The Simple Hydraulic Circuit Explained

The hydraulic circuit has several components that work together to create the desired hydraulic power.
hydraulic circuit

The Simple Hydraulic Circuit Explained

hydraulic circuit

When it comes to hydraulics, a simple hydraulic circuit can be used to accomplish a variety of tasks. Hydraulic systems power heavy machineries, such as construction equipment, forklifts, and agricultural equipment.

A hydraulic circuit is a system that uses fluid power to transfer energy from one place to another. The hydraulic circuit has several components that work together to create the desired hydraulic power. These components include the pump, the actuator, the control valve, the reservoir, and the hose. 

What Does a Hydraulic Circuit Do?

Hydraulic circuits are essential to power machinery and work by transmitting and controlling power from a mechanical input to a mechanical output. 

The transmission uses a liquid, typically oils, to power a machine hydrostatically. During this process, high pressures cause static forces to dominate over dynamic forces, transmitting energy primarily through static pressure at a low flow velocity.

A hydraulic circuit contains numerous hydrostatic components connected through piping, manifolds, or directly. These connections enable the transmission and control of power signals through the liquid.

What Parts Does a Simple Hydraulic Circuit Have?

The simple hydraulic system contains numerous components that allow it to work smoothly and effectively. A simple hydraulic circuit system consists of the following:


In basic terms, a hydraulic system’s reservoir, or oil tank, holds the hydraulic oil or liquid. Along with reserving hydraulic fluid to support the mechanic process, a reservoir provides the hydraulic system with the following:

  • A large surface area that transfers heat from the hydraulic fluid to the surrounding area
  • Enough volume to slow down any returning liquid from a high-entrance velocity, thereby allowing heavier contaminants to settle while entrained air escapes
  • A physical barrier, known as a baffle, separates the hydraulic oils entering the reservoir from the fluids entering the pump suction line.
  • Air space above the hydraulic fluid that accepts any air bubbling out of the fluid
  • Access to remove any used fluid or contaminants from the hydraulic system to add new liquid
  • Enough space for hot-fluid expansion, gravity drain-back if the system shuts down, and storage for large volumes of material needed during peak operational periods
  • A convenient surface to mount system components when necessary


The pump is the component that generates the hydraulic pressure in the circuit. It takes in fluid from the reservoir and uses mechanical energy to increase its pressure. There are several types of pumps used in hydraulic systems, including gear pumps, vane pumps, and piston pumps. 

The type of pump used in a hydraulic circuit depends on the specific application and the desired flow rate and pressure. A hydraulic pump is essential to pressurise hydraulic liquids and force the liquid throughout the entire system. There are three different types of hydraulic pumps to know about:

  1. Fixed displacement pumps: These hydraulic pumps have set flow rates, moving the same amount of hydraulic oil with a gear pump, rotor pump, or screw pump.
  2. Variable displacement pumps: Variable displacement pumps differ from fixed pumps because they do not have a set flow rate. This pump’s flow rate and outlet pressure can shift as the system operates.
  3. Hand/Manual hydraulic pumps: These pumps do not operate automatically and are controlled by hand and foot.


Control Valve

The control valve is the component that regulates the flow of fluid in the hydraulic circuit. It acts as a switch, allowing fluid to flow to the actuator when it is in the open position and stopping the flow of fluid when it is in the closed position. There are several types of control valves used in hydraulic circuits, including directional control valves, pressure control valves, and flow control valves.

Relief Valve

The relief valve in a hydraulic system is essential to safely operate machinery and control rising pressure in a hydraulic system line. If the pressure in a hydraulic line exceeds its limit, the relief valve opens and releases pressure to prevent the hydraulic system from failing. The relief valve is designed to connect with the pump delivery line on one port and the hydraulic reservoir on the other.

There are two types of relief valves standard in hydraulic systems:

  1. Direct-acting relief valves consisting of a poppet, spring, and adjustment knob
  2. Pilot-operated relief valves, consisting of a main poppet, main spring, pilot poppet, pilot spring, and an adjustment knob

3-Way Directional Control Valve

The 3-way directional control valve contains three pipe connections rather than two and helps make the process of stopping and starting the hydraulic system flow simple. This control valve has three ports: inlet, outlet, and exhaust.

The 3-way directional control valve supplies hydraulic fluid to an actuator and allows the fluid to return from the actuator. Additionally, the 3-way valve has a body orifice and a stop orifice where one is always open to allow two flow paths. Some variations of 3-way valves have a third position to block hydraulic flow from all ports.


The actuator is the component that performs the work in a hydraulic circuit. A hydraulic cylinder typically uses fluid power to generate linear motion. The control valve controls the actuator, which regulates fluid flow to the actuator and determines its speed and direction.

The Hose

The hose is the component that connects the various components in the hydraulic circuit. It transfers the fluid from one component to another and is typically made of a flexible material, such as rubber, to allow for movement and flexibility. Hoses are designed to withstand the hydraulic fluid’s high pressure and prevent leaks.

Single-Acting Hydraulic Cylinders

Single-acting hydraulic cylinders are used in hydraulic jacks and rams. The head end port of single-acting hydraulic cylinders moves in a single direction, where the hydraulic fluid is pumped into the cylinder barrel, causing the piston rod to extend. An exterior force is required to move the rod back into the barrel. When this force is applied, fluid drains from the machine’s barrel into its reservoir.

There are two primary types of single-acting hydraulic cylinders: those that use spring-extend mechanisms and those that use spring-return mechanisms, which are more common.


A hydraulic system’s connectors connect different conductors, such as hoses, pipes, or tubes, to safely move fluid between these components and allow the machinery to function. Without hydraulic connectors, machinery would be vulnerable to leaks and improper pressure. Connectors require regular preventive maintenance to ensure that everything is operating correctly.


Finally, hydraulic lines use a pressurised hydraulic fluid that outputs work in mechanical systems. The hydraulic line is helpful when transferring minerals or hydraulic fluid and spreads the fluid to different components in the hydraulic system, including valves and actuators. A hydraulic line is highly reinforced to ensure fluid is safely transferred throughout the system and that the line does not break down due to high pressure.

Hydraulic Cylinders, Made Simple

Individuals seeking a high-quality hydraulic cylinder to help operate their hydraulic systems can find what they are looking for from Kappa Engineering. Kappa Engineering provides numerous solutions to solve your hydraulic cylinder problems and get you a system that works.

Whether you need a low-pressure hydraulic cylinder for everyday use like our 150 Series cylinders, a cylinder that handles lots of power like our 250 Series, or a custom-built hydraulic cylinder, Kappa Engineering is the best supplier for your system. Check out our catalogue of hydraulic cylinders today and see how Kappa makes a difference in your hydraulic circuit.



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