What is a hydraulic pump?

The engine, hydraulic pump, and distribution valve are the three major parts of excavators that people often say. For Xiaobai who first came into contact with excavators, they must be wondering why the excavator is not powered by an engine like a car. The drive shaft drives the vehicle forward but drives the hydraulic pump to rotate through the engine, and the high-pressure hydraulic oil drives the vehicle to move through hydraulic actuators such as hydraulic motors and hydraulic cylinders? The engine provides power for the hydraulic pump, the hydraulic pump, hydraulic oil pipeline, hydraulic motor, hydraulic cylinder, etc. perform hydraulic transmission, and the distribution valve performs hydraulic control. Today we will talk about what is a hydraulic pump. Then step by step talk about hydraulic knowledge.

What is a plunger pump and what is a gear pump?

Hydraulic pumps convert mechanical energy into liquid pressure energy. We generally see gear pumps and plunger pumps (for excavators and loaders).

What they have in common: They all generate pressure on the liquid by changing the volume.

Difference: The mechanism is different, and the volume position is different. 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 a plunger pump and a gear pump to form a hydraulic pump assembly. Generally, the main pump is a plunger pump (with high output hydraulic oil pressure) for the hydraulic travel motor, hydraulic swing motor, and hydraulic cylinder. Oil; the pilot pump supplies oil to the distribution valve for the gear pump (the output hydraulic oil pressure is small).

Gear Pump

Gear pumps work by closed movement in the form of two meshing gears rotating. The gear pump is driven by gears to provide power, and the gear pump is a quantitative pump, which is mostly used for low-precision medium and low-pressure control.

Its main features are simple structure, convenient manufacture, low cost, low price, small size, lightweight, good self-priming performance, insensitivity to oil pollution and reliable operation.

Its main disadvantages are large flow and pressure pulsation, high noise, and unadjustable displacement.

It is widely used in various low-voltage systems. Gear pumps have the lowest requirements for oil. In the earliest days, they were generally used in low-pressure systems (pilot pumps) because of their low pressure. Now, gear pumps can have a pressure of about 25MPA and are often used in machinery with low-pressure requirements. The oil pulsation is large and cannot be variable. The advantage is that the self-priming performance is good.

working principle:
The external gear pump is a commonly used hydraulic pump in the hydraulic system of loaders and some small excavators. There is a gear with the same module and the same number of teeth in the pump body, and the two end faces of the gear are sealed by the pump cover. The pump body, the end cover and the tooth grooves of the gears form a sealed volume, and the meshing of the two gear edges divides the sealed volume space into two parts: an oil suction chamber and an oil pressure chamber, and they do not communicate with each other during operation. Due to the meshing of the gears, the volume of the seal is gradually reduced, and the oil in the tooth groove is squeezed and discharged from the oil discharge 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.

Piston Pump

The plunger pump is powered by the reciprocating motion of the piston. The plunger pump is a variable pump, which is mostly used for high-precision high-pressure control. The plunger pump has high working pressure. ; High efficiency and convenient flow regulation.

The plunger pump has high pressure, stable performance, high cost, minimal pulsation, and can be variable. It is commonly used in high-pressure systems and construction machinery. But his self-priming performance is the worst.

When the engine drives the transmission shaft to rotate, the connecting rod pushes the plunger to reciprocate in the cylinder block, while the side of the connecting rod drives the piston to rotate together with the cylinder block, and the oil distribution plate is fixed.

When working, under the action of the cam and the plunger spring, the plunger moves up and down repeatedly to complete the oil pumping task. When the convex part of the cam turns over, under the action of the plunger spring, the plunger moves downward, and the upper part of the plunger is the pump oil chamber to generate vacuum, and the oil inlet on the plunger sleeve at the upper end of the plunger will open. , the hydraulic oil in the upper oil passage of the oil pump enters the pump oil chamber through the oil inlet hole, the plunger moves to the bottom, and the oil inlet ends.
When the camshaft turns to the convex part of the cam to lift the rolling body, the plunger spring is compressed, the plunger moves upward, the hydraulic oil is pressurized, and part of it flows back to the upper body oil cavity through the oil hole. When the top surface of the plunger covers the oil inlet hole, the oil distribution chamber at the top of the plunger becomes a sealed space due to the small matching gap between the plunger and the cylinder liner, the plunger continues to rise, and the oil pressure in the pump oil chamber rises rapidly When the pump oil pressure is greater than the oil outlet spring, the hydraulic pump is pushed out, and the high-pressure liquid enters the oil cylinder through the main operating valve.
When the plunger is supplied with oil, it is connected with the chute on the plunger and the oil return hole on the cylinder liner. The oil valve is closed under the action of the spring to stop the oil supply. The plunger continues to go up, and when the convex part of the cam turns over, under the action of the spring, the plunger goes down again to start the next cycle.

Kawasaki K3V pump is used more on excavators. The main pump of the excavator is generally a double pump, the rated pressure is 34MPA, and the instantaneous maximum pressure can reach 39MPA. The reason why the pump oil pressure of the plunger pump is higher than that of the gear pump is that its work and volume efficiency is higher. At present, a large number of hydraulic excavators use swash plate variable displacement axial piston pumps. Usually, a double pump is used, and two plunger pumps are connected in series with a through shaft, so it is also called a through shaft pump. The through shaft pump used on the excavator can also be connected with a pinion pump as a servo pump (that is, a pilot pump), which greatly simplifies the parts of the excavator.

Here we are talking about some fur knowledge of hydraulic pumps so that everyone has some superficial understanding of the three major parts of excavators. In the later stage, we will also introduce more detailed knowledge of hydraulic components, as well as some knowledge of excavator engines and distribution valves. Please continue to pay attention.