Hydraulic Solenoid Valve Guide: How the HFD VE/B Series Delivers Reliable Two-Way Flow Control

What Is a Hydraulic Solenoid Valve?

A hydraulic solenoid valve is a solenoid-controlled directional valve that opens, closes, or redirects the flow of hydraulic fluid inside a hydraulic system. A control spool inside the valve moves to direct the flow of hydraulic fluid, and fluid enters and exits through a set of ports: a pressure port (P) where fluid enters under pressure from the pump, working ports (A and B) that connect to the actuator, and a return port (T) that routes fluid back to the reservoir.

Because these valves are electrically actuated rather than manually operated, they let equipment designers control cylinders, motors, and other actuators remotely or through automated logic, without a person physically moving a lever at the valve itself. This is what makes solenoid valves foundational components in modern hydraulic circuit design, from construction machinery to industrial processing lines.

Directional solenoid valves are typically classified by their number of ports and switching positions. A 2/2 valve — two ports, two positions — provides straightforward on/off control of flow, with the solenoid coil generating a magnetic field that repositions the valve internals, opening the required passage while blocking off others. This 2/2 configuration is the basic architecture behind two-way valves like the VE/B series discussed below.

This type of valve is also known in trade literature as a discrete, or “bang-bang,” valve — it switches between fixed positions such as extend, retract, and neutral, rather than proportionally metering flow. This distinguishes directional/on-off solenoid valves from proportional valves, which control both direction and flow rate simultaneously.

Direct-Acting vs. Pilot-Operated Solenoid Valves

Not all hydraulic solenoid valves move fluid the same way. The two main actuation methods are direct-acting and pilot-operated, and the difference matters for flow capacity, power draw, and valve size.

Direct-acting valves use the solenoid to move the spool or plunger directly. This is simple and fast, but the solenoid must supply all the force needed to shift the spool, which limits practical flow capacity — larger flows require impractically large, power-hungry coils.

Pilot-operated valves take a different approach. Instead of moving the main spool directly, the solenoid controls a small pilot valve, which uses the system’s own hydraulic pressure to shift the larger main spool. A pilot-operated solenoid valve consists of two functional sections: a pilot valve section containing the solenoid coil, armature, spring, and pilot orifice, which requires only a small electromagnetic force and therefore consumes less electrical power, and a main valve section that directly controls the main flow passage.

This staged design produces several practical advantages that are well documented across hydraulic and fluid-control literature:

The trade-off is that pilot-operated valves need a minimum pressure differential across the valve to function reliably. An indirect (pilot-operated) valve requires a minimum pressure difference between its ports to shift the main element, unlike direct-acting valves, which work without a pressure differential. In practice, this is rarely a limitation in mobile and industrial hydraulic systems, which typically operate well above the required threshold — but it is a design factor worth confirming against your system’s minimum operating pressure.

Introducing the VE/B Series: Two-Way Pilot-Operated Solenoid Valves

The VE/B series is HFD Hydraulic’s line of two-way, pilot-operated directional solenoid valves, purpose-built to bring the flow-capacity and power-efficiency advantages of pilot operation to general-purpose two-way flow control.

Each valve in the series is available in two functional states, shown in the hydraulic diagram below:

• Open position: fluid flows freely between the E and U ports.
• Closed position: flow is blocked, holding the circuit in a static state.

This straightforward two-way, two-position (2/2) architecture makes the VE/B series suited to applications that need simple, reliable on/off flow control rather than complex multi-port switching.

VE/B Technical Reference

With five flow variants spanning 20 to 160 L/min, the VE/B series covers a considerably broader flow range than HFD’s VE/B/RO series, which tops out at 40 L/min and is designed specifically for single-acting cylinder control in equipment such as dump trucks, tippers, and liftgates. Where the VE/B/RO is a specialist valve for one type of application, the VE/B series is a general-purpose two-way solenoid valve intended to serve a wider range of OEM and industrial hydraulic circuits — anywhere a circuit needs a straightforward, pilot-operated on/off flow path at pressures up to 350 bar.

Built-In Emergency Manual Override

Across HFD’s pilot-operated solenoid valve designs, including the VE/B series, an integrated emergency manual override is a key safety feature. This override allows manual valve actuation even when electrical power is unavailable, giving operators a way to move the valve to a safe or working position during a power interruption or electrical fault, rather than leaving the actuator stranded. Manual override mechanisms of this kind are a long-established design feature in dual-solenoid and pilot-operated hydraulic valves specifically to address power-loss scenarios. Such mechanisms typically use a push pin at the valve end that can be manually pushed and held to actuate the valve if power fails.

For equipment that cannot tolerate an actuator freezing in place — lifting equipment, mobile machinery, or safety-relevant circuits — this override is a meaningful operational safeguard, not just a convenience feature.

Reading the Flow-Pressure Drop Curves

Each VE/B model is characterized by a flow-pressure drop curve, plotting pressure drop (bar) against flow rate (L/min) across the valve’s flow paths (for example, E→U, U→E). These curves are the practical tool for verifying that a given valve size will not introduce excessive pressure loss — and therefore energy loss and heat generation — at your system’s actual operating flow rate.

As a general design principle in hydraulic circuit engineering, valve sizing decisions should be checked against manufacturer flow-pressure drop data rather than rated flow alone, since pressure drop rises non-linearly as flow approaches and exceeds a valve’s rated capacity. Selecting a VE/B model whose rated flow comfortably covers your circuit’s expected flow rate — rather than one operating near the top of its curve continuously — helps minimize pressure drop, reduce heat generation, and support component longevity.

We do not have independently verified third-party data on the specific pressure-drop values shown in the VE/B curves beyond what is published in HFD’s own datasheet; the curves themselves should be treated as the authoritative reference for exact figures at each flow rate.

Where Two-Way Pilot-Operated Solenoid Valves Are Used

Two-way, pilot-operated directional solenoid valves like the VE/B series are common wherever a hydraulic circuit needs remote or automated on/off flow control rather than manual valve operation. Solenoid-actuated directional valves are used across equipment such as excavators, injection molding machines, and lift tables, automating start/stop or directional actions, and the same principle extends to a wide range of OEM and industrial hydraulic machinery: material handling equipment, industrial presses, mobile hydraulic circuits, and fluid power systems where a compact, electrically controlled valve needs to handle moderate-to-high flow without a correspondingly large and power-hungry solenoid.

This class of valve is broadly applied across industrial machinery, engineering machinery, metallurgical machinery, and marine machinery, reflecting how widely the two-way solenoid valve architecture is used once a system calls for electrically actuated, pilot-assisted flow control rather than a simple manual shutoff.

Selecting a VE/B Model: Key Considerations

Hydraulic solenoid valves remain one of the most fundamental building blocks of modern fluid power systems, converting an electrical signal into precise, remote-controlled flow direction. Pilot-operated designs like HFD’s VE/B series extend that capability to higher flow rates and pressures without oversized, power-hungry solenoids, while the built-in emergency manual override adds a layer of operational resilience that matters in real-world equipment.

With five variants spanning 20 to 160 L/min at up to 350 bar, the VE/B series is designed as a general-purpose, two-way solenoid valve option for OEMs and system integrators working across a broad range of hydraulic equipment. For applications specifically involving single-acting cylinders — such as dump trucks, tippers, and lift gates — HFD’s VE/B/RO series remains the purpose-built alternative worth comparing against.

For a deeper look at how directional solenoid valves work across 2/2, 3/2, and 4/3 configurations, see HFD’s [Complete Guide to Directional Solenoid Valves]. For the single-acting-cylinder-focused pilot-operated valve line, see [Pilot-Operated Directional Solenoid Valves: Advanced Control for High-Flow Hydraulic Systems].