Hydraulic Oil Additive Packages

The Selection Principle: Hydraulic Is a Chemistry Choice, Not a Tier

This is where the thin “AW 46” listings stop and the real decision begins. A hydraulic package is selected by the operating environment, in this order:

• Fire risk decides first — and it is a hard safety constraint. Near molten metal, furnaces or ignition sources (steel mills, die-casting, underground mining), a mineral oil is unsafe. You must use a fire-resistant fluid: HFC (water-glycol, PA555) or HFDU (synthetic ester, PA50899). This is not a preference — it is governed by the system’s fire classification.
• Then zinc vs ashless — driven by filterability, water and environment. Conventional ZDDP (zinc) anti-wear (PA5201) is the robust, economical default. You move to ashless / zinc-free (PA5202 family) when the system needs superior filterability (fine servo valves clog on zinc soaps and water reaction products), better water tolerance and demulsibility, longer thermal-hydrolytic life, or low-ash / environmental compliance. Low-zinc (PA5000) is the middle ground for non-ferrous (yellow-metal) compatibility.
• Then pump type and pressure. High-pressure axial-piston pumps (>350 bar) demand the most robust anti-wear — a high-quality zinc package or the ashless high-pressure grade (PA5202H). The OEM pump-wear tests (Denison HF-0/HF-2, Eaton/Vickers, Bosch Rexroth) set the bar the finished fluid must clear.
• Then viscosity and VI. Pick the ISO VG and whether the duty needs HLP (standard) or HVLP (added viscosity–temperature control) for mobile, all-season equipment. Phosphorus-free (PA5202P) is selected where eco-labels restrict phosphorus.

So the decision order is: fire risk → zinc vs ashless (filterability / water / eco) → pump & pressure → ISO VG & HLP/HVLP. The three families below put that into practice.

What a Hydraulic Package Does

A hydraulic fluid is the classic “looks simple, hard to formulate” industrial oil — a multi-objective balance carried at a light treat rate (typically around 0.6–1.5 wt% of performance additive):

• Anti-wear. Protects vanes, pistons and gears — via ZDDP (zinc family) or an ashless anti-wear/EP system (zinc-free family).
• Oxidation & thermal stability. Antioxidants suppress sludge and varnish to extend fluid life at high bulk temperatures.
• Rust & yellow-metal protection. Rust inhibitors protect ferrous surfaces; copper passivators protect bronze and brass pump components.
• Demulsibility & foam/air control. Demulsifiers shed water quickly; antifoam and air-release additives prevent spongy response, cavitation and noise.

The CheMost Range — Three Families, Seven Grades

One range structured by chemistry family. Open a grade to request its data sheet.

Zinc (ZDDP) anti-wear

Ashless / zinc-free

Fire-resistant

Specifications — Mineral AW & Ashless Grades data on request

The concentrate fingerprint for the mineral-based grades — zinc and phosphorus (the family discriminators), nitrogen, sulfated ash, copper-corrosion and viscosity — published per grade as test data is confirmed. The fire-resistant grades (PA555 HFC, PA50899 HFDU) report a different property set (water content, density, pH or TAN); request their data sheets directly.

Properties are reported as concentrate (package) values to the ASTM methods shown, not finished-fluid values; published per grade as test data is confirmed. Request the current TDS for any grade.

Performance Coverage

These are formulation targets per grade against the public ISO categories, at the appropriate treat rate in a suitable base fluid — not OEM approvals or fire-resistance certifications. The grades are formulated against the OEM pump-wear tests the finished fluid must clear (Denison HF-0/HF-2, Eaton/Vickers, Bosch Rexroth); the OEM approval itself — and any fire-resistance approval such as Factory Mutual — is held by the finished-fluid marketer who tests and approves the finished fluid, not by the additive package.

The Hydraulic Standards Map

Two ISO families frame the range:

• ISO 11158 (mineral hydraulic) — HH / HL / HM / HV / HG. HM is the standard anti-wear oil; HV adds viscosity–temperature control (the market HLP / HVLP language). PA5201, PA5000 and the PA5202 family serve HM and HV.
• ISO 12922 (fire-resistant) — HFC and HFDU. HFC is water-glycol (fire resistance from water content); HFDU is a water-free synthetic ester (fire resistance with lubricity). PA555 serves HFC; PA50899 serves HFDU.
• Zinc vs ashless is orthogonal to grade. A zinc-free fluid is not a “higher” HM — it is the same duty met without metallic ash, chosen for filterability, water tolerance or environmental reasons.

Common Applications

• General industrial hydraulics (HM): machine tools, injection moulding, presses and factory equipment — PA5201 (zinc) or PA5202 (ashless).
• Mobile & all-season hydraulics (HV): construction and agricultural equipment needing viscosity–temperature control — PA5202 with a VI improver.
• High-pressure systems (>350 bar): severe-duty axial-piston circuits — PA5202H.
• Servo-valve & long-life systems: filterability-sensitive circuits — ashless PA5202 or low-zinc PA5000.
• Eco-labelled fluids: phosphorus-restricted finished fluids — PA5202P.
• Mining & foundry (fire risk): water-glycol HFC — PA555.
• Steel mills & die-casting (fire risk): synthetic-ester HFDU near flame or molten metal — PA50899.

Quick Reference