HYDAC 0660 D 010 ON vs 0660 R 010 ON: Dimensions and Bypass Differences

These elements are not directly interchangeable. D is for pressure filters and R for return filters. Their outside diameters, bores and end-cap arrangements differ despite the shared 0660, 010 and ON markings.

The 0660 D 010 ON has a 91 mm outside diameter and 48 mm bore. The 0660 R 010 ON has a 114 mm outside diameter and 68 mm bore. Those mounting dimensions alone prevent treating them as the same spare part.

Side-by-side specifications

Lengths differ by only 4 mm, but outside diameters differ by 23 mm and bores by 20 mm. Trial fitting after delivery wastes downtime and cannot correct an incompatible sealing interface.

0660 is a size-series code, not a 660 L/min flow rating. Filter capacity also depends on the housing, media area, viscosity and acceptable differential pressure.

D filters the pressure line; R treats returning oil

A pressure filter generally sits downstream of the pump or upstream of a component needing protection. Filtered oil continues into the working circuit. A return filter treats oil returning from actuators and other branches to the reservoir.

For a servo-valve hydraulic unit, the pressure filter protects oil entering the control circuit, while the return filter captures particles in returning circulation. Both D and R elements can be present on one machine, each in its own housing.

A spare 0660 R 010 ON therefore cannot replace a 0660 D 010 ON simply because it is already in stock. Flow function, mounting dimensions and end sealing differ.

The 0660 D 010 ON model and specifications cover the base D element; this comparison addresses the differences from R.

The R bypass end cap is a functional difference

The 0660 R 010 ON compared here has a bypass end cap with a listed opening pressure of 3 bar. The D element has a closed end cap. Do not transfer the R bypass specification to the D element.

When bypass opens, part of the flow can avoid the media. This maintains a flow path under high restriction, but that oil is unfiltered by the element. Bypass design therefore affects the response to clogging and cold-oil differential pressure.

A D element without that end-cap assembly does not prove the complete pressure-filter housing has no bypass. A separate assembly may be fitted in the housing or head.

Confusing these arrangements can remove a required bypass function or create unintended bypass through failed sealing. See filter bypass and filtration performance.

Why a 20 bar collapse rating can coexist with high system pressure

The 20 bar figure describes the element's resistance to differential pressure. The housing's system-pressure rating is a different parameter.

For example, 160 bar outside the element and 157 bar at its centre give a 3 bar differential. The housing must suit a 160 bar system; the element sees the 3 bar difference.

As clogging increases differential pressure, indication and appropriate protection become necessary. A high-pressure housing does not make every element inside capable of the same differential pressure.

Return elements also encounter high differential pressure from cold oil, peak return flow or clogging. A return-line location does not remove the need to consider restriction and end sealing.

Return flow can exceed pump flow during cylinder retraction

Cylinder area ratio can explain an underestimated return-filter duty. Suppose cap-end area is 50 cm² and effective rod-end area is 30 cm². Supplying 30 L/min to the rod end during retraction produces approximately 50 L/min returning from the cap end.

Sizing return filtration solely from 30 L/min pump flow misses that 50 L/min stage. Simultaneous cylinder movement or accumulator discharge can raise peak return flow further.

This calculation describes branch duty; it does not assign a fixed flow rating to the 0660 R. After matching the element, check housing capacity and cold-start differential pressure for the actual movement.

Conclusion

Both elements use 10 μm ON media, but mounting dimensions and end caps differ. Match D replacements to D housings and R replacements to R housings. The R variant compared here also includes a 3 bar bypass end. Matching the complete code is more reliable than matching only 0660 or 10 μm.