4WEH16 Solenoid Operated Valve
NG16 Electro-Hydraulic Pilot

A solenoid can only generate a limited amount of force. On an NG6 or NG10 valve that force is enough to push the main spool directly against its centring springs and flow forces. As the spool grows to NG16 size, the required shifting force exceeds what a practical solenoid can deliver — so the design changes.

In the 4WEH16, the solenoid drives a small pilot valve mounted on top of the main body. That pilot valve directs hydraulic pressure to one end of the main spool, and hydraulic force — not magnetic force — does the shifting. The result is a valve that handles 300 L/min while its solenoids stay the same modest size as those on a small direct valve.

This architecture introduces one requirement that direct valves do not have: the pilot circuit needs pressure to function. Where that pilot oil comes from — the main P line (internal pilot) or a separate supply (external pilot) — and where the pilot return goes (internal or external drain) are configuration choices that must match your circuit. Section 4 covers how to choose.

This is the configuration choice that causes most commissioning problems on pilot-operated valves, and it comes down to two independent questions.

Where does pilot oil come from? Internal pilot taps the main P port — simplest plumbing, no extra line. But it only works if P-port pressure stays above the minimum pilot pressure whenever the valve must switch. External pilot uses a separate control-pressure line, which is required when the main circuit unloads to near-zero pressure during part of the cycle.

Where does pilot oil return? Internal drain returns to the main T port. This is fine when T-line back pressure is low and stable. External drain runs a dedicated return to tank, and becomes necessary when the T line carries significant or fluctuating back pressure — because back pressure acting on the pilot spool can prevent clean centring.

Practical warning: pairing a J or L spool with internal pilot supply is a classic commissioning fault. Both spools connect P to T in neutral, so the moment the valve centres, pilot pressure collapses and the valve cannot be switched again until pressure is restored some other way. If your model needs J or L, plan for external pilot.

Choose 4WEH16 when:

• ›Branch flow exceeds 120 L/min — beyond what the NG10 direct valve can pass without excessive pressure drop.
• ›The existing manifold is machined to ISO 4401-07 — in a replacement job the mounting decides for you.
• ›The machine is a heavy forging press, large injection moulding clamp circuit, baling press or similar high-flow actuator system.
• ›Smoother shifting is wanted at high flow — hydraulic shifting of the main spool is inherently gentler than solenoid impact, reducing shock in large-volume circuits.