◆ The output power of the hydraulic pump
Hydraulic pump is the power source of the hydraulic system, and its output power directly affects the pressure of the hydraulic machine. The output power of the hydraulic pump is related to its displacement and speed. Displacement is the volume of liquid discharged by the hydraulic pump per turn of the week, the speed of the hydraulic pump is the number of rotations per minute. According to the formula (where is the power, is the pressure, is the flow rate), in the flow rate (and the displacement and speed of rotation) a certain situation, the greater the power, the greater the pressure that can be produced.
The type of hydraulic pump also affects pressure. Common types of hydraulic pumps are gear pumps, vane pumps and piston pumps. Piston pumps are capable of higher pressures, typically reaching tens or even hundreds of megapascals, due to the fact that the principle of operation of a piston pump allows it to seal and deliver hydraulic fluid more efficiently at high pressures, whereas gear pumps have relatively low pressures, usually between a few megapascals and a dozen megapascals.
◆ Size of the hydraulic cylinder
The effective area of a hydraulic cylinder has a significant effect on the pressure of a hydraulic press. According to Pascal's law (where is the pressure, is the force, is the area of action), the smaller the effective area of the piston of the hydraulic cylinder, the greater the pressure, given a constant force.
The strength of a hydraulic cylinder's block and piston also limits the maximum pressure of a hydraulic press. If the pressure is too high, the cylinder may rupture or the piston may be damaged. Therefore, when designing a hydraulic press, it is necessary to select the right strength of hydraulic cylinder material and construction based on the expected maximum pressure.
◆ Nature of hydraulic fluid
The viscosity of the hydraulic fluid affects pressure transfer. Higher viscosity hydraulic fluids create greater resistance to flow through pipes and hydraulic components, which can affect the pressure build-up in a hydraulic press. At low temperatures, the viscosity of the hydraulic fluid may increase, resulting in increased pressure loss in the hydraulic system and lower pressure actually applied to the working parts. Conversely, in the proper viscosity range, hydraulic fluids are able to transmit pressure more efficiently.
The compressibility of the hydraulic fluid is also critical. Although hydraulic fluid is often thought of as incompressible, it actually has some compressibility. When the pressure is high, the compressibility of the hydraulic fluid can have an effect on the pressure of the hydraulic press. If the hydraulic fluid is more compressible, the volume of the hydraulic fluid will change more under pressure, which will lead to delays and losses in pressure transfer, thus reducing the effective pressure of the hydraulic press.
◆ Load and resistance of the system
The amount of external load a hydraulic press is subjected to directly determines the required pressure. For example, when a hydraulic press is used to press sheet metal, factors such as the hardness and thickness of the sheet metal determine the amount of resistance that needs to be overcome during the pressing process. If thicker, harder metal sheets are to be pressed, higher pressures are required to provide enough force to overcome this resistance.
Resistance within the hydraulic system also affects pressure. This includes resistance along the pipe (created by the flow of hydraulic fluid through the pipe) and localised resistance (e.g. at valves, elbows). These resistances consume the energy generated by the hydraulic pump, making the actual pressure acting on the working parts lower. Therefore, optimising the piping layout of the hydraulic system and selecting appropriate valves and other components can reduce system resistance and increase the effective pressure of the hydraulic press.
