From the elevator, you ride to work to the dump truck you see on the road, hydraulic systems power some of the largest machines out there. But how do they work?
3D printing allows hydraulic component manufacturers to reduce weight and space in their designs. One example is a hydraulic manifold that's half the size and 75 percent lighter than its predecessor.
Pumps
The pump is one of the most important pieces of powered machinery in a hydraulic system. As such, a functional understanding of pumps and how they work is essential to process plant operations today. The function of a pump is to add energy to liquids so that they can be moved either vertically or horizontally in a piping network system.
Hydraulic fluid is pressurized in the pump and then transferred to actuators (either rotary or linear) which convert the hydraulic energy into mechanical power. The fluid is then utilized in the operation of various devices and equipment in many different sectors.
Pumps come in a variety of shapes and sizes, but they all serve the same purpose – to transfer mechanical energy into hydraulic energy. A good hydraulic pump will be able to move a large amount of liquid at high speeds in an efficient manner, and will also be able to maintain that rate over long periods of time.
The temperature of the hydraulic fluid is another important factor, as it affects its viscosity and density. The higher the temperature of the fluid, the lower its viscosity and density will be. The temperature of the fluid at the inlet to the hydraulic pump should also be taken into account, as this will impact the efficiency of the pump.
There are a variety of valves that can be installed in the pump circuit to ensure optimum operation. These include a pressure relief valve, which opens and bypasses the hydraulic fluid when its pressure exceeds its set value. A pressure-reducing valve is also used to maintain reduced pressures in specified locations of the hydraulic system. Finally, a sequence valve is used to ensure that the hydraulic fluid has reached its target pressure in one branch of the circuit before the next section is activated.
Valves
Valves work to open and close passageways in the hydraulic system so that pressurized oil can reach actuators and be converted into mechanical power. Without these valves, the hydraulic system would not have the means to direct the flow of fluid or change its direction. Valves also play a critical role in maintaining the pressure of the hydraulic fluid and keeping contaminants from entering the system.
First on the list of main hydraulic valve types are flow control valves, which are used to regulate the speed of actuators. They accomplish this by changing the amount of energy transferred to the actuators based on the flow rate. The amount of energy transferred equals the actuator force multiplied by the distance it travels or stroke. Actuator speed is a function of the flow rate, which in turn depends on the size of the valve’s orifice (the opening through which the hydraulic fluid passes).
Check valves, which are another essential components of the hydraulic system, are designed to prevent the backflow of fluid. They are normally closed and only open when the system’s pressure rises above a preset limit. This is an important safety feature that helps prevent the system from overflowing and causing potential damage to components or equipment.
Other hydraulic system valves that are sometimes included in a hydraulic system include a sequence valve, which ensures that a specific pressure level is achieved in one branch of the circuit before the other is activated; and a fixed orifice valve, which restricts the amount of fluid or oil that can pass for a given pressure. These valves are available in a variety of sizes, styles, and mounting options depending on the application.
Cylinders
The cylinders in hydraulic systems are the "muscles" of the system, converting hydraulic pressure and oil flow into linear (translatory) mechanical force. This is used for lifting, lowering, and moving or locking heavy loads.
Cylinders are available in a range of different designs to suit your application and load requirements. They can be manufactured from steel, aluminum, or a combination of both. The design and material of a cylinder is critical to the operation and performance of the system as it is designed to withstand large amounts of internal pressure. Cylinders can be single or double acting and are usually coated with hard chrome plating to reduce wear and corrosion. They are also typically painted to a standard that is acceptable for the environment in which they will be used and maintained.
There are a variety of cylinder seal options, from basic seals to specialist ones that incorporate backup rings and extremely tight closures. The rod seal is a very important component as it is the part that sees the highest number of pressure spikes and variations, so it is commonly made from materials such as Zurcon or PTFE to ensure its performance under these conditions.
Control/Monitor Computer
In addition to reducing downtime by quickly and easily identifying potential issues, condition monitoring helps improve preventative maintenance scheduling. Often times this will result in significant savings in repair costs and unscheduled downtime. Having test points pre-installed along hydraulic lines allows for instant pressure testing and system diagnostics which can help to identify the root cause of an expected or actual failure and avoid having it happen again in the future.
Depending on the application and type of machine, the fluid may also contain special lubricants, dispersants, foam inhibitors, or emulsion stabilizers. These additives can provide many benefits including extending component life, improving performance, and enhancing the safety of the equipment.
The current research on these devices includes the following topics:
1. Obtaining complete state information by using sensors or indirect acquisition methods on electro-hydraulic valves.
2. Developing the controllers of these electro-hydraulic valves.
3. Fault diagnosis methods for the inner faults of electro-hydraulic valves, such as sliding mode control and model-based diagnostics.
The research on these electro-hydraulic control valves is oriented to the development trends of Industry 4.0. The key to achieving closed-loop controls is to acquire the valves' states. This can be done by either directly obtaining the signals or indirectly by using external sensors. These sensors can collect a range of data, including position, pollution, and particulate sensors. These sensors can build a network for the state acquisition of the electro-hydraulic control valves, and this enables monitoring, control, and fault diagnosis.
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