The function and application of hydraulic valves within heavy construction equipment

If the hydraulic fluid is the muscle of an excavator or a crane, the hydraulic valves are the brain and nervous system. These oftentimes complicated looking components hold the key to precision, speed, and safety that allows an operator to skillfully manage multi-ton machinery on a bustling construction site.

Hydraulic valves are specialized control mechanisms that allows a continuous flow, pressure, and/or direction of fluid through a hydraulic circuit. Hydraulics have the ability to provide power specifically where and when it is required with the understanding of issuing raw energy of fluid to movement that has purpose.

1.The Three Functions of Hydraulic Valves 

Hydraulic valves are classified by their specific control function:

A.Directional Control Valves 

Directional control valves determine the path the fluid will take, thus directing it to the appropriate cylinder or motor to accomplish a specific movement (e.g. extend, retract, clockwise, counterclockwise).

• Function: Start, stop, reverse fluid flow.
• Application of Heavy Equipment: If an operator moves the joystick in order to extend the boom arm of an excavator, the directional valve will shift to allow the pressurized fluid to flow to the appropriate side of the cylinder piston / port, thus extending the boom arm out. If the joystick is moved in another direction,

B. Pressure Control Valves

Pressure valves restrict the maximum allowable pressure in the system to protect components from damage and ensure safe operation. They are also useful for controlling the output force or torque applied to the actuators.

• Function: To limit or regulate pressure in the system.
• Heavy Equipment Application: The Relief Valve is the most important pressure control valve type. If for example an excavator is trying to raise a load greater than what it can support, the pressure in the system will increase. The relief valve will respond by opening immediately to direct excess fluid back to the reservoir to avoid hoses bursting or pump damage.

C. Flow Control Valves 

Flow control valves control the amount of fluid flow (flow rate), which ultimately provides the amount of speed to the actuator.

• Function: To regulate fluid flow.
• Heavy Equipment Application: If an operator needs to place a load slowly and gently with a crane, she uses a flow control valve to meter oil into the cylinder at an amount that provides smooth placement instead of rapid movement.

2. Real-Life Uses in Construction

Hydraulic valves are found in every high-power function on a construction site:

Equipment                              Hydraulic Valve Application                               Function Managed

Excavator                                    Directional & Flow               Controlling boom, stick, and bucke movement.
Crane                                          Flow and pressure              Controlled and gentle lifting of heavy loads.
Bulldozer                                     Directional & Pressure        Control of blade raising, lowering, and tilting.
Forklift/Lift                                   Directional & Flow               Controlled moving of the forks/platform up/down.
Dump Truck                                Directional                           Tipping and lowering the bed of the truck.

The Application of Modern Control

Heavy equipment of today uses sophisticated proportional and servo valves. The advanced directional and flow control valves apply electronic signals from the cab controls and booster machine sensors to control the flow of fluid proportionally to the operator input. This allows for extremely fine-tune movements, greatly improving efficiency, eliminating the bucking, uncontrolled motions of older, simpler hydraulic systems. 

In summary, hydraulic valves are the unsung heroes in the construction industry, responding to delicate commands from the human operator, and translating that input into a monstrous and controlled use of power required to build our modern world.