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Selection of hydraulic system stroke cooler
Sep 14, 2018

Selection of hydraulic system stroke cooler

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The air-cooled oil cooler (referred to as air cooler) is an aluminum alloy plate-fin heat exchanger with air as a cooling source, which is characterized in that heat exchanger fins are arranged in the oil passage and the air passage of the heat exchanger core. The same volume ratio is larger than the heat exchange area, the heat transfer efficiency is high, and the heat is exchanged by using air as a medium. Compared with the water-cooled cooler, it is not only easy to install and maintain, but also avoids mixing of oil and water caused by copper tube bursting, causing serious damage to the system. Secondly, for equipment that needs to change the working place (such as construction machinery), there is no need to consider the supply of water source, there is no disassembly and reconstruction of the water circulation system, and it is an increasingly environmentally  product. At present, there are many domestic wind cooler manufacturers, and the models are not the same. The performance parameters and installation dimensions are different which causes certain troubles for the user's selection and use. Here, combined with the experience of our factory development and production and customer use, we should talk about the problems that should be paid attention to in the selection of air coolers for your reference. When designing a product, the first consideration is to achieve its functionality. This is the most basic element of the design as same as the apply of air cooler.


According to temperature cooling requirements, its functionality is highlighted in three main areas:

First, the applicable pressure; 

Second, the applicable flow; 

Third, the heat exchange efficiency. 


When using an air cooler, these three aspects must be met at the same time, in order to basically meet your requirements. 


Let's talk about these three aspects. 

1. Applicable pressure: Generally it refers to the maximum allowable working pressure, or design pressure. The air cooler belongs to the pressure vessel. In the hydraulic system, it is only suitable for the return oil cooling of the circuit. Therefore, the air cooler should be selected according to the maximum pressure of the circuit. Why is it only used for oil cooling? Regardless of the cause of the increase in oil temperature, the pressure resistance of the heat-dissipating body (heat exchange core) is limited in terms of the air cooler itself. The pressure resistance of the plate-fin aluminum alloy heat exchanger core depends on its material. Physical properties, structure and processing technology. For example, the structure and processing technology are the same, the material is the same, the thickness of the oil passage material is different, the pressure resistance is also different, and the thicker the pressure resistance is. The design pressure of the plate-fin type aluminum alloy air cooler is generally less than 3.5Mpa, which is usually less than 2.0Mpa based on cost and practicality, and the design pressure of foreign counterparts is mostly 1.6 Mpa, which is much smaller than the maximum working pressure of the oil circuit. Obviously, excessive pressure can cause the heat exchanger core to burst and damage. The design of the air cooler products on the market is generally divided into three levels: 1, 1.0Mpa (such as AF series); 2, 2.0Mpa (such as AH series); 3, 3.5Mpa. The design pressure of 1.0 MPa is only applicable to the drain cooling of the variable vane pump. In view of the unstable pressure of the hydraulic system circuit and the high-voltage pulse that may be generated at the time of oil return, in order to ensure the service life of the air cooler, the manufacturer strongly recommends that the independent circulation cooling method be preferred. The independent cycle means that the air cooler is no longer connected to the working hydraulic system circuit, but a separate cooling circuit is set up, that is, a cooling pump is added, and the high-temperature hydraulic oil is directly sucked from the oil tank, and is directly sent through the air cooler. Return to the tank so that the return pressure is too high and the air cooler is damaged. The flow rate of the independent circulating cooling pump is usually chosen to be less than one third of the volume of the hydraulic oil. When it is necessary to connect the return pump to the oil return cooling, the designer should consider the instability of the return pressure in the hydraulic system, connect the air cooler to the return port of the overflow valve, and enter the air cooler. A back pressure valve with a pressure of 0.5 MPa is connected in parallel between the oil outlets. This is the correct method of use (see the figure below). When used for variable oil pump cooling, since the pressure is usually less than 1Mpa, as long as the flow rate is right, it can be directly connected to the variable pump drain port. The author encountered such a case: a customer will connect a model AH0608TL (applicable pressure 2.0M0pa, flow rate 50L/min) to a fast-forward-work-return work machine, and the result is in the process of mechanical debugging. The heat exchange core was found to leak oil, and the oil passage exploded. The customer originally used a water cooler, and the air cooler was changed to the user's request. Since the air cooler was directly connected to the return line, the back pressure valve was not installed, and the system returned quickly, and the oil returned. When the pulse pressure is too high, the wind cooler will be blasted.


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