Many industries are largely dependent on hydraulic systems. Among them, the most prominent ones are open and closed center systems, which offer benefits that vary in nature. Let’s look at their differences and details.
- Agricultural Machinery: Machinery such as tractors, combiners, and harvesters for activities that require immediate response.
- Construction Equipment: Excavators, loaders, and cranes for functions such as boom and bucket movement and steering the stabilizer.
- Material Handling Equipment: Devices such as forklifts, pallet jacks, and conveyor systems, which facilitate tasks like lifting, sloping, etc.
- Automotive Industry: Heavy-duty trucks and specialty vehicles use center hydraulic systems for steering as well as for operations that require immediate response and continuous flow.
- Marine Applications: Steering controls, and crane handling.
Open-center and closed-center hydraulic systems give the best solution in areas where heavy-duty machine operations are needed. As you can see each has a different form of operation each meant to meet your needs
What is the Open Center Hydraulic System?
An open-center hydraulic system is a type of hydraulic system whereby the pump does not stop flowing fluids even when other parts, such as actuators, stop working.
Usually, you will find that in a neutral state, the control valve stays open. As a result, hydraulic fluid to backflow into the reservoir when it is flowing elsewhere besides the actuators.
Components of Open Center Hydraulic System
The core of the system remains to produce pressurized fluid flow continuously. You can picture it as a high-speed water pump. Hydraulic pumps convert mechanical energy from a prime mover into hydraulics (pressure) form of energy. The pressure energy is then used to drive an actuator. The pump pulls hydraulic fluid to cause flow.
Directional control valve.
The energy within this hydraulic system is managed using a directional control valve. The directional control valve achieves this by guiding the fluid and allowing it to move in the required direction. It regulates the on, off, and direction of fluid movement.
The fluid that is used in this system is stored in a reservoir which then feeds the whole system in case of losses due to leaks and evaporation. It has enough space to allow the liquid to expand. This allows the fluid to cool and air to leave the tank. The reservoir tank is either venerated or pressurized.
A filter is fitted to help in trapping any foreign material that might cause damage to the open-center hydraulic system. The filter includes a strainer and a magnetic plug to trap debris and metallic objects like steel or iron. This component help remove impurities that might affect the performance of the whole system
Hydraulic actuators convert pressure energy into mechanical force and motion. Actuator comes in two variations, linear or rotational. Linear actuator creates movement in one direction. It may also be called a cylinder, ram, reciprocating motor or linear motor.
When the system is in operation, pressure may increase over time. With the help of a pressure control valve, the system is protected by maintaining a proper range of system pressure. Moreover, as the output force and pressure are directly proportional to each other, this relief valve ensures that there is no malfunction of the actuator and that it will provide the required force.
Working Principle of Open Center Hydraulic System
The system’s operation starts with the hydraulic pump. Normally, a gear pump withdraws hydraulic fluid from the reservoir and pressurizes it.
The hydraulic fluid is pumped at a steady rate through the lines, valves, and actuators in such a way that it keeps on moving, continuously forming one complete loop. Even if the valve is in its neutral position, it permits fluid to flow back into the reservoir.
If no actuator is activated, the control valve remains idle. In this condition, the hydraulic fluid is returned to the reservoir, where it can always find a pathway for flow.
If an operator acts on a control lever, then the corresponding hydraulic actuator (such as cylinders or motors) is energized by directing hydraulic flow.
Pressurized hydraulic fluid makes the actuator move. This displacement causes mechanical force.
Consequently, your entire system can do work such as lifting, lowering, and moving components in machinery. When the actuator reaches its target location, however, it keeps circulating hydraulic fluid until system pressure is sustained.
This provides a faster response when another task demands it. When idle, the system stays on standby. The dynamic pressure is maintained in the system as long as the pump continues to feed fluid.
Advantages of Open Center Hydraulic Systems
Ease of use: The simplicity of its design makes it easy to understand, operate, and maintain. This reduces the amount of complexity within a system as well as minimizes possible points for failure.
Lower Upfront Cost: They have comparatively low installation and maintenance costs as compared to the closed system of hydraulic drives.
Continuous Flow: The system offers a nonstop flow of pressurized fluid, allowing an immediate response as quickly as a start is made when the actuators are activated.
Disadvantages of Open Center Hydraulic Systems
Reduced Efficiency: The constant operation of the pump leads to higher power consumption and reduced efficiency. Which results in expensive energy conservation costs and negative environmental impacts.
Limited Precision: The constant flow of hydraulic fluid may lead to lower accuracy and control than closed-center systems. Hence, it limits its usage in activities that require high precision or precise load control.
Heat Accumulation: Since hydraulic fluid is kept in constant motion, the system accumulates heat, which usually leads to overheating problems.
What is a Closed-center Hydraulic System?
In a closed-center hydraulic system, the actuators may receive fluid from this pump only when they are operating. Unlike in the case of an open-center system, pressure is maintained by a pump even if actuators are not used. However, the fluid flow ceases until an actuator is activated.
Components of Closed-Center Hydraulic Systems
· Pressure-Compensated Pump
This core of the system adapts its flow rate according to pressure demand from actuators. It runs smoothly, producing only what is required.
· Directional Control Valve
Like an open-center valve, it directs the fluid flow to actuators. Yet in neutral, it totally shuts off the pump flow and stops any circulation unless an actuator calls for it.
Just like in open-center systems, they turn hydraulic pressure into mechanical force that can push, pull, or even rotate.
As in the open center, it stores and cools hydraulic fluid but also takes part in pressure compensation.
· Load Sensing Lines
These link the valve and pump, delivering pressure information to the pumps about demand so that they may adapt their flow in an automated way.
· Relief Valve
Like open-center systems, it safeguards the system against crossing safe pressure limits by diverting excess flow into the reservoir.
Working Principle of Closed-Center Hydraulic Systems
The operating principle of a closed-center hydraulic system is controlled flow that meets demand through actuators.
Usually, the hydraulic pressure is generated by the variable displacement pump, which withdraws fluid from the reservoir and sends it to the control valve. Pressurized fluid from the pump goes to a control valve, which in turn sends it through actuators as necessary.
In the normal position, the valve could shut down flow or reroute fluid back to a reservoir, which would prevent a drop in system pressure.
When an operator actuates a control mechanism, the pressurized fluid is routed from the valve itself to the selected actuator, like a cylinder or motor. The actuator starts moving or generates mechanical force, and the pressurized hydraulic fluid enters it.
This action does the required work, namely lifting, lowering, or rotating components. When the actuators move, the pressure inside the system changes. The control valve regulates the flow and pressure of fluid, which ensures effective performance and increases protection for components.
Hydraulic fluid will then return to the reservoir, where it may be filtered, cooled, and reused in the system. This closed-loop circulation guarantees the optimal use of hydraulic fluid. During periods of idleness, the pump can run at a reduced flow rate to maintain adequate system pressure.
Advantages of Closed Center Hydraulic System
The closed center system is cheaper since the pump flows only in areas of utilization due to actuators will activate.
You will realize that this results in a reduction of energy use, heat generation as well as the total power cost.
A closed-loop design allows for precise control of hydraulic functions, which ensures a smooth performance overall and delivers better results with improved accuracy across various applications.
Closed center systems provide better control over pressure, flow rate, and direction of the hydraulic fluid. This permits different functions which can be used in several types of applications.
Disadvantages of Closed-Center Hydraulic Systems
Closed-center systems are more complicated and require the installation of pressure control units along with variable displacement pumps. This complexity leads to high installation costs and a higher need for maintaining and troubleshooting inconveniences.
The closed center system has more complex maintenance demands which require expert technicians to ensure its effective functioning and troubleshooting. Detecting and remedying any malfunctions or leaks within the system may be more challenging.
Comparing Open and Closed Center Hydraulic Systems
In an open-center system, the hydraulic fluid continuously circulates even when actuators are inactive. During the neutral state, the opening of the control valve is enough as it allows returning flow to the reservoir. Actuator demand governs the fluid flow in a close-center system.
The open center systems have lower efficiency than the closed ones, as they lead to unnecessary pumping that consumes more energy and produces heat constantly. The closed-center system is energy efficient because the pump only provides fluid when necessary and does not use power during heat generation.
The open-center systems offer less precise control in comparison to the closed-center systems. The constant movement of fluid leads to poorer positioning and slower reaction times. The closed-center systems allow for more precise control of hydraulic functions, which leads to smoother operation, better performance, and accuracy in different uses.
Open-center systems are simpler in design and have lower initial costs as compared to closed-center systems. The closed-center systems are more complicated because they require additional elements like pressure control devices and variable displacement pumps.