Parker Gear Pump description: the trapped oil, leakage and radial imbalance of the external gear pump are the three major problems affecting the performance and life of the gear pump.
A, trapped oil phenomenon
1) Causes of trapped oil
In order to ensure the continuous smooth running of the gear, and to separate the oil suction port from the pressure oil port, the coincidence degree (engagement number) of the gear meshing must be greater than 1,
Before the pair of gears are disengaged, the other pair of teeth begin to engage again, thus forming a closed volume between the two teeth.
2) Adverse consequences caused by trapped oil
The high-pressure oil is forcibly extruded from all gaps that may leak, causing the shaft and the bearing to be subjected to large radial forces, while the reactive power loss is increased and the oil is heated.
A partial vacuum is formed to separate the dissolved gas in the oil, causing cavitation, causing noise and cavitation.
3) Method of eliminating trapped oil
Principle: a) → b) the closed volume is reduced to make it through the oil port; b) → c) the closed volume is increased to make it through the suction port; b) the sealing volume is the smallest, and the suction oil is separated.
Elimination method: Open and unload the groove on the front and rear end caps (or bearing seats) to eliminate trapped oil.
B, radial imbalance force
Cause: The hydraulic pressure is reduced from the pressure oil chamber to the oil suction chamber along the circumference, and decreases along the outer circle of the gear.
Consequences: The greater the working pressure, the greater the radial imbalance force. When the degree reaches a certain level, the shaft is bent, the top of the tooth comes into contact with the housing, and the bearing wear is accelerated and the bearing life is reduced.
1) Reduce the pressure port to reduce the pressure oil area;
2) increase the inner surface of the pump and the tip clearance;
3) Opening the pressure balance tank will reduce the volumetric efficiency.
There are three possible leaks in the gear pump: the flank leakage (the tooth surface of the two gears) - about 5% of the total leakage of the gear pump; the radial leakage (between the outer circle of the gear and the bore of the housing) ——About 15%~20% of the total leakage of the gear pump. End face leakage (between the gear end face and the end cap) - about 75% to 80% of the total leakage of the gear pump. In general, the higher the pump discharge pressure, the greater the amount of leakage.
Advantages and disadvantages
Advantages: simple structure, small size and quality, convenient manufacturing, low price, reliable work, strong self-priming ability, insensitive to oil pollution, easy to maintain.
Disadvantages: bearing unbalanced radial force, severe wear, large leakage, limited working pressure, large flow pulsation and noise, and displacement is not adjustable