Hydraulic Main Pump Kubota U55 U55-4 PN RD551-61115

Compatible with the following equipment:

KUBOTA

• U55
• U55-4

Part number:  RD551-61112 RD55161112 RD551-61115 RD55161115

What is the Hydraulic Main Pump?

The main pump (often just called the hydraulic pump or main hydraulic pump) is the heart of the machine's hydraulic system. Its primary function is to convert the mechanical power from the engine into hydraulic energy (fluid flow and pressure). This pressurized oil is then distributed to various hydraulic actuators (cylinders and motors) to perform work like digging, lifting, swinging, and traveling.

Critical Functions & Features

• Flow Generation: Provides the volume of hydraulic oil needed for fast cylinder and motor movement (speed).

• Pressure Creation: Creates the necessary pressure (measured in psi or bar) to overcome resistance, enabling powerful digging and lifting force.

• Power Management: Electronically or hydraulically controlled to match output to the workload, optimizing engine power and fuel efficiency.

• Load Sensing: A key feature. The pump constantly monitors the highest pressure required by any function and adjusts its output pressure to be just slightly higher, minimizing energy waste.

• Negative Flow Control (NPC) / Positive Flow Control (PFC): These are control methodologies.

  • NPC (Common in older/some Japanese systems): Pilot pressure from the control levers reduces pump flow when levers are neutral.

  • PFC (Common in modern systems): Pilot pressure from the control levers increases pump flow to the demanded function.