Hydraulic Directional Control Valves: Selection & Application Guide

Hydraulic directional control valves control the direction, starting, stopping and routing of hydraulic oil in a hydraulic system. Selecting the correct valve is critical to proper hydraulic system operation, efficiency, heat control and actuator performance.

Foster Hydraulics designs and builds custom hydraulic power units using manual and solenoid-operated directional control valves, monoblock valves, sectional valve banks, manifold-mounted valves, flow controls and pressure controls.

The correct hydraulic valve depends on several factors, including:

Hydraulic pump type
System flow in GPM
Maximum operating pressure in PSI
Cylinder or hydraulic motor operation
Required spool configuration
Number of hydraulic functions
Manual or electrical operation
Simultaneous-function requirements
Power-beyond requirements
Load-sensing requirements

How Do You Choose a Hydraulic Directional Control Valve?

Start with the hydraulic pump type.

A fixed-displacement gear pump generally requires an open-center hydraulic circuit that provides a low-pressure path back to the reservoir when no function is being operated.

A pressure-compensated variable-displacement pump is generally paired with a closed-center hydraulic valve system. When all directional valves are in neutral, flow is blocked. System pressure rises to the pump’s compensator setting and the pump reduces its displacement, or destrokes, to provide only the flow necessary to maintain standby pressure and make up system leakage.

After determining the pump type, the valve must be selected for the required GPM, PSI, actuator type, spool configuration and number of functions.

Open-Center vs. Closed-Center Hydraulic Valves

One of the most important decisions in hydraulic circuit design is selecting the correct center condition for the pump and application.

Valve/System Type	Neutral Condition	Common Pump Type	Typical Application
Open Center	Pump flow has a path to tank	Fixed-displacement gear pump	Mobile and basic hydraulic systems
Tandem Center	P connects to T; A and B are blocked	Fixed-displacement pump	Cylinder circuits where the actuator must remain stationary
Closed Center	P, A, B and T are typically blocked	Pressure-compensated variable-displacement pump	Industrial and higher-efficiency systems
Float Center	Work ports connect to tank; exact P condition depends on spool	Application dependent	Cylinders requiring a float/coast condition

Open-Center Hydraulic Systems

In an open-center hydraulic system, pump flow is provided with a path back to the reservoir when the directional control valve is in neutral.

Open-center circuits are commonly used with fixed-displacement gear pumps because a fixed-displacement pump continues producing flow whenever it is turning.

If this flow were completely blocked without another means of unloading the pump, pressure would rapidly increase until the system relief valve opened.

Open-center systems are popular because they are:

Simple
Reliable
Economical
Easy to troubleshoot
Well suited for many mobile and industrial hydraulic applications

Closed-Center Hydraulic Systems

A closed-center directional valve blocks pump flow in neutral.

Closed-center valves are commonly used with pressure-compensated variable-displacement piston pumps.

When the valve returns to neutral, system pressure rises toward the pump compensator setting. The pump responds by reducing displacement until it supplies only the flow required to maintain standby pressure and compensate for leakage.

When an operator shifts a valve and creates a demand for oil, pressure at the pump outlet responds to the load and the pump increases displacement as required to supply the circuit.

This makes closed-center systems particularly useful where multiple hydraulic functions or varying flow demands are involved.

What Hydraulic Valve Should Be Used With a Gear Pump?

A fixed-displacement hydraulic gear pump normally requires an open-center hydraulic circuit or another method of unloading pump flow when the actuators are not operating.

Because a gear pump produces approximately the same displacement per revolution, its flow needs somewhere to go whenever the pump is running.

In a typical open-center system:

Reservoir → Gear Pump → Directional Control Valve → Reservoir

When the valve is in neutral, oil circulates back to the reservoir at relatively low pressure.

When the valve spool is shifted, pump flow is directed to the hydraulic cylinder or motor.

A relief valve is normally included to protect the pump and hydraulic system from excessive pressure.

What Hydraulic Valve Should Be Used With a Pressure-Compensated Pump?

A closed-center directional control valve is normally used with a pressure-compensated variable-displacement hydraulic pump.

A pressure-compensated pump automatically changes its displacement according to system demand.

When all directional valves are centered:

Pump flow is blocked by the closed-center valve.
System pressure increases toward the compensator setting.
The pump reduces its displacement.
Pump flow decreases to the amount required to maintain standby pressure and compensate for leakage.

When a directional valve opens:

Oil is allowed to flow to the actuator.
System pressure responds to the load.
The pump increases displacement as required.
The pump supplies the flow demanded by the hydraulic circuit, up to its displacement and power limits.

This arrangement can reduce unnecessary flow and heat compared with continuously forcing full pump output across a relief valve.

Pressure-Compensated Flow Controls With Pressure-Compensated Pumps

A pressure-compensated flow control valve can be used to regulate actuator speed by maintaining a relatively constant controlled flow despite changes in load pressure, within the valve’s operating range.

However, a pressure-compensated flow control and a pressure-compensated pump perform different jobs.

The pump compensator primarily controls pump displacement in response to pressure.

The pressure-compensated flow control regulates flow to the selected circuit or actuator.

When these components are used together, the circuit must be designed so the pump has sufficient pressure margin to overcome the load plus the pressure drop required across the flow control and other components.

Excessive throttling can waste energy and generate heat, so the entire circuit should be evaluated rather than selecting the pump and flow control independently.

Pressure-Compensated vs. Load-Sensing Hydraulic Pumps

Pressure compensation and load sensing are related but different methods of controlling a variable-displacement hydraulic pump.

Pressure-Compensated Pump

A standard pressure-compensated pump reduces displacement as system pressure approaches the compensator setting.

It is commonly used in closed-center hydraulic systems.

Load-Sensing Pump

A load-sensing pump receives a pressure signal representing the load being operated.

The pump attempts to maintain a predetermined pressure margin above the load pressure.

For example, if a hydraulic function requires 1,500 PSI and the pump is designed to maintain a 300 PSI load-sense margin, the pump would attempt to operate at approximately 1,800 PSI, subject to its settings and system conditions.

The exact margin depends on the pump and control design.

Load-sensing systems can improve efficiency because the pump does not necessarily have to operate continuously at its maximum pressure-compensator setting.

Types of Hydraulic Directional Control Valves

Directional control valves are described by the number of ports, number of spool positions, center condition and method of actuation.

3-Way, 3-Position Hydraulic Valve

A 3-way, 3-position valve has three hydraulic ports and three spool positions.

These valves are commonly used to operate single-acting hydraulic cylinders.

The valve can provide functions such as:

Extend
Neutral/hold
Retract by gravity or external load

The exact function depends on the spool configuration.

4-Way, 3-Position Cylinder Spool Valve

A 4-way, 3-position directional valve is one of the most common valves used with double-acting hydraulic cylinders.

Typical ports are:

P — Pressure
T — Tank
A — Work port
B — Work port

The three positions typically provide:

Cylinder extend
Neutral
Cylinder retract

The center condition must be selected to match the pump and application.

Detent Hydraulic Valves

A detent mechanically holds the directional valve spool in a selected position instead of requiring the operator to continuously hold the lever.

Detents are useful where continuous operation is required.

Depending on the application, a valve may have a detent in one or both operating positions.

Hydraulic Motor Spool Valves

Hydraulic motors have different stopping requirements than hydraulic cylinders.

Certain motor spool configurations connect the motor work ports to tank in neutral, allowing the motor to coast instead of abruptly stopping when the valve returns to center.

The proper motor spool depends on the motor, load, braking requirements and circuit design.

For loads with significant rotational inertia, additional components such as cross-port relief valves, anti-cavitation checks, counterbalance valves or braking valves may also be required.

Float Spool Hydraulic Valves

A float spool allows both cylinder work ports to communicate with the reservoir in the float position.

This allows the hydraulic cylinder to move in response to an external force instead of being hydraulically held in one position.

Float circuits are commonly used for equipment such as:

Snowplows
Loader attachments
Grading equipment
Agricultural implements
Applications where a cylinder must follow the ground or external load

3-Way, 2-Position Hydraulic Valves

A 3-way, 2-position valve is commonly used for switching, selector and ON/OFF hydraulic functions.

Depending on its internal configuration, it can be used to:

Direct flow to an auxiliary circuit
Select between hydraulic functions
Control a single-acting actuator
Provide certain unloading or switching functions

The internal flow path should always be verified before applying a valve to a particular circuit.

Cylinder Spool vs. Motor Spool Hydraulic Valves

Cylinder and motor spools should not automatically be considered interchangeable.

Cylinder Spool

A cylinder spool is designed around the requirements of a hydraulic cylinder.

Depending on the center condition, the work ports may be blocked in neutral to help hold the cylinder stationary.

Motor Spool

A motor spool may allow the work ports to communicate with tank in neutral so the hydraulic motor can coast.

This can reduce abrupt stopping and help prevent pressure spikes or cavitation in certain applications.

The correct spool must be selected according to the actuator and required neutral behavior.

Monoblock vs. Sectional Hydraulic Valves

Multi-spool directional control valves are commonly available as either monoblock or sectional designs.

Monoblock Hydraulic Valves

A monoblock valve contains multiple valve spools in a single cast body.

Advantages can include:

Compact size
Simple installation
Fewer external connections
Economical construction

Monoblock valves are a good choice for many standard hydraulic applications.

Sectional Hydraulic Valves

A sectional valve bank is assembled from individual valve sections.

Each section can potentially be configured for a different hydraulic function.

Advantages include:

Greater flexibility
Multiple spool configurations
Different functions within one valve bank
Easier customization
Larger numbers of hydraulic functions

Sectional valves are often preferred for more complex equipment.

Manual vs. Solenoid-Operated Hydraulic Valves

Directional control valves can be operated in several ways.

Manual Hydraulic Valves

Manual valves typically use:

Hand levers
Mechanical linkages
Foot controls
Cable controls

They are simple, rugged and commonly used on mobile and industrial equipment.

Solenoid Hydraulic Valves

Solenoid-operated valves use an electrical signal to shift the valve spool.

Common electrical configurations include:

12 VDC
24 VDC
120 VAC

Solenoid valves are particularly useful for:

PLC-controlled equipment
Automated machinery
Remote controls
Push-button stations
Safety interlocks
Sequenced hydraulic operations

Multi-Spool Hydraulic Valve Circuits

The internal flow path of a multi-spool valve determines how multiple hydraulic functions interact.

Open-Center Series Circuits

In a series-type open-center circuit, oil flows through the valve sections before returning to the reservoir.

These systems are simple and economical but may limit the ability to operate multiple functions independently.

They are often best suited to applications where only one hydraulic function is required at a time.

Open-Center Series/Parallel Circuits

Series/parallel valve arrangements provide pump flow through the valve bank while allowing oil to be available to multiple valve sections.

When two functions are operated simultaneously, flow and pressure will not necessarily divide equally.

Without additional flow-sharing or priority controls, the actuator requiring the least pressure may receive the greatest portion of the available flow.

For machines requiring predictable simultaneous movement, the valve and pump circuit should be designed specifically for that requirement.

What Is Power Beyond on a Hydraulic Valve?

Power beyond allows pressurized oil exiting one directional valve to supply another downstream valve or hydraulic circuit.

A typical power-beyond arrangement separates:

High-pressure carryover flow
Return-to-tank flow

This distinction is important because the tank port of many valves is not designed to withstand full system pressure.

A valve must be specifically designed or configured for power-beyond operation. A tank port should not simply be used as a pressure outlet unless the valve manufacturer permits it.

How Do You Size a Hydraulic Directional Control Valve?

A hydraulic directional control valve should not be selected only by port size.

Important selection criteria include:

Pump flow (GPM) — Determine maximum flow that will pass through the valve.
Maximum operating pressure (PSI) — Valve pressure rating must meet or exceed system requirements.
Pressure drop — A valve that is too small can create excessive pressure loss and heat.
Pump type — Fixed-displacement, pressure-compensated or load-sensing.
Actuator type — Single-acting cylinder, double-acting cylinder or hydraulic motor.
Spool center condition — Open, closed, tandem, float or another specialized configuration.
Number of functions — Determine the number of required valve sections or spools.
Actuation method — Manual, mechanical, solenoid or proportional.
Simultaneous operation — Determine whether multiple functions must operate at the same time.
Power beyond — Determine whether additional downstream valves require pump flow.
Load holding — Determine whether pilot-operated checks, counterbalance valves or other load-control components are required.
Flow control — Determine whether actuator speed must remain controlled as load changes.

Valve pressure-drop data should be checked at the expected operating flow whenever possible.

Why Hydraulic Valve Selection Matters

An incorrectly selected hydraulic directional control valve can cause:

Excessive hydraulic oil temperature
Slow cylinder movement
Excessive pressure drop
Poor motor performance
Unstable actuator speed
Unwanted cylinder movement
Pump operation against the relief valve
Excessive engine or motor load
Hydraulic component damage
Reduced system efficiency

The directional valve should therefore be selected as part of the complete hydraulic circuit, not as an isolated component.

Hydraulic Valve & Circuit Design From Foster Hydraulics

Foster Hydraulics specializes in designing and manufacturing custom hydraulic power units for industrial, mobile and specialty applications.

Hydraulic systems can be designed around:

Fixed-displacement gear pumps
Pressure-compensated variable-displacement piston pumps
Load-sensing pump systems
Manual directional control valves
Solenoid-operated directional valves
Monoblock valves
Sectional valve banks
Manifold-mounted directional valves
Pressure-compensated flow controls
Relief valves
Check valves
Pilot-operated check valves
Counterbalance and load-control valves
Hydraulic motors
Single-acting cylinders
Double-acting cylinders
PLC-controlled hydraulic systems

Correctly matching the pump, directional valve, spool center, flow controls and actuator is essential for reliable hydraulic system performance.

Foster Hydraulics manufactures electric, gasoline and diesel hydraulic power units that can be customized with the hydraulic valve and control package required for the application.

Frequently Asked Questions About Hydraulic Valves

What is a hydraulic directional control valve?

A hydraulic directional control valve directs hydraulic oil to different parts of a circuit. It determines when and in which direction oil flows to a hydraulic cylinder, motor or other actuator.

What is the difference between an open-center and closed-center hydraulic valve?

An open-center system provides a path for pump flow to return to the reservoir while the valve is in neutral. A closed-center valve blocks pump flow in neutral.

Open-center systems are commonly used with fixed-displacement pumps, while closed-center systems are commonly used with pressure-compensated variable-displacement pumps.

What valve should I use with a hydraulic gear pump?

A fixed-displacement gear pump normally uses an open-center valve system or another circuit that provides an unloading path for pump flow when no function is operating.

What valve should I use with a pressure-compensated piston pump?

A pressure-compensated variable-displacement piston pump is normally used with a closed-center directional valve system.

Can an open-center valve be used with a pressure-compensated pump?

It may be physically possible in some specialized circuits, but a conventional open-center valve continuously creates a flow path to tank and therefore generally defeats the normal standby behavior of a standard pressure-compensated closed-center system. The pump and valve circuit should be designed together.

What is the difference between a cylinder spool and motor spool?

A cylinder spool is designed around cylinder operation and may block the work ports in neutral to hold the cylinder. A motor spool may connect the work ports to tank in neutral to allow the motor to coast.

Exact port connections depend on the selected spool.

What does float mean on a hydraulic valve?

Float allows both cylinder work ports to communicate with the reservoir so the cylinder can move in response to an external load.

What is a tandem-center hydraulic valve?

A common tandem-center spool connects the pump port to tank while blocking the A and B work ports in neutral. This unloads pump flow while helping hold a cylinder stationary.

Can two hydraulic valve spools operate at the same time?

Yes, but whether two actuators operate predictably at the same time depends on the pump, valve design, available flow, load pressures and flow-control arrangement.

In a basic circuit, the actuator requiring less pressure may receive more flow and move first or faster.

How many GPM should my hydraulic valve be rated for?

The valve should be selected to handle the maximum expected system flow without creating excessive pressure drop. The manufacturer’s pressure-drop-versus-flow data should be reviewed when available.

Choosing a valve solely because its advertised maximum GPM exceeds the pump flow may not provide the best system performance.

What is power beyond on a hydraulic valve?

Power beyond provides a high-pressure carryover path that allows one valve to supply pressurized oil to another downstream hydraulic valve or circuit while maintaining a separate low-pressure return-to-tank path.

What is the difference between pressure compensation and load sensing?

Pressure compensation causes a variable-displacement pump to reduce output as system pressure reaches its compensator setting.

Load sensing allows a pump control to respond to the pressure required by the active load and maintain a designed pressure margin above that load.

Can Foster Hydraulics help select a hydraulic valve?

Yes. Foster Hydraulics designs custom hydraulic power units and hydraulic circuits using gear pumps, pressure-compensated pumps, load-sensing systems, directional control valves, flow controls and other hydraulic components.

Providing the required GPM, PSI, pump type, actuator type and desired machine functions is the best starting point for selecting the proper hydraulic valve and circuit.