Anyone buying industrial fluids eventually hits the same wall. The maintenance manual says ISO VG 150 compressor oil, the tender document says IS 1115, the imported compressor's plate says DIN 51506 VDL, and the gearbox nameplate says AGMA 5 EP. Four different standards, one purchase order. This guide decodes each of them and ends with the question buyers actually have: which grade do I order for my compressor, my hydraulic system or my gearbox?
ISO VG: the viscosity grade, and nothing more
ISO 3448 defines the viscosity classification used on nearly every industrial oil label. The rule is simple: the grade number is the midpoint kinematic viscosity in centistokes at 40°C, with a tolerance of plus or minus 10 percent. ISO VG 46 therefore means 41.4 to 50.6 cSt at 40°C. ISO VG 220 means 198 to 242 cSt.
What ISO VG does not tell you is just as important. It carries no information about the additive package, the base oil group, the oxidation life or the load-carrying capacity. Two ISO VG 220 oils can sit side by side, one a rust-and-oxidation circulating oil and the other a heavy extreme-pressure gear oil, and both are correctly labelled. Viscosity grade answers "how thick"; the performance specification answers "what for".
| ISO VG grade | KV at 40°C (cSt) | Approx. SAE equivalent | AGMA lubricant no. | Typical application |
|---|---|---|---|---|
| ISO VG 10 | 9.00 – 11.0 | SAE 5W | — | Spindle oils, light circulating systems |
| ISO VG 22 | 19.8 – 24.2 | SAE 5W – 10W | — | High-speed spindles, light hydraulics, some cutting fluids |
| ISO VG 32 | 28.8 – 35.2 | SAE 10W | — | Hydraulic systems in cooler ambients, machine tools |
| ISO VG 46 | 41.4 – 50.6 | SAE 20 | AGMA 1 | The default industrial hydraulic grade; rotary screw compressors |
| ISO VG 68 | 61.2 – 74.8 | SAE 20W | AGMA 2 | Hydraulics in hot ambients, rotary compressors, light gears |
| ISO VG 100 | 90.0 – 110 | SAE 30 | AGMA 3 | Reciprocating air compressors, light-duty gearboxes |
| ISO VG 150 | 135 – 165 | SAE 40 | AGMA 4 | Hot or high-pressure reciprocating compressors, light industrial gears |
| ISO VG 220 | 198 – 242 | SAE 50 / SAE 90 gear | AGMA 5 | The default enclosed industrial gearbox grade |
| ISO VG 320 | 288 – 352 | SAE 85W-140 gear | AGMA 6 | Heavily loaded or slower-speed gearboxes |
| ISO VG 460 | 414 – 506 | SAE 140 gear | AGMA 7 | Very heavy, slow-speed drives, kilns, mills, crushers |
| ISO VG 680 | 612 – 748 | SAE 250 gear | AGMA 8 | Open gears, worm drives, heavy cylinder duty |
The SAE column is an approximation offered for orientation only. SAE engine and SAE gear scales are separate systems measured at different reference temperatures, which is why an ISO VG 220 lines up with both an SAE 50 engine oil and an SAE 90 gear oil. Never substitute across the columns on the strength of this table alone — order to the ISO VG grade the equipment builder specifies.
DIN 51506: the compressor oil classes
DIN 51506 is the German standard for lubricating oils used in air compressors, and it is the specification most often stamped on imported reciprocating and rotary units. It classifies oils by the final compression temperature the oil must survive, and the trailing L marks the classes that add mandatory ageing-resistance and corrosion-protection requirements.
| Class | Max. final compression temperature | Ageing resistance required | Corrosion protection required | Where it is used |
|---|---|---|---|---|
| VB | 140°C | No | No | Older, lightly loaded reciprocating compressors |
| VBL | 140°C | Yes | Yes | As VB, where condensate and rust are a concern |
| VC | 160°C | No | No | Mid-temperature reciprocating duty |
| VCL | 160°C | Yes | Yes | Mid-temperature duty with extended drain expectations |
| VD | 220°C | No | No | High-temperature duty, basic requirement |
| VDL | 220°C | Yes | Yes | The modern default for reciprocating and rotary air compressors |
Carbon residue is the heart of the standard, because carbon deposits on discharge valves and in delivery lines are what cause compressor fires. DIN 51506 caps the Conradson carbon residue of the fresh oil, and for the L classes it goes further: the Pneurop ageing test under DIN 51352 Part 2 ages the oil with an iron oxide catalyst at elevated temperature and limits the increase in Conradson carbon residue to 3 percent by mass. That single test is why a VDL oil behaves so differently from an untested mineral oil after two thousand hours in a hot compressor.
If you buy one thing from this article, buy the L. A VDL oil has proven it does not turn into varnish and carbon at temperature. A plain VD oil has not been asked the question.
The ISO equivalent: ISO 6743-3
ISO has its own parallel classification, ISO 6743-3, which places air-compressor oils in the DA family — DAA, DAB, DAG, DAH and DAJ — with the letters distinguishing reciprocating from flooded-rotary designs and light from severe duty. In Indian and export tenders you will most often see DIN 51506 quoted, sometimes alongside an ISO 6743-3 category. Axabull's compressor oils are formulated for these duties on Group II+ base stock.
IS 1115: the Indian Standard for steam cylinder and heavy oils
IS 1115 is the Bureau of Indian Standards specification covering steam cylinder and heavy lubricating oils — the very high-viscosity products used where steam, heat and heavy sliding loads meet. It appears constantly in Indian plant tenders, which is why so many buyers search the standard number directly without much published explanation to find.
Two features distinguish it from the ISO VG world. First, grades are defined by kinematic viscosity at 100°C rather than 40°C, which makes sense for an oil that only reaches its working state when hot. Second, the standard controls the properties that matter in steam service: flash point (necessarily high), Conradson carbon residue, ash content, neutralisation value and water content. Some grades are compounded with a fatty additive to maintain lubricity in the presence of wet steam.
When you quote IS 1115 on a purchase order, always quote the grade designation as well as the standard number, and confirm whether a straight mineral or a compounded grade is required. The two are not interchangeable in wet-steam service.
ISO 6743 and AGMA: where gear and hydraulic oils are classified
Viscosity grade fixes the thickness; these families fix the duty.
- Hydraulic oils — ISO 6743-4 defines HL (rust and oxidation inhibited), HM (anti-wear), HV (anti-wear with high viscosity index) and HG (with anti-stick-slip additives). The German equivalents in DIN 51524 are Part 1 (HL), Part 2 (HLP) and Part 3 (HVLP). Most industrial and mobile systems want an HM/HLP oil; equipment working across wide temperature swings wants HV/HVLP.
- Industrial gear oils — ISO 6743-6 defines CKB (rust and oxidation inhibited), CKC (mild extreme pressure), CKD (higher-temperature EP) and CKE (compounded, for worm gears). ISO 12925-1 sets the performance requirements. A modern enclosed gearbox usually calls for CKC or CKD.
- AGMA numbers — the American Gear Manufacturers Association numbering maps one-to-one onto ISO VG, as the table above shows. AGMA 5 EP is an ISO VG 220 extreme-pressure gear oil; AGMA 7 EP is an ISO VG 460. If a nameplate gives you an AGMA number, convert it and order the ISO VG grade.
- Transformer oils sit outside this system entirely. They are specified by dielectric strength and oxidation stability under IEC 60296 or IS 335, not by ISO VG. See transformer oils.
Which grade do I actually order?
| Equipment | Typical ISO VG | Specification to quote |
|---|---|---|
| Industrial and mobile hydraulic systems | VG 46 (VG 32 in cool ambients, VG 68 in hot) | ISO 6743-4 HM or HV; DIN 51524 Part 2 or Part 3 |
| Rotary screw air compressors | VG 46 – VG 68 | DIN 51506 VDL; ISO 6743-3 |
| Reciprocating air compressors | VG 100 – VG 150 | DIN 51506 VDL |
| Enclosed industrial gearboxes | VG 220 – VG 460 | ISO 6743-6 CKC/CKD; ISO 12925-1; AGMA 5 – 7 EP |
| Slow-speed, heavily loaded drives, kilns and mills | VG 460 – VG 680 | AGMA 7 – 8 EP |
| Steam cylinders and heavy lubricating duty | VG 460 and above | IS 1115, by grade |
| Machine tools, neat cutting oils | VG 15 – VG 46 | ISO 6743-7 |
| Transformers and switchgear | Not ISO VG rated | IEC 60296 or IS 335 |
Three rules that make the choice reliable
Three rules make the decision reliable every time. Start with the OEM manual, because the equipment builder has already accounted for clearances, pump type and cooling. Adjust for ambient temperature, moving one grade up in sustained heat and one grade down in cold, but only within the range the builder allows. And never let viscosity grade substitute for performance class — an ISO VG 150 rust-and-oxidation oil is not a substitute for an ISO VG 150 VDL compressor oil, however identical the two look on a viscometer.
Base oil quality sits underneath all of this. Oxidation rate roughly doubles for every 10°C rise in temperature, so in a continuously running compressor or gearbox the base stock decides how long the specification holds. Axabull refines its industrial range from imported Group II+ base oils for exactly that reason; the grade-by-grade detail is set out in our guide to Group II base oil grades.
Sourcing to specification
Axabull Industries Pvt. Ltd., founded in 2013 in Surat, Gujarat, manufactures a full industrial lubricants range built to these classifications: hydraulic oils, compressor oils, industrial gear oils, cutting oils and transformer oils, alongside greases and coolants. Supply runs through a pan-India network of more than 5,000 retailers and five depots, and to 16 export markets across the Middle East, South Asia, Africa, the Caribbean and South America via an overseas hub in Sharjah, UAE. Bulk and private-label supply are available for B2B partners.
If you have a nameplate specification in front of you and want it matched to a product and a pack size, that is a five-minute conversation. Importers and distributors can start on the global B2B and export page; plant and maintenance buyers in India can contact the Axabull team with the equipment, the grade and the annual volume, and we will send the technical data sheets to match.