Understanding 4/3-Way Float-Centre Hydraulic Valves: Working Principle, Applications, and Selection Guidelines

[Part 1 of the 4/3-Way Valve Centre Configuration Series]

Hydraulic motors driving high-inertia loads and hydraulic cylinders operating under external forces often require a valve that enables controlled movement when the valve’s actuating lever is released. The float-centre configuration of a 4/3-way (directional control) valve provides this capability by connecting both actuator ports to the tank while blocking the pressure port. This article explains how the valve works, why it is used, and when it should be selected.

Construction

The cross-sectional view and symbol of a hydraulic 4/3-way float-centre valve are shown in Figures 1(a) and 1(b). The valve has four ports and three switching positions. It can be actuated manually or electrically using solenoids. The valve snaps to the centre position using springs when no other actuating force is present.

Figure 1 | 4/3-way float-centre valve

Neutral Position

In the neutral (centre) position of the hydraulic valve, the actuator ports (A and B) are internally connected to the tank port (T), and the pressure port (P) is blocked, as shown in Figure 1. By connecting both actuator ports to the tank, hydraulic pressure cannot be trapped on either side of the actuator. Consequently, the actuator is not hydraulically locked and can respond freely to external forces.

This centre position allows a connected hydraulic motor to freewheel or a cylinder to float and move freely under external forces. With the pressure port blocked in the centre position, the pump output is available for other actuators.

Principle of Operation

The positions, connections, and functions in the left-actuated, centre, and right-actuated positions of the valve are given in Table 1.

Table 1 | A hydraulic 4/3-way float-centre valve

Left-actuated position

Centre (Neutral) position

Right-actuated position

P – Pressure port T – Tank port A & B – Working ports (Imagine the ports are fixed while valve positions change)
P -> A B -> T	A, B -> T P -> Blocked	P -> B A -> T
A connected cylinder extends	The cylinder floats	The cylinder retracts
A connected hydraulic motor rotates in one direction	The motor stops smoothly and can freewheel	The motor rotates in the opposite direction

Logic Diagram

Figure 2 highlights the concepts for the valve’s neutral position presented in the previous section.

🟥Pressure Port (P) -> Blocked

🟩Working Ports (A & B) -> Connected to Tank

🟦Engineering Result

✔No trapped pressure

✔Free movement

✔Smooth stopping

✔Floating cylinder

Figure 2 | Logic diagram illustrating the fundamental principles of float-centre position.

Why Choose a Float Centre Valve?

In tandem-centre and closed-centre 4/3-way valves, ports A and B are blocked in the neutral position. Consequently, the associated actuator lines may trap pressure when the valve is shifted to its neutral position. This results in jerky movement when a motor attempts to halt, and freewheeling the motor becomes unfeasible. Additionally, it is not possible to allow a hydraulic cylinder to float when smooth movement under external forces is required.

A float centre valve in its centre position, with ports A and B connected to the tank T, can provide a smooth stop for a hydraulic motor and allow the motor’s output shaft to spin freely with minimal resistance. This configuration also allows hydraulic cylinders to float and move freely under external forces.

Key Engineering Concepts

Let’s start by getting familiar with the key terms and conditions that relate to actuators controlled by float-center valves, before we move on to their applications.

Smooth Stop of a Hydraulic Motor: An abrupt stop of a hydraulic motor coupled to a high-inertia load can cause shock pressures that can crack pipes, ruin hoses, and wear out motor parts. Therefore, it is necessary to stop the motor smoothly. That is, a smooth stop is a controlled deceleration of the motor that prevents sudden jerks, loud noises, and damaging pressure spikes as the motor comes to a stop. It is achieved using special components such as float-centre valves or cross-port relief valves.

Freewheeling of a Hydraulic Motor: A hydraulic motor can be used to drive loads in industrial and mobile systems in the working mode or freewheeling mode. In the working mode, the associated hydraulic motor can drive heavy loads at lower speeds. For example, a hydraulic motor can move the vehicle off-road for high traction. In the freewheeling mode, the motor shaft can rotate freely with minimal resistance and power loss. Therefore, the motor’s drive shaft can spin at high speeds when subjected to external forces.

Floating of Hydraulic Cylinders: A hydraulic float-centre valve, in its centre position, can float a hydraulic cylinder. In that position, the valve blocks the pressure port P while connecting both working ports A and B directly to the tank T. In the absence of pressurized fluid in the cylinder, the piston floats, and external factors such as weight, surface irregularities, or terrain can facilitate the free movement of the piston. Therefore, attachments such as bulldozer blades or loader buckets can follow ground contours under their own weight, thereby preventing damage to the machine.

A Basic Circuit for the Control of a Hydraulic Motor by a 4/3-way Float-Centre Valve

Figure 3(b) shows the normal position of the circuit for controlling a hydraulic motor using a float-centre valve. A powerpack with a fluid-filled tank and a fixed-displacement pump (A variable-displacement pump is even better) supplies the fluid to the system.

The left-actuated position of the valve can direct pressurized fluid to one side of a hydraulic motor, enabling rotation in one direction (say, anticlockwise direction), as shown in Figure 3(a).

The right-actuated position of the valve can direct pressurized fluid to the other side of a hydraulic motor, enabling rotation in the other direction (i.e., clockwise), as shown in Figure 3(c).

When the valve is in its neutral position, the motor ports are connected to the tank, and fluid from both ports vents freely to the tank, preventing fluid from trapping pressure on either side of the motor. This helps the motor to come to a smooth stop without jerks or shocks. Further, the motor can freewheel without making any internal contact with the cam, allowing external forces to move it freely.

Figure 3 | Multiple positions of a hydraulic circuit with a hydraulic motor controlled by a 4/3-way float-centre valve

A Basic Circuit for Controlling a Hydraulic Cylinder Using a 4/3-way Float-Centre Valve

Figure 4(b) shows the normal position of the circuit for controlling a hydraulic cylinder using a float-centre valve. A powerpack with a fluid-filled tank and a pump supplies the fluid to the system.

The left-actuated position of the valve directs pressurized fluid to the piston side of a hydraulic cylinder while allowing fluid from the piston-rod side to drain, enabling the cylinder to move forward and providing the thrust for the end application, as shown in Figure 4(a).

The right-actuated position of the valve directs pressurized fluid to the piston-rod side of the cylinder while allowing fluid from the piston-rod side to drain, enabling the cylinder’s return motion, as shown in Figure 4(c).

When the valve is in its neutral position, the cylinder ports are connected to the tank. Fluid from both cylinder ports can be dumped back into the reservoir, allowing the cylinder piston to float and move in response to an external force.

Figure 4 | Multiple positions of a hydraulic circuit with a hydraulic cylinder controlled by a 4/3-way float-centre valve

Now, let us look at some end-user applications for 4/3-way float-centre valves.

Applications of 4/3-way Float-centre Valves

The float-centre configuration finds applications in hydraulic motors, cylinders, load-locking, and pilot valve controls. These methods are briefly explained below.

Motor Applications

The float center position, with the actuator ports (A and B) internally connected to the tank port (T), allows a running hydraulic motor coupled with a high-inertia load and connected to the valve to stop smoothly by quickly relieving the fluid pressure in the motor, thus preventing pressure spikes and motor jerks.

A float-centre valve can also be used to control freewheeling by connecting both motor ports directly to the tank and dropping the pressure to zero on both motor lines when the valve is in its centre position. Applications for freewheeling include trailers, graders, harvesters, mining, and hoisting. For example, the float-center valve connected to the hydraulic motor in a winch control system allows the winch drum, coupled to the motor, to freewheel so that an operator can pull the associated cable.

Limitations: A purely hydraulic approach to achieving free-spooling without a mechanical clutch introduces significant operational hazards. (1) A float-centre valve cannot hold a suspended load in the valve’s neutral position. The load will immediately pull the cable out, causing the winch to drop uncontrollably. (2) Pulling the drum cable by hand while forcing a heavy hydraulic motor to spin creates substantial mechanical drag. It requires significantly more physical effort to pull the line out than a mechanical clutch disconnect does.

Safety Precautions: To safely use a float-centre valve for free-wheeling, an external, spring-applied, hydraulically released mechanical brake should be integrated. This brake must be able to lock the drum manually or hydraulically when required to hold the load.

Cylinder Applications

A hydraulic cylinder controlled by a float-centre valve can float and move in response to external forces. The end-user applications include snow plow equipment and floating buckets on tractors and skid steers. Let us now understand these applications with floating cylinders.

Snow Plow Equipment: Hydraulic cylinders controlled by 4/3-way valves are essential components of modern snow plow equipment used to clear snow from roads, highways, parking lots, and other surfaces. A large, adjustable blade mounted on trucks can push snow aside. In this application, it is necessary to lift and lower the blade and tilt it to maintain optimal contact with the surface using hydraulic cylinders controlled by float centre valves.

Floating Buckets on Tractors and Skid Steers: A floating heavy bucket in a tractor or skid steer is directly connected to the hydraulic lift and tilt cylinders that control its movement. The valve can be used to lower the bucket attached to the lift cylinder to the ground. The float-center position allows the heavy bucket coupled to the floated hydraulic cylinder to ride smoothly over rough terrain without digging into the earth.

Engineering Note

(1) A float-centre valve should not be used where a suspended load must remain stationary unless additional load-holding devices such as pilot-operated check valves or counterbalance valves are incorporated.

(2) If an external force drives an actuator faster than the hydraulic supply can deliver, cavitation can occur.

Load-locking Applications

The float-centre configuration is a correct choice for load-locking applications where a cylinder can be hydraulically locked using pilot-operated check valves (or counterbalance valves), as shown in Figure 5. The configuration allows pilot pressure to drop and the pilot-operated check valves (counterbalance valves) to close tightly. It prevents accidental load drops, equipment drift, and catastrophic failure if a hose bursts or system pressure is lost.

Figure 5 | Hydraulic circuits with 4/3-way float-centre valves

Pilot Valve Applications

Although float-centre valves are widely used as main directional valves, they are also commonly employed as pilot control valves for larger hydraulically operated directional valves.

Figure 6 shows a directional control hydraulic valve block with a main valve controlled by a hydraulic pilot control valve. The pilot control of the main valve allows a low-power pilot signal to control a high-flow main valve effortlessly. The directional valve consists of a 4/3-way spring-centered main valve and a 4/3-way solenoid-operated float-centre pilot control valve. The centre position of the main valve can have any centre configuration. The main valve is held in the neutral position by the springs. In the normal position, the two spring chambers of the main valve are connected to the tank through the float-centre of the pilot control valve.

Figure 6 | A directional control valve block with a main valve controlled by a pilot control valve

When the pilot control valve is actuated by energizing solenoid ‘A’, the pilot control valve is brought to the left envelope position, and spring chamber ‘Z’ of the main valve is pressurized with pilot pressure. The main valve is then brought to its left envelope position, connecting port P to port A and extending the cylinder. When the solenoid is switched off, the pilot control valve returns to the centre position and the spring chamber Z is unloaded to the tank.

When solenoid ‘B’ is energized, the pilot control valve shifts to the right, pressurizing spring chamber ‘Y’ and moving the main valve to connect port P to B, thereby retracting the cylinder. Turning off the solenoid returns the valve to neutral, unloading chamber Y to the tank.

Advantages and Limitations

Advantages and limitations of float-centre valves are summarized in Table 3.

Table 3 | Advantages and disadvantages of 4/3-way float centre valve

Table 3 | Advantages and Limitations

Advantages	Limitations
✔ Smooth motor stopping ✔ Freewheel capability ✔ Floating cylinders ✔ Low shock ✔ Good for mobile hydraulics	✘ Cannot hold suspended loads stationary ✘ Load can drift ✘ Additional load-holding valves are required ✘ Vulnerable to cavitation ✘ Not suitable for every hydraulic system

When Should You Choose a Float-Centre Valve?

Use float-centre valves when:

✔ hydraulic motors require smooth stopping

✔ motors require freewheeling

✔ cylinders must float

✔ mobile equipment should follow ground contours

✔ load-locking double pilot-operated check valves are used

✔ the pump output should be available for the independent operation of other actuators

Avoid using float-centre valves when:

✘ cylinders must remain rigid

✘ suspended loads must be held using the centre position of the valve

✘ abrupt motor braking is required

✘ a fixed-displacement pump is used

Typical Machines Using Float-Centre Valves

Machines use hydraulic float-centre valves whenever cylinders or attachments must move freely following external counters without hydraulic resistance or hydraulic motors should stop smoothly and freewheel. Table 4 summarises machines and their floating components.

Table 4 | Summary of machines and their floating components

Machine	Why Float Centre?	Floating Component
Snow plough	Blade follows road	Lift cylinder
Tractor loader	Bucket follows terrain	Lift cylinder
Skid steer	Ground following	Loader arm
Winch	Controlled free-spooling	Hydraulic motor
Motor grader	Blade contouring	Lift cylinder
Trailer drive	Auxiliary traction disengagement	Wheel motor

Conclusion

The float-centre configuration of a 4/3-way valve is particularly suitable where hydraulic motors require smooth stopping or freewheeling, and where hydraulic cylinders must respond freely to external forces. However, because the valve cannot hold suspended loads in its neutral position, it should be selected only after carefully considering the application requirements and any necessary load-holding devices. Understanding the operating characteristics of each centre configuration enables engineers to select the most appropriate valve for reliable and safe hydraulic system performance.

Key Takeaways

✔ Float-centre valves connect both actuator ports to tank.

✔ Hydraulic motors stop smoothly.

✔ Hydraulic cylinders can float.

✔ Suspended loads require additional load-holding devices.

✔ Best suited for mobile hydraulic systems.

Joji Parambath

About the Author

Joji Parambath is a fluid power engineer, author, and corporate trainer with more than 25 years of experience in hydraulics, pneumatics, and industrial automation. He is the founder of Fluidsys Training Centre Pvt. Ltd., Bangalore, and the author of numerous engineering books on fluid power systems.

References

Books

1. Book on ‘Hydraulic Circuits – Identification of Components and Analysis’ by Joji Parambath

2. Book on ‘Industrial Hydraulic Systems and Circuits -Basic Level (In the SI Units)’ by Joji Parambath

3. Book on ‘Industrial Hydraulics -Basic Level (In the English Units)’ by Joji Parambath

Manufacturer Information

4. Information on ‘Freewheeling solutions’, Poclain

5. Information on ‘Freewheeling Valve PTV-FW1’, WESSEL-HYDRAULIK GmbH

6. Information sheet Freewheeling on MCR motors, RE 15225-02, Edition: 06.2014, Bosch Rexroth Limited, Scotland

7. Information on ‘Hydraulic cylinders for snow plow equipment’, SEA Hydrosystems India Private Limited, Tamil Nadu, India.

8. Information on Freewheeling Instructions, SAI, Italy http://www.saispa.com