Hydraulic Directional Valve Selection Guide
Size, Spool, Voltage & Flow

Step 1 — Mounting Size (ISO 4401)

The mounting interface is the first and most rigid constraint. Hydraulic directional valves bolt onto a sub-plate or manifold whose bolt pattern and port positions are standardised by ISO 4401 (formerly CETOP RP 121H, and dimensionally aligned with DIN 24340). If your manifold is machined for one size, only a valve of that same size will fit — there is no adapter shortcut in production machinery.

Two sizes cover the overwhelming majority of industrial hydraulic circuits: NG6 and NG10. The table below shows the practical differences that drive selection.

How to identify what you already have: read the valve nameplate first — a model beginning 4WE6 or DSG-02 is NG6; 4WE10 is NG10. If the nameplate is unreadable, measure the sub-plate bolt spacing: the NG6 pattern is noticeably narrower than NG10, and NG10 bodies are roughly 50 percent wider. For new designs, size from peak circuit flow (Step 4) rather than from the pump rating.

Step 2 — Spool Function

The spool function defines what happens to the four ports (P = pump, T = tank, A and B = actuator) when the valve sits in its neutral, de-energised position. This single choice determines whether your cylinder holds load, drifts, floats, or whether the pump unloads. It is the most frequently mis-specified parameter in replacement orders.

Cross-brand note: Yuken-type valves use a different code set. DSG-02-3C60 corresponds functionally to the E spool (all ports closed), 3C2 is the standard four-way arrangement, and 3C4 is its reverse. When cross-referencing between Rexroth-type and Yuken-type valves, match the neutral-position behaviour, not the letter. Our 4WE6 cross reference table maps these directly.

Step 3 — Coil Voltage & Connector

Coil selection has one safety-relevant consequence that catches maintenance teams out. A DC coil draws constant current regardless of armature position. An AC coil draws a high inrush current that only drops once the armature has pulled in. If a spool jams mid-stroke on an AC valve, the coil remains at inrush current and can overheat and burn out within minutes. The same jam on a DC valve simply results in no motion, with the coil running at its normal current.

For this reason, DC 24V is the default for any PLC-controlled machine built in the last two decades. It also switches faster because there is no AC magnetising delay. AC 220V remains in service on legacy relay-controlled equipment, where replacing like-for-like avoids rewiring the control cabinet.

On the YXCHK catalog, the voltage appears in the model suffix: CG24N9Z5L denotes DC 24V with rectifier, impulse manual override and a right-angle DIN 43650 plug; AW220N9Z5L denotes AC 220V with the same override and connector. Because DIN 43650 (also catalogued as ISO 4400) is a shared industry footprint, coils from Rexroth, Parker, Vickers and Yuken-type valves all mate with the same plug — an electrical swap requires no rewiring.

Protection class: YXCHK coils are rated IP65, meaning dust-tight and protected against low-pressure water jets. That covers machine-tool coolant splash and general workshop washdown, but not submersion. For marine deck machinery or high-pressure washdown, specify the requirement at inquiry so the engineering team can confirm suitability.

Step 4 — Flow & Pressure Verification

Two numbers must be checked against the valve rating: peak system pressure and peak circuit flow. Both are hard limits, but they fail in different ways.

Pressure: exceeding the rated working pressure risks spool deformation, seal extrusion and, in the worst case, body fracture. YXCHK Rexroth-type valves (4WE6, 4WE10) are rated at 31.5 MPa; Yuken-type valves (DSG-02) at 21 MPa. If your relief valve is set above 21 MPa, a DSG-02-class valve is not an acceptable substitute regardless of mounting compatibility. This is the single most common mistake when engineers substitute across the two families purely on bolt pattern.

Flow: undersizing produces excessive pressure drop, heat and slow actuator speed. Oversizing is also a real cost: a larger spool needs more solenoid force, and its internal leakage becomes proportionally significant at low flow. Aim for rated flow at or modestly above peak circuit flow — roughly 20 percent headroom — rather than several times larger.

Do not forget the T-port limit. Both YXCHK NG6 and NG10 series accept a maximum 16 MPa back pressure on the tank line. Circuits with counterbalance valves, long return lines, or a shared return manifold can exceed this without anyone noticing until spool response degrades. Measure the actual T-line pressure during peak duty rather than assuming it is near zero.

Step 5 — Seal Material

Seal compatibility is decided by the hydraulic fluid, not by pressure. YXCHK supplies NBR (nitrile) as standard, covering mineral oils and water-glycol fluids across a −20 °C to +80 °C range — this is the correct choice for the large majority of industrial installations.

Specify Viton (FKM) when the circuit runs phosphate-ester fire-resistant fluid, when ambient temperatures at the valve body run persistently high, or in marine and offshore installations where salt-laden air accelerates elastomer degradation. Viton is a paid option and should be requested explicitly at the inquiry stage — retrofitting seals in the field voids the factory test certification.

Worked Example