An important European Union Directive concerning noise is encouraging machine builders to reduce the sound level of their products and systems in order to protect the health of operators. In the development of our new Second Generation Radial Piston Pump, our designers worked closely with customers to find ways to reduce noise from one common source in hydraulic systems: the hydrostatic pump. The noise is caused by the physical phenomenon that within 2-5 ms the pressure level in the piston chamber changes between the tank (0 bar) and high pressure (up to 350 bar, (5,000 psi)) and vice versa. The result is a dynamic load acting on the inner parts and the housing that leads to vibration and sound emission from the pump.
To accurately measure the sound emission of pumps an anechoic chamber is necessary. This chamber enables the sound level of the pump to be measured free of any influence of other sound sources (e.g. electrical motor, HPU). Moog invested in an anechoic chamber in our Böblingen, Germany facility that was designed and built according to the demands of the European Norm for sound (DIN45635 part 26) and which enables a measurement of sound levels with a tolerance of 1dB(A).
The anechoic chamber is a room, equipped with absorbers of 65-centimeter (25.59 in.) in thickness at the walls and a soundproof floor. These absorbers enable the anechoic measuring of frequencies higher than 125 Hz. The acoustic conditions are then similar to a free field. The measurement of sound levels is performed according to the so called “Quarter Method” (DIN45635 part 26). That means all sound waves emitted by the pump, are led to two reflection boards (horizontal and vertical). The six microphones have defined positions in relation to the pump surface and it frames a virtual box around the pump. With mathematical equations and the size of this predefined box it is possible to calculate the total emitted sound level of the RKP.
With the help of the anechoic chamber it is easily possible to determine the influence of design modifications on the sound emission of the pump. This tool helped Moog engineers to design one of the quietest piston pumps available on the market. The result is that the RKP Second Generation models do not generally exceed 70-decibels, even in demanding conditions.
Author
Daniel Flach works as a designer and specialist of noise investigations in the Radial Piston Pump engineering department. He studied mechanical engineering at the Technical University, Zwickau.