Ucon Lubricant 50-HB-260 O-Ring Compatibility: Which Compounds Hold Up

Ucon Lubricant 50-HB-260 O-Ring guide for PAG compressor, hydraulic, and metalworking fluids: chart ratings, which elastomers to use, and which lack data.

Sep 8, 2026 by O-Ring Expert

Small black round-cord O-Ring beside a clear beaker of pale amber PAG lubricant, modern rotary screw compressor softly blurred in the background

Ucon Lubricant 50-HB-260 is a water-soluble polyalkylene glycol (PAG) base stock used in compressor oils, hydraulic and gear fluids, metalworking lubricants, textile spin finishes, and related process lubricants. Seals on compressors, pumps, valves, and lubrication skids see this fluid as a formulated lubricant or as a washable PAG intermediate. Pick the wrong O-Ring family and you risk swell, softening, or early leak-off when the fluid chemistry and temperature stack against the elastomer.

This guide maps the handbook Chemical Compatibility Chart row for Ucon Lubricant 50-HB-260 to practical compound choices.

Where it shows up

Compressor lubricants: PAG base stocks for centrifugal, reciprocating, rotary-screw, and sliding-vane machines handling air and process gases
Hydraulic and gear oils: water-soluble synthetic lubricants where deposit control and washability matter
Metalworking fluids: cutting, grinding, drawing, and forming lubricity packages
Textile and rubber processing: fiber spin finishes and rubber mold or assembly lubricants
Specialty process fluids: antifoam and intermediate uses tied to the same 50-HB chemistry

Service is usually lubricant contact, ambient to moderately warm unless the compressor or hydraulic loop runs hotter. Chart ratings assume a generic commercial compound near room temperature.

How Ucon Lubricant 50-HB-260 stresses an O-Ring

50-HB fluids are alcohol-started PAGs with roughly equal oxyethylene and oxypropylene content, so they are water soluble and more polar than mineral oil. That polarity is friendlier to many common seal families than aromatic solvents, but formulated packages, temperature, and co-fluids still change outcomes. Confirm grade, viscosity package, and duty before locking a compound. See Chemical Compatibility and Failure Analysis for swell and softening modes.

Handbook chart ratings for Ucon Lubricant 50-HB-260

Same rating badges and layout as the interactive chart. Search Ucon Lubricant 50-HB-260 on the Chemical Compatibility Chart to pin the live row.

Ratings 1Excellent 2Good 3Poor 4Not recommended XNo data ~70°F / room temp unless noted

Ucon Lubricant 50-HB-260 O-Ring chemical compatibility by compound. Ratings 1 excellent through 4 not recommended.
Fluid	Best	N Nitrile	H HNBR	E EPDM	C Neoprene	S Silicone	V Viton®	P Urethane	F FVMQ	A Aflas®	B Butyl	K FFKM	T PTFE
Ucon Lubricant 50-HB-260	N	1	1	1	1	1	1	X	1	X	1	1	1

Best family on the chart row: Nitrile (N). HNBR, EPDM, neoprene, silicone, FKM, fluorosilicone, butyl, FFKM, and PTFE also rate excellent (1) on this row. Polyurethane and Aflas lack data (X) on the handbook matrix.

Recommended O-Ring materials

First choice: Nitrile (Buna-N) and HNBR

Nitrile (NBR) is rated excellent (1) and is the chart’s preferred letter for Ucon Lubricant 50-HB-260. Use it for ambient to moderately warm lubricant service when cost and availability matter. HNBR matches that chemical rating with more heat and wear margin for compressor and pump duty.

Also usually serviceable

EPDM 1Excellent Strong fit for water-soluble PAG service; confirm if petroleum co-fluids share the loop.
Neoprene (CR) 1Excellent Solid general-purpose rating; check heat and continuous immersion for your grade.
Viton® / FKM 1Excellent Use when temperature climbs or mixed hydrocarbon traces are present.
Fluorosilicone (FVMQ) 1Excellent Helpful when cold flexibility matters alongside lubricant contact.
Silicone (VMQ) 1Excellent Usually fine for static service; watch tear and abrasion in dynamic glands.
Butyl (IIR) 1Excellent Good polar-fluid resistance; watch heat and dynamic wear.
FFKM 1Excellent Overkill for many PAG lubricant lines; use for mixed aggressive streams.
PTFE 1Excellent Chemically inert but not an elastomer. Consider PTFE-encapsulated when you need rebound.

Materials to treat as unknown

Polyurethane XNo data No reliable handbook rating for this fluid. Test before specifying.
Aflas® (FEPM) XNo data Insufficient chart data. Do not assume steam or amine grades are automatic fits here.

Physical properties to match (after chemistry)

A chart 1 means the polymer family usually survives the fluid. It does not finish the spec. After you shortlist nitrile or HNBR (or another excellent family above), lock the physical properties the gland and machine actually need.

Hardness (Shore A / durometer)

70 Shore A is the everyday default for static covers, flanges, and low-to-moderate pressure lubricant lines.
90 Shore A (or 70 plus a back-up ring) when pressure and clearance gap push extrusion risk, common on compressor and hydraulic ports.
Soft grades (50–60) seal rough faces better but give up extrusion margin.

See Shore A Hardness for the extrusion-gap chart and feel references.

Temperature

Handbook chemical ratings are near room temperature. PAG compressor and hydraulic loops often run warmer. As a starting frame:

Family	Typical handbook range (grade dependent)	Notes for PAG lube duty
Nitrile	about −40°F to +250°F	Everyday pick when heat stays moderate
HNBR	about −40°F to +300°F	Extra heat and wear margin for compressors / pumps
FKM	about −20°F to +400°F	When discharge or ambient heat exceeds nitrile
EPDM	about −65°F to +300°F	Fine chemically here; avoid if petroleum oil shares the loop
Silicone	about −75°F to +400°F	Static / wide temp; weaker tear in dynamic glands

Confirm the formulated lubricant’s temperature window (stabilizers, antioxidants) as well as the elastomer’s.

Static vs dynamic duty

Static face and cover seals: chemical rating + hardness + squeeze usually dominate.
Dynamic shafts, rods, and reciprocating glands: add abrasion, extrusion, and friction. HNBR or a harder nitrile often outlasts soft general-purpose NBR in lubricated motion. Check groove design and seal types.

Size and squeeze

Lock ID × CS (or the AS568 dash) on the Master O-Ring Size Chart before you argue compound. Wrong size fails faster than a second-choice polymer that fits the groove.

Hygroscopic / washable PAG notes

50-HB fluids are water soluble and can pick up moisture. That rarely changes the chart letter by itself, but wet PAG, neat PAG, and additive packages are not identical duties. If the loop sees water rinse, steam-out, or dilute antifoam service, say so when you specify the ring.

Practical selection checklist

Confirm the fluid package. Neat 50-HB-260 base stock versus a fully formulated compressor, hydraulic, or metalworking lubricant.
Temperature. Room-temperature transfer is milder than hot compressor discharge or hydraulic loops.
Hardness and pressure. Default 70 Shore A; step to 90 or add a back-up ring when gap and psi demand it.
Static or dynamic. Rotary shafts and reciprocating glands need abrasion and extrusion resistance beyond a chemical rating alone.
Confirm on the chart, then test. Pin Ucon Lubricant 50-HB-260 on the Chemical Compatibility Chart. For critical service, contact The O-Ring Store with fluid grade, temperature, hardness, and duty cycle.

Quick answers

Which O-Ring for Ucon Lubricant 50-HB-260?
Start with nitrile (Buna-N) or HNBR at 70 Shore A for general static duty, or 90 Shore A / back-up rings when pressure and gap climb. EPDM, neoprene, silicone, FKM, fluorosilicone, butyl, FFKM, and PTFE also rate excellent on the handbook row. Treat polyurethane and Aflas as unproven here until you test.

Is this the same as other Ucon 50-HB grades?
Related 50-HB PAG lubricants share the water-soluble chemistry family, but viscosity and formulation differ. Always match the exact fluid name on the chart and on the SDS.

Chart ratings are guidance for generic commercial compounds near room temperature. Concentration, temperature, and co-fluids change outcomes. Evaluate specific parts before use in critical applications.