Hydac NF Large-Flow Inline Filter, up to 3500 l/min and 25 bar

Large-flow filtration for lube oil and hydraulic circuits up to 25 bar

The Hydac NF is an inline filter for high-flow circuits where oil volume, not pressure, is the design problem: lube oil systems, cooling and circulation loops, and large hydraulic power units. A filter housing with a threaded cover plate holds one element on the small sizes and up to four on the largest, which brings flow up to 3500 l/min.

Nominal pressure is 25 bar, with a maximum operating pressure of 30 bar for a limited number of cycles. A bypass valve and a clogging indicator port are standard. The tube is steel up to NF 750 and aluminium from NF 950 upward.

Technical specifications

Ordering code and options

The sheet’s example is NF ON 2640 D P 10 D 2 .X /-L24: series, element medium, size, pressure letter D (25 bar), connection letter, filtration rating, indicator letter and type code, then the supplementary details. Indicator choices are A (plug), BM (visual with manual reset), C (electrical) and D (visual and electrical). The datasheet advises using only the BM version when a visual indicator is chosen.

Supplementary details include a special bypass cracking pressure (B6 for 6 bar), a manual vent with shut-off valve (EM), a permanent vent through a Minimess hose (EP), a mounting flange for NF 1340 and 2640 (FF), no bypass (KB), a 4 mm filling line (SB4), FPM seals (V) and lamp voltage or LED. Accessories listed are mounting brackets for NF 1310 and 1340, foot brackets for several sizes, a filling connection on the contaminated side for selected sizes, a quick-release coupling on the filling connection and a check valve on the clean side for NF 160, 240 and 280.

Selecting a size

Size the filter on flow and the element differential pressure at your oil viscosity. For applications up to 40 bar the datasheet asks for a separate request on NF 950, 1350 and 2650. The port table in the datasheet marks some sizes as discontinued models, so confirm availability of a specific size and port before you order.

Compatible fluids include hydraulic oils H to HLPD, lubrication oils, compressor oils, biodegradable HETG, HEES and HEPG, and fire-resistant HFA to HFD; high-water fluids on request. The housing must be earthed and electrical indicator power switched off before unplugging the connector. Send the nameplate code, flow, oil type and micron rating with your enquiry.

Key design features

• Multi-element sizes: NF 5240, 7840 and 10440 hold two, three or four 2600 R elements, so very large flows are handled in one housing instead of a bank of smaller filters.
• Threaded cover plate: elements are removed from the top, which keeps element changes clean and quick on a lube oil console.
• Standard bypass valve: the 3 bar bypass protects the element from collapse during cold starts or when it is heavily loaded.
• Clogging indicator port: the VM differential pressure indicator, set at 2 bar, warns before the bypass opens, giving time to plan the change.
• Choice of media: from glass-fibre Optimicron and Betamicron grades to paper, wire mesh and water-absorbing Aquamicron, so one housing can serve different cleanliness targets.

Choosing the element media

The housing sets the flow capacity; the element sets the cleanliness the system will reach. Glass-fibre media such as Optimicron are the usual choice for hydraulic and turbine lube circuits where a defined cleanliness class is specified. Paper elements are a lower-cost option for less critical circulation duties. Stainless steel wire mesh is cleanable and suits coarse protection or fluids where disposable media are not wanted. Aquamicron elements absorb free water, which is useful on systems exposed to condensation.

When selecting the filtration rating, start from the most sensitive component in the circuit, such as a servo valve, a high-speed bearing or a gear set, and the cleanliness code the equipment maker specifies. A finer element gives cleaner oil but a higher clean pressure drop, so size the housing so that the clean differential pressure stays well below the 2 bar indicator setting at the design flow and oil viscosity.

Viscosity, temperature and pressure drop

Pressure drop through a filter rises with oil viscosity. A lube oil system that starts cold will see much higher differential pressure until the oil warms up, which is one reason the bypass valve is fitted as standard. In the Gulf, ambient temperatures are high for most of the year, but outdoor equipment can still start with cool oil in winter mornings. Size for the coldest realistic operating viscosity, not only the normal running temperature. The stated temperature range of –10 to +100 °C covers typical mineral oil circuits.

Installation and maintenance

• Leave enough headroom above the housing to lift elements out through the cover.
• Fit a drain and vent so the housing can be emptied before an element change.
• Connect the clogging indicator to the control system so a change is triggered by condition, not by the calendar alone.
• Keep spare elements and cover seals in stock; dust and sand ingress in desert sites shortens element life, especially where reservoir breathers are not maintained.
• Check the seal material is compatible with the fluid in use.

Typical applications in Oman and the GCC

Large-flow inline filters of this kind are used on turbine and compressor lube oil consoles in oil and gas plants, on circulation systems for large gearboxes and paper or steel mill equipment, on cooling loops for hydraulic power units, and on offline flushing rigs used during commissioning.

What to include in an RFQ

Send the full Hydac model code if available, or the size (for example NF 1310), element media and filtration rating, connection type and size, fluid type and viscosity, design flow, operating pressure, indicator type, and seal material. State whether you need complete filters, replacement elements only, or both, together with quantities.

Documents and quotation

The datasheet (E 7.112.7/11.16) is attached. Related: filter housings and the Hydac RFM return line filter.