Fault Phenomenon: XCMG HB52K concrete pump truck pumps normally when cold. After reaching operating temperature (oil temp 85℃), the boom action is weak, main pump pressure cannot be established, and no fault codes are displayed on the dashboard.

Troubleshooting Process:
– Checked hydraulic oil level and suction filter: oil level normal, filter not clogged.
– Checked main relief valve and pilot pressure: valve spool not stuck, pilot pressure stable.
– Checked main pump proportional valve supply voltage: voltage stable.
– Measured main pump displacement control current at operating temperature: found the current signal cuts out as temperature rises.

Root Cause: Internal coil of the main pump’s electric proportional valve experiences insulation failure due to heat, making it unable to adjust the swashplate angle.

Required Parts: Main pump electric proportional valve assembly.