Storing an air compressor correctly is essential to prevent corrosion, bearing damage, lubricant degradation, and electrical failure during periods of inactivity. Improper storage commonly leads to moisture ingress, component seizure, and non-compliance with UK pressure system regulations, resulting in costly repairs and delayed recommissioning.
This guide sets out an evidence-based storage framework covering depressurisation, lubrication preservation, environmental control, and legal obligations, informed by field experience from J Ll Leach, a UK-based specialist in compressor maintenance, storage, and recommissioning.
Why Does Storage Cause Compressor Damage?
Dormancy exposes equipment to specific degradation mechanisms that are naturally mitigated during operation by heat generation and lubricant circulation. Failure to address these static risks results in component seizure and electrical faults.
Atmospheric Corrosion
Internal air contraction during cooling draws humid ambient air into the oil separator and compression element. UK humidity causes water to condense on internal metal parts. This water mixes with old oil to create acids which acids eat into rotors, cylinders, and bearings.
J Ll Leach engineers identify atmospheric corrosion as a primary cause of seizure in recommissioned units. Preventing moisture ingress maintains internal tolerances and operational efficiency.
False Brinelling
The rotor’s weight pushes bearings through the oil film, causing metal to touch metal. Vibration from nearby machines makes the rolling elements grind against the race. This damage is called “false brinelling.”
These surface defects lead to premature bearing failure upon restart. Isolating the unit from ground vibration protects bearing integrity and ensures the compressor remains restart-ready.
Electrical Hygroscopy
Motor windings soak up moisture from the air, often in just 4–8 weeks. Wet insulation fails. This causes short circuits or ground faults when you hit the start button. Dry motors prevent these failures and save you the cost of a rewind.
What Are the UK Legal Requirements for Storage?
Storage triggers specific duties under the Pressure Systems Safety Regulations 2000 (PSSR 2000). A machine you simply switch off is still “in service” if it holds pressure. To legally classify it as “out of service,” you must meet three conditions:
- Isolation: The unit must be physically disconnected from the electrical supply and downstream air network.
- Depressurisation: The air receiver tank and all pipework must be vented to atmospheric pressure (0 bar).
- Drainage: All condensate traps and fluids should be drained to prevent corrosion and bacterial growth.
In many cases, if the storage period exceeds the scheduled examination interval defined in your Written Scheme of Examination (WSE), you may need a new examination by a Competent Person before returning the unit to service.
How Do You Prepare the Lubrication System?
Oil condition determines the success of storage preservation. Used compressor oil contains combustion by-products, water, and acidic contaminants. These impurities typically degrade within 12–18 months in storage, attacking the oil cooler and bearings.
The Golden Rule of Preservation
Change the oil before storage, which coats internal parts in clean lubricant.
- Short-Term Storage (<6 months): Refill the sump with standard service oil. Run the machine for 60 minutes to circulate fresh fluid through the oil cooler and injection lines.
- Long-Term Storage (>6 months): Switch to a preservation fluid like Atlas Copco’s Roto Synthetic Fluid ULTRA. These fluids use stable additives to stop oxidation and keep vertical surfaces coated. J Ll Leach stocks these fluids to match OEM warranty rules.
What Are the Specific Storage Protocols by Type?
Different compression technologies require distinct preservation strategies. A protocol that protects an oil-injected unit may cause damage if applied to an oil-free machine.
Oil-Injected Rotary Screw (e.g., Atlas Copco GA Series)
These units rely on oil for sealing. The objective is to coat internal rotors to prevent rust.
- Inlet Fogging: Remove the air intake filter. While manually rotating the drive coupling, spray a Vapour Phase Corrosion Inhibitor (VCI) oil into the intake valve. The rotation draws the mist into the compression element.
- Sealing: Immediately seal the air inlet and discharge flange with heavy-gauge plastic and duct tape. This creates a closed atmosphere where the VCI vapour protects the metal.
- Drive Train: Loosen V-belts to stop them from setting in one shape.
Oil-Free Rotary Screw (e.g., Atlas Copco Z Series)
Caution: Keep oil, VCI spray, and liquids out of the compression chamber. These substances destroy the rotor coating.
- Desiccant Protection: Put silica gel or activated alumina bags inside the intake and discharge pipes.
- Hermetic Sealing: Bolt blind flanges onto the inlet and outlet. This makes the seal airtight.
- Tagging: Put a warning tag on the start button: “REMOVE DESICCANT BAGS BEFORE STARTING.”
Piston Compressors (e.g., LE/LT Series)
Reciprocating units rust easily.
- Cylinder Fogging: Crank the flywheel slowly by hand while spraying preservation oil into the intake. This coats the cylinder walls and rings.
- Crankcase Breather: Plug the breather to stop moisture entering the oil sump.
Portable Diesel Compressors (e.g., XAS Series)
Diesel units suffer from fuel degradation and “diesel bug” (bacteria).
- Fuel Treatment: Add a biocide to the tank to kill bacteria. Fill the tank to the top to reduce air space and stop condensation.
- Engine Run: Run the engine for 15 minutes. This gets treated fuel into the injectors.
- Exhaust Sealing: Cap the exhaust pipe. Rainwater in an open exhaust flows past valves and ruins cylinders.
How Do You Protect Electrical Components?
Damp conditions destroy modern compressor electronics.
Motor Windings
Keep motors with anti-condensation heaters connected to a live supply. The heaters keep windings warmer than the air to stop moisture. Store motors without heaters in a dry, warm room.
Variable Speed Drives (VSD)
Inverters contain electrolytic capacitors that degrade when unpowered. The internal oxide insulation layer breaks down over time.
- Reforming: Recommission stored drives according to manufacturer guidance. This prevents drive failure when you switch the power on.
What Maintenance Is Required During Storage?
Storage is an active process. Implementing a periodic maintenance schedule helps prevent seizures and ensures the machine is ready for reactivation. Review our maintenance checklist for a complete overview of standard inspection points that apply even during dormancy.
| Component | Action | Frequency | Reason |
| Drive Shaft | Rotate manually (3 full turns) | Monthly (Oil-Injected) Weekly (Oil-Free) | Prevents false brinelling and rotor seizure. |
| Air Receiver | Open the drain valve | Weekly | Ensures any accumulated managing air compressor condensate is removed. |
| Silica Gel | Check the colour indicator | Quarterly | Replace if saturated to maintain dry air. |
| Motor Insulation | Megger Test (IR) | Every 6 months | Detects moisture ingress before it causes a fault. |
How Do You Recommission a Compressor Safely?
Upper bearings and rotors dry out after months of inactivity. A strict restart procedure stops start-up faults and downtime.
- Unseal: Remove all plastic covers, tape, and desiccant bags.
- Prime the Element: Pour 0.5L to 1L of clean oil into the intake valve (unloader). This provides instant lubrication for the first seconds of rotation.
- Electrical Check: Verify motor integrity with a final Insulation Resistance (IR) test.
- No-Load Run: Confirm the discharge valve is open. Start the machine and run it unloaded for 15 minutes. Check that the oil temperature rises, confirming circulation through the cooler.
Conclusion
Storage is a precise engineering task. You must control corrosion and manage lubrication to keep the machine operational. Air end repairs cost thousands of pounds. Preservation saves this money.
If you lack the facility space or technical resources to store a unit properly, consider alternatives. Many businesses choose to sell underutilised assets and use Air Compressor Hire for peak demand periods to eliminate storage risks entirely.
For critical assets returning from long-term storage, we recommend a professional pre-start audit. Our compressed air engineers in Stoke-on-Trent, Birmingham, and Shrewsbury can assist with VSD reforming, oil analysis, and safe recommissioning.