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The maintenance of PDM is divided into two types: on-site maintenance and workshop maintenance. In principle, the drill should be checked each time before being sent into the well. Before repairing the PDM, it is necessary to fully understand its structure, and disassemble by following the proper sequence and requirements; the casings of the PDM (except the bypass valve and motor coupling) and the main internal connection parts are all coated with anaerobic paste. Heat them to 300 °C with a blowtorch before demolishing the shackles, and clean the threads at the same time. When disassembling the threads at the lower end of the stator, be careful to protect the rubber on the stator against thermal aging. In the process of assembly, both the external and the internal threads should be rinsed with alkyd thinner or acetone first, before fixing them with the coating of anaerobic paste to prevent tripping.

Onsite maintenance:
1. Rinse the bypass valve body on the drill with water after removing the drill bit. Move the spool up and down, and make sure there is no obstruction.
2. Rinse the PDM with water from the inside of the female screw of the spindle, and then keep it flat; if it is not used for a long time, it is recommended to inject a small amount of mineral oil into the drill to prevent corrosion, and avoid sunlight. It is strongly forbidden to inject diesel.

The content of workshop maintenance includes the following items:
1. Check the axial runout of the thrust bearing;
a) Lift the drill vertically, and measure the gap L1 between the lower end face of the bearing housing and the drive shaft
b) Erect the drill upright on the ground, to press on the thrust bearing with the drill’s own weight. Measure the gap L2 between the lower end face of the bearing housing and the drive shaft;
c) Calculate the axial runout of the thrust bearing: L = L1-L2: when the thrust bearing runout L exceeds the specified range (see table below), it is necessary to replace the thrust bearing.

Drill model 73 89 95/102 120 165/172 197/203 215 244
L(mm) 3 3 4 5 6 7 7 8

2. Maintenance of bypass valve assembly: remove the parts of the bypass valve and clean it, replace damaged filter casing, the o-ring and the damaged parts. Assemble them after being coated with grease. Move the spool to see whether it has any seizures.
3. Maintenance of the motor assembly
Disassemble the motor and check the rotor and the stator after cleaning.
a) Check whether the rubber on the stator has any obvious defects, such as, cracks and unglued parts. Both ends of the stator should be free of rust or bumps, and the thread should not be damaged.
b) The surface of the rotor should be smooth, and free of erosion, rust, coating flaking, trenches or any other damages; otherwise, it should be replaced.
At the end of the inspection, load the rotor into the stator, and lift the motor upright and then inject water for the static sealing test. The leakage of a drill with an outer diameter of more than 165 should be 13L/min, and that of a drill with an outer diameter less than 165 should be 7 L/min. Any drill with a value exceeding the above standards should have its motor replaced. After conclusion of the test, dry the moisture, coat the surface of the rotor with grease and then load it into the stator to be assembled. If conditions allow, it is necessary to conduct ground liquid motor test or the whole-machine test.
4. Maintenance of cardan shafts:
Petals cardan shaft: the supporting part shall be free of deformation or excessive wearing. The petal gaps shall not exceed a certain range and shall be free of any defects that may affect the strength. Petals gap exceeding the values in the following table should be replaced in principle.

PDM Model Petal Gaps(mm)
5(7)(9)LZ95/102 6
5LZ120 6
5LZ165/5(9)172 10
5(9)LZ197/203 12
5LZ215 12
5(9)LZ44 12

5. Radial bearing:
If the radial bearing has any cracks, drop-off of carbide blocks, or the matching gap exceeds 1mm, it should be replaced with a new radial bearing in principle.
6. After being used, the surface of the spindle should not have any serious defects. In principle, it should be used after conducting the defect detection once again.
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