The principle of the same hydraulic transmission pressure of the hydraulic equipment system, the larger the area under pressure, the greater the pressure, and the smaller the area, the smaller the pressure. There is also the principle of the task of leverage.
Jack is the simplest lifting equipment with a small lifting height (less than 1m). It has two types: mechanical and hydraulic. There are two types of mechanical jacks: rack type and screw type. Because of the small lifting capacity and laborious operation, the hydraulic cylinders are only used for mechanical maintenance tasks, which is not practical in the bridge repair process. Hydraulic jacks have a compact structure, bumpy tasks and self-locking functions, so they are widely used. The disadvantages are limited lifting height and slow lifting speed.
Hydraulic jacks are divided into general and special types.
The special hydraulic jack makes the special tensioning machine apply tension to the prestressed steel bars when manufacturing the prestressed concrete members. Special hydraulic jacks are mostly double acting. Rarely used are through-heart and cone anchor.
Through-hole jacks are actually used for tensioning steel bars or steel wire bundles. They are mainly composed of tension cylinders, jacking cylinders, jacking pistons and springs. It is characterized in that there is a through-hole channel along the axis of the stretching machine, and the steel bar (or steel wire) is anchored and anchored by the tail tool after penetration.
Effect of low temperature on hydraulic oil
1. Low temperature makes the viscosity of hydraulic oil larger. If the viscosity is too high, the self-priming ability of the oil pump will decrease, the pressure loss of the hydraulic system will increase, and the power loss will increase. It is generally believed that when the viscosity is 1000mm2 / s or more, the hydraulic system cannot work normally, and when the viscosity is 2000mm2 / s or more, the hydraulic system cannot start normally.
2. The low temperature causes the water in the hydraulic oil to solidify, and the condensed water adheres to the parts of the hydraulic valve, the oil filter and other surfaces, which may cause the hydraulic valve to be stuck and the oil filter to be blocked, making the hydraulic system unable to work normally.
3. Low temperature shrinks and hardens the rubber sealing material in the hydraulic system, reducing the sealing performance and even causing the seal to fail.
4. The low temperature causes the hydraulic oil to shrink itself, especially the hydraulic oil in the closed container, which is a drop in pressure or even negative pressure.
Influence of high temperature on hydraulic oil
1. At high temperature, the viscosity of hydraulic oil becomes small, the viscosity is too low, the leakage of hydraulic system increases, the efficiency decreases, and even the hydraulic system cannot work normally.
2. The high temperature makes the oxidation of hydraulic oil worse. Some ketones, acids, gums, and asphaltenes are gradually formed in the hydraulic oil, which contaminates the hydraulic oil and shortens the service life of the hydraulic oil. When the hydraulic oil is oxidized to a certain degree, the hydraulic oil fails and cannot be used.
3. The high temperature causes chemical decomposition of the oil film formed on the metal surface of the friction part, which damages the lubricating film.
4. High temperature often causes the corrosion of steel and other metals in hydraulic oil to increase. Causes damage to the surface of the part, and simultaneously generates corrosion. Hydraulic equipment system