Damping of Low Frequency Pressure Oscillation

Abstract

A hydraulic line between a hydraulic pump and an actuator comes under much stress when a pulsatile actuator is used. It causes a huge pressure oscillation in the hydraulic system and thus decreases reliability. For example in a rock drill transferable hydraulic power is tens of kilowatts, so efficiency is also significant. The operating frequency of the rock drill is usually between 30 and 60 Hz. The frequency of the pressure oscillation is then very low compared for example to pressure oscillation of a hydraulic pump.

The aim of this thesis is study pressure dampers when the damped frequency is low and when they work as a part of a wider system. After theoretical inspection, pressure dampers were simulated and then different dampers were tested with a pure sine wave pressure oscillation and then with the real rock drill. Different sizes of accumulators, a Helmholz resonator, a T-pipe and an inline suppressor were used in tests.

Dimension theories of dampers worked even though the operating frequency was low. The simulation models used operated well enough so that they can be utilised for a definition of the pressure damper.

The accumulator damped pressure oscillation of the rock drill well when it was installed near the hydraulic main line but it didn t damp pressure oscillation of the rock drill as expected when it was tuned by the natural frequency method. The T-pipe was easy to tune and the damping capacity was promising even with the rock drill. The Helmholtz-resonator damped well, but the size of the damper was too big for mobile hydraulic applications. The inline-suppressor didn t damp pressure oscillation between 30-60Hz much but it damped high pressure oscillation (1200Hz) well.