What is a combined cylinder? Working principle and structure diagram of gas-liquid damping cylinder and gas-liquid boosting cylinder

What is a combination cylinder?


Combined cylinders generally refer to gas-liquid damping cylinders, gas-liquid boosting cylinders, etc. formed by the combination of cylinders and hydraulic cylinders.


As we all know, the working medium usually used in cylinders is compressed air, which is characterized by fast movement, but the speed is difficult to control. When the load changes greatly, it is easy to "crawl" or "self-propelled";while the working medium used in hydraulic cylinders is It is generally considered that incompressible hydraulic oil is characterized by not being as fast as the cylinder, but the speed is easy to control. When the load changes greatly, appropriate measures are taken, and generally "crawling" and "self-propelled" phenomena will not occur. The clever combination of air cylinders and hydraulic cylinders, complementing each other's strengths, has become a commonly used gas-liquid damping cylinder in pneumatic systems.


The working principle of the gas-liquid damping cylinder is shown in Figure 1. It is actually a gas cylinder and a hydraulic cylinder connected in series, and the two pistons are fixed on the same piston rod. The hydraulic cylinder does not need a pump to supply oil, as long as it is filled with oil, a hydraulic check valve, a throttle valve and an oil replenishing cup are installed between the inlet and outlet. When the right end of the cylinder is supplied with air, the cylinder overcomes the load and drives the hydraulic cylinder piston to move to the left (the left end of the cylinder is exhausted). At this time, the left end of the hydraulic cylinder drains the oil, the one-way valve is closed, and the oil can only flow into the right chamber of the hydraulic cylinder through the throttle valve and In the oil cup, if the throttle valve port is opened wide at this time, the oil will be discharged from the left chamber of the hydraulic cylinder smoothly, and the two pistons will move faster. On the contrary, if the throttle valve port is closed small, the oil will be discharged from the left chamber of the hydraulic cylinder. If blocked, the movement speed of the two pistons will slow down. In this way, by adjusting the opening size of the throttle valve, the movement speed of the piston can be controlled. It can be seen that the output force of the gas-liquid damping cylinder should be the difference between the force (thrust or pulling force) generated by the compressed air in the cylinder and the damping force of the oil in the hydraulic cylinder.





Figure 1 Gas-liquid damping cylinder


1—throttle valve;2—oil cup;3—one-way valve;4—hydraulic cylinder;5—cylinder;6—external load





There are many types of gas-liquid damping cylinders.


According to the connection form of the cylinder and the hydraulic cylinder, it can be divided into two types: series type and parallel type. The previous description is a series type, and Figure 2 shows a parallel type gas-liquid damping cylinder. The tandem cylinder block is longer;the coaxiality requirements are higher during processing and installation;sometimes gas and oil blow-by occur between the two cylinders. The parallel cylinder has a short body and a compact structure;the gas and liquid cylinders are separated, which will not cause gas and oil leakage;because the working pressure of the hydraulic cylinder can be quite high, the hydraulic cylinder can be made into a very small diameter (it does not have to be the same diameter as the cylinder) );However, because the gas and liquid cylinders are installed on different axes, additional torque will be generated, which will increase the wear of the guide rail device and may also cause "crawling" phenomena. The series type pneumatic-liquid damping cylinder also has the hydraulic cylinder in front or in the back. The hydraulic cylinder is in the back. See Figure 1. The two ends of the hydraulic cylinder piston have different areas. Oil storage or oil replenishment is required during the working process. The oil cup is relatively large. big. If the hydraulic cylinder is placed in the front (the cylinder is in the back), then there are piston rods at both ends of the hydraulic cylinder, and the effective areas of both ends are equal. There is no problem of oil storage and oil replenishment except for supplementary leakage, and the oil cup can be very small.





Figure 2 Parallel gas-liquid damping cylinder


1—Hydraulic cylinder;2—Pneumatic cylinder





According to the speed regulation characteristics, it can be divided into:


1) Slow forward and slow back;


2) Slow forward and fast reverse;


3) Fast forward, slow forward and fast reverse.


Its speed regulation characteristics and applications are shown in Table 1.


As far as the structure of the gas-liquid damping cylinder is concerned, it can be divided into many forms: the throttle valve and the one-way valve are set separately or installed on the cylinder head;the one-way valve is installed on the piston (such as the baffle type one-way valve );holes and grooves on the cylinder wall, sliding column type in the cylinder, mechanical floating connection type, stroke valve control rapid approach type, etc. The gas-liquid damping cylinder with a baffle check valve on the piston is shown in Figure 3. There is a baffle check valve on the piston. When the piston moves to the right, the baffle leaves the piston, the one-way valve opens, and the oil in the right chamber of the hydraulic cylinder flows to the left through the hole on the piston (that is, the baffle check valve hole). cavity to achieve fast rewind, and the number and size of the holes on the piston are used to control the speed during fast retraction. When the piston moves to the left, the baffle blocks the hole in the piston, the one-way valve closes, and the oil in the left chamber of the hydraulic cylinder flows to the right chamber through the throttle valve (through the pipeline outside the cylinder). Adjusting the opening of the throttle valve can adjust the slow advance speed of the piston. Its structure is relatively simple and its manufacturing and processing is convenient.


Figure 4 is a schematic diagram of a rapid approach gas-liquid damping cylinder using mechanical floating connection. There is an idle stroke s1 between the T-shaped top block at the end of the hydraulic cylinder piston rod and the hook at the end of the cylinder piston rod, which realizes the rapid approach of the idle stroke, and then drives the hydraulic cylinder piston through the throttling resistance.