What “reconditioned” really means
“Reconditioned” is not a standard grade. One seller uses it for a machine that was cleaned, painted and given new filters. Another uses it for a full airend rebuild, new bearings, a new motor bearing set, rewired panel and fresh hoses. Both machines might look the same on delivery day. The difference only shows up months later, in oil consumption, temperature and breakdowns.
That is why acceptance starts with the promise, not the paint. Before you inspect anything, be clear which of these levels you are buying:
| Level of work | What it usually includes | What it usually does not include |
|---|---|---|
| Cosmetic refurbishment | Cleaning, paint, new filters and oil | Any internal inspection or wear-part change |
| Service-level reconditioning | Full service kit, belts or coupling insert, hoses, valve checks, control and safety checks | Airend or pump opening |
| Major overhaul | Above plus airend or cylinder opening, bearings, seals, rings or valves as measured, cooler cleaning | Motor rewind, new vessel, new controller unless stated |
| Full package restoration | Overhaul plus motor or engine work, electrical panel, coolers, vessel inspection, instrumentation | A factory-new warranty unless separately agreed |
Ask for the scope as a list of tasks, not a label. “Airend overhauled” means little; “airend opened, bearings and shaft seal replaced, rotor clearances measured and recorded” means something you can check.
Agree acceptance criteria before work starts
Most disputes over reconditioned machines happen because nobody agreed what “good” looked like. Settle these points in the order or quotation:
- The working pressure and the flow you need at that pressure, in cfm or m³/min.
- Where the test will happen: in the workshop, at your site, or both.
- How long the loaded run will be, and at what ambient conditions.
- Which readings will be recorded: pressures, temperatures, motor current, oil or crankcase condition, vibration where relevant.
- Which safety devices will be proven working, and how.
- What accessories are included: dryer, filters, receiver, drains, hoses, starter.
- What happens if a test point fails: repair and retest, price adjustment or rejection.
- Which known limitations remain, written down and accepted by both sides.
This is exactly what we do with buyers of our used and reconditioned machines. A short written test plan protects both the buyer and the seller.
Documents to ask for
A reconditioned compressor should come with a short dossier. It does not need to be elaborate, but it must be specific to that serial number.
- Make, model and serial number of the package, and of the airend or pump and motor where these have their own plates.
- As-found report: what was wrong before work began, with photos.
- Parts list: every part replaced, with part numbers and whether each is genuine or a named aftermarket part.
- Measurements taken during the work, such as bearing clearances, rotor end float or cylinder bore readings.
- Settings: load and unload pressures, safety valve set pressure, temperature trips, motor overload setting.
- Pressure vessel details: receiver or separator tank nameplate, last inspection record and safety valve information.
- Test record: readings from the loaded run, signed by the person who ran it.
- List of items not opened or not replaced.
That last list matters as much as the rest. A machine where the motor bearings were “checked by sound” is different from one where they were replaced, and the buyer should know which one they are getting.
Physical inspection on delivery
Before the first start, walk round the machine with the dossier in hand.
- Confirm the serial numbers match the paperwork.
- Check for oil and coolant leaks, damaged hoses and loose fittings.
- Check oil level and grade, and that filters carry fresh dates or are visibly new.
- Inspect belts or couplings, guards and the condition of the cooler fins.
- Look at the electrical panel: tight terminals, correct cable size, earthing, labelled wiring, no bypassed protections.
- Check the safety valve is the right set pressure for the vessel and is not painted over or gagged.
- Confirm the pressure vessel inspection status is current and the plate is legible.
- For portable diesel units, check engine oil, coolant, battery, fuel system, tyres, drawbar and lights.
The loaded run: what to watch
A machine that starts and runs unloaded for ten minutes has proved very little. Acceptance needs a loaded run long enough for temperatures to settle, at the pressure you will actually use.
| Reading | What a good result looks like | Warning signs |
|---|---|---|
| Discharge temperature (oil-injected screw) | Stable, typically about 75–95 °C once settled | Climbing steadily or near the trip setting |
| Delivered pressure | Holds working pressure under the agreed load | Cannot reach unload pressure, or long load times |
| Motor current | Within the motor’s rated current and balanced between phases | High current, imbalance or tripping |
| Oil carry-over | Little visible oil at drains and downstream filters | Oil mist at drains or tools |
| Noise and vibration | Smooth, without knocks or rumbles | Bearing noise, knocking or rising vibration |
| Control behaviour | Loads and unloads cleanly at the set points | Short cycling, hunting or failure to unload |
Where flow matters, a pump-up test on a receiver of known volume gives a simple check. Time how long the machine takes to raise pressure between two points with the outlet closed and compare with the expected figure for its rated flow. It is not a laboratory test, but it shows whether a machine is far off its rating. For a full flow measurement, an air audit with a flow meter is the better method.
Proving the safety devices
Every reconditioned machine must have its protection devices proven, not just present. Typical checks include:
- High discharge temperature shutdown operates at its setting.
- Motor overload and phase-failure protection are set and functional.
- Emergency stop stops the machine and needs a manual reset.
- Safety valve is correctly rated and in date; it is never tested by blocking the outlet against a running machine without a proper procedure.
- On diesel units, low engine oil pressure and high coolant temperature shutdowns work.
- Blowdown valve vents the separator tank on stop.
A compressor with a bypassed or missing trip should be rejected until it is fixed, whatever its other merits.
Workshop release and site acceptance are different
A machine can pass every workshop test and still struggle on site. The site may be hotter, dustier or have a weaker electrical supply. The ventilation may be poor, so the compressor recirculates its own hot air. The downstream dryer, filters and piping may drop more pressure than expected.
Treat workshop release and site acceptance as two separate steps. At site, repeat the key readings after installation, at real ambient conditions. In Indian summers, with ambient at 40–45 °C, and above 45 °C on open sites, check that the cooler and room ventilation can cope before blaming the machine.
After acceptance: the first months
Acceptance is the start of the machine’s second life, so the readings taken on handover become the baseline. Over the first months:
- Record running hours, load hours and temperatures weekly.
- Watch oil consumption and top-up frequency.
- Check for new leaks at fittings that were disturbed during the rebuild.
- Carry out the first service at the interval agreed with the seller.
- Report any change quickly; early faults are easier to resolve while the job is fresh.
Ongoing care is covered in our preventive maintenance and compressor AMC pages.
How Reddy Compressors helps
Since 2002, Reddy Compressors has sold new and used or refurbished compressors, rented them and serviced them from our office at Tarnaka, Secunderabad. We work across brands such as ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair and Doosan as an independent multi-brand specialist, not an authorised dealer of any brand. We have tie-ups with all major and reputed brands.
When we supply a reconditioned machine, we state the scope of work, the parts replaced and what was not opened, and we run it loaded before dispatch. We can also act on your side when you are buying a reconditioned machine from someone else: reviewing the scope, inspecting the unit and witnessing the test. Our 20+ service engineers and technicians cover the whole of Telangana and Andhra Pradesh, and we supply machines and spares across India. If your own machine is out for overhaul, a rental compressor from our fleet can keep production running.
What to send us
- Make, model, serial number and nameplate photos of the machine.
- The seller’s scope of work or quotation, if buying from a third party.
- Your working pressure, required flow and running hours per day.
- Site conditions: indoor or outdoor, ventilation, ambient temperature, power supply.
- Accessories needed, such as dryer, filters, receiver or hoses.
- Location of the machine and your target date.
Frequently asked questions
Is a reconditioned air compressor worth buying?
It can be, if the scope of work is clear and the machine is tested at your duty. A well-reconditioned compressor costs less than new and can serve for years. The risk lies in vague scopes where only cosmetic work was done. Ask for a parts list, a list of items not opened, measurements and a loaded test record before you pay the balance.
What is the difference between used, refurbished and reconditioned compressors?
A used compressor is sold as it is, with whatever wear it has. Refurbished and reconditioned usually mean some work was done, but the words have no fixed definition and sellers use them differently. What matters is the written list of tasks: which parts were replaced, which assemblies were opened and measured, and what testing was done. Judge the machine by that list.
How long should a test run be for a reconditioned compressor?
Long enough for temperatures and pressures to settle under load at your working pressure. A short unloaded run proves only that the machine starts. Agree the duration and readings in advance, and include a check of load and unload behaviour and the safety shutdowns. Where possible, repeat key readings after installation at site, at real ambient conditions.
Which safety checks are essential before accepting a used compressor?
Prove the high discharge temperature trip, motor overload and phase protection, emergency stop and blowdown valve. Check the safety valve rating and its date, and the pressure vessel inspection status. On diesel units, prove the low engine oil pressure and high coolant temperature shutdowns. Reject any machine with bypassed protections until they are restored and tested.
Does a reconditioned compressor come with a warranty?
That depends entirely on the seller and what was agreed. Some reconditioned machines are sold with a defined cover on replaced parts or workmanship; others are sold without. Never assume cover from the word “reconditioned”. Get the terms, duration and exclusions in writing, and keep the test record, because it is the reference point for any later claim. For reference, every used and refurbished compressor we sell carries a six-month warranty from the delivery or invoice date, covering the whole compressor and excluding consumables, misuse or wrong oil, service by others, and accident or site damage.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Receiver pump-up test: Estimated free air delivery
Time how long the compressor takes to raise the pressure of a receiver of known volume (outlet closed) between two pressures, and convert it into an approximate free air delivery to compare with the rating.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Receiver volume (litres): 1000
- Connected pipe volume up to the closed outlet (litres): 0
- Start pressure (bar g): 6
- End pressure (bar g): 7
- Measured pump-up time (s): 10
- Atmospheric pressure (bar a): 1.013
- Intake air temperature (°C): 30
- Air temperature in the receiver at the end (°C): 30
- Rated FAD to compare with (m³/min; 0 to skip): 7
Result
- Volume pressurised: 1,000 litres
- Free air pumped in: 987 litres of free air for 1 bar
- Estimated FAD: 5.92 m³/min = 98.72 L/s = 209.2 cfm
- Timing sensitivity: ±10% for a ±1 s timing error
- Expected time at the rated FAD: 8.5 s
- Measured delivery as a share of rating: 84.6% of 7 m³/min
Method. FAD ≈ V × (p_end − p_start) ÷ p_atm ÷ t × (T_intake ÷ T_receiver), with V in m³ (receiver plus connected pipe), pressures in bar, t in minutes and temperatures in kelvin. With equal temperatures the correction is 1 (isothermal). Expected time at the rated FAD = V × Δp ÷ (p_atm × FAD_rated) × (T_intake ÷ T_receiver). It is a screening test: warm air in the receiver, an unknown pipe volume and a 1 s timing error all move the result, so a machine is judged far off its rating only with a clear margin. For a definitive figure use a flow meter or an air audit.
What to take from it. Run the test at the working pressure band after the machine is warm, repeat it three times and use the average time. Record the receiver volume from its nameplate.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 7 November 2026. How our engineering content is reviewed.
Performance acceptance check
Compare measured flow, specific power and pressure with the agreed requirement and tolerance, and reach a disposition: accept, accept with conditions, hold or reject.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Required FAD (m³/min): 20
- Measured FAD, corrected per the agreed method (m³/min): 19.5
- Measured package input power (kW): 126
- Declared specific power (kW per m³/min): 6.4
- Agreed flow tolerance (%): 4
- Agreed specific power tolerance (%): 5
- Required minimum pressure at the agreed point (bar g): 7
- Lowest pressure measured there while drawing the required flow (bar g): 7
- Measurement uncertainty to allow beyond the tolerance (%; 0 if the tolerance already includes it, as ISO 1217 Annex C tolerances do): 0
- Mandatory evidence (dew point, pressure band, safety trips, documents): All recorded and valid
Result
- Flow deviation: -0.5 m³/min (-2.5% of required; tolerance −4%)
- Measured FAD: 689 cfm
- Specific power: 6.46 kW per m³/min
- Deviation from declared specific power: +0.96 % (tolerance +5%)
- Pressure margin at the agreed point: 0 bar
- Disposition: Accept file the record as the baseline for future service
Method. Flow deviation = (measured FAD − required FAD) ÷ required × 100. Specific power = package input kW ÷ measured FAD; its deviation is against the declared value. Pressure margin = lowest measured pressure at the agreed point − required minimum. Disposition: mandatory evidence missing or test invalid → Hold; a pressure shortfall, or a flow or specific-power result outside tolerance by more than the measurement uncertainty → Reject; outside tolerance but within the uncertainty → Hold (shortfall not proven, retest); all within tolerance → Accept, or Accept with conditions if minor items are open. Enter the tolerance the contract states (0 if the full figure is required). For reference, the ISO 1217 Annex C bands for machines above 15 m³/min are commonly quoted as ±4% flow and ±5% specific energy; confirm from the standard. ISO 1217 Annex C tolerances already include measurement uncertainty; do not add it again when the contract uses them. The Hold-within-uncertainty rule is a default screening rule used by this tool; use the decision rule written in your contract. Default: the page example (20.0 m³/min required, 19.5 measured, 126.0 kW, declared 6.4 kW per m³/min).
What to take from it. The tool applies a default rule (outside tolerance by more than the stated uncertainty = Reject). Replace it with the rule in your contract. One favourable number does not make an acceptance if evidence is missing.