Design, Development&Analysis of Hydraulic Noise Suppressor

In any hydraulic system, the pump is the main source of pulsations and vibrations. While pump manufacturers have made noise reduction a design goal, every pump still produces some ripple - the pump manufacturers' term for pulsations. Ripple produces the line vibrations which cause additional noise. System designers cannot change how much ripple the pump produces, so they must find ways to control the propagation of that ripple out through the rest of the system. One of the first areas that should be reviewed when attempting to reduce power-unit noise is the hydraulic conductors. Somewhat surprisingly, one factor that can contribute much to the noise level is improper use of hydraulic hose. Recent research at a large pump manufacturer showed that they could take an average of 5 dB (A) out of a standard power unit merely by changing the configuration of the hydraulic hose. Frequently, a 90? curved hose is used when a horizontal line has to be connected to a vertical line, and 180? hose curves also are quite common. Experiments show that both of these configurations actually increase system noise level. The solution don't bend hydraulic hose, instead, substitute bent metal tubing. Only use hose in a relatively straight line. It is well known that introducing a compressible medium such as nitrogen into the relatively incompressible medium of hydraulic fluid will help reduce pulsations. The challenge is to get the fluid to interact with the nitrogen so the nitrogen compresses and the fluid merely loses its pulsation. Over the years, nitrogen-charged accumulators have been installed in many hydraulic circuits to absorb pulsations. At first, accumulators were used as appendage devices - teed off the hydraulic line. The designer hoped that the pulsations would wander into the accumulator. However, experience showed that the majority of the pulsations bypassed the line leading to the accumulator. Different designs then evolved in which the full flow was diverted into the accumulator. Correctly sizing this type of accumulator is complicated and the circuit that directs flow into the accumulator is very expensive. Also, pressure drop through these accumulators may be unacceptably high. Another method of using compliant nitrogen to deal with noise-causing pulsations is to mount an in-line nitrogen-charged noise suppressor right at the outlet of the pump. (This suppressor is described in detail in the box at right. ) This design is more efficient than a large conventional accumulator because the fluid flow-path to the bladder is short and unrestricted, and the fluid contacts a much greater bladder area.