve action) 3. What are piston rings for? A. To open the valves B. To convert rotary motion to reciprocating C. To store air D. To seal the gap against leakage and carry heat to the wall Answer: D. Rings seal the piston-cylinder gap and conduct heat to the cylinder wall. (Key point: Piston rings) 4. What happens to the clearance air after delivery? A. It remains and re-expands as the piston moves back until the suction valve opens B. It is fully delivered C. It is sucked out by the filter D. It condenses Answer: A. Trapped clearance air re-expands before fresh air can enter. (Key point: Clearance air) ## Related in Applied Thermodynamics - [Work of single-stage compressor without clearance](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_thermodynamics%3Asingle-stage-compressor-work-derivation) — Applied Thermodynamics, chapter 2 - [Single-stage compressor power numerical](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_thermodynamics%3Asingle-stage-compressor-numerical) — Applied Thermodynamics, chapter 2 - [Two-stage compressor with perfect intercooling](https://www.bctengineer.com/question.md?key=semester_3%2Fapplied_thermodynamics%3Atwo-stage-compressor-intercooling-numerical) — Applied Thermodynamics, chapter 2 ## Related in other subjects - [Reciprocating pump working, slip and air vessel](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Areciprocating-pump-slip-air-vessel) — Fluid Machines, chapter 4 - [Single phase motor working; effect of air gap](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Aspim-working-air-gap-effect) — Electrical Machines, chapter 7 - [Working principle of centrifugal and reciprocating pumps](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Acentrifugal-reciprocating-working) — Hydro Power, chapter 7 - [Air compressor: heat transfer rate](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Acompressor-air-heat-transfer-rate) — Fundamental of Thermodynamics & Heat Transfer, chapter 4