Silencer

1. A silencer comprising:

a housing including a draw-in portion drawing in fluid, and a plurality of sound attenuating portions arranged in a flowing direction of the fluid;

a first partition provided with an intermediate communicating portion communicating a most downstream attenuating portion with an adjacent attenuating portion located adjacent to the most downstream attenuating portion;

a valve portion disposed in the most downstream attenuating portion, the valve portion being capable of closing the intermediate communicating portion;

a valve holding portion holding the valve portion, the valve holding portion being detachably attached to the housing;

a draw-out portion provided in a portion of the most downstream attenuating portion other than the valve holding portion, the draw-out portion drawing out the fluid from the most downstream attenuating portion; and

a biasing member elastically biasing the valve portion so as to close the intermediate communicating portion,

wherein, in a space formed between the valve portion and the first partition, followed by pressing of flow of the fluid onto the valve portion, a virtual extended area that is an area of a region acquired by extending an inner circumferential face of the intermediate communicating portion to an end face of the valve portion on the side of the first partition is larger than a path sectional area of the draw-in portion.

2. The silencer according to claim 1 , wherein a path sectional area of the most downstream attenuating portion, and a path sectional area of the adjacent attenuating portion each are larger than a path sectional area of the intermediate communicating portion.

3. The silencer according to claim 1 , wherein the plurality of attenuating portions includes a low frequency-side attenuating portion attenuating sound in a lower frequency range, and a high frequency-side attenuating portion attenuating sound in a higher frequency range.

4. The silencer according to claim 3 , wherein the adjacent attenuating portion is the high frequency-side attenuating portion in which a sound absorbing member is disposed, and wherein the first partition is detachably attached to the housing.

5. The silencer according to claim 3 , wherein the adjacent attenuating portion is the high frequency-side attenuating portion, and

wherein the draw-in portion has a bent configuration.

6. The silencer according to claim 4 , wherein the draw-in portion is connected to a discharge port of a compressor body, and

wherein the most upstream attenuating portion is disposed so as to be invisible from the discharge port of the compressor body.

7. The silencer according to claim 3 , wherein the most upstream attenuating portion is the low frequency-side attenuating portion, and

wherein the draw-in portion is disposed on a side wall of the housing defining the most upstream attenuating portion.

8. The silencer according to claim 7 , wherein the most upstream attenuating portion is provided with a bypass pipe.

9. The silencer according to claim 3 , wherein the high frequency-side attenuating portion includes:

a tubular perforated plate having a plurality of through holes;

a rear fluid layer provided between the perforated plate and the housing; and

a second partition partitioning the rear fluid layer into a first region and a second region arranged in a flowing direction of the fluid in the perforated plate.

10. The silencer according to claim 9 , wherein a gap is provided between the second partition and a side wall of the housing or the perforated plate.

11. The silencer according to claim 9 , wherein the first region and the second region have different effective thicknesses defined as a ratio of a volume of the rear fluid layer to a porous area that is a sum of areas of the through holes.

12. The silencer according to claim 11 , wherein the second partition partitions the rear fluid layer such that the first region and the second region partially overlap each other.

13. The silencer according to claim 9 , wherein the most upstream attenuating portion is the low frequency-side attenuating portion,

wherein the high frequency-side attenuating portion is adjacently provided downstream of the low frequency-side attenuating portion, and

wherein the draw-in portion has a bent configuration.

14. The silencer according to claim 9 , wherein the most upstream attenuating portion is the low frequency-side attenuating portion,

wherein the high frequency-side attenuating portion is adjacently provided downstream of the low frequency-side attenuating portion, and

wherein a direction in which the fluid is introduced into the low frequency-side attenuating portion in the draw-in portion is different from a direction in which the fluid flows from the low frequency-side attenuating portion to the high frequency-side attenuating portion.

15. The silencer according to claim 3 , wherein the attenuating portion adjacently disposed upstream or downstream of the high frequency-side attenuating portion has a length that is a half of a length of the rear fluid layer.

16. The silencer according to claim 15 , wherein the attenuating portion having the length that is a half of the length of the rear fluid layer is adjacently provided upstream of the high frequency-side attenuating portion.