What is the Oil Trapping Phenomenon?
3 Answers
During normal operation of a hydraulic pump, the varying sealed volume should be connected to the corresponding oil suction and discharge chambers of the oil distribution device. The "occluded volume" formed due to the pump's structure (not connected to the suction or discharge chambers) is called the oil trapping phenomenon. The related introduction is as follows: Consequences of Oil Trapping: "Oil trapping" causes the liquid to be compressed, leading to increased pressure or the creation of a partial vacuum resulting in cavitation. The consequences include increased power loss, elevated oil temperature, noise and vibration, affecting the smooth operation and lifespan of the pump. Working Process of a Hydraulic Pump: The oil trapping phenomenon and the working process of a positive displacement hydraulic pump are generally divided into three stages: first, the volume of the suction chamber increases to create a vacuum and draw in the liquid (suction stage), then it goes through an intermediate stage (transition stage where neither suction nor discharge occurs), and finally, the volume of the discharge chamber decreases to expel the liquid into the system (discharge stage).
After driving for so many years, I've heard about the phenomenon of oil trapping many times. Simply put, in a gear pump, when two pairs of gears mesh together, they form a small enclosed space, just like a dead end. As the gears rotate, this small space first shrinks, compressing the oil inside forcefully—like popping a balloon—causing a sudden surge in pressure. Then, this small space suddenly expands again, creating a vacuum inside, and the air in the oil escapes, forming bubbles. These bubbles move into the high-pressure zone and suddenly burst, producing a sharp noise and generating shockwaves. Over time, this can even crack the pump body. It's like slamming on the brakes and then suddenly releasing them—the whole car jerks and rattles, causing significant damage to the components.
The phenomenon of oil trapping is quite troublesome in hydraulic systems. Simply put, when the gear pump rotates, it creates enclosed cavities whose volume alternately decreases and increases. When the volume decreases, the oil is violently compressed, causing an instant pressure surge and a rise in oil temperature. When the volume increases, a vacuum zone forms, drawing air out of the oil and creating bubbles. The collapse of these bubbles generates strong impact forces, leading to noise and system vibrations. The result is a shortened pump lifespan and excessive heat generation. To address this, engineers add relief grooves to the gear pump housing, allowing oil to flow during volume changes in the enclosed cavities and preventing pressure fluctuations.
