Usage and maintenance of mechanical hydraulic plunger pump

The efficiency of the hydraulic system of the construction machinery mainly depends on the volumetric efficiency of the hydraulic pump. When the volumetric efficiency drops to 72%, routine maintenance is required to replace the bearings and the aging seals, and the friction pair that exceeds the fit clearance is to be replaced or repaired. Its performance is restored. In this paper, the main axis swash plate type piston pump is mainly used to introduce its use and maintenance methods.

1. Hydraulic pump oil supply

Straight-axis swash plate type piston pumps are classified into two types, self-priming oil type. Most pressure-feed hydraulic pumps use pneumatic fuel tanks, and hydraulic pumps have their own charge pump to provide pressure oil to the hydraulic pump inlet. The self-priming hydraulic pump is highly self-priming and requires no external force for oil supply.

Hydraulic fuel tanks that rely on air pressure, after each start of the machine, must wait until the hydraulic tank reaches the operating pressure before operating the machine. If the hydraulic tank is under pressure when the pressure is insufficient, it will cause a pull-off phenomenon in the hydraulic pump and the slide whip, which will cause abnormal wear of the return plate and the pressure plate in the pump body. After using the plunger pump for the oil pump, after 3000 hours, the operator needs to check the plunger pump 1-2 times a day to check whether the sound of the hydraulic pump running is normal. If it is found that the speed of the hydraulic cylinder is reduced or the vehicle is boring, the charging pump should be disassembled and inspected to check whether the edge of the impeller is scratched or if the clearance of the internal gear pump is too large.

For self-priming piston pumps, the fluid in the hydraulic tank must not fall below the lower limit of the oil scale, and a sufficient amount of hydraulic fluid must be maintained. The higher the cleanliness of the hydraulic fluid, the longer the service life of the hydraulic pump.

2. Bearings for hydraulic pumps

The most important part of the plunger pump is the bearing. If there is clearance in the bearing, the normal clearance of the three friction pairs inside the hydraulic pump cannot be guaranteed. At the same time, the thickness of the hydrostatic bearing oil film of each friction pair is also destroyed, and the bearing of the plunger pump is reduced. Service life. According to the information supplied by the hydraulic pump manufacturer, the average service life of the bearing is 10,000 hours. If it exceeds this value, a new one needs to be replaced.

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

In the replacement of bearings, should pay attention to the original bearing of the English letters and models, most of the piston pump bearing load capacity, it is best to buy the original manufacturer, the original specifications of the product, if you replace another brand, you should consult the bearing experience The personnel look-up table exchange, the purpose is to maintain the bearing precision grade and load capacity.

3. Three pairs of friction inspection and repair 3.1 Plunger rod and cylinder bore

Table 1 shows the replacement standards for plunger pump parts (see Figure 1). When the various gaps listed in the table are out of tolerance, they can be repaired as follows:

(1) The cylinder sleeve fitted with copper sleeves can be repaired by replacing the copper sleeve. First, a set of plunger rods are trimmed to a uniform size, and then the outer diameter is polished with more than 1000# sandpaper.

Three methods for installing copper sleeves in cylinders:

(a) Cylinder heating hot pack or copper sleeve cold extrusion, interference fitting; (b) Adopting Loctite adhesive assembly, this method requires a groove on the outer diameter surface of the copper jacket; (c) Cylinder Hole tapping, copper sheath outer diameter processing thread, coated with Loctite, screwed into the assembly.

(2) The cylinder body and the copper sleeve of the fusion burning method are as follows:

(a) Using abrasive rods, manually or mechanically grinding the reconditioning cylinder bores; (b) Using coordinate boring mills to re-punch cylinder bores; (c) Reaming cylinder bores with reamers.

(3) Adopt "surface engineering technology" as follows:

(a) Electroplating technology: Plating a layer of hard chrome on the surface of the plunger; (b) Brush plating technique: brushing wear-resistant material on the surface of the plunger; (c) Thermal spraying or arc spraying or electrospraying: spraying high carbon horses (D) Laser cladding: A high hardness wear-resistant alloy powder is deposited on the surface of the plunger.

(4) Cylinder bore The cylinder material without copper sleeve is mostly ductile iron, and an amorphous film or coating is prepared on the inner wall of the cylinder. Because of the special material on the inner wall of the cylinder bore, a hard-hard paired friction pair can be formed. If the cylinder bore is blindly ground and the surface material of the inner wall of the cylinder bore is ground, the structural performance of the friction will be changed. The friction pair removed from the coating, if used forcibly, will have a sharp increase in the friction surface temperature and the plunger rod will stick to the cylinder bore.

In addition, a unique thin-film coating is prepared on the surface of the plunger rod. The coating contains wear-reduction+wear-resistance+lubrication function. This pair of friction pair is actually a hard-soft pair. Once the coating is changed by people, it also destroys the most. The friction pair of good paired materials, repairs these special piston pumps, must send to the specialized repair factory.

3.2 Slipper and swash plate

The sliding friction between the sliding shoe and the swash plate is the most complicated pair of three friction pairs of the swash plate piston pump.

Table 1 shows the clearance between the plunger rod ball joint and the sliding shoe socket (see Figure 2). If the plunger and the shoe clearance are too bad, the high pressure oil in the plunger chamber will move from the plunger ball head to the shoe clearance. Leakage, slippery and swash plate oil film thinning, in serious cases will cause static pressure support failure, slippery shoes and swash plate metal contact friction, slide shoes ablation off, the plunger ball head scratches the swash plate. When the plunger rod ball head and sliding shoe socket exceed 1.5 times tolerance, they must be replaced in groups.

Plunger rod and cylinder bore Plunger rod diameter φ16φ20φ25φ30φ35φ40

Standard clearance 0.0150.0250.0250.0300.0350.040

Limit clearance 0.0400.0500.0600.0700.0800.090

Plunger rod ball head

Standard clearance with sliding shoes ball socket 0.0100.0100.0150.0150.0200.020

The limit clearance is 0.300.300.300.350.350.35

After the swash plate acts for a period of time, the swash plate plane will appear concave. Before using the platen grinding, the original size and plane hardness should be measured first. After polishing, the amount of grinding is measured. If the amount of grinding is 0.18 or less, there is no obstacle to the use of the plunger pump. If it exceeds 0.2 mm, the nitride layer should be used to maintain the original nitride layer thickness.

When the plane of the swash plate is scraped off by the plunger ball, the laser can be used to repair the alloy powder. Laser cladding technology can not only ensure the bonding strength of the material, but also ensure the hardness of the refill material, and does not completely reduce the hardness of the surrounding tissue.

It is also recommended to use a chromium phase electrode for manual build-up welding. The repaired swash plate surface needs to be reheated, and heat treatment using a nitriding furnace is preferred. Regardless of the method used to repair the swash plate, the original dimensional accuracy, hardness, and surface roughness must be restored.

3.3 Repair of Flow Plate and Cylinder Flow Distribution Surface

The distribution plate has two forms of plane distribution and spherical distribution.

The friction pair of the spherical flow distribution is repaired by the grinding means when the scratches on the flow surface of the cylinder body are relatively shallow. When the groove of the flow surface of the cylinder is deep, the groove should be filled with the "surface engineering technology" before grinding. , not blindly grinding, in order to prevent the copper layer from thinning or leaking out of the steel base.

The flat-flow friction pair can be ground on a relatively high-precision platform.

Before grinding the cylinder block and the valve plate, it is necessary to measure the total thickness dimension and the size that should be ground before compensating to the adjustment pad. When the amount of grinding disc is large, it should be re-heated after grinding to ensure the hardness of the hardened layer (see Table 2).

Plunger Rod Recommended Hardware HS84

Plunger Rod Ball Head Recommended Hardness >HS90

Swash plate surface recommended hardness >HS90

Hard disk with recommended hardness >HS90

After the cylinder body and the valve plate are repaired, the following method can be used to check the leakage of the mating surface, that is, apply Vaseline oil on the valve plate, block the drain channel, and place the oil flow plate flat on the platform or plate glass. Then put the cylinder on the valve plate and inject diesel oil into the cylinder hole. It is necessary to inject the oil at intervals, ie one hole for oil injection and one hole for oil injection. Observe for more than 4 hours. There is no leakage and collusion of diesel oil in the plunger hole, indicating the cylinder body and flow distribution. Plate grinding qualified.

4. Conclusion

The length of life of the plunger pump is related to the usual maintenance, the quantity and quality of the hydraulic oil, and the cleanness of the oil. It is also an effective way to prolong the life of the plunger pump by avoiding the wear of the piston pump friction pair by the particles in the oil.

In the maintenance of replacement parts should try to use the original production of parts, these parts are sometimes more expensive than other counterfeit parts, but the quality and stability is better, if you buy cheap counterfeit parts, seems to save money in the short term, However, this brings hidden dangers and may also cause greater harm to the use of the plunger pump.