Working Characteristics Of Gear Pumps

simple and compact structure, small size, light weight, good manufacturability, low price, strong self-suction, insensitive to oil pollution, large speed range, resistance to shock loads, easy maintenance, and reliable work.

unbalanced radial force, large flow arteries, high noise, low efficiency, poor interchangeability of parts, difficult to repair after wear, and cannot be used as a variable pump.

Reason: During the operation of the in-volute gear pump, because the enclosed volume at the intersection of the gears changes with time, part of the hydraulic oil is often sealed between the teeth. As shown in Figure 2, it is called the phenomenon of oil trapping. The in-compressible hydraulic oil will cause great vibration and noise to the external gear, which will affect the normal operation of the system.

Open unloading grooves on the front and rear cover plates or floating sleeves, and the principle of opening the unloading grooves: the distance between the two grooves is the minimum closed volume, and the closed volume is changed from large to small to communicate with the pressure oil chamber, and the closed volume It communicates with the oil suction cavity when changing from small to large

The leakage of the gear pump is relatively large. The leakage path of the external meshing gear is as follows: one is the gear head clearance, the second is the clearance test, and the third is the meshing clearance.

Among them, the end face backlash leakage is relatively large, accounting for 80%-85% of the total leakage. When the pressure increases, the former will not change, but the latter will greatly increase the deflection. This is the main reason for the leakage of external gear pumps, volumetric efficiency It is low, so it is not suitable for use as a high-pressure pump.

The end face gap compensation adopts static pressure balance measures, and a compensation part is added between the gear and the cover, such as a floating bushing and a floating side plate.

The right side is the oil pressure chamber, and the left side is the oil suction chamber. The pressure of the two chambers is unbalanced; in addition, the pressure of the oil pressure chamber decreases gradually due to the leakage of the tooth top. The two unbalanced pressures act on the radial unbalanced pressure of the gear and the shaft scale. The higher the oil pressure, the greater the force will accelerate bearing wear, reduce bearing life, bend the shaft, and increase the wear of tooth tops and shaft holes.

Use pressure balance grooves or reduce pressure oil chambers.

start

(1) Check the tightness of all pipeline flanges and joints before starting.

(2) Rotating coupling, no friction and collision sound.

(3) The pump should be filled with delivery liquid for the first start.

(4) Fully open the valves in the suction and discharge pipelines before starting, and it is strictly forbidden to start with closed valves.

(5) After verifying the rotation direction of the motor, start the motor.

Stop

(1) Turn off the motor.

(2) Close the inlet and outlet valves of the pump.

(1) Trouble phenomenon: the pump cannot discharge

Reasons for failure: a. The direction of rotation is opposite; b. The suction or discharge valve is closed; c. There is no material at the inlet or the pressure is too low; d. The viscosity is too high and the pump cannot bite the material.

Countermeasures: a. Confirm the direction of rotation; b. Confirm whether the valve is closed; c. Check the valve and pressure gauge; d. Check the viscosity of the liquid to see if the flow rate proportional to the speed appears when running at low speed. If there is flow, the inflow is insufficient

Insufficient flow

(2) Failure phenomenon: insufficient pump flow

Reasons for failure: a. The suction or discharge valve is closed; b. The inlet pressure is low; c. The outlet pipeline is blocked; d. The stuffing box leaks; e. The speed is too low.

Countermeasures: a. Confirm whether the valve is closed; b. Check whether the valve is open; c. Confirm whether the discharge volume is normal; d. Tighten; When a large amount of leakage affects production, stop the operation and disassemble for inspection; e. Check the actual speed of the pump shaft

Abnormal sound

(3) Failure phenomenon: abnormal sound

Causes of failure: a. Large eccentricity of the coupling or poor lubrication b. Motor failure; c. Abnormal reducer; d. Poor installation of shaft seal; e. Shaft deformation or wear

Countermeasures: a. Align or fill with grease; b. check the motor; c. check the bearings and gears; d. check the shaft seal; e. check the dis-assembly of the vehicle

Over-current

(4) Failure phenomenon: excessive current

Reasons for failure: a. The outlet pressure is too high; b. The melt viscosity is too large; c. The shaft package is poorly matched; d. The shaft or bearing is worn out; e. Motor failure

Countermeasures: a. Check the downstream equipment and pipelines; b. Check the viscosity; c. Check the shaft seal and adjust appropriately; d. Check after parking and check whether the hand crank is too heavy; e. Check the motor

(5) Trouble phenomenon: the pump stops suddenly

Reasons for failure: a. Power failure; b. Motor overload protection; c. Coupling damage; d. Excessive outlet pressure and interlocking reaction; e. Abnormal bite in the pump; f. Adhesion and jamming of shaft and bearing

Countermeasures: a. Check the power supply; b. Check the motor; c. Open the safety cover and turn the car for inspection; d. Check the instrument interlocking system; e. After parking, confirm the forward and reverse cranking; f. Confirm the cranking

(6) Trouble phenomenon: seal oil leakage

Causes: a. The shaft seal is not adjusted well; b. The seal ring is worn and the gap is large; c. The friction surface of the mechanical seal dynamic and static ring is damaged; d. The spring is loose

Countermeasures: a. Readjust; b. Tighten the gland bolts or replace the sealing ring appropriately; c. Replace the dynamic and static rings or re-grind; d. Replace the spring