I. Insufficient output flow or no oil delivery at all from fully hydraulic drilling rigs

1. High suction resistance; for example, the oil tank level is too low, the suction filter is clogged, the suction pipe is too long and has too many elbows, causing large frictional resistance losses along the suction passage and resulting in insufficient output flow;

2. Pipe joints on the suction line exposed to the atmosphere are not tightened or are poorly sealed, allowing air ingress, making it difficult to form the necessary vacuum inside the pump; atmospheric pressure cannot force oil into the pump. Before starting the pump, the oil temperature and the corresponding pump shut-off valve must be checked, and the pump must be filled with oil;

3. Insufficient concentricity during installation of the coupling between the motor and the oil pump, or damage to the coupling and elastic element;

4. Damage to the pump's centering spring, causing the plunger return stroke to be insufficient or impossible, resulting in loss of sealing performance between the cylinder block and the valve plate;

5. Dirt jamming or scoring on the mating surface between the valve plate and the cylinder block; clean and lap the mating surface between the valve plate and the cylinder block;

6. Wear or scoring/grooves between the plunger and the cylinder block;

7. For constant-pressure variable pumps, this is possible, such as jamming of the plunger controlling the swashplate, causing the swashplate angle to be too small or even zero;

8. During disassembly and reassembly, the valve plate holes are not aligned with the positioning pins installed on the pump cover, so they push against each other and prevent the valve plate and cylinder block from fitting closely, causing high- and low-pressure oil to short-circuit and preventing oil delivery;

9. Oil temperature too high, resulting in large internal leakage in the pump;

10. Large leakage losses caused by faults in other system components.

II. Pressure does not increase or does not build up at all

①. All the causes listed above for “insufficient output flow or no oil delivery at all” can also lead to pressure not increasing or not building up at all;

②. The variable angle is too small, making the output flow too low; the variable angle can be appropriately increased;

③. For pressure-compensated variable pumps, the spring controlling the variable characteristics may not be properly adjusted, or the pressure-regulating mechanism may be faulty;

④. Faults in other components of the hydraulic system;

⑤. Incorrect motor rotation direction, etc.

III. High pump noise and large pressure fluctuations

①. Air entering the pump oil line, causing high noise and large pressure fluctuations;

②. The servo piston and variable piston do not move smoothly, causing occasional or frequent pressure fluctuations;

③. For variable pumps, this may be due to too small a deflection angle of the variable mechanism, making the flow too low and relatively increasing internal leakage, so continuous oil supply cannot be maintained; flow pulsation causes pressure pulsation;

④. Looseness in the fit between the plunger ball head and the slipper.

IV. Pump overheating and excessively high oil temperature rise

①. Wear and scoring between the pump plunger and cylinder block bore, and between the valve plate and cylinder block mating surface, cause increased internal leakage, which is converted into heat energy and causes temperature rise;

②. Severe wear and scoring of moving pairs inside the pump;

③. Causes such as excessively high oil viscosity, too small oil tank volume, or excessive leakage in the oil pump or system;

④. Wear of the pump bearings or insufficient concentricity between the pump and motor coupling.

V. Serious leakage from the oil pump leakage pipe

①. Severe wear of parts such as the cylinder block and valve plate, and the plunger and cylinder block bore, leads to increased internal leakage;

②. Wear of the variable piston or servo piston causes leakage;

③. Fault in the pressure-regulating mechanism.