In axial piston pumps, the valve plate must maintain stable axial contact with the cylinder block to ensure correct port sealing between suction and discharge zones. In the Volvo PVG130 Pump, spring elements are used to maintain controlled axial preload between the valve plate and the rotating group during operation. Fatigue of these springs can alter contact pressure and introduce dynamic delays in pressure transition across the valve plate interface.
Core Mechanism / Physics of Failure
The valve plate spring assembly maintains axial force that presses the valve plate against the cylinder block. This contact is necessary to maintain hydraulic separation between adjacent ports on the valve plate. During pump operation, the spring assembly experiences continuous cyclic loading due to pressure variation and rotating group forces.
Primary mechanisms that lead to spring fatigue include:
Cyclic compression loading: Each pressure cycle in the pump produces axial force variation that repeatedly compresses and relaxes the spring elements.
Material fatigue accumulation: Repeated stress cycles initiate microcracks within the spring material that gradually propagate through the cross section.
Thermal cycling: Temperature fluctuations during operation alter the material properties and accelerate fatigue processes.
Surface corrosion or contamination: Chemical exposure or particle contamination can create localized stress concentrations that initiate fatigue cracks.
Loss of preload due to permanent deformation: Over time, plastic deformation may occur if the spring operates near its yield limit.
As spring stiffness decreases, the axial force maintaining valve plate contact becomes insufficient. This can introduce small axial separation between the cylinder block and the valve plate during pressure transitions. Such separation alters the timing of port sealing and may produce delayed pressure response during flow commutation.
Diagnostic Markers
Spring fatigue in the valve plate support system can produce measurable hydraulic and mechanical effects.
Typical indicators include:
Delayed pressure response during load changes: Pressure build-up occurs more slowly due to transient leakage between valve plate ports.
Increased pressure ripple amplitude: Axial instability of the valve plate affects commutation smoothness.
Abnormal noise during pressure transitions: Small axial impacts may occur as the valve plate recontacts the cylinder block.
Surface wear patterns on the valve plate: Uneven contact pressure may produce localized polishing or wear marks.
Variation in case drain flow: Intermittent leakage across the valve plate interface may increase return flow.
During troubleshooting, pressure response measurements and inspection of the valve plate assembly help differentiate spring fatigue from wear in the rotating group or control system components.
Engineering Solution
Restoring proper axial preload requires inspection of the spring assembly and associated contact surfaces.
Recommended engineering procedure:
Controlled disassembly of the rotating group: Remove the valve plate and associated spring components.
Spring dimensional inspection: Measure free length, compression characteristics, and visible fatigue damage.
Contact surface evaluation: Inspect the valve plate and cylinder block interface for signs of uneven loading or wear.
Spring replacement: Springs showing fatigue cracks, permanent deformation, or loss of stiffness must be replaced.
Verification of valve plate flatness: Ensure that the sealing surface maintains the correct geometry.
Assembly preload control: Install new springs with the correct compression to restore axial contact force.
Rotating group alignment inspection: Confirm that the cylinder block rotates concentrically relative to the pump shaft.
Operational testing: After reassembly, monitor pressure response, flow stability, and vibration levels.
Preventive maintenance includes monitoring hydraulic pressure stability, maintaining fluid cleanliness, and inspecting the valve plate support components during scheduled service intervals.
Aspect Plus Integration
Aspect Plus supplies valve plates, spring assemblies, rotating group components, and service parts for hydraulic units including the Volvo PVG130 Pump, supporting restoration of correct axial preload and stable hydraulic commutation.
