What are the causes of overheating in the hydraulic system of a concrete pump? How to rule it out?

1. Introduction

Concrete pumps are construction equipment that convey concrete through pipelines by pressure. The hydraulic system of concrete pumps is generally a high-pressure and high-flow system. From the investigation of the use of concrete pumps, it was found that for many types of concrete pumps, the temperature of the hydraulic system can reach 60 ° C after about 40 minutes of use, and the thermal equilibrium temperature of the hydraulic system can exceed 70 ° C after about 2 hours of use. However, the normal thermal equilibrium temperature of the hydraulic system of concrete pumps should be around 50 ° C. As a result, the problem of excessively high oil temperature in the hydraulic system of the concrete pump, that is, the overheating issue, emerged.

2. Hazards of heating in the hydraulic system of concrete pumps

The heating of the hydraulic system of the concrete pump directly affects the normal operation of the concrete pump. The hazards caused by the heating phenomenon mainly include the following points:

(1) When the temperature of the working fluid rises, its viscosity decreases, the leakage of the pump increases, and the actual flow rate of the pump drops.

(2) The sealing parts of the hydraulic system and components deteriorate at high temperatures, with their elastic deformation capacity reduced, which leads to a decrease in sealing performance and even seal failure, increasing leakage.

(3) When the materials of the valve core and the valve body of the hydraulic valve components are different and their coefficients of thermal expansion are not the same, the valve core may get stuck due to thermal expansion between the valve core and the valve body, causing the concrete pump to fail to operate.

When the viscosity of the working fluid decreases, the lubricating performance of the working fluid is reduced, the wear of hydraulic components accelerates, the wear failure of components is accelerated, and the service life of components is shortened.

To avoid the occurrence of the above phenomena as much as possible, some concrete pumps have to be stopped after being used for a certain period of time to cool down the system, thereby reducing the operating rate of the concrete pumps and affecting the construction progress. Therefore, corresponding measures should be taken in response to the causes of system heating to control the temperature of the hydraulic system and ensure the normal operation of the concrete pump.

3. Main causes and elimination methods of heating in the hydraulic system of concrete pumps

The heating of hydraulic systems can be classified into two major categories based on the causes of heating: one is the heating caused by design reasons; One type is overheating caused by faults in hydraulic components or improper use. Obviously, the causes of fever vary, and so do the methods of elimination.

3.1 Unreasonable design causes overheating of the hydraulic system and its elimination

Improper selection of the hydraulic oil grade may cause the hydraulic system to heat up. When the oil temperature of the selected hydraulic oil is low, the system operates normally. However, after the system has been working for a period of time, the oil temperature rises and the viscosity of the hydraulic oil decreases, resulting in an increase in internal leakage of the system. With the increase in leakage, the oil temperature rises even more, forming a vicious cycle of oil temperature. The solution is to select hydraulic oil with an appropriate viscosity based on the system's load and normal operating temperature requirements.

(2) The design of the oil tank is unreasonable, which reduces the heat dissipation effect of the hydraulic system and causes the system to overheat. The main function of the oil tank is to store hydraulic oil, but it also has the functions of heat dissipation, sedimentation of impurities and separation of water. The design of the oil tank is unreasonable, mainly manifested in two aspects: First, the volume of the oil tank is designed too small. As the concrete pump is a mobile hydraulic device, the volume of the oil tank is generally about twice the flow rate of the hydraulic pump. Therefore, both the heat dissipation area and the oil storage capacity of the oil tank are relatively small. Secondly, some oil tanks have an unreasonable structural design. The suction pipe opening and the return pipe opening are too close, and there is no partition in between. This shortens the cooling circulation of the oil in the oil tank and the path for settling impurities. In some cases, most of the return oil even directly enters the suction pipe, reducing the heat dissipation effect of the oil tank and causing the oil temperature to rise. The solution is as follows: Appropriately increase the volume of the fuel tank to (1125~115) Q, and try to increase the distance between the suction pipe opening and the return pipe opening. A partition should be set between the suction and return pipes to ensure the required heat dissipation power of the fuel tank.

(3) The heat dissipation flow is relatively small, and the installation position of the cooler is unreasonable, which reduces the heat dissipation capacity of the system. There are two cooling methods for concrete pumps: air cooling and water cooling. Users can choose according to the actual situation, but air cooling is generally more commonly used. Some concrete pumps, considering the pressure-bearing requirements of the cooler, install the cooler on the return oil line of the mixing system, only cooling the oil in the mixing system. Due to the small flow rate of the mixing system, the cooling effect of the entire system is poor, causing the system to overheat. The solution: First, an independent cooling circuit can be adopted to enhance the cooling effect. The second approach is to install the cooler on the main return oil line of the system to increase the heat dissipation flow and enhance the cooling effect. However, two issues should be noted at this time. The first one is the rotational speed of the cooling fan. The rotational speed of the cooling fan should not be too low, otherwise the cooling effect will be reduced. An electric motor can be used to drive the fan, or a low-voltage drive motor can be installed on the main return oil line. Match the motor speed with the heat dissipation flow rate, and at the same time, it can also solve the influence of the main circuit pressure shock on the pressure-bearing capacity of the cooler. The second issue is the impact of the pressure shock of the main system on the pressure-bearing capacity of the cooler if an electric motor is used to drive the fan. At this time, a low-pressure relief protection valve or a check valve can be installed in parallel with the cooler on the return oil line to provide the maximum pressure-bearing protection for the cooler.

(4) Improper selection of hydraulic components causes system overheating. The hydraulic system of a concrete pump is generally a high-pressure and high-flow system. If the specifications of the hydraulic components in the system, mainly the directional control valve, relief valve and sequence valve, are not reasonably selected and cannot meet the high-flow requirements, during use, the flow rate of the liquid at the valve port will be too high, resulting in significant pressure loss and an increase in oil temperature. Therefore, When selecting and designing hydraulic components in the design of a hydraulic system, it is essential to choose the components based on the maximum working pressure they can withstand, the maximum flow rate they can pass through, and the required pressure and flow rate adjustment range. This is to minimize the pressure loss at the valve port and thereby reduce system heating caused by unreasonable selection of hydraulic component specifications.

(5) Unreasonable design and installation of pipelines result in large pressure loss, converting pressure energy into heat energy. In the design of hydraulic systems, the design and installation of pipelines cannot be ignored. The pipe diameters of each pipeline should be strictly designed according to its working pressure and flow rate to avoid being designed too small, which may cause excessive flow rate and excessive pressure loss along the way, leading to heating. At the same time, attention should also be paid to the installation of pipelines. It is necessary to ensure a neat appearance while avoiding pipeline accumulation and sharp turns, which may affect the natural heat dissipation of the pipelines or cause excessive local pressure loss and lead to overheating.

3.2 Overheating of the hydraulic system caused by improper use of the hydraulic system or component failure and its elimination

When the oil level of the hydraulic oil in the oil tank is lower than the minimum liquid level, the heat dissipation power of the oil tank will be reduced. During the operation of the concrete pump, the oil level height of the hydraulic oil in the oil tank should be observed at all times and kept within the normal oil level range to ensure the heat dissipation effect of the oil tank. When the oil level of the hydraulic oil in the oil tank is lower than the minimum liquid level, oil should be added to the oil tank in time.

(2) The cooling effect of the cooler decreases, causing the oil temperature to rise and the system to overheat. The reduced cooling effect of the cooler may be caused by the following reasons: If there is internal blockage or excessive dirt on the surface of the a1 cooler, it will cause the safety device of the cooler to be activated, reducing the flow rate of the cooler and thus decreasing the heat dissipation flow. Or if the cooler has poor ventilation, it will lower the heat transfer coefficient of the cooler and reduce the cooling effect. Therefore, during the use of the concrete pump, it is necessary to regularly inspect and unclog the cooler, and regularly remove the dirt on the surface of the cooler. Ensure the internal smoothness and external cleanliness of the cooler to guarantee its cooling performance

But the effect. The opening pressure of the safety valve or check valve of the b1 cooler is lower than the standard value, causing the safety protection device of the cooler to open when the cooler is not clogged, resulting in overflow diversion and reducing the heat dissipation flow of the cooler. Therefore, before using the cooler, it is necessary to correctly adjust the opening pressure of the safety protection device, and during use, the opening pressure value of the safety protection device should be regularly checked and corrected.

(3) Improper pressure adjustment of the hydraulic system causes system overheating. In the hydraulic system of concrete pumps, due to performance requirements, safety valves, relief valves, and sequence valves, etc. are often installed in the system. If the pressure of the safety valve is set too low, the safety valve will open frequently, causing overflow loss and resulting in system overheating. If the pressure is adjusted too high, it will increase the leakage inside the system and cause the system to heat up. Therefore, the safety valve and pressure value should be correctly calculated and adjusted according to the load requirements of the hydraulic system to ensure that the system operates within the specified pressure range. When the main circuit of the concrete pump pumping system is a closed system, a heat exchange circuit must be set up in the pumping system. The set pressure of the relief valve in the heat exchange circuit should be given due attention. If the set pressure is too low, the reversing impact of the pumping hydraulic cylinder will increase. If the set pressure is too high, the overflow loss will be excessive and the system temperature will rise too high. Therefore, the adjustment pressure value of the relief valve in the heat exchange circuit should be reasonably determined. Generally, the adjustment value of this relief valve is (1 to 115) MPa, and the working pressure of the oil replenishment circuit in the pumping system is 215MPa. When setting sequence valves in the hydraulic system of concrete pumps, it is essential to understand the working characteristics of the sequence valves and correctly adjust the working pressure of the sequence valves. If the adjusting pressure of the internal control sequence valve is too high, when the working pressure of the working hydraulic cylinder is lower than its adjusting pressure, there will be pressure loss at the valve port of the sequence valve, causing temperature rise and system overheating. Reasonably determining the set pressure of the internal control sequence valve can make the working pressure of the working cylinder higher than the opening pressure of the sequence valve. When the sequence valve is working, the valve port will be fully open, and there will be basically no pressure loss at the valve port. This thus avoids system heating caused by improper setting pressure of the sequence valve.

(4) Increased internal leakage can cause the oil temperature to rise and the system to heat up. The internal leakage of the hydraulic system of the concrete pump includes that of the hydraulic pump, hydraulic cylinder, hydraulic motor and hydraulic valve. During the leakage process of the pressure oil, the pressure drops and the temperature rises. If the internal leakage of the system increases, it will cause the oil temperature to rise, the system to overheat. In severe cases, it will lead to a drop in system pressure, weak pumping, reduced pumping displacement, weak stirring, and a decrease in stirring speed, etc. Therefore, it is necessary to regularly inspect these components, replace the corresponding sealing elements on a regular basis, promptly replace or repair damaged or scratched parts, and even replace the corresponding hydraulic components, so as to avoid system overheating caused by component leakage.

The heating problem of the hydraulic system of concrete pumps during operation has become one of the issues that cannot be ignored. Due to the heating of the hydraulic system, many faults of the concrete pump will occur. For concrete pump manufacturers, efforts should be made to start from the design to reduce the heat generation of the hydraulic system to the lowest level. This not only increases the operating rate of the user's concrete pump and extends its service life, but also saves energy and reduces maintenance costs. For users of concrete pumps, efforts should be made to start from usage and maintenance. They should strictly follow the requirements of the manufacturer to correctly use, debug, inspect and maintain the concrete pump, so as to reduce the failure rate and minimize system overheating caused by improper use. In conclusion, by taking certain measures to address the different causes of heat generation, the heat generated by the hydraulic system can be controlled or reduced, increasing the operating rate of the concrete pump and extending its service life.