Compressor Oil Rotary Screw vs Reciprocating — How to Choose for Thai Factories

The compressor is the heart of the compressed air system in industrial factories of every type — from welding and conveyor belts to pneumatic tools, and on to food and pharmaceutical packaging systems. Choosing a compressor oil that matches the type (rotary screw vs reciprocating) + viscosity grade + OEM spec directly affects:

• Machine service life — the wrong oil causes bearing seizure in <500 hours
• Air quality — the wrong viscosity causes oil carry-over that contaminates the air line (a problem in food / pharma work)
• Electricity cost — viscosity that is too high makes the compressor consume 8-15% more power
• Drain interval — PAO/PAG synthetic 8,000 hr vs mineral 2,000 hr

This article summarizes the engineering differences between the rotary screw compressor (RSC) and the reciprocating compressor (piston) — along with an oil-selection table per ISO 6743-3 / DIN 51506 and the OEM specs of Atlas Copco, Ingersoll-Rand, Kaeser, and ELGi, for maintenance and procurement teams.

Mechanical Differences — Why the Oils Differ

Rotary Screw Compressor (RSC)

• Mechanism: a pair of rotors (male + female) rotating continuously — no pistons
• Oil-air mixing point temperature: 80-100°C continuously at the separator
• Oil function: sealing (closing the gap between rotor + housing) + cooling + lubricating bearings + sealing the shaft
• Oil carry-over: high — oil is mixed with air constantly, passing through a separator + 2-stage filter before release
• Oil requirements:
  • Medium viscosity (ISO VG 46) — thin enough for smooth rotor drive, but thick enough to seal
  • High oxidation stability (continuous operation at 80-100°C → mineral oxidizes quickly)
  • High demulsibility (must be able to separate condensate water from the oil)
  • Good foam resistance

Reciprocating Compressor (Piston)

• Mechanism: a piston moving up and down in a cylinder, with a crankshaft + connecting rod
• Temperature: crankcase 60-90°C; head + cylinder peak 180-220°C during compression
• Oil function: lubricate the piston ring + cylinder wall + crankshaft bearing
• Oil carry-over: low (designed for splash or pressure feed — not fully mixed with air)
• Oil requirements:
  • High viscosity (ISO VG 100-150) — withstands pressure at the ring + cylinder wall
  • High flash point (≥240°C) — the combustion chamber is close
  • Anti-wear (ZDDP or ashless EP additives)
  • High carbon deposit resistance

Core rule: Never use reciprocating oil (VG 100-150) in a rotary screw — viscosity that is too high causes rotor stall + bearing damage before 500 hr. And never use rotary screw oil (VG 46) in a reciprocating compressor — viscosity that is too thin will escape into the combustion chamber under pressure.

Oil Selection Table per ISO 6743-3 + DIN 51506

Compressor Type	ISO 6743-3	DIN 51506	Recommended ISO VG	Base Oil	Example OEM Spec
Rotary Screw — Standard duty	DAB	VDL	VG 46	Mineral Group II / III	Atlas Copco Roto-Z, Ingersoll-Rand X-Tend
Rotary Screw — High temp / continuous duty	DAH	VDL	VG 46	PAO Group IV	Atlas Copco Roto-Inject Fluid (RIF), Kaeser SIGMA Fluid SC
Rotary Screw — Food grade (H1)	DAH + NSF H1	—	VG 46	PAG or White Mineral	Atlas Copco Food Grade Fluid, ELGi Endura Lube FG
Rotary Screw — Hot summer / heavy load	DAH	VDL	VG 68	PAO	Kaeser SIGMA S-460
Reciprocating — General industrial	DAA	VCL	VG 100	Mineral Group II	Mobil Rarus 427, Shell Corena P
Reciprocating — High pressure / high temp	DAB	VDL	VG 150	Mineral or PAO	Mobil Rarus 829, Shell Corena S4 P
Reciprocating — Breathing air (medical)	DAA + NSF	—	VG 100	Synthetic Diester	Anderol 555

Note: SAHA distributes ZIC HYDRO ISO VG 32/46/68 (DIN 51524 HLP) for rotary screw — and SK ZIC X-9000 or X-Diesel pail oils for reciprocating work that requires high viscosity. Contact the sales team for details.

Signs the Oil Is Wrong — Check Before Bearing Failure

Rotary Screw

• Oil carry-over rises >5 ppm at the outlet: oil too thin, or separator element too old
• Shutdown temperature 105°C or higher: viscosity too high, or cooler clogged
• Foam in the sight glass: demulsifier degraded — drain ahead of schedule
• Color turns dark brown + burnt smell: severe oxidation — change immediately

Reciprocating

• Carbon deposit at the valve plate / discharge port: oil too thin, or flash point too low — change
• Crankcase pressure increases: ring wear from low lubricity
• Oil consumption increases >2x baseline: ring sealing degraded, or wrong viscosity

Drain Interval Guide

Compressor Type	Mineral Oil	PAO/PAG Synthetic
Rotary Screw — standard	2,000-4,000 hr	6,000-8,000 hr
Rotary Screw — clean room	1,500-3,000 hr	5,000-7,000 hr
Reciprocating — general	1,000-2,000 hr	3,000-5,000 hr
Reciprocating — outdoor	500-1,500 hr	2,000-4,000 hr

Life-extension technique: Take an oil sample at 50% of the drain interval and send it to a lab to check TAN/TBN/water content/wear metals — if TAN < 2.0 mg KOH/g and water < 500 ppm → you can continue draining later.

How to Choose When Ordering

Request a tax invoice + spec sheet from SAHA — specify:

1. Compressor brand + model (e.g., Atlas Copco GA75 VSD+)
2. Application (oil-flooded screw / oil-free / piston single-stage / piston multi-stage)
3. Actual discharge pressure in service (bar)
4. Service environment (indoor / outdoor / clean room / food grade / explosive zone)
5. OEM warranty status — if the machine is still under warranty, OEM-spec'd oil or an ASLE-/NSF-approved equivalent must be used

Related Services

• SK ZIC HYDRO 32/46/68 oil, 18L pail + 200L drum, with nationwide delivery
• Oil sampling kit + lab analysis (TAN/TBN/water/wear metals) — via the NACE/AMPP lab network
• Compressor PM contract (oil change + filter element + separator) — annual
• Onsite oil flushing service for compressors switching base oil chemistry (mineral → PAO)

Summary for Procurement

If you must spec compressor oil in a TOR or PR:

1. Cite ISO 6743-3 + DIN 51506 as the baseline (use the phrase "or equivalent")
2. Specify a single viscosity grade — e.g., "ISO VG 46", not "VG 32-46"
3. Specify the base oil type — e.g., "Group II mineral or PAO Group IV"
4. Specify OEM equivalence — e.g., "equivalent to Atlas Copco RIF or Kaeser SIGMA Fluid SC"
5. Request MSDS + COA for every lot delivered
6. Set the drain interval separately by base oil — mineral 2,000 hr / synthetic 8,000 hr
7. Define the disposal method — used oil must go through a waste-oil disposal company holding a วอ. license

For factories in the automotive / electronics / food / pharma groups — we recommend choosing PAO synthetic for every rotary screw because the 5-year TCO is 18-25% lower than mineral when you include the reduced electricity cost + the longer drain interval.

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This article is engineering reference information, not advice that replaces checking the OEM manual or consulting your plant engineer — for special applications (oil-free / clean room / food grade), contact the Sahawatthanakit (1988) engineering team for a spec suited to your factory.