Pump Noise (Part 2) – How to Reduce

Previously on iHydrostatics N13, iEditor summarized the various sources of noise in axial piston pump, SBN and FBN together form the framework of noise basis. If you missed this post, please reply N13 in Wechat iHydrostatics to get the detailed explanations. Any questions are always welcomed, iEditor encourages you to leave your comments in iHydrostatics QQ Group: 426372753.


In Pump Noise (Part 2), noise topic will be continued. While in this episode, iEditor will show you kinds of researches on the pump noise reduction have been done and ongoing from past decades. Flow ripple and swash plate moment are the two major factors, what can we do to reduce that?

1Noise Reduction Research
Over the past few decades, lots of work has been reported detailing different techniques for reducing fluid-borne and structure-borne noise. The earliest research on this topic dated from 1976 by Yamauchi and Yamamoto.
Most of the methods reported so far detailed mainly on valve plate modification to achieve ideal pre-compression which would reduce the flow ripple as well as the force amplitude on the swash plate.
Here is the brief summary of the techniques investigated from the very beginning, advantages and shortcomings are also included in order to let you have a complete picture of each technique.
1Ideal Timing
It is simple and one of the oldest solutions where the cylinder opening to discharge port is delayed. The pre-compression is achieved by the forward motion of the piston. When designed properly, ideal timing reduces the flow ripple considerably for a particular operating point. Because of high sensitivity to operating conditions reduction in flow ripple is not guaranteed at other than the designed operating points.

2Relief Grooves
The opening to the discharge port care controlled using the grooves. Grooves offer similar reduction in flow pulsations as ideal timing. This technique is also sensitive to operating conditions. The rate of pressurization inside the displacement chamber is faster than ideal timing which affects the forces applied on the swash plate. Possibility of overshooting the desired pressure is high if the operating conditions are changed.

3Pre-Compression Filter Volume (PCFV)
Pre-compression is achieved by pressurized fluid stored in a small volume known as the filter volume. Sensitivity of PCFV to operating conditions is low and guarantees effective reduction in a wide range of operating conditions. But at speeds above 3000 rpm pre-compression is not fully accomplished due to inertia effect of the fluid transferred between PCFV and displacement chamber. PCFV does not guarantee gradual pre-compression, i.e. the rate of pressure rise is higher than that of using relief grooves or ideal timing. High pre-compression rate increases the force exerted on the swash plate and hence adverse effect on SBN.

4Relief Check Valves
The displacement chamber is connected to discharge port through a relief valve. Once pressure inside displacement chamber reaches the discharge value, the relief valve opens and avoids pressure peaks. Conceptually this is ideal pre-compression, but the implementation proved that the reduction is not any better than relief grooves or ideal timing. Main problem is that the poppet in the relief valve doesn’t respond fast enough leading to pressure peaks; also undamped oscillations of the poppet create additional noise. The pump becomes noisier at higher pressures.

5Highly Damped Check Valves (HDCV)
Undamped oscillations of relief check valve solution are remedied by heavily damping the poppet. Implementation is expensive and the reduction is not better than using PCFV. The effect of HDCV on the structure borne noise needs investigation. Also performance of HDCV for speeds above 1500 rpm is not reported. Swash plate instability reported during the operation.

6Cross Angle
This provides a secondary inclination (α) to the swash plate angle ( β) which changes position of dead centers of the piston. Cross angle reduces sensitivity of pre-compression to operating conditions by advancing/delaying piston dead center. Even though this offers reduction of flow ripple in wide operating range, the SBN aspect of this solution is not fully addressed. Also, cross angle is mainly suited for constant pressure application because it is sensitive to pressure changes.

7Active Cancellation Devices
These are fast acting actuators designed to cancel flow pulsations. Their implementation is often expensive; address mainly flow pulsations; do not change the rate of pressurizations; usually require complex control strategy. Such devices are designed mostly to cancel flow pulsations outside of the pump. Weingart (2004) used a piezo actuator to change the pre-compression in displacement chamber to reduce the flow ripple. He reported a 30% reduction in flow ripple and states that further reduction is possible with more efficient piezo crystals which offer higher volume changes. Reduction in flow ripple is not large when compared to other passive techniques.

2More about PCFV
Unfortunately, though various solutions have been proposed so far, only few of them has been applied on the real product. PCFV (Pre-Compression Filter Volume) solution is a typical example of those. Eaton, Linde and Parker all have similar products which was designed based on this solution, practical experience and data show that this kind of product is highly competitive to traditional design.

Getting interesting in PCFV? Keep up following with iHydrostatics ! More detailed information will be shared in the next episode – Pump Noise (Part 3) – Product with PCFV.

REFERENCES

[1]. Ganesh Kumar SEENIRAJ. NOISE REDUCTION IN AXIAL PISTON MACHINES BASED ON MULTI-PARAMETER OPTIMIZATION. Proc. of 4th FPNI-PhD Symp.
[2]. Zhang Junhui. Study on Valve Plate Design and Insensitive Flow-Distribution Method of Axial Piston Pump. Ph.D thesis. University of Zhejiang University.
[3]. Parker Technical Manual.
[4]. Linde Hydraulics Website. Http:// www.linde-hydraulics.com /.
[5]. Ganesh Kumar Seeniraj. EFFECT OF COMBINING PRECOMPRESSION GROOVES, PCFV AND DCFV ON PUMP NOISE GENERATION. International Journal of Fluid Power 12 (2011) No. 3.

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