Estimated reading time: 8 minute
1. Why Should The Hydraulic Cylinder be Sealed?
When the hydraulic cylinder works, one side is the high-pressure chamber (pump pressure oil) and the other is the low-pressure chamber (through the oil tank). The oil in the high-pressure chamber will leak to the low-pressure chamber. It is called internal leakage; the oil in the hydraulic cylinder may also leak to the outside, which is called external leakage. Due to the internal and external leakage of the hydraulic cylinder, the volumetric efficiency of the hydraulic cylinder is reduced, which affects the working performance of the hydraulic cylinder. In serious cases, the system pressure cannot go up or even cannot work. In addition, the external leakage will pollute the environment Therefore, to prevent leakage, corresponding sealing measures must be taken where sealing is required in the hydraulic cylinder.
1. What is the Function of The Hydraulic Cylinder Seal?
• Prevent mutual series leakage (internal leakage) between the two chambers of the hydraulic cylinder, such as the piston seal.
• Prevent hydraulic oil from leaking out of the cylinder (external leakage), such as piston rod seal and cylinder head seal.
• Prevent external dust from entering the cylinder, such as the dust seal on the piston rod.
3. What Are The Common Sealing Forms of The Hydraulic Cylinder?
• clearance seal
Sealing principle: the tiny gap between the mating surfaces of relative moving parts is used to prevent leakage. When the piston adopts gap sealing, several balance grooves (pressure equalizing grooves) are often cut on the piston, which is used to automatically align the center and reduce the friction; it increases the leakage resistance, reduces the eccentricity, improves the sealing performance, stores oil and automatically lubricates.
Characteristics and application of clearance seal: simple structure, low friction resistance, high-temperature resistance, but large leakage, which increases with time, and high processing requirements. It is mainly used for hydraulic cylinders or various valves with small size, low pressure, and high speed.
• piston ring seal
Sealing principle: the elastic metal ring installed in the piston annular groove is close to the cylinder body to realize sealing.
Features and application: it has a good sealing effect, adapts to a wide range of pressure and temperature, automatically compensates for the influence of wear and temperature change, works under high-speed conditions, has small friction, reliable operation, and long service life. However, due to the metal contact between the piston ring and its corresponding sliding surface, it can not be completely sealed, and the processing of the piston ring is complex and the processing accuracy of the inner surface of the cylinder is high. It is generally used for high-pressure and high-speed High-temperature occasions.
• sealing ring
The types of hydraulic cylinder sealing rings include O-type, Y-type, YX type, V-type and combined sealing rings, etc. at present, domestic and foreign hydraulic cylinders mostly use combined sealing rings such as lattice ring, Stefan seal, and SIMCO seal to seal all parts of the hydraulic cylinder.
1. Where Does the Hydraulic Cylinder Need to be Sealed?
The parts to be sealed in the hydraulic cylinder are mainly the piston, piston rod, and end cap.
• The piston needs to be sealed (dynamic seal) to prevent internal leakage and channeling between the two chambers (high and low-pressure chambers) of the hydraulic cylinder.
• Sealing (dynamic sealing and static sealing) is required between the piston rod and the guide sleeve and Hongyi to prevent oil leakage of the hydraulic cylinder and external dirt and air entering the cylinder.
• Sealing (static sealing) is required between the cylinder head and cylinder block to prevent oil leakage of a hydraulic cylinder.
• A few hydraulic cylinder piston rods are provided with separate oil drain ports, which also need to be sealed.
5. Why Should The Hydraulic Cylinder be Equipped With a Buffer Device? Under What Circumstances Should The Hydraulic Cylinder be Equipped With a Buffer Device?
When the mass of the moving parts is large and the moving speed is high, the inertia force and momentum are large, especially in large, high-pressure, or high-precision hydraulic equipment, when the piston moves to the end of the red Jane; the mechanical collision between the piston and the end cover will be caused due to inertia, resulting in great impact and noise, affecting the machining accuracy, and even causing destructive accidents. Therefore, the structure of the high-pressure and large flow cylinder is often damaged A buffer device is often set to increase the oil return resistance when the piston approaches the terminal, slow down the moving speed of moving parts from the surface and avoid hitting the end cover of the hydraulic cylinder. Therefore, a buffer device should be set in the hydraulic cylinder or a buffer circuit should be set in the hydraulic system.
When the movement speed of the hydraulic cylinder piston is less than 0.1m/s, the buffer device is not necessary; when it is more than 0.2m/s, the buffer device must be set.
6. What Buffer Device Can Make The Hydraulic Cylinder Slow Down And Buffer?
The working principle of the buffer device is to convert all or part of the oil in the low-pressure chamber (oil return chamber) of the cylinder barrel into heat energy through throttling, and the heat energy is brought out of the hydraulic cylinder by the oil return.
1. What is The Specific Structure of The Buffer Device?
As shown, the specific structure of the buffer device at the end of the hydraulic cylinder is shown. Piston 1 is installed on the piston rod through the buffer sleeve. When the conical buffer sleeve 2 enters the hole of the cylinder bottom 3, with its opening gradually decreasing, the liquid flow leaving the piston cavity 4 finally becomes zero. Piston chamber 4 fluid can only flow out of hole 5 and adjustable flow valve 6. The buffering effect should be set through the throttle valve. The smaller the flow cross-sectional area, the better the end buffers effect.
When setting the buffer position, the throttle valve can prevent screw 7 from loosening, and the buffer setting can be protected by locking nut 8. The use of check valve 9 helps to complete the extension action when the hydraulic cylinder is started. Therefore, when the hydraulic cylinder is extended, the fluid flows around the throttle port. The gas in the face hydraulic cylinder can be discharged through the vent valve screw 10. For the hydraulic cylinder without end buffer, only the vent valve screw can be installed. The throttle valve and check valve are made of the same components, so they can be interchanged.
1-Poisson 2-Conical buffer sleeve 3-Cylinder bottom 4-Piston chamber 5-Hole
6-Adjustable flow valve 7-Screw 8-Nut 9-Check valve 10-Bleed valve nut
- Why is The Hydraulic Cylinder Equipped With an Exhaust Device? Where is The Exhaust Set?
The highest position on both sides of the hydraulic cylinder is often the place where air accumulates, and a special exhaust device must be set. If the exhaust valve is improperly set or not set, air will still be stored in the cylinder after the pressure oil enters the hydraulic cylinder. Because the air has compressibility and hysteresis expansibility, it will cause the hydraulic cylinder and the whole hydraulic system to flutter and crawl in operation, affecting the normal operation of the hydraulic cylinder. For example, in the machining process of hydraulic guide grinder, if there is air in the feed hydraulic cylinder of the worktable, it will cause chatter and crawling during the feed of the worktable, which will not only affect the roughness and form and position tolerance level of the machined surface but also damage the grinding wheel, grinding head and other mechanisms; If this phenomenon occurs in the hydraulic cylinder of the dumping device of the steelmaking converter, it will cause the turbulent pouring of molten steel, which is very dangerous.
To avoid this phenomenon, in addition to preventing air from entering the hydraulic system, an exhaust valve must be installed on the hydraulic cylinder. Because the hydraulic cylinder is the last actuator of the hydraulic system, it will directly reflect the harm of residual air.
The position of the exhaust valve should be reasonable. The horizontal installation of the hydraulic cylinder should be located at the top of the two-cavity end of the cylinder block. The vertical installed hydraulic cylinder should be located above the end cover and should be communicated with the pressure chamber to exclude the air in the hydraulic cylinder after installation and debugging. Because air is lighter than oil, it always floats upward, so there will be no residual dead corner in the air.