Pressure meters serve as the "weather vane"  reflecting pressure changes in the working cylinders of the HPHT Hydraulic Cubic Press.

It analyzes how the system pressure gauge (9) and ultra-high pressure gauges (45a–45d) reflect specific hydraulic faults under the conditions of the new hydraulic system.

1. Reactions and Corresponding Faults of System Pressure Gauge (9)
System pressure gauge 9 (located in the system's return oil circuit) primarily reflects the system's pressure status during pressure adjustment and the quick return step.
Pointer Oscillation or Instability: If the pointer of pressure gauge 9 swings back and forth or oscillates violently during system pressure adjustment, it suggests pressure fluctuations in the system.
    Air ingress into the oil pump suction pipe is a major cause. Because air enters the suction chamber of oil pump 3 or 3B along with the oil, the output pressure becomes extremely unstable due to the presence of air. This causes the pointer of pressure gauge 9 to oscillate violently, and in severe cases, local hydraulic shock can lead to abnormal pump noise.
    Damage to the screw plug sealing ring of relief valve 8 can also cause the pointer to swing back and forth. Damage to the sealing ring results in the leakage of some pressure oil, leading to pressure fluctuations.
Inability to Adjust System Pressure: If system pressure gauge 9 reaches a fixed value and the pressure remains unchanged regardless of adjustment to relief valve 8, it indicates an incorrect configuration of the system's pressure regulation circuit. This is because relief valve 8 (high pressure, used for the quick return step) and relief valve 7 (low pressure, used for the idle advance step) form a multi-stage pressure regulation circuit in the return oil path. If the set pressure of relief valve 7 is greater than the set pressure of relief valve 8, then adjusting relief valve 8 is ineffective.
2. Reactions and Corresponding Faults of Ultra-High Pressure Gauges (45a–45d)
Ultra-high pressure gauges (45a–45d) are primarily used to display pressure changes in the high-pressure cylinders during the liquid filling transition to the super-pressurization step and the depressurization step.
Pressure Rise Delay or Zero Pressure During Super-Pressurization Transition: When transitioning from the liquid filling phase to the super-pressurization phase, the high-pressure gauges may show the pointer rising only after a certain time (a pause), or even no reaction (zero system pressure).
    This fault is related to the pressure relationship between balance valve 47 (used to prevent the upper cylinder piston from dropping due to self-weight) and pilot-operated check valve 17.
    Abnormalities occur if the set pressure of balance valve 47 is greater than the opening pressure of pilot-operated check valve 17 (0.04 MPa).
        When the pressure difference between the two is small, pilot-operated check valve 17 has a small opening. The pressure oil entering the lower chamber of intensifier 22 needs a certain amount of time to accumulate, forming pressure that pushes the spool of check valve 17 closed, leading to a pressure rise delay.
        When the pressure difference between the two is large, pilot-operated check valve 17 remains in a normally open state . The pressure oil entering the lower chamber of intensifier 22 returns to the oil tank through this valve, resulting in zero system pressure.
No Reaction on High-Pressure Gauges During Depressurization: In the new hydraulic system, which uses non-powered depressurization (unloading without turning on the pump), all high-pressure gauges (45a–45d) fail to reflect the drop in oil pressure during the depressurization operation.
    This is caused by fluid resistance  generated in the total return pipeline. This resistance may result from the total return pipe being too thin, the bending radius being too small, or the filter screen in the total return filter being too fine.
    This generated fluid resistance force returns to the system, acts on the spool of the two-position seven-way valve 44 via the two-position four-way solenoid valve 43, and pushes the spool to close the two-position seven-way valve. This cuts off the connection between the six high-pressure cylinders (48–53) and the intensifier 22. Consequently, the oil pressure in the high-pressure cylinders cannot be relieved as the intensifier descends, and the high-pressure gauges therefore cannot reflect the pressure drop.
In summary, pressure meters are like the "palm print" of the machine, exhibiting regular reactions to changes within the hydraulic system of the press. Grasping these reactions and interpreting the surface phenomena allows technical personnel to make quick and accurate fault judgments, thereby saving considerable unnecessary time and achieving twice the result with half the effort. .