Start Air Compressor
medium
9 models total
A start air compressor is a reciprocating machine built to push air to 25-30 bar for main and auxiliary engine starting, a duty defined by pressure rather than by the throughput that dominates service or control-air compressor selection.
Read more — Start Air Compressor explained ▾
What sets a start air compressor apart
Main and auxiliary diesel engines start by admitting high-pressure air directly into the cylinders to turn the crankshaft, which means the compressor supplying that air has to reach 25-30 bar, well above the 7-10 bar typical of a service or control air compressor. That pressure requirement pushes the design toward a multi-stage reciprocating machine rather than a screw compressor: screw compressors dominate low-pressure service and instrument air because they run continuously and quietly, but they do not reach starting-air pressure efficiently or reliably enough to be trusted for engine starting.
Main components
Cylinders and stages
Typically two or three stages in a V or W arrangement, each stage raising pressure further, with intercoolers between stages to keep discharge temperature and compression work down.
Intercoolers and aftercooler
Water- or air-cooled heat exchangers between stages and after the final stage, dropping air temperature and condensing out moisture before it reaches the receiver.
Crankcase and drive
A crankshaft-driven arrangement similar in principle to a small diesel engine's bottom end, usually electric motor driven, with splash or forced lubrication.
Safety and relief valves
Fitted at each stage to protect against a blocked downstream line overpressurising an earlier, lower-rated stage.
Unloading and control system
Automatic start/stop or load/unload control tied to receiver pressure switches, so the compressor cuts in as starting air is consumed and cuts out once the receivers are topped up.
Selection and sizing
Sizing is driven by the number and size of starting air receivers to be recharged, the time allowed to recover full pressure after a set of engine starts, and the redundancy required. Most vessels carry at least two compressors so a single failure does not leave the ship unable to start its main engine. Capacity is usually expressed as free air delivery in Nm3/h or l/min at rated discharge pressure, matched to the receiver volume specified for the vessel's engine.
Regulations and class
Class rules require at least two independent means of charging the starting air receivers on vessels where main propulsion depends on compressed-air starting, and set minimum receiver capacity relative to the number of starts required without recharging. Safety valves on each compressor stage and on the receivers are subject to periodic survey and testing. IACS UR machinery requirements cover starting air system arrangement, including non-return valves and bursting discs to prevent a receiver explosion propagating back through the piping.
Typical faults
- Worn piston rings or valve plates: falling volumetric efficiency, so the compressor runs longer to reach set pressure, raising running hours and wear.
- Intercooler fouling on the water side: rising interstage temperature, higher risk of oil carbon deposits igniting in the receiver, a recognised cause of starting air line fires.
- Safety valve seat wear or seizure: either premature lifting and lost capacity, or failure to lift, risking overpressure downstream.
- Condensate drain valves left closed or blocked: moisture carries into the receivers, promoting internal corrosion and freezing of pilot lines in cold climates.
- Automatic unloader stuck: the compressor runs continuously against a closed valve and overheats.
What to look for in a supplier
- Class type approval for the discharge pressure and duty class specified for the vessel.
- Spare parts commonality with compressors already on board, where a sister-ship fleet standard exists.
- Documented interstage and final relief valve settings matched to the receiver design pressure.
- Service network able to supply piston rings, valve plates and cooler gaskets without a long lead time, since a starting air compressor failure is a departure-affecting defect.
Drain the intercoolers and receivers before every watch change, not just on the planned maintenance schedule - carbon-laden condensate sitting in a hot receiver is how starting air line fires start.
4 manufacturers · 9 models
Sauer Compressors
3
WP33L
33 m³/h FAD @ 30 bar
· 11.0 kW
· Air
· oil‑lubricated two‑stage piston start‑air compressor
Medium
Air
Power (kW)
11
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Valve disc fatigue
- Cylinder bore wear
- Aftercooler fin fouling
- Oil carry-over
Service: Air-cooled — ensure adequate ventilation. Valve overhaul every 4000 hrs. Oil change every 1000 hrs.
Spare Parts: Sauer Compressors: Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Compact footprint suitable for vessels with limited engine‑room space
- Low electrical power demand (11 kW) while meeting typical 30 bar start‑air requirements
- Robust two‑stage design gives reliable pressure build‑up even in hot climates
- Straightforward maintenance schedule – valve overhaul every 4 000 h and oil change every 1 000 h
- Air‑cooled unit eliminates need for a separate cooling water circuit
Weaknesses
- Oil‑lubricated design can introduce oil carry‑over into the start‑air system if filtration is inadequate
- Aftercooler fin fouling reduces efficiency and requires regular cleaning
- Maximum flow rate limited compared with larger screw compressors, restricting use on very high‑power engines
- Requires adequate ventilation in the installation space to dissipate heat
Typical Vessels:
Product tanker (up to ~30 000 dwt)Container feederOffshore supply vesselBulk carrier (handy‑size)Cruise ship auxiliary plant
Decision Guide: Choose if: you need a reliable, compact start‑air source for medium‑sized diesel engines, have limited space and can accommodate oil‑lubricated operation with regular maintenance. Avoid if: an oil‑free (oil‑free screw) compressor is required, the vessel demands very high air flow rates, or ventilation constraints prevent safe air‑cooled installation.
Use Cases: The WP33L is typically installed in the engine room to supply start‑air for main and auxiliary diesel engines, fire‑pump starters, and deck‑machinery pneumatic systems on vessels where space and power budgets are moderate. It is common on tankers, container feeders, and offshore support ships that operate with standard 30 bar start‑air pressure.
WP61L
61 m³/h FAD @ 30 bar
· 18.5 kW
· Air
· oil-lubricated two-stage piston compressor
Medium
Air
Power (kW)
18.5
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Suction valve failure
- Piston ring wear
- Oil separator element saturation
Service: Replace oil separator element every 2000 hrs. Valve service every 4000 hrs. Drain condensate.
Spare Parts: Sauer Compressors: Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Provides high pressure (30 bar) suitable for large marine diesel engines
- Robust two‑stage design offers reliable performance in harsh sea conditions
- Clear maintenance intervals (oil separator every 2000 h, valve service every 4000 h)
- Compact power rating (18.5 kW) fits well within typical engine room space constraints
- Widely used and supported by Sauer’s global service network
Weaknesses
- Requires oil management and periodic replacement of the oil separator element
- Piston ring wear and suction valve failures are known failure modes
- Condensate must be regularly drained to avoid corrosion
- Not an oil‑free design, so unsuitable where oil‑free air is mandated
- Noise level higher than screw or scroll compressors
Typical Vessels:
TankerBulk CarrierContainer ShipOffshore Supply VesselGeneral Cargo Ship
Decision Guide: Choose if: you need a proven, high‑pressure start‑air source for large marine engines and can accommodate routine oil‑related maintenance. Avoid if: an oil‑free air supply is required, space or noise constraints are critical, or you lack capability for regular condensate drainage and oil separator replacement.
Use Cases: Installed in the engine room to generate start air for main and auxiliary diesel engines on tankers, bulk carriers, and offshore vessels; also used to pressurise pneumatic control systems that rely on clean, high‑pressure air.
WP85L
85 m³/h FAD @ 30 bar
· 27.0 kW
· Air
· water-cooled 2-stage air compressor
Medium
Air
Power (kW)
27
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Intercooler leakage
- High-stage piston ring failure
- Unloader solenoid stuck
Service: Water-cooled version for tropical operations. Valve OH every 4000 hrs. Monitor stage pressures.
Spare Parts: Sauer Compressors: Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Water‑cooled design tolerates tropical ambient temperatures without overheating
- Two‑stage compression improves efficiency and reduces discharge temperature
- Moderate power demand (27 kW) fits typical ship engine rooms
- Scheduled valve overhaul every 4,000 hrs simplifies maintenance planning
- Integrated stage‑pressure monitoring aids early fault detection
Weaknesses
- Water‑cooling system adds piping, pumps and risk of intercooler leakage
- Historical high‑stage piston ring failures require close wear monitoring
- Unloader solenoid can seize, leading to over‑pressurisation if not inspected
- Maximum pressure limited to 30 bar may be insufficient for some high‑pressure start‑air systems
- Requires a reliable fresh‑water supply and coolant maintenance
Typical Vessels:
TankerBulk CarrierContainer ShipGeneral Cargo VesselOffshore Supply VesselCruise Ship
Decision Guide: Choose if you need a robust start‑air source for tropical operations, value the efficiency of two‑stage compression and can accommodate a water‑cooling loop. Avoid if space or weight is at a premium, you require pressures above 30 bar, or you prefer oil‑free screw compressors with fewer coolant‑related components.
Use Cases: The WP85L is typically installed in the main engine room to supply start air for large diesel propulsion engines and auxiliary generators. It is also used on vessels that operate continuously in warm climates where air‑cooled units would overheat, providing reliable start‑air even during prolonged high ambient temperatures.
Tanabe
3
H-63
63 m³/h FAD @ 30 bar
· 18.5 kW
· Air
· 2-stage oil-lubricated piston compressor
Medium
Air
Power (kW)
18.5
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Suction/delivery valve failure
- Piston ring wear
- Cooler tube leakage
- Unloader malfunction
Service: Very common on Japanese tonnage. Valve OH every 4000 hrs. Genuine Tanabe spares recommended.
Spare Parts: Tanabe: Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Delivers the required 30 bar start‑air pressure in a compact footprint
- Proven reliability on Japanese‑built tonnage with long service history
- Standard valve overhaul interval of 4,000 hrs simplifies maintenance planning
- Genuine Tanabe spare parts are widely stocked and supported globally
- Relatively low initial cost compared with screw‑type start‑air units
Weaknesses
- Oil‑lubricated design requires filtration to avoid contamination of the start‑air system
- Cooler tube leakage has been reported as a recurring issue
- Noise level higher than oil‑free or screw compressors, may need additional insulation
- Flow capacity is lower than larger screw‑type units, limiting use for high‑demand applications
- Unloader valve failures can cause start‑air pressure loss if not inspected regularly
Typical Vessels:
TankerBulk CarrierContainer ShipOffshore Supply VesselCruise Ship
Decision Guide: Choose if: you need a compact, proven start‑air source for Japanese low‑speed diesel engines and have access to Tanabe spare parts; the 30 bar pressure and 4,000‑hr valve overhaul schedule fit your maintenance regime. Avoid if: an oil‑free air supply is required, you demand higher flow rates for auxiliary systems, or noise constraints are critical.
Use Cases: The H-63 is typically installed in engine rooms to charge start‑air receivers for main propulsion diesel engines, providing rapid high‑pressure air for reliable engine cranking and emergency start procedures on a wide range of merchant vessels.
H-64
64 m³/h FAD @ 30 bar
· 18.5 kW
· Air
· oil-lubricated reciprocating compressor
Medium
Air
Power (kW)
18.5
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Valve plate cracking
- Intercooler fouling
- Piston ring blow-by
Service: Improved valve design over H-63. Same maintenance intervals: 4000 hrs valves, 8000 hrs rings.
Spare Parts: Tanabe: Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Compact 2‑stage unit provides the required 30 bar start air for medium‑size diesel engines
- Improved valve plate design over the H-63 reduces cracking incidents
- Standardised maintenance intervals (4000 h valves, 8000 h rings) simplify planning
- Power rating (18.5 kW) matches typical start‑air demand on tankers and bulk carriers
Weaknesses
- Intercooler fouling can increase pressure drop and requires regular cleaning
- Piston ring blow‑by may lead to oil carry‑over into the air system
- Valve plate cracking remains a reported failure mode despite redesign
- Oil‑lubricated design introduces potential contamination risk compared with oil‑free alternatives
Typical Vessels:
TankerBulk CarrierContainer ShipGeneral Cargo VesselOffshore Supply Vessel
Decision Guide: Choose if you need a compact, 2‑stage start‑air compressor around 18.5 kW delivering 30 bar with known maintenance intervals and an improved valve design. Avoid if higher pressure or power is required, oil‑free operation is mandatory, or the vessel operates in environments where intercooler fouling would be difficult to manage.
Use Cases: Commonly installed to supply start air for medium‑speed diesel main engines, pneumatic deck machinery, and emergency blow‑down systems on merchant vessels of up to 150 000 dwt.
VLH-22
22 m³/h FAD @ 30 bar
· 7.5 kW
· Air
· V-type 2-stage oil-lubricated start-air compressor
Medium
Air
Power (kW)
7.5
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Valve failure
- V-belt slip
- Oil carry-over
Service: V-type compact design. Belt tension check every 1000 hrs. Valve service every 3000-4000 hrs.
Spare Parts: Tanabe: Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Compact V‑type layout saves valuable engine‑room space
- Two‑stage design reaches the required 30 bar for most shipboard starters
- Low power consumption (7.5 kW) minimises impact on the vessel’s electrical load
- Simple belt drive with tension check every 1,000 h simplifies routine maintenance
- Predictable service intervals – valve overhaul every 3,000‑4,000 h
Weaknesses
- Belt‑driven system can slip if tension is not regularly checked
- Valve wear may lead to failure; relatively frequent valve servicing required
- Oil carry‑over risk necessitates downstream filtration or oil‑free equipment
- Maximum pressure limited to 30 bar, which may be insufficient for high‑speed, high‑pressure starters
- No built‑in redundancy – a single unit means loss of start air if it fails
Typical Vessels:
Bulk CarrierContainer ShipTankerGeneral Cargo VesselOffshore Supply VesselCruise Ship
Decision Guide: Choose the VLH-22 when space is at a premium, you need a reliable two‑stage start‑air source up to 30 bar and prefer low electrical load with straightforward maintenance. Avoid it on vessels that require higher than 30 bar starter pressure or where belt‑drive reliability cannot be guaranteed.
Use Cases: Installed in the main engine room of merchant ships to supply high‑pressure air for starting large diesel engines, especially on vessels where space constraints favour a compact unit and where periodic maintenance can be scheduled during planned dry‑dock periods.
Wärtsilä
2
2TM4
60 m³/h FAD @ 30 bar
· 18.5 kW
· Air
· oil-lubricated two-stage screw compressor
Medium
Air
Power (kW)
18.5
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Valve plate fatigue
- Intercooler tube pitting
- Crosshead guide wear
- Oil scraper ring failure
Service: Robust design with long service life. Valve overhaul every 4000-6000 hrs. Spares now via Wärtsilä.
Spare Parts: Hamworthy (Wärtsilä): Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Proven robust design with long service intervals (valve overhaul every 4 000–6 000 h)
- Compact footprint and high power‑to‑size ratio for shipboard installation
- Integrated oil filtration system reduces contamination risk
- Capable of delivering the high pressure (30 bar) required by medium‑speed diesel engines
- Spare parts now supported through Wärtsilä’s global service network
Weaknesses
- Oil‑lubricated design requires regular oil management and filtration
- Wear items such as valve plates, intercooler tubes and crosshead guides need periodic inspection
- Maximum pressure limited to 30 bar – higher‑pressure alternatives exist for specific applications
- Periodic overhaul (4 000–6 000 h) adds scheduled downtime
- Weight and mounting requirements may be restrictive on very small vessels
Typical Vessels:
TankerBulk CarrierContainer ShipCruise VesselOffshore Supply Vessel
Decision Guide: Choose if: you need a reliable, high‑pressure start‑air source for medium‑speed diesel engines on ocean‑going vessels and value a proven, class‑approved screw compressor with an established service network. Avoid if: oil‑free air is mandatory (e.g., fire‑fighting systems) or you require higher than 30 bar pressure without additional boosting equipment.
Use Cases: The 2TM4 is typically installed in the main engine room to supply start‑air for the primary propulsion diesel engine and auxiliary generators, often paired with a dedicated air receiver and control panel. It serves as the primary source of compressed air for engine cranking during normal operation and as backup after loss of shore power.
4TF6
100 m³/h FAD @ 30 bar
· 30.0 kW
· Air
· oil‑lubricated twin‑stage piston compressor
Medium
Air
Power (kW)
30
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- Valve failure
- Cooler tube corrosion
- Crankshaft bearing wear
- Safety valve lifting prematurely
Service: 4-cylinder design for high capacity. Monitor crankcase pressure. Spares via Wärtsilä aftermarket.
Spare Parts: Hamworthy (Wärtsilä): Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- High airflow capacity suitable for large fire‑main and engine start requirements
- Robust four‑cylinder design provides redundancy and smooth operation
- Integrated crankcase pressure monitoring reduces risk of oil carry‑over
- Wärtsilä aftermarket support ensures ready availability of spares
- Compact footprint relative to output, fitting constrained machinery spaces
Weaknesses
- Oil‑lubricated design requires regular oil maintenance and filtration
- Two‑stage configuration adds complexity to servicing compared with single‑stage units
- Documented failure modes include valve wear, cooler tube corrosion, bearing wear, and premature safety‑valve lift
- Higher electrical power demand (30 kW) than some modern oil‑free screw compressors for the same pressure
- Requires dedicated cooling water circuit and periodic inspection
Typical Vessels:
TankerBulk CarrierContainer ShipCruise VesselOffshore Supply Vessel
Certifications:
DNVIMO Type Approval
Decision Guide: Choose if you need a proven high‑capacity start‑air source, have space for a piston unit, and value strong OEM support. Avoid if you prefer oil‑free low‑maintenance technology, have strict power‑budget constraints, or require the smallest possible footprint.
Use Cases: Provides start air for main engines and auxiliary generators, supplies fire‑main systems on large commercial vessels, powers pneumatic control valves and safety equipment where reliable high‑pressure air is critical.
Atlas Copco
1
LT Series
40-200 m³/h FAD @ 30-40 bar
· 30.0 kW
· Air
· Oil-free rotary screw compressor
Medium
Air
Power (kW)
30
Pressure (bar)
30
Stages
2
Common Failures & Inspection Points
- PTFE piston ring wear (oil-free)
- Intercooler moisture carryover
- Valve seat erosion
Service: Oil-free design — no oil contamination in air system. Higher ring wear rate vs. lubricated. Ring change every 4000 hrs.
Spare Parts: Atlas Copco: Ventilsätze und Kolbenringe an Bord vorhalten. Lead time: 2-6 Wochen. Ölfilter und Dichtungssätze als Standard-Bordvorrat.
Strengths
- Oil‑free operation eliminates contamination of the vessel's air system
- Compact footprint suitable for limited engine‑room space
- Fast start‑up and reliable pressure delivery for main‑engine ignition
- Low routine maintenance compared with oil‑lubricated units (no oil changes)
- Integrated intercooler improves efficiency at 30 bar output
Weaknesses
- PTFE piston rings wear faster than lubricated designs – requires replacement roughly every 4,000 h
- Moisture can be carried over from the intercooler if not properly drained
- Valve‑seat erosion reported in long‑term service
- Higher initial purchase price versus conventional oil‑lubricated compressors
- Requires a dedicated ring‑change schedule to avoid unexpected downtime
Typical Vessels:
TankerContainer shipBulk carrierOffshore supply vesselCruise liner
Decision Guide: Choose if: you need guaranteed oil‑free start air, have limited engine‑room space, and can accommodate a regular ring‑change interval. Avoid if: your maintenance regime cannot reliably schedule the 4,000 h ring replacement or if moisture control in the compressed‑air system is a critical concern.
Use Cases: Provides start‑air for main propulsion engines, auxiliary generators, inert‑gas systems and fire‑pump starters on commercial vessels where oil contamination must be avoided. Commonly installed alongside other shipboard air‑handling equipment to supply clean, high‑pressure air on demand.