Hydraulic Pump Maintenance Methods And Key Considerations

The efficiency of a hydraulic pump system depends on the volumetric efficiency of the hydraulic pump. When the volumetric efficiency drops to 72%, routine maintenance is required. This includes replacing bearings and aging seals, and repairing or replacing parts that exceed the wear limits of the friction pairs to restore the pump's performance.

Oil Supply Methods for Hydraulic Pumps: There are two oil supply methods for axial piston pumps: pressure oil supply and self-priming oil supply.

1) The pressure oil supply type generally uses an oil tank with air pressure, or some hydraulic pumps have a replenishing pump to supply pressure oil to the pump's intake.

2) The self-priming oil supply type hydraulic pump has a strong self-priming ability, and does not require external assistance for oil supply.

For piston pumps using a replenishing pump, after 3000 hours of operation, workers need to inspect the pump 1-2 times a day, checking whether the hydraulic pump operates with normal sound.

If there is a decrease in hydraulic cylinder speed or the machine stalls, the replenishing pump should be disassembled and checked. Inspect for any scratches on the impeller edges and check if the gap in the internal gear pump is too large. For self-priming piston pumps, the oil level in the hydraulic oil tank must not drop below the lower limit of the oil gauge, and a sufficient amount of hydraulic oil should be maintained.

Bearings in Hydraulic Pumps: The most important component in a hydraulic pump is the bearing.

If the bearing has play, it will prevent the normal gap between the three friction pairs (the piston and piston hole, the slipper and swash plate, and the cylinder block and distribution plate). It will also damage the thickness of the static hydraulic support oil film of the friction pairs, reducing the bearing life of the piston pump.

According to data provided by hydraulic pump manufacturers, the average lifespan of bearings is 10,000 hours. Beyond this period, replacement is necessary. Bearings that are removed cannot be checked for play without professional testing equipment; they can only be inspected visually. If discoloration or scratches are found on the roller surface, the bearing must be replaced.

When replacing the bearing, attention should be paid to the model and letters on the original bearing. Most piston pump bearings use high-load capacity bearings. It is best to purchase products from the original manufacturer with the same specifications. If a different brand is chosen, consultation with an experienced professional is necessary to ensure that the bearing's precision grade and load capacity are maintained.

Inspection and Repair of Friction Pairs:

1) If the cylinder block is equipped with a bronze bushing, it can be repaired by replacing the bushing. First, the diameter of a set of piston rods should be trimmed to a uniform size, then polished with sandpaper of 1000# or higher.

There are three methods for installing the bronze bushing in the cylinder block: (a) Heat installation of the cylinder block or freezing of the bronze bushing for press-fit assembly. (b) Using Loctite adhesive for installation, requiring grooves on the outer diameter of the bronze bushing. (c) Tapping the cylinder hole, processing threads on the outer diameter of the bronze bushing, applying Loctite adhesive, and screwing it into place.

2) For cylinder blocks and bronze bushings with a fusion bonding method, the repair method includes: (a) Using grinding rods to manually or mechanically grind the cylinder hole. (b) Reboring the cylinder hole using a coordinate boring machine. (c) Using a reamer to repair the cylinder hole.

3) The “Surface Engineering Technology” methods include: (a) Electroplating technology: Plating a layer of hard chrome on the piston surface. (b) Electrobrush plating technology: Electroplating wear-resistant materials on the piston surface. (c) Thermal spraying, arc spraying, or electric spraying: Spraying high-carbon martensitic wear-resistant materials. (d) Laser cladding: Cladding high-hardness wear-resistant alloy powders onto the piston surface.

4) For cylinder blocks without bronze bushings, the cylinder material is typically ductile cast iron. The interior surface of the cylinder block can be treated with an amorphous thin film or coating. This creates a hard-hard friction pair when used in combination with the piston.

If the cylinder block hole is blindly ground and this special surface material is removed, the friction characteristics of the pair will change. If the coating is removed from the friction pair, and it is forcibly used, it will cause a sharp rise in temperature at the friction surface, leading to galling between the piston rod and cylinder hole.

5) Additionally, a unique thin film coating can be applied to the piston rod surface. This coating has anti-friction, wear-resistant, and lubrication functions. The friction pair is a hard-soft combination, and once the coating is altered, it destroys the optimal friction pair material. Repairing such special piston pumps requires sending them to a specialized repair shop.