Spiral pumping stage and vacuum pump incorporating such pumping stage
View Patent ↗A molecular spiral-type vacuum pumping stage comprises a smooth surfaces rotor disk cooperating with a stator body. The stator body comprises a plurality of spiral channels on at least one surface facing the rotor disk. The cross-section area (σ) of these channels are reduced from the center to the outer periphery of the stator body so that the condition is satisfied according to which the internal channel speed, i.e. the product of the channel cross-section area and half the rotor velocity normal to the aforesaid area, is constant throughout the channels. Due to this arrangement, it is possible to avoid the risk of internal compression or re-expansions, this limiting the power losses. The present invention also refers to a vacuum pump comprising at least one pumping stage as described above.
1. Molecular spiral vacuum pumping stage comprising:
a rotor disk ( 7 ; 7 ′) having smooth surfaces and cooperating with a stator body ( 1 ; 11 ; 21 ), at least on one surface of the stator body facing said rotor disk comprising at least one spiral channel with a cross-section area (σ),
said spiral channel comprising an inlet ( 6 ; 6 ′) and an outlet ( 8 ; 8 ′) for pumping gas there through, wherein the cross-section area (σ) of said at least one channel is reduced from the center to the outer periphery of said stator body ( 1 ; 11 ; 21 ) according to the condition, to be respected within a maximum deviation of ±10%, where:
S
=
V
n
×
σ
=
2
πω
H
(
R
)
R
2
ⅆ
R
R
ⅆ
ϕ
1
+
[
ⅆ
R
R
ⅆ
ϕ
]
2
=
CONSTANT
,
wherein
S is the volumetric channel speed
V n is half the rotor velocity normal to area σ,
R is the distance from the center of the stator body ( 1 ; 11 ; 21 );
ω=V T /R is the rotor angular velocity;
V T is the local velocity of the rotor;
H(R) is the height of the channel, possibly variable as a function of R;
φ is the winding angle of the channel spiral.
2. Molecular spiral vacuum pumping stage of claim 1 , wherein said inlet ( 6 ) is provided at or close to the outer periphery of said stator body and said outlet ( 8 ) is provided at or close to the center of said stator body, so that the gas flows through said at least one channel in centripetal direction.
3. Molecular spiral vacuum pumping stage of claim 1 , wherein said inlet ( 6 ′) is provided at or close to the center of said stator body and said outlet ( 8 ′) is provided at or close to the outer periphery of said stator body, so that the gas flows through said at least one channel in centrifugal direction.
4. Molecular spiral vacuum pumping stage of claim 1 , wherein said stator body is provided with a plurality of spiral channels ( 3 a , 3 b , 3 c , 3 d ; 13 a , 13 b , 13 c , 13 d ; 13 a ′, 13 b ′, 13 c ′, 13 d ′; 23 a , 23 b , 23 c , 23 d , 23 e , 23 f ) connected in parallel and separated from each other.
5. Molecular spiral vacuum pumping stage of claim 4 , wherein said channels ( 3 a , 3 b , 3 c , 3 d ; 13 a , 13 b , 13 c , 13 d ; 13 a ′, 13 b ′, 13 c ′, 13 d ′) are defined and separated by corresponding spiral ribs ( 5 a , 5 b , 5 c , 5 d ; 15 a , 15 b , 15 c , 15 d ; 15 a ′, 15 b ′, 15 c ′, 15 d ′).
6. Molecular spiral vacuum pumping stage of claim 5 , wherein the number of said channels ( 3 a , 3 b , 3 c , 3 d ; 13 a , 13 b , 13 c , 13 d , 13 a ′, 13 b ′, 13 c ′, 13 d ′) is selected so that any radius vector originated at the center of the stator body intercepts at least two of said ribs ( 5 a , 5 b , 5 c , 5 d ; 15 a , 15 b , 15 c , 15 d , 15 a ′, 15 b ′, 15 c ′, 15 d ′) when moving in the radial direction from the center to the outer periphery of the stator body.
7. Molecular spiral vacuum pumping stage of claim 4 , wherein said stator body ( 21 ) comprises an outer ring ( 27 ) carrying cantilever curved vanes ( 25 a , 25 b , 25 c , 25 d , 25 e , 25 f ) defining therebetween corresponding spiral channels.
8. Molecular spiral vacuum pumping stage of claim 7 , wherein the number of said channels ( 23 a , 23 b , 23 c , 23 d , 23 e , 23 f ) is selected so any radius vector originated at the center of the stator body intercepts at least two of said ribs ( 25 a , 25 b , 25 c , 25 d , 25 e , 25 f ) when moving in the radial direction from the center to the outer periphery of the stator body.
9. The vacuum pump of claim 8 , wherein said one or more pumping stages being centripetal pumping stages ( 301 a , 301 b , 301 c ) are connected in series with a corresponding number of said one or more pumping stages being centrifugal pumping stages ( 303 a , 303 b , 303 c ), which are alternated with said centripetal stages.
10. The vacuum pump according to claim 8 , wherein said one or more pumping stages being one or more centrifugal pumping stages ( 505 a , 505 b , 505 c , 505 d , 505 e ) connected in parallel to each other.
11. The vacuum pump according to claim 8 , wherein said one or more pumping stages being one or more centripetal pumping stages ( 605 a , 605 b , 605 c , 605 d , 605 e ) connected in parallel to each other.
12. Molecular spiral vacuum pumping stage of claim 1 , wherein said stator body ( 11 ) is provided on both opposite surfaces with at least one spiral channel, the cross-section area (σ) of said channels on both opposite surfaces of said stator body ( 11 ) being reduced from the center to the outer periphery of said stator body ( 1 ; 11 ; 21 ) according to the condition, to be respected within a maximum deviation of ±10%, where:
S
=
V
n
×
σ
=
2
πω
H
(
R
)
R
2
ⅆ
R
R
ⅆ
ϕ
1
+
[
ⅆ
R
R
ⅆ
ϕ
]
2
=
CONSTANT
.
13. The vacuum pump of claim 12 , further comprising a stator body ( 11 ) provided on both surfaces ( 11 a , 11 a ′) with spiral channels, a first rotor ( 17 ) having smooth surfaces and facing a first surface ( 11 a ) of said stator ( 11 ) and cooperating therewith for forming at least one said centripetal spiral pumping stage and a second rotor ( 17 ′) having smooth surfaces and facing a second surface ( 11 a ′) of said stator ( 11 ) and cooperating therewith for forming said centrifugal pumping stage.
14. A vacuum pump, comprising:
an inlet for the gas to be pumped;
an outlet for the pumped gas;
a plurality of pumping stages located between said inlet and said outlet, one or more pumping stages of said plurality comprising:
a rotor disk ( 7 ; 7 ′) having smooth surfaces and cooperating with a stator body ( 1 ; 11 ; 21 ), at least on one surface of the stator body facing said rotor disk comprising at least one spiral channel with a cross-section area (σ),
said spiral channel comprising an inlet ( 6 ; 6 ′) and an outlet ( 8 ; 8 ′) for pumping gas there through, wherein the cross-section area (σ) of said at least one channel is reduced from the center to the outer periphery of said stator body ( 1 ; 11 ; 21 ) according to the condition, to be respected within a maximum deviation of ±10%, where
S
=
V
n
×
σ
=
2
πω
H
(
R
)
R
2
ⅆ
R
R
ⅆ
ϕ
1
+
[
ⅆ
R
R
ⅆ
ϕ
]
2
=
CONSTANT
.
15. The vacuum pump according to any of the claims 8 to 13 , wherein said one or more pumping stage is connected in series to a turbomolecular pumping stage.
16. The vacuum pump according to any of the claims 8 to 13 , wherein said one or more pumping stage is connected in series to a Gaede pumping stage and/or to a regenerative pumping stage.