Construction Machinery Hydraulic Piston Pump Usage and Maintenance

The hydraulic system efficiency of a construction machine depends mainly on the volumetric efficiency of the hydraulic pump. When the volumetric efficiency drops to 72%, routine maintenance, replacement of bearings and aged seals are required, and replacement or repair of friction pairs beyond the mating clearance is required Its performance has been restored.
In this paper, direct-axis swash plate piston pump-based, describes its use and maintenance methods.

1 hydraulic pump oil supply form

Straight shaft swash plate piston pump is divided into two types of self-suction oil pressure type. Most of the pressure supply type hydraulic pump with air pressure tank, there are hydraulic pump itself with a charge pump to the hydraulic pump inlet to provide pressure oil. Self-priming oil pump self-priming oil capacity, no external oil supply.

By hydraulic pressure oil tank, each time you start the machine, you must wait for the hydraulic pressure box to reach the use of air pressure before operating machinery. If the pressure of the hydraulic tank is low, it will cause the pull-off phenomenon in the hydraulic pump and the slippery whip, which will cause abnormal wear of the return plate and the pressure plate in the pump body. The use of charge pump piston pump, use 3000h, the operator needs to check the plunger pump 1-2 times a day to check the hydraulic pump running sound is normal. If you find the hydraulic cylinder speed or boring car, you should disassemble the charge pump check, check the edge of the impeller scratches, internal gear pump clearance is too large.

For self-priming piston pumps, the fluid in the hydraulic tank should not be lower than the lower limit of the oil standard, and a sufficient amount of hydraulic oil should be maintained. The higher the cleanliness of the hydraulic fluid, the longer the life of the hydraulic pump.

2 hydraulic pump bearings

Piston pump is the most important part of the bearing, if the bearing appears clearance, you can not guarantee the hydraulic pump within the three pairs of normal friction pair, but also destroy each friction pair hydrostatic bearing oil film thickness, reduce piston pump bearing Service life. According to information provided by the hydraulic pump manufacturer, bearing the average service life of 10000h, more than this value will need to replace the new port.

Demolition of the bearings, there is no professional testing equipment can not detect the bearing clearance, can only be visually, if the surface of the roller scratches or discoloration, it must be replaced.

In the replacement of bearings, bearings should pay attention to the original letters and models, most of the piston pump bearing load capacity of large bearings, it is best to buy the original manufacturer, the original specifications of the product, if the replacement of another brand, should consult the bearing experience Staff look-up table swap, the purpose is to maintain the bearing accuracy level and load capacity.

3 pairs of friction pair inspection and repair

3.1 Plunger rod and cylinder bore

Table 1 for the replacement parts of the piston pump (see Figure 1), when the table listed in the various types of clearance tolerance can be repaired as follows:

(1) cylinder inlaid copper sleeve, copper sleeve can be replaced by the method of repair. First set a set of plunger rod diameter trim to a uniform size, and then over 1000 # polished sandpaper outside diameter.

Three ways to install copper sleeve cylinder:

(A) Low-temperature cryogenic extrusion of the cylinder block or copper sleeve, and interference fit; (b) Loctite adhesive assembly, which requires a groove on the outer diameter surface of the copper jacket; (c) Hole tapping, copper outer diameter processing thread, Tu Le Thai plastic, screw into the assembly.

(2) Molten combination of the cylinder block and copper sleeve, repair as follows:

(A) Grinding the cylinder bore using a grinding rod, either manually or mechanically; (b) Re-boring the cylinder bore using a jig boring machine; and (c) Reaming the cylinder bore using a reamer.

(3) the use of "surface engineering technology", the method is as follows:

(A) electroplating technology: coating a hard chromium layer on the plunger surface; (b) brush plating technology: brushing wear-resistant material on the plunger surface; (c) thermal spraying or arc spraying or electrospraying: (D) laser cladding: the surface of the plunger welding high hardness wear resistant alloy powder.

(4) Cylinder hole copper-free sleeve cylinder materials are mostly ductile iron, the cylinder wall to prepare amorphous film or coating. Because of this special material on the inner wall of the cylinder bore, it is possible to form a hard-hard paired friction pair. If you blindly grind the cylinder bore, the surface material inside the bore of the cylinder bore is removed and the more structural properties of the friction change. Was removed coating friction pair, if forced to use, the friction surface temperature will rise sharply, the plunger rod and cylinder bore gluing.

In addition to the surface of the plunger rod to prepare a unique film coating, the coating contains anti-wear + wear + lubrication function, this group of friction actually hard or soft match, once people change the coating, it will destroy the most Good matching pair of friction materials, repair these special plunger pump, it is necessary to send a professional repair shop.

3.2 Slippers and swash plate

Sliding friction between slipper and swashplate is the most complex pair of three pairs of swashplate piston pump.

Table 1 shows the clearance between the plunger rod and the ball socket (see Figure 2). If the gap between the plunger and the shoe is out of tolerance, the high pressure oil in the plunger chamber will leak from the clearance between the ball head and the shoe In the leakage, slippery shoes and swash plate thinning, severe hydrostatic pressure caused by failure of the support, slipper and swash plate metal contact friction, slipper ablation off, plunger ball head scratched swashplate. Plunger rod ball head and sliding ball socket beyond the tolerance 1.5 times, it must be replaced in groups.

Plunger rod and cylinder piston rod diameter φ16 φ20 φ25 φ30 φ35 φ40
Standard gap 0.015 0.025 0.025 0.030 0.035 0.040
Limit clearance 0.040 0.050 0.060 0.070 0.080 0.090
Piston rod ball head and sliding ball socket standard gap 0.010 0.010 0.015 0.015 0.020 0.020
The limit clearance is 0.30 0.30 0.30 0.35 0.35 0.35

Swashplate role after a period of time, the swashplate surface will appear concave phenomenon, before using the platform grinding, the first measurement of the original size and plane hardness. Grinding, and then measure the amount of grinding is, such as within 0.18 plunger pump use without interference; if more than 0.2mm above, you should use nitriding method to maintain the thickness of the original nitride layer.

When the swash plate plane is scraped out of the groove by the plunger ball head, the method of laser alloy powder can be used for repairing. Laser cladding technology can not only ensure the bonding strength of the material, but also ensure the hardness of the filler material, and does not reduce the hardness of the surrounding tissue.

Also Shun to adopt chromium welding rod for manual surfacing, welding of the swash plate plane to be re-heat treatment, the best nitriding furnace heat treatment. Regardless of the method used to repair the swashplate, you must restore the original dimensional accuracy, hardness and surface roughness.

3.3 with the flow plate and cylinder with flow surface repair

With a flat plate with a flat surface with the flow of two forms.

Spherical with the flow of friction pair, the cylinder with flow surface scratches relatively shallow, by means of grinding repair; cylinder with flow grooves deep, should first use "surface engineering" means to fill the trench, and then grinding , Can not be blind grinding, to prevent copper thinning or leakage of steel base.

Friction pair in the form of plane flow can be grinded on the platform with high accuracy.

Before the grinding of the cylinder body and the valve plate, the total thickness dimension and the size that should be ground off should be measured before compensation to the adjusting mat. With a larger flow plate, the grinding should be re-heat treatment to ensure the hardened layer hardness (see Table 2).

Table 2 piston pump parts hardness standards

Plunger bar recommended hardware HS84
Plunger Rod End Recommended Hardness> HS90
Swashplate surface recommended hardness> HS90
Disc Recommended Hardness> HS90

After the cylinder body and the valve plate are repaired, the following methods can be used to check the leakage of the mating surface, that is, the oil flow plate is coated with petroleum jelly, the drainage channel is blocked, the oil-filled flow plate is evenly coated on the platform or the flat glass, Then put the cylinder on the valve plate, the cylinder bore injection of diesel, to the interval of injection, that is, a hole oil, a hole without oil, observe 4h above, the plunger hole no leakage and collusion of diesel, indicating the cylinder and the distribution Dish grinding qualified.

4 Conclusion

Piston pump life, with the usual maintenance, the number and quality of hydraulic oil, oil cleanliness and so on. Avoid oil particles in the piston pump friction caused by wear and tear, but also to extend the effective life of the plunger pump.

In the maintenance of replacement parts should try to use the original production of parts, these parts sometimes fake parts than other expensive, but the quality and stability is better, if the purchase of counterfeit parts cheaper prices in the short term seems to be saving costs, However, this poses a hidden danger, may also cause greater damage to the use of the plunger pump.