Title of the invention: Multistage vacuum pump

[0001] The present invention relates to a multistage vacuum pump. The invention relates in particular to a vacuum pump of the dry type.

[0002] Multistage vacuum pumps have a plurality of pumping stages in series, in which a gas to be pumped circulates between a suction and a discharge. Among known vacuum pumps, a distinction is made between those with rotary lobes, also known as “Roots” pumps, with two or three lobes, or those with double claws, also known as “claw” pumps, or else those of the screw type. Pumps with rotary lobes comprise two rotors with identical profiles, rotating inside a stator in opposite directions. During rotation, the gas to be pumped is trapped in the free space between the rotors and the stator, and is driven by the rotors towards the following stage or, after the last stage, towards the discharge outlet. These vacuum pumps are called “dry” since, in operation, the rotors rotate inside a stator without any mechanical contact between the rotors and the stator, this making it possible not to use oil in the pumping stages.

[0003] A constant objective is to make assembling such vacuum pumps easier while at the same time reducing the costs. To this end, the stators can be produced in a plurality of pieces. According to a known solution, the stator is formed by assembling at least two complementary half-shells. Such a half-shell architecture makes it possible to reduce the assembly time and also makes it possible to reduce the risk of accumulation of alignment defects.

[0004] Furthermore, in order to reduce their energy consumption, the last pumping stages, on the discharge side, can have a swept volume, i.e. a volume of pumped gas, smaller than that of the first pumping stages, on the suction side.

[0005] During certain applications, for example for load lock pumping, the chambers of the locks are placed under vacuum from atmospheric pressure, so as to be able to transfer a substrate into a process chamber kept at low pressure. In order to decrease the pressure in the chamber from atmospheric pressure, the vacuum pump has to absorb significant initial flows of gas, which it is difficult for the last pumping stages on the discharge side to admit. All the pumping stages are however necessary at low pressure, so as to be able to reach the desired limit vacuum pressures. [0006] This same situation, in which the last stages can limit the overall pumping output of the vacuum pump, may occur for the pumping of the process chambers. Even if the process chamber is normally continually under vacuum, the vacuum pump has to be able to absorb a significant pumping flow when first placed under vacuum.

[0007] It is therefore essential to shorten these pressure drop periods so as not to slow down the manufacturing methods taking place in the process chamber, with high added value.

[0008] Some vacuum pumps therefore provide an offloading device connecting the outlet of a pumping stage to be offloaded to the discharge. The offloading device makes it possible to evacuate the surplus flow of gas coming from the outlet of the pumping stage to be offloaded directly to the discharge of the vacuum pump.

[0009] To this end, an enclosure external to the vacuum pump is generally disposed below the stator comprising pumping stages. Such an enclosure comprises, for each pumping stage to be offloaded, a channel connecting the outlet of this pumping stage to be offloaded to the discharge of the vacuum pump.

[0010] However, joining the enclosure to the stator of the vacuum pump requires an additional operation, increases the cost of the vacuum pump and increases the bulk, notably the height, of the vacuum pump. In addition, the channels for the connection of the pumping stages to the discharge can prove complicated to produce and involve as many additional seals to manage.

[0011] An aim of the present invention is to propose an improved vacuum pump that makes it possible to at least partially solve one of the abovementioned drawbacks of the prior art.

[0012] To this end, the invention relates to a multistage vacuum pump having a plurality of pumping stages respectively comprising an inlet and an outlet, the pumping stages being mounted in series between a suction and a discharge of the vacuum pump, a stator comprising at least one stator element produced by assembling two complementary halfshells that meet at a joining surface, at least one evacuation channel connected to the outlet of a pumping stage and in fluidic communication with the discharge, and at least one valve associated with the evacuation channel.

[0013] According to the invention, the evacuation channel is provided in one of the halfshells, opening in at least one mouth in the joining surface. The associated valve is arranged between the two half- shells, being at least partially mobile so as to shut off or free up the mouth of the evacuation channel, depending on a difference in pressure on either side of the valve.

[0014] The arrangement of the valve between the half-shells makes it possible to avoid joining an additional enclosure to the stator of the vacuum pump, so as to perform for example an offloading and/or discharge function. This makes it possible to reduce the cost and the bulk of the vacuum pump. In addition, the evacuation channel is produced in a simple manner within one of the half-shells. Finally, in the absence of an additional enclosure, such a solution makes it possible to minimize the seals to be managed with the outside.

[0015] The vacuum pump may also have one or more of the following features described below, considered separately or in combination.

[0016] The evacuation channel or one of the evacuation channels may be an offloading channel connected to the outlet of a pumping stage to be offloaded and in fluidic communication with the discharge.

[0017] According to one embodiment, the successive pumping stages are connected in series by a respective inter-stage channel connecting the outlet of a preceding pumping stage to the inlet of a following pumping stage.

[0018] A common channel may be connected at the outlet of the pumping stage to be offloaded. This common channel may be connected to at least two bypass portions, of which a first portion forms, with the common channel, an inter-stage channel connected to the inlet of the following pumping stage and a second portion forms, with the common channel, the offloading channel.

[0019] The evacuation channel or one of the evacuation channels may be a discharge channel connected to the outlet of the last pumping stage and in fluidic communication with the discharge.

[0020] The vacuum pump may have at least two valves respectively associated with a pumping stage. The valves may be dimensioned differently depending on the associated pumping stage. The valves may be dimensioned differently depending on set pressures.

[0021] The valve is mounted so as to be at least partially able to move in a cavity provided in the half-shell opposite the half-shell comprising the evacuation channel, the valve being arranged facing the mouth of the evacuation channel in the joining surface. [0022] The vacuum pump may have at least one outlet channel fluidically connecting the cavity to the discharge. This outlet channel may be provided in one of the half-shells.

[0023] According to an exemplary embodiment, the valve or at least one of the valves has a ball.

[0024] At least one annular seal may be arranged in the mouth of the evacuation channel associated with the valve.

[0025] The seal has for example a base accommodated in a first groove of the mouth of the evacuation channel. The base may be of toric overall shape. The first groove has for example a cylindrical overall shape.

[0026] The base may be surmounted by a portion delimiting a valve seat for example for the ball and accommodated in a second groove of the mouth of the evacuation channel, provided above the first groove. The portion delimiting the valve seat may be frustoconical. The second groove may have a frustoconical overall shape complementary to the frustoconical portion of the seal.

[0027] The vacuum pump may have at least one injection channel opening via at least one injection orifice configured to inject a purging gas onto the valve and/or onto a bearing face of a valve seat.

[0028] The vacuum pump may have a discharge duct arranged to connect the outlet of the last pumping stage to the discharge and fluidically connected to the evacuation channel. This discharge duct has for example a housing for accommodating a silencer of the vacuum pump, interposed between the outlet of the last pumping stage and the discharge.

[0029] The discharge duct may be fastened to one or other of the half- shells.

[0030] Furthermore, the vacuum pump comprises for example two shafts of rotors, configured to rotate synchronously in opposite directions in the pumping stages so as to drive a gas to be pumped between the suction and the discharge.

[0031] The stator may comprise at least one end piece. The stator element is axially joined to the end piece or to another stator element.

[0032] The invention also relates to a pumping unit having at least one vacuum pump. This vacuum pump may for example be as defined above. [0033] The pumping unit may also have at least one additional pump upstream of the vacuum pump in the direction of circulation of the gas.

[0034] Advantageously, the pumping unit may have at least one other valve arranged so as to be able to move between the stators of the additional pump and of the vacuum pump. It is configured to shut off or free up a mouth of a pipe connected to the discharge of the vacuum pump, depending on a difference in pressure on either side of the valve.

[0035] The stator of the vacuum pump defines for example a seat for the valve.

[0036] The valve may be accommodated in a cavity provided in the stator of the additional pump.

[0037] Other features and advantages of the invention will become more clearly apparent upon reading the following description, which is given by way of illustrative and nonlimiting example, and the appended drawings, in which:

[0038] [Fig. 1] is a perspective view showing in part a stator of a multistage vacuum pump according to a first exemplary embodiment.

[0039] [Fig. 2] is a schematic depiction of elements of a vacuum pump according to a second exemplary embodiment.

[0040] [Fig. 3] is a view in cross section of the stator in Figure 1 showing a valve of an offloading device of the vacuum pump in the closed position.

[0041] [Fig. 4] is a view in longitudinal section of a part of the stator in Figure 1 showing two valves of offloading devices of the vacuum pump in the closed position.

[0042] [Fig. 5] is a schematic depiction of elements of a vacuum pump according to a third exemplary embodiment.

[0043] [Fig. 6] is a schematic depiction of elements of a vacuum pump according to a fourth exemplary embodiment.

[0044] [Fig. 7] is a schematic depiction of elements of a vacuum pump according to a fifth exemplary embodiment.

[0045] [Fig. 8a] is a schematic depiction of elements of a vacuum pump according to a sixth exemplary embodiment.

[0046] [Fig. 8b] is a schematic depiction of elements of a vacuum pump according to a seventh exemplary embodiment. [0047] [Fig. 9] is a schematic depiction of elements of a vacuum pump according to an eighth exemplary embodiment.

[0048] [Fig. 10] is a schematic depiction of a pumping unit having the vacuum pump in Figure 7 and an additional pump.

[0049] In these figures, identical or similar elements bear the same reference numerals. The figures have been simplified for the sake of clarity. Only the elements necessary for understanding the invention are shown.

[0050] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment or that the features apply to a single embodiment. Individual features of different embodiments can also be combined or interchanged to provide other embodiments.

[0051] Figure 1 illustrates an exemplary embodiment of a multistage vacuum pump 1, i.e. a vacuum pump having a plurality of stages (at least two). The vacuum pump 1 is in particular of the dry type.

[0052] This vacuum pump 1 may be a primary vacuum pump that is able to be started at atmospheric pressure. Such a primary vacuum pump is configured to draw in, transfer and then discharge the pumped gases at atmospheric pressure.

[0053] The vacuum pump 1 has a stator 2 that forms at least two pumping stages that are mounted in series between a suction 4 and a discharge 5 and in which a gas to be pumped can circulate.

[0054] In the example illustrated in Figure 1, the vacuum pump 1 has for example five pumping stages. Of course, this number is not limiting. Figure 2 shows another exemplary embodiment of a multistage vacuum pump 1, having for example three pumping stages 3a-3c.

[0055] The vacuum pump 1 also has two shafts of rotors 6, configured to rotate synchronously in opposite directions in the pumping stages 3a-3c such that the rotors 6 drive a gas to be pumped between the suction 4 and the discharge 5.

[0056] The rotors 6 have for example rotary lobes with identical profiles, for example of the “Roots” type. As a variant, they may be lobes of the “claw” type or else of the screw type or based on another similar vacuum pump principle. The shafts of rotors are driven in rotation by at least one motor (not shown) of the vacuum pump 1. The motor is situated for example at one end of the vacuum pump 1.

[0057] Each pumping stage 3a, 3b, 3c is formed by a compression chamber accommodating the rotors 6. The compression chambers comprise a respective inlet E and outlet S. During rotation, the gas drawn in through the inlet E is trapped in the volume created by the rotors 6 and the stator 2, and is then transferred by the rotors 6 towards the following stage and so on as far as the discharge 5.

[0058] The vacuum pump 1 is called “dry” since, in operation, the rotors 6 rotate inside the stator 2 of the vacuum pump 1 in opposite directions without any mechanical contact between them or with the stator 2, this making it possible not to use oil in the pumping stages 3a-3c.

[0059] The successive pumping stages 3a-3c are connected in series one after another by respective inter-stage channels 7 connecting the outlet S of the preceding pumping stage 3a-3b to the inlet E of the following pumping stage 3b-3c. The inlet E of the first pumping stage 3a, also called “suction stage”, communicates with the suction 4 of the vacuum pump 1. The outlet S of the last pumping stage 3c, also called “discharge stage”, communicates with the discharge 5. The one or more pumping stages mounted in series between the suction stage 3a and the discharge stage 3c are also called intermediate stages.

[0060] Furthermore, the stator 2 has for example at least one stator element produced by assembling a first and a second complementary half- shell 2 A, 2B. A stator casing (not shown) may optionally surround the joined half-shells 2A, 2B. The stator 2 may also have at least one end piece (not shown), for example two end pieces on either side of the two half-shells 2A, 2B. The one or more end pieces form for example supports for the bearings of the shafts of rotors 6. The half-shells 2A, 2B and the optional end pieces are joined together for example by axial assembly. The axial direction is defined as the longitudinal direction of the vacuum pump 1, in which the axes of the shafts of rotors 6 extend. The assembly can be done by any appropriate known fastening means, for example by means of a hardenable adhesive and/or by screwing. One or more seals (not shown) may be provided so as to ensure the sealing between the various joined elements of the vacuum pump 1. [0061] The two half-shells 2A, 2B, when assembled, meet at a joining surface 8, so as to form the compression chambers of the pumping stages 3a-3c. The compression chambers and the inter-stage channels 7 are partly formed in the first half-shell 2A and partly in the second half-shell 2B. The inter-stage channels 7 are for example provided on the sides of the compression chambers, in the half-shells 2A, 2B. They may extend from a single side of the compression chambers or from both sides of the compression chambers. There is for example an inter-stage channel 7 between two successive pumping stages 3a, 3b, 3c that are mounted in series or two inter-stage channels 7 that are mounted in parallel between these two pumping stages 3a, 3b, 3c on each side of the compression chamber.

[0062] The joining surface 8 can be flat. It passes for example through a median plane of the dry primary vacuum pump 1. This joining surface 8 may be strictly flat or may have for example complementary raised shapes or grooves or slots for example for seals between the half-shells 2A, 2B. In the state in which the two half-shells 2A, 2B are assembled, the axes of the shafts of rotors 6 are for example contained between the half- shells 2 A, 2B at the joining surface 8.

[0063] In a known manner, orifices are provided in transverse walls of the half-shells 2A, 2B separating the compression chambers, and optionally in the end pieces for the passage of the shafts of rotors 6.

[0064] The stator 2 may have a plurality of stator elements and at least one end piece, for example two end pieces on either side of the stator elements (not shown). Each stator element is assembled axially (i.e. in a direction parallel to the axis of the shafts of rotors 6) with another stator element or with an end piece of the stator 2, so as to form the compression chambers of the pumping stages 3a-3c accommodating the rotors 6. At least one, or even each, of the stator elements may be produced by assembling two complementary half-shells that meet at a joining surface.

[0065] The vacuum pump 1 also has at least one channel, also called evacuation channel, and a valve, which are associated with a pumping stage 3a, 3b, 3c to be connected to the discharge 5. Specific examples of such associated channels and valves are described in detail below. In particular, they may be a discharge channel and valve and/or an offloading channel and valve.

[0066] The evacuation channel is provided in one of the half-shells 2A or 2B, opening in at least one mouth in the joining surface 8. This mouth may be shut off or freed up by the associated valve. Thus, the evacuation channel ends at the joining surface 8. In particular, the evacuation channel is connected via a first end to the outlet S of the associated pumping stage 3a-3c. Its second end is the mouth in the joining surface 8 that can be shut off or freed up by the associated valve.

[0067] The associated valve is notably metallic. This associated valve is arranged between the two half-shells 2A, 2B. It is arranged facing the mouth (or second end) of the associated evacuation channel in the joining surface 8. The valve is at least partially mobile so as to be able to free up or shut off the mouth of the associated evacuation channel. Such a valve is configured to open depending on pressure differentials on either side of the valve, more specifically when the difference in pressure is above a predefined threshold. The valve may be mounted so as to be able to move in a cavity provided in the other half-shell 2B, 2A. When the valve frees up the mouth (or second end), the evacuation channel then opens into the cavity.

[0068] In a nonlimiting manner, the valve may have a ball, for example made of steel. The valve may be configured to move in translation, in rotation or else with a combined movement.

[0069] By arranging the valve between the two half-shells 2A, 2B, joining an additional enclosure to the stator of the vacuum pump is avoided, and this reduces the cost and the bulk of the vacuum pump. In addition, it is simple to produce the evacuation channel and achieve the sealing.

[0070] According to one embodiment, the vacuum pump 1 has at least one channel 11 and an offloading valve 13, which are associated with a pumping stage 3a, 3b, to be connected to the discharge 5.

[0071] Specifically, in order to reduce the energy consumption of the vacuum pump 1, the discharge stage 3c, or even also at least some of the last intermediate stages, has a swept volume, i.e. a volume of pumped gas, smaller than that of the one or more first stages. In order to absorb the strong flows of gas coming notably from the start of placing a chamber at atmospheric pressure under vacuum, the vacuum pump 1 may have at least one offloading device 9 of a pumping stage 3 a, 3b.

[0072] The offloading device 9 makes it possible to evacuate any surplus flow of gas coming from the outlet S of a pumping stage to be offloaded towards the discharge 5 of the vacuum pump 1. The choice of the pumping stage to be offloaded depends on the geometry of the vacuum pump 1 and more particularly on the swept volume in the pumping stages. Generally, the pumping stage having the highest compression ratio is offloaded. Since the swept volume decreases with the increase in pressure, the pumping stages to be offloaded are usually the low-pressure pumping stages such as the first or second pumping stage. It can also be envisaged to offload a plurality of pumping stages, for example the first two pumping stages.

[0073] The or each offloading device 9 has the offloading channel 11 and the offloading valve 13.

[0074] The offloading channel 11 is connected to the outlet S of the pumping stage to be offloaded 3 a, 3b and is in fluidic communication with the discharge 5 of the vacuum pump 1. It is notably connected via a first end to the pumping stage to be offloaded 3a, 3b.

[0075] The offloading channel 11 forms an evacuation channel provided in one of the halfshells 2A or 2B. In the examples illustrated, the offloading channel 11 is provided in the lower half-shell 2B with reference to the orientation of the vacuum pump 1 in the assembled state.

[0076] This offloading channel 11 may be separate from the inter-stage channel 7 at the outlet of the pumping stage to be offloaded 3 a, 3b. According to an alternative that is not shown, a common channel connected at the outlet S of the pumping stage 3 a, 3b to be offloaded may be connected to two bypass portions, of which a first portion forms an inter-stage channel 7 connected to the inlet E of the following pumping stage and a second portion forms the offloading channel 11 opening onto the joining surface 8.

[0077] Depending on the dimensions and/or pumping capacities of the vacuum pump 1, the latter may have only a single offloading device 9 with a single mouth of the offloading channel 11 and an associated offloading valve 13. As an alternative, a plurality of offloading devices 9 mounted as bypass may be provided so as to offload a greater flow of gas while preserving a reduced bulk. By way of example, two offloading channels and two associated valves may be provided so as to offload a single pumping stage. Furthermore, a plurality of offloading devices 9 may be provided so as to offload a plurality of pumping stages.

[0078] When a plurality of offloading devices 9 are provided so as to offload a plurality of pumping stages, the various offloading valves 13 may be dimensioned differently according to the associated pumping stage to be offloaded and/or depending on set pressures.

[0079] The or each offloading valve 13 is arranged so as to be able to free up or shut off the mouth (or second end) of the associated offloading channel 11.

[0080] More specifically, such an offloading valve 13 is arranged at least partially in a cavity 15 provided in the other half-shell, i.e. in the half-shell opposite the offloading channel 11, facing the mouth (or second end) of the associated offloading channel 11. In the examples illustrated, the cavity 15 is provided in the upper half-shell 2A.

[0081] A single offloading valve 13 may be arranged per cavity 15 or by contrast a plurality of offloading valves 13 may be arranged in a common cavity 15. In the latter case, the cavity 15 may have its own housing in which each offloading valve 13 can move.

[0082] The offloading valve 13 operates like a plug that opens so as to prevent undesirable overpressures in the vacuum pump 1. Thus, during normal operation of the vacuum pump 1, i.e. for pumping a flow of gas dimensioned for the pumping capacity of the vacuum pump 1, the mouth (or second end) of the or each offloading channel 11 is closed by the associated offloading valve 13. Likewise, in the event of an overpressure in the associated pumping stage 3a, 3b, the offloading valve 13 is configured to open.

[0083] In particular, when the pressure difference is below the set threshold of the offloading valve 13, the latter is in a shut-off position, preventing the passage of the gases towards the discharge 5. This prevents the pumped gases from bypassing the following pumping stages. The pumped gas follows the path shown by the arrows Fl in solid line. It is drawn in via all the pumping stages 3a-3c and leaves at the outlet S of the discharge stage 3c. Then, the gas circulates as far as the discharge 5 of the vacuum pump 1.

[0084] When the pressure difference is above the set threshold of the offloading valve 13, the latter frees up the passage of the gas to be pumped that can be evacuated from the offloaded pumping stage 3a, 3b towards the discharge 5. This makes it possible to bypass the one or more last pumping stages 3c of the vacuum pump 1 that could limit the overall swept-volume output. The offloaded gas follows the path shown by the white arrows F2 of which the outline is shown in dashed line.

[0085] In general, in the shut-off position, the offloading valve 13 is in contact with a bearing face of an associated valve seat. Such a valve seat has a passage or an opening in fluidic communication with the offloading channel 11. When the offloading valve 13 is in the shut-off position, it closes the opening of the valve seat. By contrast, when it opens, the offloading valve 13 is for example away from the valve seat and frees up the passage of the gases.

[0086] According to the example of the offloading valve 13 comprising a ball, such a valve 13 may be opened with a translational movement of the ball in the direction of a corresponding end wall 16 of the cavity 15. For example, a surplus of gas lifts the one or more balls from their respective valve seat.

[0087] Furthermore, the offloading valve 13 is configured to close in a sealed manner. To this end, as can be seen in Figures 3 and 4, the offloading device 9 may have at least one annular seal 17 arranged in the mouth (or second end) of the offloading channel 11. Such a seal 17 defines the valve seat.

[0088] When the offloading valve 13, which is for example in the shape of a ball, rests on the seat formed by the seal 17 and is partially housed in the cavity 15 facing the mouth (or second end) of the offloading channel 11, it shuts off the mouth of the offloading channel 11 in a sealed manner.

[0089] The shape of the seal 17 is complementary to the shape of the offloading valve 13 and to the shape of the mouth (or second end) of the offloading channel 11.

[0090] According to a particular exemplary embodiment, the seal 17 may be of frustoconical overall shape, and this allows the ball forming the offloading valve 13 to centre itself.

[0091] The seal 17 also makes it possible to guide by cushioning the fall of the ball when it drops back onto the valve seat, for example when the flow of gas decreases and can again be absorbed by the vacuum pump 1.

[0092] By way of example, the seal 17 has a base 17a surmounted by a portion 17b defining the valve seat. Such a seal 17 is preferably produced in one piece for example by moulding. The seal 17 has at least one material chosen from an elastomer material, a silicone material, and this makes it possible to improve its mechanical integrity and its resistance to high temperatures of the vacuum pump 1.

[0093] The base 17a is housed in a first groove 21 complementary to the mouth of the offloading channel 11. This makes it possible to secure the seal 17 in the offloading channel 11. The base 17a has for example a toric shape. The first groove 21 has for example a cylindrical overall shape, and this makes it possible to leave a clearance around the toric base 17a of the seal 17 allowing elastic nesting thereof in the first groove 21.

[0094] According to one embodiment, the portion 17b delimiting the valve seat may have a frustoconical external shape. It is accommodated in a second groove 23 complementary to the mouth of the offloading channel 11, provided above the first groove 21. In a complementary manner, the second groove 23 may be of frustoconical shape. Thus, the external frustoconical portion 17b of the seal 17 matches the complementary shape of the frustoconical portion of the mouth of the offloading channel 11. The reinforcement provided by the frustoconical mouth of the channel 5 makes it possible to improve the mechanical integrity of the annular seal 17 and its fastening in the mouth.

[0095] As schematically shown in Figure 5, an elastic return member 25 may be arranged and configured to urge an associated offloading valve 13 towards the position shutting off the mouth of the facing offloading channel 11. The elastic return member 25 has for example a spring, such as a coil spring, interposed between the offloading valve 13 and the half- shell, in this case the half- shell 2 A, of the stator 2 facing the offloading channel 11. In particular, the spring may be as one with an end wall 16 of the cavity 15. This spring also makes it possible to guide the movement of the offloading valve 13.

[0096] As an alternative, it is also possible not to use such an elastic return. In this case, the offloading valve 13 is urged into the shut-off position by the force of gravity.

[0097] Advantageously, injection of a purging gas may be provided so as to clean the offloading valve 13 or the valve seat. The purging gas is for example nitrogen. The injection of purging gas, which may be continuous or discontinuous and targeted over time, makes it possible to prevent the presence of deposits and avoid contamination at the offloading valve 13, which could harm the operation of the offloading valve 13 and cause a leak. This cleaning makes it possible for the sealing function in the shut-off position and the opening function of the offloading valve 13 in the event of overpressure to be ensured for longer between two maintenance periods.

[0098] To this end, the vacuum pump 1 may have at least one injection channel 27 shown in dashed line in Figure 6, opening via at least one injection orifice (not visible in the figures). According to an exemplary embodiment, such an injection channel 27 may be provided in one of the half-shells; in the example illustrated, it is the lower half-shell 2B. The injection orifice may for example be obstructed by the offloading valve 13 when it closes and shuts off the mouth of the offloading channel 11, and freed up when the offloading valve 13 opens and frees up the mouth.

[0099] The purging gas may be injected onto a bearing face of the valve seat. As a variant or in addition, the purging gas can be injected onto the offloading valve 13, notably the part bearing on the valve seat in the position shutting off the mouth of the offloading channel 11. The purging gas can be injected for example when the offloading valve 13 is open and frees up the mouth (or second end) of the offloading channel 11. As a variant or in addition, the purging gas can be injected when the offloading valve 13 is closed, and shuts off the mouth (or second end) of the offloading channel 11. In this case, the injection orifice opens outside the valve seat.

[0100] In the example in Figure 6, only one injection channel 27 is shown. This number is not limiting. A plurality of injection channels 27 may be arranged to clean a single offloading valve 13 and/or associated valve seat. As a variant, a plurality of injection channels 27 may be provided for various offloading valves 13 and/or valve seats.

[0101] Furthermore, the vacuum pump 1 also has at least one outlet channel 29 fluidically connecting the or each cavity 15 to the discharge 5. Such an outlet channel 29 may be provided in the half-shell (for example 2B in this case) having the offloading channel 11, as shown in Figures 2 and 5. Alternatively, the outlet channel 29 may be provided in the half-shell (for example 2A) having the cavity 15, as shown in Figures 7 to 8b.

[0102] Thus, when the or one of the offloading valves 13 opens, the gas at the outlet S of a offloaded pumping stage 3a, 3b passes beneath the offloading valve 13 into the cavity 15 before being introduced into the outlet channel 29 and then reaches the discharge 5 of the vacuum pump 1 (arrows F2).

[0103] Finally, the vacuum pump 1 generally has a discharge valve 31 (also called non-retum valve) arranged at the outlet of the last pumping stage 3c (Figure 2). As described above, such a valve 31 is configured to open depending on pressure differentials on either side of the valve 31. It may be urged into the closed position via an elastic return member such as a spring 33 or by the force of gravity. The discharge valve 31 makes it possible to prevent the pumped gases from returning into the vacuum pump 1.

[0104] In the examples in Figures 2, 5 and 6, the discharge valve 31 is mounted in a discharge duct 35 arranged to connect the outlet S of the last pumping stage 3c to the discharge 5 of the vacuum pump 1. The discharge duct 35 may be disposed beneath the pumping stages 3a-3c and be fastened to the lower half-shell 2B by any appropriate fastening means. As a variant, the discharge duct 35 may be disposed above the pumping stages 3a-3c, being fastened to the upper half-shell 2A as in the examples in Figures 8a, 8b. The discharge gases are generally hotter than those of the first stages (as a result of the compression ratios and the increase in pressure in the stages known as high-pressure stages, i.e. the one or more last pumping stages). In the case of a vacuum pump used to pump process gases, such as those used in methods for manufacturing semiconductor elements notably, it may be desirable to control the temperature of the discharge gases. To this end, the discharge duct 35 may be insulated and/or heated in order to keep the discharge gases at high temperature. The discharge duct 35 fastened to one or other of the half-shells 2A, 2B thus makes it possible to reach the temperatures required in the vacuum pump 1 by using the heat from the discharge gases to heat the stator 2.

[0105] In particular, the discharge duct 35 may extend above or below the one or more first pumping stages. When the discharge duct 35 is situated above the pumping stages 3a-3c, it can be extended so as to be crossed by an inlet duct connecting the suction 4 to the inlet of the first stage 3 a as shown in the example in Figure 8b. The heat of the discharge gases thus makes it possible to heat the pumping stages, notably the stages known as low- pressure stages, i.e. the one or more first pumping stages, or even to heat the inlet duct connected to the suction 4.

[0106] Furthermore, the or each outlet channel 29 fluidically connected to at least one offloading channel 11 opens into this discharge duct 35.

[0107] In addition, the discharge duct 35 may have a housing for accommodating a silencer of the vacuum pump 1, interposed between the outlet S of the last pumping stage 3c and the discharge 5. The silencer is therefore fluidically connected to the outlets of the or each outlet channel 29 and to the outlet S of the last pumping stage 3c. The discharge valve 31 is generally arranged upstream of the silencer in the direction of circulation of the gas.

[0108] Alternatively, as shown in Figures 7 to 9, the discharge valve 31 is arranged between the two half-shells 2A, 2B similarly to the offloading valves 13, as described above. According to this embodiment, the evacuation channel associated with the discharge valve 31 is a discharge channel 37 connected to the outlet S of the last pumping stage 3c. The discharge channel 37 is provided in one of the half-shells, opening in at least one mouth in the joining surface 8. This discharge channel 37 may be arranged in the same half-shell as the one or more offloading channels 11. In the examples illustrated, it is arranged in the lower half-shell 2B.

[0109] In addition, the discharge valve 31 is mounted so as to be at least partially able to move in a cavity 39 fluidically connected to the discharge 5 of the vacuum pump 1. This cavity 39 is also referred to as discharge cavity. Such a cavity 39 is provided in the halfshall opposite the discharge channel 37, for example the upper half-shell 2A. This discharge cavity 39 may be provided in the same half-shell as the cavities 15 housing the offloading valves 13.

[0110] As shown in Figure 7, the discharge cavity 39 may be provided in the same half-shell as the outlet channel 29 and open into this outlet channel 29. Thus, all the gas discharged or offloaded may be evacuated from the half-shell via the outlet channel 29. In this case, a silencer may be interposed between the discharge 5 and the outlet of the outlet channel 29. Such a silencer may be simplified relative to the embodiments with a plurality of outlets connected to the silencer. The vacuum pump 1 is even more compact.

[0111] It can also be envisaged that the discharge cavity 39 and the one or more outlet channels 29 open into a common discharge duct 35 connected to the discharge 5. The discharge duct 35 may be fastened above the first half-shell 2A (Figure 8a or 8b) or below the second half-shell 2B (Figure 9). In particular, when the discharge duct 35 is fastened above the first half shell 2A, this discharge duct 35 may stop before the suction 4 (Figure 8a), or by contrast the inlet duct connecting the suction 4 to the inlet of the first stage 3a may cross this discharge duct 35 (Figure 8b). As described above, these configurations make it possible to reach the temperatures required in the vacuum pump 1, or even to heat the inlet duct connected to the suction 4 (Figure 8b).

[0112] Similarly to the operation of the offloading valves 13, the discharge valve 31 is arranged so as to shut off or free up the mouth of the discharge channel 37 connected to the outlet of the last pumping stage 3c. When it is closed, the discharge valve 31, such as a ball, may bear on a valve seat and when it opens it may move away therefrom. The valve seat may be defined by a seal 17 as described with reference to Figures 3 and 4. The discharge valve 31 may be urged towards the closed position shutting off the mouth of the channel 37 by the force of gravity or via an elastic return member, such as a spring 25, as described with reference to Figure 5. [0113] Furthermore, in the examples in Figures 7 to 9, the half-shells 2A, 2B house between them both a discharge valve 31 and offloading valves 13. According to another embodiment, the discharge valve 31 may be arranged between the half-shells 2A, 2B without otherwise making provision to interpose, between the latter, offloading valves 13.

[0114] Figure 10 shows an exemplary embodiment of a pumping unit 100 having a vacuum pump 1 and at least one additional pump 200. The additional pump 200 is in this example arranged upstream of the vacuum pump 1, in the direction of circulation of the gas. This additional pump 200 may complement the vacuum pump 1 according to one or other of the embodiments described above with reference to Figures 1 to 9.

[0115] Such an additional pump 200, which is also called a “booster”, makes it possible to increase the pumping speed. It may in particular be a Roots vacuum pump or compressor, also known as “Roots blower”, which may comprise one stage or be multistage. Each pump has a drive motor configured to drive the rotors in rotation.

[0116] The pumping unit 100 may have one or more pipes 41, 43 between the additional pump known as “ booster” 200 and the vacuum pump 1.

[0117] In such a pumping unit 100, during opening of a valve (not shown), the pumps 1, 200 are subjected to a pressure wave that can stress the mechanical parts. In order to intermittently absorb significant pumping flows at the inlet of the additional pump known as “booster” 200, the pumping unit 100 has at least one valve 45, also called offloading valve.

[0118] This valve 45 may be arranged between the additional pump known as “ booster” 200 and the vacuum pump 1. The offloading valve 45 may be arranged between the stators of the additional pump known as “ booster” 200 and of the vacuum pump 1. More specifically, the offloading valve 45 is arranged so as to bypass the stages 3a-3c of the vacuum pump 1. The offloading valve 45 may be fluidically connected to the discharge 5 of the vacuum pump 1. To this end, the valve 45 is arranged so as to be able to move between the stators of the two pumps 1, 200, so as to shut off or free up a mouth of a pipe 43, depending on a difference in pressure on either side of the valve 45.

[0119] The offloading valve 45 may be produced in a similar manner to the offloading valve 13 or to the discharge valve 31 of the vacuum pump 1.

[0120] A pipe 41 may be connected to the outlet of the additional pump known as “ booster”

200. This pipe 41 may have at least two bypass portions, of which a first portion is connected to the inlet of the first pumping stage 3 a of the vacuum pump 1 and a second portion is connected to the offloading valve 45. The other pipe 43 may be connected at the outlet of the offloading valve 45 and to the discharge 5 of the vacuum pump 1.

[0121] In the example illustrated in Figure 10, the pipe 43 at the outlet of the offloading valve 45 opens into the outlet channel 29 provided in one of the half-shells 2A of the vacuum pump 1. According to a variant that is not shown, this pipe 43 may open into a discharge duct 35 of the vacuum pump 1 as described above.

[0122] The offloading valve 45 makes it possible to bypass the pumping stages 3a-3c of the vacuum pump 1 in the event of overpressure. When the pressure difference is below the set threshold of the offloading valve 45, the pumped gas follows the path shown by the arrows Fl in solid line and is drawn in via the first pumping stage 3a. By contrast, when the pressure difference is above the set threshold of the offloading valve 45, the gas at the outlet of the additional pump 200 follows the path shown by the white arrows F2’ of which the outline is shown in solid line, so as to “bypass the vacuum pump” and be evacuated towards the discharge 5 of the vacuum pump 1.

[0123] In addition, one or more pipes 41, 43 between the additional pump or “booster” 200 and the vacuum pump 1 may be provided in the stator of one or both pumps 1, 200. Notably, the pipe 43 at the outlet of the offloading valve 45 and connected to the discharge 5 of the vacuum pump 1 may pass through the stator 2 of the vacuum pump 1.

[0124] In particular, it can be envisaged that the stator of one of the pumps, for example the stator 2 of the vacuum pump 1, acts as seat for the offloading valve 45. In this case, the offloading valve 45 may be arranged so as to be able to move in a cavity provided in the stator of the additional pump known as “ booster” 200. The valve seat 45 is defined facing the cavity.

[0125] Thus, according to one or other of the variant embodiments described above, one or more valves 13, 31 may be integrated directly into the functional pumping block, between the half-shells 2A, 2B, without it being necessary to provide an external enclosure to be added to the vacuum pump 1. The joining surface 8, i.e. the joint plane of the half-shells 2A, 2B, is used and shaped to accommodate such valves 13, 31. For each valve 13, 31, an associated evacuation channel 11, 37 for the connection of at least one pumping stage 3a, 3b, 3c to the discharge of the vacuum pump 1 can be provided in a simple manner in one of the half-shells, opening onto the joining surface 8. [0126] This can be implemented both for offloading a pumping stage, such as the first pumping stage 3a and/or an intermediate pumping stage 3b, and for the discharge at the outlet of the last pumping stage 3c. It is therefore no longer necessary to assemble an external enclosure to perform these offloading/discharge functions. The vacuum pump 1 is thus more compact (notably in terms of height). In addition, there is less sealing to manage with the outside of the vacuum pump 1, relative to the solutions known from the prior art with an added external enclosure for the offloading and/or discharge.

[0127] Finally, all the gas discharged and/or offloaded may be evacuated from a half-shell via a single channel connected to the discharge 5 of the vacuum pump 1 and into which open the one or more cavities 15, 39 housing a respective valve 13, 31 and fluidically connected to the outlet of a pumping stage 3a-3c. When the vacuum pump 1 comprises a silencer, the latter may be produced in a very simple manner.

[0128] Furthermore, a discharge duct 35 may be integrated in the vacuum pump 1, being fastened to one of the half-shells 2A, 2B, such that the discharge gases circulate in the pieces of the pumping cell. This is advantageous in order to heat, using these discharge gases, the pieces of the pumping cell, in particular the first low-pressure stages, or even the inlet duct connected to the suction 4.