Introduction of Hydraulic Pumps
The ones we usually see (for excavators and loaders) are gear pumps and plunger pumps.
Commonality: Both create pressure on liquids by changing volume.
Difference: The liquid volume of the gear pump is between the two gears, and the liquid volume is changed by the rotation of the gears. The volume of the plunger pump is in each plunger cylinder.
Common large and medium-sized excavators generally combine plunger pumps and gear pumps to form a hydraulic pump assembly.
Gear pump: The gear pump works by the closed movement of two meshing gears rotating. The gear pump uses gear transmission to provide power. The gear pump is a fixed-displacement pump and is mostly used for low-precision, medium and low-pressure control.
Characteristic: Simple structure, easy manufacturing, low cost, low price, small size, light weight, good self-priming performance, intensitive to oil pollution and reliable operation etc.
Shortcoming: Large flow and pressure pulsation, loud noise and unadjustable displacement.
Working principle: External gear pumps are commonly used hydraulic pumps in the hydraulic systems of loaders and some small excavators. There is a gear with the same module and number of teeth in the pump body, end cover and gear teetch form a sealed volume. The meshing of the two gear edges divides the sealed volume into two parts: the oil suction chamber and the oil pressure chamber, and they are not connected to each other during operation. Due to the meshing of the gears, the volume of the seal gradually decreases. The oil in the tooth groove is squeezed and discharged from the oil drain port. The gears rotate continuously, and the volume of the oil suction and oil discharge chambers changes when the gears mesh, so that the oil suction chamber continuously absorbs oil and the oil pressure chamber continuously presses oil.
Plunger pump: The plunger pump is powered by the reciprocating motion of the piston. The plunger pump is a variable displacement pump, mostly used for high-precision high-pressure control. The working pressure of the plunger pump is high, and its working pressure is generally 20-40MPa, and the maximum can reach 1000MPa. It also has the advantages of compact structure, high efficiency and convenient flow regulation.
The plunger pump has high pressure, stable performance, high cost, minimal pulsation, variable speed, and is commonly used in high-pressure systems and engineering machinery.
Working principle: When the engine drives the transmission shaft to rotate, the connecting rod pushes the plunger to reciprocate in the cylinder. At the same time, the side of the connecting rod drives the piston to rotate together with the cylinder. The oil distribution plate is fixed.
During operation, under the action of the plunger and the plunger spring, the plunger moves up and down repeatedly to complete the oil pumping task. When the cam protrusion turns, the plunger moves downward under the action of the plunger spring. The pump oil chamber generates a vacuum, and the oil inlet on the plunger sleeve at the upper end of the plunger opens, and the hydraulic oil in the oil channel of the oil pump enters the pump oil chamber through the oil inlet hole. The plunger moves to the bottom and oil filling ends.
When the camshaft rotates to the raised part of the cam to lift the rolling element, the plunger spring is compressed and the plunger moves upward. The hydraulic oil is under pressure, and part of it flows back to the upper body oil chamber through the oil hole. When the top surface of the plunger covers the oil inlet hole, the oil distribution chamber on the top of the plunger becomes a sealed space due to the small clearance between the plunger and the cylinder sleeve. The plunger continues to rise, and the oil pressure in the pump oil chamber increases rapidly. When the pump oil pressure is greater than the oil outlet spring, the hydraulic pump is pushed out and the high-pressure fluid enters the cylinder through the main operating valve. When the plunger supplies oil, the inclined groove on the plunger is connected with the oil return hole on the cylinder sleeve, and the low-pressure oil circuit of the pump oil chamber is connected with the middle hole and the inclined groove on the plunger head. The oil pressure drops, and the oil outlet valve closes under the action of the spring to stop supplying oil. The plunger continues to move upward, and when the raised part of the cam turns over, the plunger moves downward again under the action of the spring to start the next cycle.