A Brief Discussion on the Installation and Commissioning of Closed Hydraulic Systems for Construction Machinery

With the rapid development of infrastructure construction such as transportation and energy in our country, the demand and inventory of large and medium-sized construction machinery have been growing continuously and rapidly in recent years. Among the numerous types of construction machinery, especially imported equipment, the use of hydraulic transmission and full hydraulic drive is very common, such as tunnel boring machines, shield machines, large-tonnage girder transporters, cranes, lifting trolleys, as well as pavers, excavators, bulldozers, etc. The closed hydraulic circuit has low energy consumption, compact structure and is easy to achieve stepless speed regulation, and has been widely applied in the hydraulic systems of construction machinery. However, compared with the open circuit, the installation and commissioning of the closed circuit have higher difficulty and technical requirements. The following is a brief summary of the key points of the installation and commissioning of the closed circuit.

1. Preparations before installation

1.1 Keep system components clean: Carefully inspect the pump and motor as well as all system parts: oil tank, pipelines, valves, joints, radiators, etc., to ensure there is no damage or contamination. The chips on the processing parts of the valve blocks should be thoroughly cleaned and washed.

1.2 Cleaning of hydraulic oil: Pay attention to the contamination and humidity of the oil to prevent any dirt from entering the oil tank. When refueling, it must pass through a filter. If the interior of the fuel tank is coated with a coating, it must be compatible with the oil used.

2. Implementation of the installation process

2.1 It is strictly prohibited to apply strong force to the hydraulic system to prevent the pipeline system and components from being subjected to lateral forces and internal stresses. It is essential to pay attention to protecting the pipeline system!

2.2 It is prohibited to use hemp thread or adhesives as sealing materials, otherwise it will contaminate the system and may cause system failure.

2.3 Arrange the hoses correctly to avoid twisting, tightness, scratches and bumps.

2.4 The connection of the system must comply with the recommended standards. All system pipelines must be reliably connected and sealed without any leakage.

3 Put into operation and debugging

If the hydraulic system is installed as required, it can be put into operation for the commissioning of the hydraulic system. Before commissioning, as much clean hydraulic oil as possible should be added to the hydraulic oil tank. At the same time, oil should be injected into the pump, motor housing, main system pipelines, etc. This is mainly because the viscosity of the oil is high and the pipelines are long, and the air in the oil pump suction pipeline cannot be discharged. If in addition, the installation workers have to rapidly increase the speed of the diesel engine from the start-up speed to the maximum speed within 30 seconds during the commissioning shutdown, The early wear of the make-up oil pump is inevitable.

When the system is initially started, it is best to operate in accordance with the following procedures to protect the hydraulic components such as pumps and motors to the greatest extent

3.1 Install a pressure gauge of an appropriate range at the oil replenishment pressure measurement port to detect the oil replenishment pressure during the start-up and commissioning process.

3.2 Disconnect the input control signals of the pump (mechanical connecting rods, hydraulic control circuits, electrical control plugs, etc.) to ensure that the pump is in the neutral position.

3.3 Take necessary measures to remove the system load (lift the main unit to lift the drive wheels off the ground, disconnect the motor load, etc.).

3.4 Start the prime mover at the lowest possible speed until the oil replenishment pressure is established.

After the oil replenishment pressure is established, increase the prime mover to the rated speed and measure the oil replenishment pressure value. If the oil replenishment pressure does not meet the requirements, immediately turn off the prime mover, identify the cause and solve it. If the oil replenishment pressure is normal, turn off the prime mover, connect the control signal of the pump properly and restart the prime mover to check whether the neutral state of the pump is good.

3.6 Increase the prime mover to the rated speed, input control signals to the pump, make the system start working as slowly as possible, and check the forward and reverse working conditions of the system. (Note: In a typical system configuration, when the system is out of the neutral position and operates in both forward and reverse directions, the fuel replenishment pressure value will slightly decrease.)"

3.7 Let the system alternate between forward and reverse directions continuously and slowly for at least five minutes.

3.8 Turn off the prime mover, check the oil level in the fuel tank, and if necessary, add oil to the specified value.

3.9 If there are many bubbles in the oil, wait for them to disappear and then start the prime mover again. Let the system alternate between forward and reverse operation for several minutes. Then turn off the prime mover. If necessary, this process should be repeated many times until the bubbles completely disappear

3.10 Inspect all pipelines and joints to ensure there is no leakage or looseness, and make sure that no water or other impurities enter the fuel tank.

In conclusion, only by installing and commissioning the closed hydraulic system in accordance with the correct operation methods can the hydraulic components such as pumps and motors be fully protected, enabling them to perform their maximum functions and significantly reducing the failure frequency of the main machine.