4 hours ago
The Hitachi FH150 (often branded Fiat‑Hitachi FH150LC in some markets) is a mid‑sized excavator produced in the 1990s and early 2000s, combining Japanese engineering with Fiat industrial components for construction and earthmoving tasks. Hitachi Construction Machinery, founded in 1910 and later diversified through partnerships, became known for reliable application‑specific hydraulics, rugged undercarriage designs, and engines suitable for heavy‑duty dig cycles. Despite this legacy, aging machines like the FH150 can develop complex hydraulic problems that challenge even seasoned technicians.
One recurring symptom reported by FH150 owners is a loud banging or knocking noise under load followed by intermittent loss of pressure from one of the main hydraulic pumps, leading to reduced track or boom response. This behavior is particularly concerning when it occurs at the end of ram travel or under heavy dig loads, and then causes a temporary power loss that can only be “reset” by changing engine speed or releasing the control.
Hydraulic System Function in Hitachi Excavators
Excavators like the FH150 use multiple axial piston pumps to supply pressurized oil to different function circuits — travel, boom, arm, bucket, and swing — as well as the pilot control circuit. These pumps must maintain adequate flow and pressure under varying loads to ensure smooth operation. When one pump behaves erratically, the system can produce unusual noises, pressure fluctuations, and loss of function.
Typical Symptoms Reported
Operators experiencing this issue describe a pattern where:
1. Cavitation and Air Ingestion
Banging or knocking noises frequently indicate cavitation — where vapor bubbles form in low‑pressure areas and collapse violently as pressure recovers. Cavitation can occur when suction flow is restricted, fluid level is low, or there is air entrainment in the hydraulic fluid. Air contamination not only produces noise but also reduces effective pump displacement, leading to loss of flow and pressure under load.
2. Pump Pressure Cut‑Off and Relief Interactions
Many mechanical pump systems have cut‑off devices or pressure margin regulators that shift the pump from high pressure to a lower flow condition to protect it. If these devices malfunction or are set incorrectly, the pump may “bang” as it rapidly switches states under load. Similarly, a relief valve opening and closing erratically under heavy demand can create pressure spikes and banging sensations.
3. Internal Pump Wear or Damage
Axial piston pumps depend on tight internal clearances to maintain pressure. Wear on pistons, swashplates, or valve plates can cause cycle‑to‑cycle pressure variations that manifest as noise and intermittent loss of one pump’s output. This kind of wear often worsens as fluid ages or contaminants enter the system.
4. Contamination and Filter Blockage
Even with recent oil and filter changes, minor contamination, especially in pilot or case drain circuits, can cause unpredictable symptoms. Emulsified fluid, water ingress, or debris in fine passages causes cavitation and pressure pulsations. Proper filtration and fluid cleanliness are critical to avoid these issues.
Diagnosis and Troubleshooting Strategy
1. Check Fluid and Suction Conditions
Begin by verifying hydraulic fluid level, temperature, and appearance. Overheated or foamy fluid commonly accompanies noise issues. Inspect suction lines and screens for blockages or collapsed hose sections that can induce cavitation.
2. Pressure Testing
Install pressure gauges on the main circuits and pilot lines to observe pressure behavior under idle, light load, and heavy load conditions. Sudden drops or spikes can point to relief valve instability or internal pump clearance issues.
3. Inspect Pressure Cut‑Off and Relief Settings
Mechanically controlled pressure cut‑off or main relief valves should be checked for correct set points and adjustment. Erratic valve operation under load can mimic pump failure.
4. Rule Out External Air or Water Contamination
If fluid appears milky or contains micro‑bubbles, water contamination is likely. Water significantly reduces oil film strength and promotes cavitation. Drain and replace the fluid if contamination is suspected.
Real‑World Insight
An operator reported that this kind of banging often coincided with cold fluid conditions and reduced viscosity, which increased cavitation at higher demands. Once the system warmed up, the symptom diminished — but reappeared whenever the fluid cooled or pressure demand spiked. This aligns with general hydraulic principles: thinner fluid at temperature extremes is more prone to vapor bubble formation, while warm fluid supports stable pressure transmission.
Terminology Explained
The hydraulic banging and intermittent loss of one pump on a Hitachi FH150 under load are classic indicators of pressure instability due to cavitation, relief/cut‑off irregularities, or internal pump wear. Persistent banging noise, especially when tied to load and oil temperature changes, underscores the importance of fluid condition, correct valve settings, and thorough pressure diagnostics. With systematic troubleshooting — from fluid cleanliness to pressure testing — operators can pinpoint the root cause and implement targeted repairs, extending the life of the FH150’s hydraulic system and ensuring reliable performance in demanding excavator applications.
One recurring symptom reported by FH150 owners is a loud banging or knocking noise under load followed by intermittent loss of pressure from one of the main hydraulic pumps, leading to reduced track or boom response. This behavior is particularly concerning when it occurs at the end of ram travel or under heavy dig loads, and then causes a temporary power loss that can only be “reset” by changing engine speed or releasing the control.
Hydraulic System Function in Hitachi Excavators
Excavators like the FH150 use multiple axial piston pumps to supply pressurized oil to different function circuits — travel, boom, arm, bucket, and swing — as well as the pilot control circuit. These pumps must maintain adequate flow and pressure under varying loads to ensure smooth operation. When one pump behaves erratically, the system can produce unusual noises, pressure fluctuations, and loss of function.
Typical Symptoms Reported
Operators experiencing this issue describe a pattern where:
- The machine operates normally at light load or idle.
- Under moderate to heavy hydraulic demand (e.g., full boom extension or simultaneous functions), a loud banging or knocking noise occurs — often synchronized with the main pump output.
- A pipe (commonly near the pump outlet) visibly vibrates or shakes with the noise.
- One circuit appears to “lose” pressure or flow, such as tracks that no longer travel or slow lifting speed.
- Adjusting engine throttle or pausing controls temporarily restores normal function.
This pattern points to pressure instability or unloading events inside the hydraulic pump or control valves, rather than a simple external leak or pilot control idle issue.
1. Cavitation and Air Ingestion
Banging or knocking noises frequently indicate cavitation — where vapor bubbles form in low‑pressure areas and collapse violently as pressure recovers. Cavitation can occur when suction flow is restricted, fluid level is low, or there is air entrainment in the hydraulic fluid. Air contamination not only produces noise but also reduces effective pump displacement, leading to loss of flow and pressure under load.
2. Pump Pressure Cut‑Off and Relief Interactions
Many mechanical pump systems have cut‑off devices or pressure margin regulators that shift the pump from high pressure to a lower flow condition to protect it. If these devices malfunction or are set incorrectly, the pump may “bang” as it rapidly switches states under load. Similarly, a relief valve opening and closing erratically under heavy demand can create pressure spikes and banging sensations.
3. Internal Pump Wear or Damage
Axial piston pumps depend on tight internal clearances to maintain pressure. Wear on pistons, swashplates, or valve plates can cause cycle‑to‑cycle pressure variations that manifest as noise and intermittent loss of one pump’s output. This kind of wear often worsens as fluid ages or contaminants enter the system.
4. Contamination and Filter Blockage
Even with recent oil and filter changes, minor contamination, especially in pilot or case drain circuits, can cause unpredictable symptoms. Emulsified fluid, water ingress, or debris in fine passages causes cavitation and pressure pulsations. Proper filtration and fluid cleanliness are critical to avoid these issues.
Diagnosis and Troubleshooting Strategy
1. Check Fluid and Suction Conditions
Begin by verifying hydraulic fluid level, temperature, and appearance. Overheated or foamy fluid commonly accompanies noise issues. Inspect suction lines and screens for blockages or collapsed hose sections that can induce cavitation.
2. Pressure Testing
Install pressure gauges on the main circuits and pilot lines to observe pressure behavior under idle, light load, and heavy load conditions. Sudden drops or spikes can point to relief valve instability or internal pump clearance issues.
3. Inspect Pressure Cut‑Off and Relief Settings
Mechanically controlled pressure cut‑off or main relief valves should be checked for correct set points and adjustment. Erratic valve operation under load can mimic pump failure.
4. Rule Out External Air or Water Contamination
If fluid appears milky or contains micro‑bubbles, water contamination is likely. Water significantly reduces oil film strength and promotes cavitation. Drain and replace the fluid if contamination is suspected.
Real‑World Insight
An operator reported that this kind of banging often coincided with cold fluid conditions and reduced viscosity, which increased cavitation at higher demands. Once the system warmed up, the symptom diminished — but reappeared whenever the fluid cooled or pressure demand spiked. This aligns with general hydraulic principles: thinner fluid at temperature extremes is more prone to vapor bubble formation, while warm fluid supports stable pressure transmission.
Terminology Explained
- Cavitation — Formation and collapse of vapor bubbles in hydraulic fluid due to rapid local pressure changes, causing noise and component wear.
- Axial Piston Pump — A variable displacement pump type that uses pistons aligned parallel to the pump shaft, common in excavator hydraulics.
- Pressure Cut‑Off — A mechanical or electronic mechanism that reduces pump displacement or flow when a pressure threshold is reached, protecting the system.
- Relief Valve — Safety valve that opens to divert fluid back to tank when pressure exceeds a defined limit.
- Pilot Circuit — Low‑pressure control stream that operates control valves and proportional devices.
- Maintain Hydraulic Fluid Quality — Use the correct fluid with good anti‑cavitation properties, and ensure ISO cleanliness targets are met.
- Monitor Temperature — Avoid prolonged operation with fluid exceeding recommended temperatures (often above ~80–90°C), as this reduces oil film strength.
- Service Suction Screens and Filters — Check and clean internal tank suction screens and return filters to prevent suction starvation.
- Valve Adjustment and Pump Inspection — If testing reveals irregular pressure behavior, inspection of the pump’s internal components or control valves may be necessary to diagnose wear or improper cut‑off behavior.
The hydraulic banging and intermittent loss of one pump on a Hitachi FH150 under load are classic indicators of pressure instability due to cavitation, relief/cut‑off irregularities, or internal pump wear. Persistent banging noise, especially when tied to load and oil temperature changes, underscores the importance of fluid condition, correct valve settings, and thorough pressure diagnostics. With systematic troubleshooting — from fluid cleanliness to pressure testing — operators can pinpoint the root cause and implement targeted repairs, extending the life of the FH150’s hydraulic system and ensuring reliable performance in demanding excavator applications.
