Measurement of Free Air in the Oil Close to a Hydraulic Pump

Abstract

Noise is a well-known challenge in hydraulic systems and hydrostatic pumps are one of the largest noise contributors in a hydraulic system. The existing noise reduction features, such as pressure relief groove and pre-compression filter volume, are more or less dependent on the working condition. It is essential to know the amount of free air when designing a quiet pump; however, it is not evident how much free air the oil contains. The free air content is different if the suction port is boost pressured or self-priming. The amount of free air in a well-designed system can be as low as 0.5% while in others up to 10%. This paper uses the three-transducer method to measure the amount of free air in the oil. The oil's compressibility can be measured for different working conditions and the free air content can then be calculated. The pre-study is performed with an extensive simulation model. Various noise reduction features' sensitivity to free air content is considered.

Optimization of Pressure Relief Grooves for Multi-Quadrant Hydraulic Machines in Different System Architectures

“…[1] describes the effect of pressure relief groove design on pump flow ripple and provides analytical equations for relief groove design based on a single operating point. [2] shows possible objectives to quantify noise in hydraulic machines and investigates the formulation of different objective functions. [3] describes a multi-objective optimization of pressure relief grooves in axial piston pumps described by their start and end angles as well as the slope of the opening area over the groove angle.…”

Modeling Study on Stiffness Characteristics of Hydraulic Cylinder under Multi-Factors

“…Since different hydraulic cylinder structures have different sizes, the levels need to be demonstrated according to Eqs. (2), (3), (7), (11), (12), and (16). After that, accept or reject each factor according to the accuracy requirements of the hydraulic cylinder stiffness.…”

“…According to Eqs. (2), (3), (7), (11), (12), and (16), the values of the hydraulic cylinder stiffness and the stiffness produced by each factor can be calculated respectively. Then the percentage of the stiffness produced by each factor relative to the hydraulic cylinder stiffness is also calculated.…”

“…By combining Eqs. (12) and (15), the equivalent elasticity modulus of the flexible hose can be derived.…”

“…By using the dissolving and releasing principle of the air in the hydraulic oil [11] and [12], and after multiple cyclic loading and unloading tests, the dissolved gas can be released as the undissolved gas. Then the air is discharged through the vent valve 7.…”