Hidravlična črpalka RC788-61112 za mini bager Kubota U35-4 KX033-4

Technical Specifications: Kubota U35-4 / KX033-4 Main Pump

1. Part Identification & Supercession
This pump has undergone several engineering updates. The latest part numbers reflect improvements in seal durability and volumetric efficiency.

Kubota Genuine Part Numbers: RC788-61112, RC788-61113, RC788-61122, RC788-61123, RC788-61124 (Current Standard)

OEM Model: Nachi PVD-0B-28P-6G3-5243A (or similar suffixes)

Machine Models: Kubota U35-4, KX033-4, U30-4
2. Core Performance Data

Item,Specification,Unit
Pump Type,Variable Displacement Axial Piston,-
Number of Main Outlets,2 (P1 & P2),-
Main Pump Displacement,28.0×2,cm3/rev
Gear Pump (Pilot) Displacement,10.8,cm3/rev
Rated Operating Pressure,23.5,MPa (3408 psi)
Maximum Surge Pressure,27.0,MPa (3916 psi)
Rated Speed,2200−2400,rpm
Max. Theoretical Flow,67.2×2+25.9,L/min (@ 2400 rpm)

3. Critical Internal Components (Hard Data)
For overhaul and repair, the following internal specifications are used to determine wear limits:

Cylinder Block & Pistons:
Piston Quantity: 9 Pistons per group.
Piston Diameter: Standardized for the 28P series to ensure high-pressure sealing.
Clearance Limit: Piston-to-cylinder bore clearance exceeding $0.05$ mm usually results in significant volumetric loss.

Valve Plate:
Surface Flatness: Must be within $0.002$ mm.
Configuration: M-type or standard porting designed for "Load Sensing" (LS) signal stability.

Drive Shaft:
Spline Count: 13 Teeth or 15 Teeth (dependent on the engine flywheel coupling).
Bearing Type: High-load needle roller bearings for the swashplate support and tapered roller bearings for the main shaft.

4. Hydraulic System Pressure SettingsAfter installing a new RC788-61124 pump, the machine must be calibrated to the following factory pressures:Main Relief Pressure: $23.5 \pm 0.5$ MPa (Measured at the control valve block).Pilot Control Pressure: $3.7$ MPa ($536$ psi). If this pressure is low, the joysticks will feel "heavy" and the machine will lack speed.Unloading Pressure: $3.0 - 4.2$ MPa. This is the pressure when the controls are in neutral.LS (Load Sensing) Differential Pressure: Usually set to $1.5 - 2.0$ MPa above tank pressure to ensure immediate pump response.

5. Installation & Commissioning Protocol
To avoid "infant mortality" of the new pump, follow these precise steps:

Case Drain Priming (CRITICAL): Before starting the engine, you must fill the pump casing with clean hydraulic oil through the highest drain port. Running the pump dry for even 30 seconds will score the piston shoes.

System Decontamination: If the previous pump suffered a "catastrophic failure" (metal shards in the oil), you must flush the entire hydraulic circuit and clean the control valve spools.

Filtration: Replace the Return Filter and the Suction Strainer. Check the magnetic plug in the hydraulic tank for debris.

Air Bleeding: Start the engine and run at low idle for 5 minutes without operating the cylinders. Gradually move the cylinders to full stroke to purge air from the lines.