Double-acting Pneumatic-hydraulic Pressure Amplifier Based on Pneumatic Cylinder Yan Furong (School of Mechanical and Electrical Engin, Wuhan Institute of Tech., Wuhan 430073, China) Abstract: The working principle of a new kind of double-acting pneumatic-hydraulic pressure amplifier having two-step output pressure driven by the pneumatic cylinder with rodless piston is introduced. The output flux and the output pressure calculating formulae are also given out. Compared with the known single-acting pressure amplifier, the innovative pressure-amplifier is simple in structure and has much higher efficiency. It can also output adaptive two-step liquid pressure, which is similar with the hydraulic differential connection, thus it is easy to realize "move quickly in low pressure and move slow at high pressure". This system also fits a trend of green manufacturing for using green air as transmission medium and with closed oil without leak to hydralic output. Keywords: pneumatic-hydraulic;pressure amplifier;hydraulic output; pneumatic cylinder Introduction In industrial production, hydraulic transmission is a common technology, through the use of liquid as the working medium to transfer energy and control the transmission methods, the hydraulic transmission system is composed mainly by power components (pump), actuators (cylinder or hydraulic motor), control elements (all valve), and other auxiliary components. For the most part hydraulic transmission system has many advantages such as a small size, lightweight, easy handling, etc. , so it can be used more wide. However, the use of hydraulic transmission also has some shortages. For example, the weariness of many mechanical components is noisy, and the leakage and the vaporization of the oil has a miraculous impact on the environment. Compared with hydraulic transmission, pneumatic transmissions is a "quasi-green" drive technology[1-1], because it uses the compressed air as working medium, which is clean. But it also has an own serious shortcomings which are difficult to overcome, the system pressure can't be too high, it is easy to lead the size of device to become miraculous. Therefore, when in the occasion of the marvelous hydralic output required, People are often faced with two options: first, hydraulic drive is used directly, except the conventional hydraulic cylinder, due to noise, wear, leakage and other pollution, its development encounters the bottleneck; second, using the air-liquid transmission devise to amplify the air pressure, which is named as air-liquid composite transmission. Today, sustainable development is deeply rooted in concept of everybody; the latter option has increasingly highlighted advantages in theory.

                                        However, in engineering applications, the air-liquid composite transmission is still not more wide used than the hydraulic transmission. The reason is that the performance of the existing air-liquid composition transmission still can't meet the practical demand[1-2]. For hydraulic systems, it is relatively easy to achieve that in the void-trail phase it will have a large flux and low pressure liquid in order to get to work position quickly, furthermore in the working stroke stage, in accordance with the load changes it can automatically convert to provide a small flow but high pressure liquid, so that a larger output force can get by the actuator. The common single-step output air-liquid pressure amplifier in single-acting or double-acting does not have this function; though single-acting air-liquid transmission devise with two-step output pressure is able to achieve the mentioned above[1-3], the structure is more complex, and due to single-acting the efficiency is very low. Aiming to these structural deficiencies, some double-acting air-liquid pressure amplifier with two-step output was also developed, but due to the hydraulic cylinder piston and the pneumatic cylinder piston is coaxial, it is difficult to avoid the two-phase mixture of gas and liquid, the high-pressure air in the air chamber can be easily infiltrated into the liquid. It will generate many bubbles - "void hole", which are usually generated in the inner wall of cylinder and the surface of the piston rod, when the fluid pressure is high, the void hole will cause an explosion, the exploding stress will form "pitting" in the surface of piston rod or cylinder wall. Working principle this innovation seeks to provide double-acting air-liquid pressure amplifier with two-step output pressure which has a simple structure, better transmission performance and be easy to control[1-4]. To achieve this objective, one technical solution is adopted, whose working principle is shown as Fig. 1. From Fig. 1, we can see this pressure amplifier has two hydraulic cylinders with column plungers and one pneumatic cylinder with a rodless piston. Two column plungers are connected with the pellet in the rodless piston by the lever. Liquid is separated to four closed chamber by these two plungers: left small chamber, left large chamber and right small chamber, right large chamber. When the air is put into the lower chamber of the pneumatic cylinder, the lever will counterclockwise rotate around the bearing that is fixed pivot, which will pull the left plunger to move downward, and the right piston will move upward. What's more, large or small chambers will output hydralic low-pressure. Conversely, when the electromagnetic reversal valve direction exchanged that the right plunger will move downward driven by the lever, the left plunger move up and the one-way valve 14,15 will inhale liquid, and the right large and small chambers can also output low-pressure liquid through one-way valve 18,19. The low-pressure liquid converged to the implementation devise, so that the implementation components will approach the work site quickly. Once the loads encountered, system pressure will rise, this time one-way valve 16 (or 18) will automatically shut down, and sequence valve 26 (or 27) will open automatically; the liquid in large chamber will be back to tank by the corresponding sequence valve to achieve the what we call unloaded; the small chamber through a one-way

                                        valve 17(or 19) will output small flux but high pressure liquid into the implementation devise, so that the implementation components will obtain the desired large out Fig. 1 The structure diagram of the innovated pressure amplifier 1, pneumatic cylinder; 2, left hydraulic cylinder; 3, right hydraulic cylinder; 4, the rodless piston; 5, the upper chamber; 6, the lower chamber; 7, electromagnetic reversal valve; 8, left plunger; 9, right plunger; 10, left large hydraulic chamber; 11, right large hydraulic chamber; 12, left small hydraulic chamber; 13, right small hydraulic chamber; 14-21, the one-way valve; 22, bearing; 23, lever ;24, connecting rod; 25, pellet; 26-27, sequence valve. From the working principle of this pressure amplifier, it can be found out that there is continuous output whether the rodless piston moves up or down, which means it, has a significantly higher efficiency. Essentially, this device is a double-acting pressure amplifier with continuous two step output liquid supplement in pulse mode driven by pneumatic cylinders. Mechanical Calculation The output flux when high flow in low pressure is flow, which can be calculated by the following, and the output flux with high pressure low two formulas: (1) q1 ? ?d12l2 2l1 nl?v1 (2) 2 ?d 2 l2 2l1 nl?v 2 Where: —The piston diameter of the large hydraulic chamber; —The piston diameter of the small hydraulic chamber; —The distance between the center of the pellet and the bearing for the lever; —The distance between connecting rod and bearing for the lever; n—The rodless piston movement times in the unit time;

                                        ?v1 ,?v 2 — The volumetric efficiency when in low pressure high flow and in high pressure low flow respectively. The output pressure in low pressure oil supplement is p1, and the output pressure in high pressure oil supplement is p2, which are calculated as follows: (3) p1 ? D 2l1 p A?m1 d12l2 D 2l1 p A? m 2 2 d2 l2 (4) p2 ? Where:—The air pressure in pneumatic cylinder; D—The pneumatic cylinder diameter; —The mechanical efficiency when in low pressure high flow and in high pressure.low flow respectively. Through the calculation formulas, the curve of the output flux and the output pressure can be obtained. Applications With the trend of green manufacturing, modern companies have increasingly recognized the leakage and volatilization of oil liquid in the hydraulic system which will cause air and environmental pollution, and due to the hydraulic pump operating at the high speed, noise pollution cannot be ignored. If the devise is used, it can be a better solution to this problem. In particular, it can be appl in the following situations: (1) The situation where needs high-pressure liquid locally in the enterprise where has a compressed air supplement, it should be avoided to configure a hydraulic system specially when high-pressure liquid needed in the occasion, which can reduce air and environmental pollution caused by evaporation and leakage of oil, and noise pollution caused by pump operation. (2) The situation of outdoor operations for air-liquid integration pump now hydraulic equipment which are wide used in outdoor operation, such as hydraulic steel cutting machine, etc. , is generally configured a separate hydraulic pump in manual, and pneumatic tools need also to configure the appropriate air compressor. If using the innovated device, air compressor can be used as a power source, an air-liquid integrated pump can be formed which can provide compressed air, but also provide hydraulic pressure. Conclusion One kind of double-acting pressure amplifier with two-step output is given out, which includes the pneumatic cylinder and the left and right hydraulic cylinder[1-5]. There is a rodless piston inside the pneumatic cylinder, two ends of piston and the pneumatic cylinder will form two air pressure chambers respectively, which will

                                        connect with the air source by the electromagnetic reversal valve. The left and right plunger in left and right hydraulic cylinder respectful, can form four hydraulic chambers. The left and right plunger can be connected with the pellet in piston by the lever,and the hydraulic chambers can be connected with the tank and the implementation devise through the one-way valves. Through comparing with the existing technology, this innovation has the following advantages: The movement of hydraulic cylinder is driven by the reciprocating movement the pneumatic cylinder through the lever mechanism[1-6], at anytime the liquid will be output. Compared with the old devises, transmission efficiency is greatly improved,and the structure is relatively simple, and the control is changed to convenient; (1) This device is driven by the pneumatic cylinder, whose transmission media is no pollution. The liquid in hydraulic cylinder is in a closed cycle, which will reduce the leakage and volatilization of liquid so that to reduce environmental pollution; (2) This devise can output two-step pressure liquid, and the switch from high to low pressure is according to the load changes, which can better meet the transmission performance requirements in the majority work. Reference [1] Dai Xiaolan, Zhong Kangmin. A Pneumatic-hydraulic Composite Devise Driven by Pneumatic Muscles. Chinese Hydraulics and Pneumatics. 2008, (1):53-54 [2] Yu Hui,Cao Jing. Double-acting and Two-step Output Liquid Pressure Pneumatic-hydraulic Composite Transmission Device Driven by Pneumatic Muscles. Machine Tool & Hydruatics. 2006, (6):169-170 [3] Zhou Xiaojun,Cao Jing. A New Kind of Parallel Airdraulic Pressure Amplifier. Light Industry Machinery. 2003,(4):124-125 [4] Jia Yunfei, Cao Jing. Parallel Double acting Pneumatic-hydraulic Composite Transmission Device with Two-step Output Liquid Pressure. Chinese Hydraulics and Pneumatics. 2004, (6):59-60 [5] Li Feiming, Wang Jinliang, Meng Yong. Double-acting Piston Pump with Two-step Output Pressure Driven by Hand Lever. Machine Tool & Hydruatics. 2006, (2):133-134 [6] Cao Jing, Zhang Laibin. A New Kind of Parallel Airdraulic Pressure Amplifier. Machine Tool & Hydruatics. 2007, 35(5):148-149

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