Changing hydraulic fluid to meet a fire-risk requirement affects more than pump seals. Filter media, element adhesives, housing seals and operating viscosity must also suit the new fluid. A nominally identical micron rating does not prove compatibility.
The fluid change reaches every wetted part
A move from mineral oil to a water-glycol or other fire-resistant fluid changes chemical exposure for seals, filter media, adhesives, pumps and hoses. The filter element may look physically interchangeable while its media or bond line is unsuitable. HYDAC warns against cellulose paper media with water-glycol in its filter FAQ. That guidance applies to that fluid family; another fire-resistant formulation needs its own compatibility review, not a blanket conclusion.
HYDAC’s filter FAQ specifically warns that cellulose paper media should not be used with water-glycol. Its element information also shows material and seal variants for different fluids. This does not mean every synthetic or fire-resistant fluid needs the same element: the exact chemistry matters. Request written approval for the element, seals and housing from the suppliers. Then recheck pressure drop and bypass behavior over the new fluid’s temperature range, and document whether the change requires flushing or seal replacement elsewhere in the hydraulic system.
Compatibility and flow are separate checks
A chemically acceptable element still needs the right pressure-drop behavior. Different fluids and concentrations have different viscosity-temperature curves, and water-glycol maintenance includes concentration and corrosion control. Ask both the fluid and component suppliers for written approval of the exact product names. Check housing seals, bypass parts, indicator seals and element collapse rating, not only the media label. A conversion may also require cleaning or flushing to avoid mixing residues; follow the fluid and machine makers’ procedures.
A steel-plant conversion
A plant converts a press from mineral oil to a specified water-glycol fluid for a fire-risk area. The pump supplier approves a seal change, but the maintenance list still contains the old paper filter element. That part number must be reviewed before the first fill. Confirm the exact fluid concentration and get approval for the element media, adhesive, housing seals and all wetted parts. Update the spare-parts list and tank label so the next shift cannot reinstall the previous element by habit. After start-up, check filter differential pressure at operating temperature and examine seals for leakage.
Document the converted system
Update the reservoir label, purchasing part numbers, maintenance instructions and oil-analysis targets. Keep an approved list of replacement filter elements and seal kits so a later service does not reinstall a mineral-oil-only part. During commissioning, measure filter differential pressure at cold and warm operating points and inspect for leakage. A clean ISO particle count cannot detect chemical incompatibility, so material approval and physical inspection remain necessary.
Checks to put on the drawing or test plan
- Identify the exact fluid manufacturer, product and concentration.
- Verify element media, adhesive, seal and housing compatibility.
- Review operating viscosity and filter pressure drop after conversion.
Failure mode to avoid: Swapping fluids while leaving a paper element or incompatible seal in place can cause element damage or leakage.
Information to request before approval
- Current and proposed fluid specifications.
- Filter housing and element part numbers.
- Temperature range and cleanliness target.
For a related explanation, see seal material selection.
技术参考： HYDAC filter FAQ; HYDAC element technical data. The cited manuals and product data describe their makers’ equipment; this article is independent engineering guidance and does not assign their ratings to Yongjian products.