**4. Effect of the fins on cavitation noise reduction (Comparison with constant valve opening)**

Kimura and Ogawa(1986) clarified using measurements of cavitation erosion and noise that the cavitation around the butterfly valve occurs most intensely when the valve is halfway open (40°-45°). Therefore, noise was measured around halfway-open valves in this study, and the degree of the cavitation reduction was investigated based on these measurement results. In the experiments, cavitation noise was measured at each flow velocity, while flow velocity was increased gradually by controlling the frequency of the pump.

Figure 3 shows the results of noise measurement when the valve was kept open constantly. The effect of the fins on noise was clear in the case of TYPE-B. In the case of the normal valve without a fin, cavitation occurred at, but in the case of TYPE-B, cavitation occurred at. These results proved that cavitation occurrence was suppressed by the fins. Moreover, the maximum noise just before flashing was 5dB lower in the case of TYPE-B than in the case of the normal valve.

Fig. 3. Effect of Fins on Cavitation Noise (Normal,TYPE-A,B,C: Valve Opening=45deg).

*<sup>v</sup> p p U*<sup>2</sup> / 2 

where is upstream pressure, is saturated vapor pressure, is density of water, and *U* is average

*P <sup>U</sup>* <sup>1</sup> <sup>2</sup> 2

**4. Effect of the fins on cavitation noise reduction (Comparison with constant** 

Kimura and Ogawa(1986) clarified using measurements of cavitation erosion and noise that the cavitation around the butterfly valve occurs most intensely when the valve is halfway open (40°-45°). Therefore, noise was measured around halfway-open valves in this study, and the degree of the cavitation reduction was investigated based on these measurement results. In the experiments, cavitation noise was measured at each flow velocity, while flow

Figure 3 shows the results of noise measurement when the valve was kept open constantly. The effect of the fins on noise was clear in the case of TYPE-B. In the case of the normal valve without a fin, cavitation occurred at, but in the case of TYPE-B, cavitation occurred at. These results proved that cavitation occurrence was suppressed by the fins. Moreover, the maximum noise just before flashing was 5dB lower in the case of TYPE-B than in the case of

Fig. 3. Effect of Fins on Cavitation Noise (Normal,TYPE-A,B,C: Valve Opening=45deg).

20 30 40 50

 **Valve opening 45**゜ **Normal Valve opening 45**゜ **TYPE-A Valve opening 45**゜ **TYPE-B Valve opening 45**゜ **TYPE-C**

Cavitation Number σ

(1)

is defined by the following formula:

(2)

in this study is defined as follows:

 

velocity was increased gradually by controlling the frequency of the pump.

**3. Cavitation number and pressure loss coefficient** 

upstream flow velocity. The pressure loss coefficient

where *P* is the differential pressure across the test valve.

The cavitation number

**valve opening)** 

the normal valve.

60

70

Sound Pressure Level (dB)

80

In the cases of TYPE-A and TYPE-C, the cavitation number at cavitation inception was larger than that in the case of the normal valve. The fin promoted the occurrence of cavitation because the middle fin was fixed on the orifice side, where cavitation occurrence was intense.
