Short-time Ageing Test for Hydraulic Valves
The test rig is designed for the examination of three-body abrasion, erosion, and impact wear in hydraulic directional spool and seat valves. The influence of parameters from the fields of fluid contamination, flow conditions, and duty cycle can be investigated. A focus is set on fluid contamination with ISO MTD (A3) test dust, as this is anticipated to significantly accelerate the wear process.
The power supply of the test rig not only has to provide the testing manifold with a sufficient volume flow at a defined pressure level. Moreover, it has to realise a particle management maintaining constant test conditions. Therefore, a constant volume flow is conveyed to the filtering circuit (left figure, a), while the injection unit (b) injects new particle-contaminated fluid into the system. The contamination control of the test fluid is realised through the injected volume flow. In this way, a constant particle concentration, size distribution, and form can be achieved, even if particle wear occurs in the tested valve and in several components of the test rig. The main pump of the test rig (c) delivers up to 40 l/min at 300 bar. As it has to resist the particle contaminated fluid, a three-piston pump is used. A constant fluid temperature is achieved by a cooling circuit, fed by pump (d).
For the investigation of the wear mechanisms in a 4/3-way proportional spool valve, test results of several load cycles have to be analysed. By coupling two identical valves (right top), a constant pressure difference between working ports A and B can be achieved and the measurement results of both valves can be used for evaluation of wear. A gradient adaption algorithm acts on the positive and negative control coefficient of the upper valve. In this manner, a pressure control is realised, providing the upper valve with a command signal, which is analogous to the load cycle. The wear of poppet valves is analysed by an arrangement of two test valves in series. In this way, one can switch the volume flow through the other one. Hence, depending on the switching sequence, cycles can include closing operations both with and without volume flow through the test valves.
The stroke and pressure dependent flow characteristics of the single metering edges of the tested proportional spool valves are examined to describe their wear behaviour. Herein, the measurements are repeated after intermittent load phases, so that the progression of wear becomes obvious. The right bottom figure shows the valve manifold. By switching automated ball valves, the circuits for measurements and load cycles can be enabled automatically. Poppet valves are analysed with the same manifold. The investigation of wear on poppet valves is realised by measuring the leakage flow rate of a closed test valve by evaluating the pressure drop in an accumulator connected to the tested valve.