Hydraulic pump selection, installation and commissioning

First, the choice of hydraulic pump

 

1. Hydraulic drive system use pressure and flow

 

Taking a gear pump as an example, it can be divided into high, medium and low pressures. The low pressure is ≤2.5MPa, the medium pressure is 8～16MPa, and the high pressure is 20～31MPa. At the same time, the displacement of the gear pump is determined according to the flow rate required by the system and the rotation speed of the motor. If the system uses a plunger pump, the pressure of the system should be 70% to 80% of the pump discharge pressure, which is economical and ensures that the pump has a sufficient service life. However, the hydraulic pump does not use the hydraulic diaphragm pump as much as possible. Due to the particularity of the hydraulic system, the built-in safety valve of the hydraulic diaphragm pump is easy to jump, resulting in the system not working properly.

 

 

 

2. System requirements for noise and flow pulsation

 

The external gear pump has large noise, large flow pulsation rate, low noise of the internal gear pump, and small flow pulsation rate; the noise of the vane pump, the screw pump and the plunger pump is relatively low, and the double acting vane pump is more effective than the single action. The vane pump has lower noise. In terms of flow pulsation rate, the double-acting vane pump has the lowest flow pulsation rate, the plunger pump is the second, and the single-acting vane pump and the plunger pump have a medium flow pulsation rate.

 

3. Work reliability, service life and price

 

The double-acting vane pump has a long life, while the single-acting vane pump, the plunger pump, the gear pump, and the screw pump have a short life. Compared with the price, the plunger pump is more expensive than the gear pump and the vane pump, and the screw pump is the most expensive, but the reliability of the screw pump is the most stable, followed by the plunger pump, the gear pump and the vane pump.

 

4. Pollution factor

 

Low-pressure gear pumps have low pollution sensitivity, allowing the system to select oil filters with lower filtration accuracy; on the contrary, high-pressure gear pumps have higher pollution sensitivity. Screw pumps, plunger pumps, and vane pumps are more sensitive to oil contamination, and filtration should be strengthened.

 

5. Energy saving angle

 

In order to save energy and reduce power consumption, a variable pump should be used. It is best to use a variable vane pump with proportional pressure and proportional flow control. The use of dual pumps, triple pumps, and multiple pumps is also an energy-saving solution.

 

Second, the installation of hydraulic pump

 

1. The axis of the pump maintains a certain degree of concentricity with the axis of the motor

 

For the gear pump, the installation between the rotating shaft of the pump and the output shaft of the motor adopts an elastic coupling, the different axial degrees shall not exceed 0.1 mm, and the different axial degrees of the sleeve-type coupling shall not exceed 0.05 mm; The vane pump generally requires different shaft degrees to be no more than 0.1mm, and a flexible connection should be used between the motor and the motor; also the specific requirements for the swashplate axial mounting accuracy are also proposed:

 

 

(1) The swash plate type axial pump installed on the support, the coaxiality check tolerance is 0.1 mm;

 

(2) When installing with flange, the installation accuracy requires that the mandrel radial flange concentricity check tolerance is west = 0.1 mm: flange perpendicularity check tolerance t = 0.1 mm;

 

(3) Install the pulley or gear with the bearing bracket, and then connect with the pump through the elastic coupling to ensure that the pump's drive shaft does not bear radial and axial forces. The force that can be tolerated should be strictly controlled within the allowable range. In special cases, the rotor should be subjected to precise dynamic balance experiments to avoid resonance as much as possible.

 

2. Filter installation

 

To avoid pumping out the pump, it is strictly forbidden to use precision filters. For the gear pump, the filtration accuracy should be ≤40um, and the mesh filter is commonly used at the suction port. For vane pump, plunger pump, the cleanliness of the oil should reach the national standard level 16/19, and the filter accuracy used is mostly 25~30um. The correct selection and installation of the suction port filter will significantly reduce the hydraulic failure and the service life of each component can be greatly extended.

 

3. Piping installation requirements

 

(1) The installation height of the inlet pipe shall not exceed 0.5m. The oil inlet pipe must be cleaned, and the oil pump matched with the pump inlet port should be tightly combined. If necessary, sealant can be added to prevent air from entering the hydraulic system.

 

(2) The elbow of the oil inlet pipe should not be too much. The inlet of the oil inlet pipe should be connected with a filter. The filter must not leak out of the oil level of the fuel tank. When the pump is running normally, its oil surface should be at least 100mm away from the top surface of the filter to prevent air from entering. The effective oil-passing area of ​​the filter is generally not less than 50 times the cross-sectional area of ​​the pump inlet port, and the filter It should be cleaned frequently to avoid blockage.

 

(3) The diameter of the suction pipe, the pressure pipe and the oil return pipe shall not be less than the specified value.

 

(4) The leaking return pipe of the pump should not be connected with other return pipes of the hydraulic system, and should be inserted separately below the tank level.

 

(5) In order to prevent the vibration and noise of the pump from being transmitted to the system along the pipeline, a section of hose may be installed at the suction port and the pressure outlet of the pump, but the pressure outlet hose shall be installed vertically, and the length shall not exceed 400-600 mm, the suction port The hose should have a certain strength to avoid flattening due to the vacuum inside the tube.

 

Third, the commissioning of the hydraulic pump

 

1. Rotate the coupling by hand. It should be light and evenly stressed to identify whether the pump is installed properly.

 

 

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2. Check that the direction of rotation of the pump is consistent with the direction indicated by the label on the pump body.

 

3. Check whether the hydraulic system has a rush circuit, whether it can cause full load start and stop, and even reduce the service life of the pump and overload the motor.

 

4. Check that the safety valve in the system is at the set pressure.

 

5. Before the pump is first tested, the oil should be filled in the oil drain so that there is oil in the pump to prevent the components from being damaged due to friction when the pump starts, and the safety valve is opened at the same time.

 

6. The pump should be operated for no less than 10 minutes before the work, check whether the running sound of the pump is normal and the direction of the flow is correct.