Analysis of the reasons for self-priming and high/low pressure of gear pumps

The self-priming capacity and pressure of gear pumps are influenced by various factors, with the following specific reasons:

1、 Reasons for the strength of self-priming ability

1. Structural design

Tooth side clearance and axial clearance: Excessive clearance can lead to increased internal leakage, making it difficult to form sufficient vacuum during self suction.   

Gear mesh tightness: When the gear machining accuracy is high and the mesh is tight, the sealing performance is good and the self-priming ability is stronger.   

Oil inlet design: Large diameter and short oil inlet pipelines can reduce oil suction resistance and improve self-priming performance.

2. Characteristics of the medium

Viscosity effect: If the viscosity of the medium is too low (such as light oil), it is prone to leakage, and if the viscosity is too high (such as heavy oil), it has poor fluidity, both of which will reduce the self-priming ability of the gear pump.   

Volatile: Volatile media (such as gasoline) are prone to gasification under low pressure, leading to cavitation and affecting self-priming.

3. Speed and operating conditions

Low speed: Insufficient vacuum is formed inside the pump, resulting in insufficient oil suction; However, excessive rotational speed may cause cavitation.   

Installation height: When the liquid level is too high, the oil suction resistance increases and the self-priming ability decreases (it needs to be controlled within the allowable suction height).

4. Other factors

Sealing: Failure of pump shaft seals (such as mechanical seals) can lead to air intake and damage to the vacuum.   

Exhaust capacity: If the air inside the pump chamber cannot be completely expelled, it will hinder the suction of liquid.

2、 Reasons for high or low pressure

1. Internal leakage

Wear leads to increased clearance: The wear of gear end faces, tooth tips, and pump casings will exacerbate internal leakage, making it difficult to increase pressure.   

Poor lubricity of the medium: accelerates wear and further reduces sealing performance.

2. Drive system limitations

Insufficient motor power: unable to provide sufficient torque to maintain high voltage conditions.   

Speed mismatch: Pressure is positively correlated with speed, but excessive speed may cause cavitation or wear.

3. System load

Export resistance: Valve opening, pipeline length/diameter, filter blockage, etc. can increase system resistance and affect output pressure.   

Overflow valve setting: If the pressure setting value of the system safety valve is low, the output pressure of the pump will be limited.

4. Medium and temperature

Viscosity change: At high temperatures, the viscosity of the medium decreases, internal leakage increases, and pressure decreases.   

Gas content: Mixing air into the medium will reduce pressure stability.

3、 Measures to enhance self-priming and pressure

Optimization design: adopting high-precision gears, reducing clearance, and adding self-priming valves or auxiliary vacuum devices.   

Control operating conditions: maintain reasonable speed, oil suction height, and medium temperature.   

Maintenance: Regularly replace worn parts (such as side panels and bearings) to ensure sealing.   

System matching: Select the pump model based on pressure requirements (such as the need to strengthen the structure of high-pressure gear pumps).

summarize

The self suction capacity of gear pump mainly depends on the sealing and oil suction conditions, while the pressure of gear pump is significantly affected by internal leakage and system load. In practical applications, it is necessary to comprehensively consider design, media, operating conditions, and maintenance factors to ensure stable performance.