Hydraulic pumps in construction machines are components of great importance – their failures can effectively immobilize equipment for a long time.
Recently, we received a hydraulic pump from a Terex TC 225 excavator due to low pressure and lack of performance. We conducted a full diagnosis and repair, which we will describe in detail today.
Diagnosis – what went wrong?
At first glance, the two-section pump with variable performance did not appear to be severely damaged. However, upon disassembly, it turned out that the following were damaged:
- cylinders,
- piston rings,
- and gear transmission elements.
One of the biggest issues with this design is the lack of a separate leak circuit – debris from damaged components is not removed from the system but is sucked inside. As a result, the entire rotating group gets damaged.
Pump design and failure mechanics
The pump has a distribution plate, where performance is regulated by changing the position of the piston. This change directly affects the tilt angle of the distribution plate.
During disassembly, we noticed:
- attempts at previous sealing using silicone (ineffective),
- worn piston rings,
- clearly worn cylinders.
In addition, we assessed the condition of the control pump – this time it was in good condition, but usually, it is the one that generates additional problems.
Repair process – step by step
We replaced:
- two cylinders,
- all piston and control piston rings,
- seals.
The shafts were pressed in while maintaining the appropriate position marking (alignment of synchronizing points), and then we proceeded to assemble the auxiliary pump, valves, and closing plate.
A key stage was the precise synchronization of the shafts – incorrect positioning of the pistons could result in uneven operation of the pump.
Testing and commissioning
After assembly, the pump was placed on the test stand. Initially, it operated unevenly, which required adjustment of the settings. After their adjustment, we achieved:
- smooth operation without vibrations,
- full power and pressure,
- no leaks.
Thanks to the precise fitting of components and the use of new parts, the pump regained full efficiency.
Why is oil cleanliness crucial?
It is worth emphasizing that in this design, supply, leakage, and lubrication are shared. Contaminants from one area reach the entire pump. Debris from damaged gears can destroy the entire pumping group within minutes – acting like a vacuum cleaner that sucks them into the cylinder interior. Regular oil and filter changes are not just a recommendation but a necessary condition to avoid serious failures.
The entire video can be seen here.
