Claw booster pump

Abstract

A claw booster pump (104) comprising: a pair of parallel shafts (202, 204) arranged to rotate in opposite directions to each other; a pair of rotors (206, 208) secured to the pair of shafts (202, 204), respectively, the pair of rotors (206, 208) including a first rotor (206) having a claw portion (220) projecting in a radial direction and a second rotor (208) having a recess (228) into which the claw portion (220) enters in use; a pump chamber (210) accommodating the pair of rotors (206, 208); an inlet (114) formed in the pump chamber (210) on one side of a plane (232) containing axes of the pair of shafts (202, 204); and an outlet (116) formed in the pump chamber (210) on another side of the plane (232); wherein a maximum capacity of the claw booster pump (104) is less than or equal to 40m3 / hr.

Description

[0001] CLAW BOOSTER PUMP

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a claw pump for use as a booster pump at the inlet of a primary pump in a pumping system.

[0004] BACKGROUND

[0005] A roughing pump, or backing pump, is a vacuum pump (typically, a dry vacuum pump) that is used to initially evacuate a vacuum system. This may be done as a first stage towards achieving high vacuum in the vacuum system. The roughing or backing pump may be referred to as a “primary pump”. Once a “rough vacuum” is achieved in the vacuum system by the roughing or backing pump (i.e., the primary pump), a “secondary pump” may operate so as to establish the high vacuum in the vacuum system.

[0006] Roughing or backing pumps (i.e., the primary pump) are typically those that work efficiently at atmospheric pressure.

[0007] Many vacuum pumps, for example primary pumps used in semiconductor fabrication facilities, operate at low inlet pressures, e.g. of less than about 5mbar, for most of the time. In such cases, booster pumps (such as Roots blowers) are used at the inlet to the primary pump to give a higher pumping speed at typical process pressures. This allows for the primary pump to be much smaller, which tends to save substantial cost and power consumption.

[0008] SUMMARY OF THE INVENTION

[0009] For small primary pump applications (i.e., applications in which the primary pump has a maximum capacity of, or pumps less than or equal to, 30m3 / hr of gas, e.g. less than or equal to 20m3 / hr of gas, or less than or equal to 15m3 / hr of gas, or less than or equal to 10m3 / hr of gas), the inlet pressures at the primary pump can be similar to those of larger applications, such as semiconductor fabrication applications. For example, the inlet pressures at the primary pump may be O.l mbar to 5mbar. An example of a small primary pump application includes, but is not limited to, the pumping of gas from the exhaust of a turbo pump used in for example a mass spectrometer.

[0010] In these small primary pump applications, a booster pump may be used to reduce the size and power of the primary pump. However, conventionally, the use of booster pumps in small primary pump applications has been avoided due to the increased cost and complexity of such a system, and due to the poor compression ratio (for example, due to the high clearance leakage relative to the swept volume) of booster pumps, e.g. when scaled down.

[0011] Aspects provided herein provide a booster pump which tends to have a high compression ratio, low cost, and tends to enable significant net power saving.

[0012] In an aspect, there is provided a claw booster pump comprising: a pair of parallel shafts arranged to rotate in opposite directions to each other; a pair of rotors secured to the pair of shafts, respectively, the pair of rotors including a first rotor having a claw portion projecting in a radial direction and a second rotor having a recess into which the claw portion enters in use; a pump chamber accommodating the pair of rotors; an inlet formed in the pump chamber on one side of a plane containing axes of the pair of shafts; and an outlet formed in the pump chamber on another side of the plane; wherein a maximum capacity of the claw booster pump is less than or equal to 40m3 / hr.

[0013] The claw booster pump may be a double claw pump.

[0014] The maximum capacity of the claw booster pump may be less than or equal to 30m3 / hr. The maximum capacity of the claw booster pump may be between 10m3 / hr and 30m3 / hr.

[0015] At least one rotor of the pair of rotors may be formed from a polymer. The polymer may be selected from a group of polymers consisting of polyether ether ketone, PEEK; polyphenylene sulphide, PPS; a fibre-reinforced polymer; fibre-reinforced PPS; glass fibre-reinforced PPS. A distance between the pair of parallel shafts in the radial direction may be less than or equal to 50mm. A distance between the pair of parallel shafts in the radial direction may be less than or equal to 40mm. A distance between the pair of parallel shafts in the radial direction may be about 32mm.

[0016] The claw booster pump may further comprise a housing defining the pump chamber. The housing may have one or more dimensions selected from a group of dimensions consisting of: a length of less than or equal to 250mm, the length being in a direction parallel to the axes of the pair of shafts width height; a width of less than or equal to 150mm, the width being in a radial direction between the pair of shafts; and a height of less than or equal to 100mm, the height being in a radial direction that is perpendicular to the width.

[0017] The claw booster pump may be a multi-stage pump having at least a first pumping stage and a second pumping stage. A maximum capacity of the first pumping stage may be less than or equal to 40m3 / hr. A maximum capacity of the second pumping stage may be less than that of the first pumping stage.

[0018] The claw booster pump may further comprise a motor arranged to drive one or more of the shafts, wherein an output shaft power of the motor in typical continuous use is less than or equal to 150W. The output shaft power of the motor in typical continuous use may be less than or equal to 100W.

[0019] In some embodiments, the claw booster pump may comprise a module comprising a motor, gears, and bearings, for mounting and driving the pair of parallel shafts, the pair of parallel shafts extending out of said module into the pump chamber portion.

[0020] Having a modular form for the motor gears and bearings allows the same module to be used as a base assembly for pumps of different sizes. Different capacity pumps may be formed by mounting particular length shafts, rotor configurations and pumping chambers onto this standard module. This commonality between different pumps may reduce manufacturing costs and simplify servicing,

[0021] In some embodiments, the pair of rotors are each formed of multiple rotor slices mounted on and fixed to the respective shafts. The rotors may be formed of rotor slices that may be of a uniform size and shape and be stacked on each other to form the desired rotor thickness. Providing the rotors in slices may have advantages in simplicity and flexibility during manufacture and may also have the advantage of allowing the manufacture of larger rotors in materials such as polymers where thin rotor slices are easier to mould.

[0022] In some embodiments, the multiple stages comprise rotor sections with different numbers of rotor slices.

[0023] A multiple stage pump where each stage has a rotor portion with a different thickness may have a rotor formed of rotor slices. This allows the portions to be formed from slices manufactured using the same process, but with different numbers of slices being selected for the different stages.

[0024] The rotor slices may be aligned and fixed to the respective shafts with cross pins. Cross pins are an effective way of mounting the rotor slices which not only hold them firmly to the shaft but ensure that they are aligned.

[0025] In a further aspect, there is provided a method of pumping a fluid. The method comprises: providing the claw booster pump as aforementioned; and rotating the pair of shafts in opposite directions to each other, thereby to pump the fluid.

[0026] The pair of shafts may be driven by a motor with a continuous output shaft power of less than or equal to 150W. The pair of shafts may be driven by a motor with a continuous output shaft power of less than or equal to 100W.

[0027] In use, a swept volume per unit time of the claw booster pump may be less than or equal to 40m3 / hr. In use, a swept volume per unit time of the claw booster pump may be between 10m3 / hr and 30m3 / hr.

[0028] In a further aspect, there is provided a pumping system comprising: the claw booster pump as aforementioned, and a motor arranged to drive one or more of the shafts of the claw booster pump. An output shaft power of the motor in typical continuous use is less than or equal to 150W.

[0029] The motor may have a motor voltage of about 48V or less. A yet further aspect provides a method of manufacture of a claw booster pump comprising mounting a pair of shafts within and extending out of a drive module comprising a motor, gears and bearings; mounting at least one slice of a claw rotor onto each of said pair of shafts; fixing said slices of rotor in place; and arranging a pump chamber housing around said rotor.

[0030] Providing the claw booster pump in a modular form allows pumps of different capacities to have a common drive module with shafts extending from the module and the rotors being built onto the shafts using rotor slices.

[0031] In some cases, the method may further comprise the initial steps of determining a capacity of said claw booster pump; and selecting a number of rotor slices to mount on said pair of shafts.

[0032] When manufacturing the pump the required capacity of the pump is determined and then the appropriate number of rotor slices to mount on the pair of shafts is selected. Where it is desired to build a multiple stage pump then the capacity of the different stages may be considered and the number of rotor slices selected accordingly. In this case the pump chamber housing arranged around the rotor will be a pump chamber housing suitable for multiple stages.

[0033] The determined capacity may lie between 6 and 40m3 / hr preferably between 10 and 14m m3 / hr.

[0034] In a further aspect, there is provided a pumping system comprising: a claw booster pump as aforementioned; and a primary pump. The outlet of the claw booster pump is fluidly coupled to an inlet of the primary pump.

[0035] The primary pump may be a pump selected from a group of pumps consisting of a dry pump; a diaphragm pump; a scroll pump; a piston pump; and a rotary vane pump.

[0036] The pumping system may further comprise a secondary pump, wherein the primary pump is arranged as a backing pump for the secondary pump.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic illustration (not to scale) of a vacuum system; Figure 2 is a schematic illustration (not to scale) showing a cross section of a booster pump;

[0039] Figure 3 is a process flow chart showing certain steps of a method of pumping a fluid;

[0040] Figure 4 is a schematic illustration (not to scale) showing a pump system; and

[0041] Figure 5 is a schematic illustration (not to scale) showing a further pump system;

[0042] Figure 6 shows a bare shaft and base assembly of a modular embodiment of the claw pump;

[0043] Figure 7 shows different configurations of the modular booster pump; and

[0044] Figure 8 shows a flow diagram illustrating steps in a method of manufacturing a modular booster pump.

[0045] DETAILED DESCRIPTION

[0046] Figure 1 is a schematic illustration (not to scale) of a vacuum system 100. In this embodiment, the vacuum system 100 is a mass spectrometer system.

[0047] The vacuum system 100 comprises a chamber 102, a booster pump 104, a primary pump 106, and a secondary pump 108.

[0048] The chamber 102 is a chamber of a mass spectrometer from which a fluid (in this embodiment, a gas) is to be evacuated.

[0049] The chamber 102 is coupled to the booster pump 104 and the primary pump 106 via a roughing line 110 and a backing line 112. A roughing valve 113 is disposed along the roughing line 110 between the chamber 102 and the backing line 112.

[0050] The booster pump 104 comprises a booster pump inlet 114 coupled to the backing line 112, and a booster pump outlet 116 coupled an intermediate line 118. The booster pump 104 of this embodiment will be described in more detail later below with reference to Figure 2.

[0051] In this embodiment, the booster pump 104 is a small booster pump. More specifically, in this embodiment, the booster pump 104 has a maximum capacity of less than or equal to about 40m3 / hr, e.g. between 5m3 / hr and 40m3 / hr. Thus, in operation, the swept volume per unit time (e.g. per hour) of the booster pump 104 is less than or equal to 40m3 / hr e.g. between 5m3 / hr and 40m3 / hr. More preferably, the maximum capacity of the booster pump 104 may be between 5m3 / hr and 30m3 / hr, or between 10m3 / hr and 30m3 / hr, or less than or equal to 20m3 / hr, e.g. between about 5m3 / hr and about 20 m3 / hr. Preferably, the maximum capacity of the booster pump 104 is between 10m3 / hr and 30m3 / hr, for example about 10m3 / hr, or about 15m3 / hr, or about 20m3 / hr, or about 25m3 / hr, or about 30m3 / hr. Nevertheless, in some embodiments, the maximum capacity of the booster pump 104 may be less than or equal to 10m3 / hr, e.g. between about 5m3 / hr and about 10m3 / hr. For example, the maximum capacity of the booster pump 104 may be about 5m3 / hr, about 6m3 / hr, about 7m3 / hr, about 8m3 / hr, about 9m3 / hr, or about 10m3 / hr.

[0052] The primary pump 106 comprises a primary pump inlet 120 and a primary pump outlet 122. The booster pump outlet 116 is fluidly coupled to the primary pump inlet 120 via the intermediate line 118.

[0053] The primary pump 106 may be any appropriate type of vacuum pump. Preferably, the primary pump 106 is a roughing or vacuum pump that works efficiently at atmospheric pressure. Preferably, the primary pump 106 is a dry vacuum pump. Preferably, the primary pump 106 is a vacuum pump selected from the group of pumps consisting of a dry pump, a diaphragm pump, a scroll pump, a piston pump, a rotary vane pump, and a regenerative pump.

[0054] In this embodiment, the primary pump 106 is a small primary pump. More specifically, in this embodiment, the primary pump 106 has a maximum capacity of less than or equal to about 5m3 / hr, e.g. between 1 m3 / hr and 5m3 / hr. Thus, in operation, the swept volume per unit time of the primary pump 106 is less than or equal to 5m3 / hr. More preferably, the maximum capacity of the primary pump 106 may be less than or equal to 4m3 / hr. More preferably, the maximum capacity of the primary pump 106 may be less than or equal to 3m3 / hr. For example, the maximum capacity of the primary pump 106 may be between 0.5m3 / hr and 3m3 / hr, e.g. about 0.5m3 / hr, about 1 m3 / hr, about 1.5m3 / hr, about 2m3 / hr, about 2.5m3 / hr, or about 3m3 / hr.

[0055] In this embodiment, a ratio between the maximum capacity of the booster pump 104 and the maximum capacity of the primary pump 106 is at least 2:1 , or more preferably at least 3:1. In some embodiments, for example embodiments in which the booster pump is a single-stage booster pump, the ratio between the maximum capacity of the booster pump 104 and the maximum capacity of the primary pump 106 is at least 5:1 , or at least 8:1 , or at least 10:1. By way of example, the ratio between the maximum capacity of the booster pump 104 and the maximum capacity of the primary pump 106 may be about 3:1 , or about 4:1 , or about 5:1 , or about 6:1 , or about 7:1 , or about 8:1 , or about 9:1 , or about 10:1. In some embodiments, for example embodiments in which the booster pump is a multi-stage (e.g. two-stage) booster pump, the ratio between the maximum capacity of the booster pump 104 and the maximum capacity of the primary pump 106 is between 10:1 and 30:1. For example, this may be between 10:1 and 30:1 , or between 15:1 and 30:1 , or between 20:1 and 30: 1 , or between 25: 1 and 30: 1 , or about 30: 1 .

[0056] The chamber 102 is further coupled to the secondary pump 108 via a high vacuum line 124. A high vacuum valve 126 is disposed along high vacuum line 124 between the chamber 102 and the secondary pump 108.

[0057] The secondary pump 108 comprises a secondary pump inlet 128, a first secondary pump outlet 130, and a second secondary pump outlet 132. The secondary pump inlet 128 is coupled to the high vacuum line 124. The first secondary pump outlet 130 is coupled to the backing line 112. A backing valve 134 is disposed along the backing line 112 between the secondary pump 108 and the connection point between the backing line 112 and the roughing line 110. The secondary pump 108 may be any appropriate type of vacuum pump. Preferably, the secondary pump 108 is a high vacuum pump that works efficiently at high vacuum or ultra high vacuum pressures, e.g. pressures of less than about 5mbar, e.g. less than or equal to 1 mbar, e.g. about O.l mbar. The secondary pump 108 may be, for example, a turbopump.

[0058] In this embodiment, each of the pumps 104, 106, 108 may be driven by a respective motor. For example, as shown in Figure 1 , a first motor 140 is arranged to drive the booster pump 104, and a second motor 142 is arranged to drive the primary pump 106.

[0059] Preferably, the first motor 140 is a low voltage / low power motor which may be run on a low-voltage DC supply, e.g. 24V or 48V. in other words, the first motor 140 may have a motor voltage of less than or equal to 48V, e.g. 48V or 24V.

[0060] Preferably, the second motor 142 is a low voltage / low power motor which may be run on a low-voltage DC supply, e.g. 24V or 48V. in other words, the second motor 142 may have a motor voltage of less than or equal to 48V, e.g. 48V or 24V.

[0061] The first motor 140 and the second motor 142 may be driven by a single drive.

[0062] Preferably, the output shaft power of the first motor 140, i.e. the input power to the booster pump 104, for example in normal use, is 150W or less, or more preferably 100W or less. An output shaft power of the first motor 140 in typical continuous use (i.e. in normal use when the first motor 140 is driving the booster pump 104 to pump gas) is less than or equal to 150W, or more preferably less than or equal to 100W. In some embodiments, the output shaft power of the first motor 140 (e.g. in normal use) is 50W or less, for example 40W or less. For example, the input power to the booster pump 104 may be between 10W and 40W, e.g. about 10W, about 20W, about 30W, or about 40W.

[0063] The power consumption of the primary pump 106 depends on the type of pump. Preferably, the output shaft power of the second motor 142, i.e. the input power to the primary pump 106, for example in normal use, is 150W or less. For example, the input power to the primary pump 106 (or the power consumption of the primary pump 106) may be between 20W and 150W. In embodiments, where the primary pump is a small diaphragm pump for example, the input power to the primary pump 106 (or the power consumption of the primary pump 106) may be 20W to 40W, e.g. about 20W. In embodiments, where the primary pump is a small scroll pump for example, the power consumption of the primary pump 106 may be 100W to 150W, e.g. about 150W (e.g. for a 3m3 / hr capacity pump). In some embodiments, the input power to the primary pump 106 (or the power consumption of the primary pump 106) may be between 20W and 150W, e.g. about 20W or about 150W, or between 30W and 100W, e.g. about 30W or about 100W, or between 50W and 80W, e.g. about 50W, about 60W, about 70W, or about 80W.

[0064] In this embodiment, the booster pump 104 and the primary pump 106 are housed in a common housing, container, or enclosure 150. Preferably, the first motor 140 and the second motor 142 are also contained in the enclosure 150. This advantageously tends to facilitate transportation and installation of the booster and primary pumps 104, 106 in the vacuum system 100. Furthermore, this tends to provide protection to the enclosed pumps 104, 106 and motors 140, 142. In some embodiments, the enclosure 150 may comprise sounddampening or soundproofing to reduce noise and / or vibration.

[0065] Figure 2 is a schematic illustration (not to scale) showing a cross section of the booster pump 104.

[0066] In this embodiment, the booster pump 104 is a claw pump (i.e., a claw booster pump), more specifically a double-claw pump. The booster pump 104 comprises a pair of parallel shafts, namely a first shaft 202 and a second shaft 204; a pair of rotors, namely a first rotor 206 and a second rotor 208; and a pump chamber 210 accommodating the pair of rotors 206, 208.

[0067] The pair of parallel shafts 202, 204 are configured to rotate in opposite directions to each other. In this embodiment, in the orientation of Figure 2, the first shaft 202 is configured to rotate clockwise, as indicated by arrow 211 , and the second shaft 204 is configured to rotate anticlockwise, as indicated by arrow 212.

[0068] The pair of rotors 206, 208 are secured to the pair of rotatable shafts 202, 204, respectively. Specifically, first rotor 206 is fixed to the first shaft 202 such that rotation of the first shaft 202 causes rotation of the first rotor 206, and the second rotor 208 is fixed to the second shaft 204 such that rotation of the second shaft 204 causes rotation of the second rotor 208.

[0069] In this embodiment, the booster pump104 is a double claw pump, i.e. each rotor 206, 208 has two respective claw portions. More specifically, in this embodiment the first rotor 206 comprises a pair of opposing claw portions, namely a first claw portion 220 projecting in a first radial direction, and second claw portion 222 projecting in a second radial direction opposite to the first radial direction.

[0070] In this embodiment, the second rotor 208 comprises a pair of opposing claw portions, namely a third claw portion 224 projecting in a third radial direction, and fourth claw portion 226 projecting in a fourth radial direction opposite to the third radial direction.

[0071] The third claw portion 224 defines a first recess 228. The fourth claw portion 226 defines a second recess 230.

[0072] The booster pump inlet 114 is formed in the pump chamber 210. The booster pump inlet 114 is on a first side of a plane 232 defined through or containing the axes of the pair of shafts 202, 204. In the orientation of Figure 2, the booster pump inlet 114 is located in an upper portion of the pump chamber 210, above the plane 232.

[0073] The booster pump outlet 116 is formed in the pump chamber 210. The booster pump outlet 116 is on a second side of the plane 232, the second side being opposite to the first side. In the orientation of Figure 2, the booster pump outlet 116 is located in a lower portion of the pump chamber 210, below the plane 232. Minute clearances are provided between the pair of rotors 206, 208 and between each rotor 206, 208 and the wall surface of the pump chamber 210. The small clearances advantageously tend to prevent or oppose back flow within the pump chamber 210, thereby improving efficiency.

[0074] As discussed above with reference to Figure 1 , a maximum capacity of the booster pump 104 is less than or equal to 30m3 / hr, such as less than or equal to 20m3 / hr, or less than or equal to 10m3 / hr.

[0075] In this embodiment, at least one rotor of the pair of rotors 206, 208 is formed from a polymer, e.g. a plastic. Preferably, both rotors 206, 208 are formed from a polymer. Preferably, both rotors 206, 208 are formed from the same polymer. The polymer may be a polymer selected from a group of polymers consisting of polyether ether ketone (PEEK), polyphenylene sulphide (PPS), a fibre-reinforced polymer, fibre-reinforced PPS, and glass fibre- reinforced PPS.

[0076] In this embodiment, a distance between the pair of parallel shafts 202, 204 in a radial direction is less than or equal to about 50mm. For example, the shortest distance between the axes of the parallel shafts 202, 204 is less than or equal to about 50mm, e.g. about between about 20mm and about 50mm. This distance is indicated in Figure 2 by a double-headed arrow and the reference symbol d. More preferably, the distance between the pair of parallel shafts 202, 204 in the radial direction (e.g. the distance d) is less than or equal to about 40mm, such as between about 20mm and about 40mm, or between about 30mm and about 40mm, e.g. about 30mm, about 31 mm, about 32mm, about 33mm, about 34mm, about 35mm, about 36mm, about 37mm, about 38mm, about 39mm, or about 40mm.

[0077] The height of the rotors may be between 3mm and 40mm, for example about 15mm.

[0078] The booster pump 104 further comprises a housing 236 defining the pump chamber 210.

[0079] Preferably, the housing 236 has a width w of less than or equal to about 150mm, e.g. about between about 60mm and about 150mm. The width w is in a radial direction between the pair of shafts 202, 204, i.e. parallel with the distance d. More preferably, the width w is less than or equal to about 120mm, such as between about 60mm and about 120mm, or between about 90mm and about 120mm, or between about 90mm and about 100mm e.g. about 90mm, about 91 mm, about 92mm, about 93mm, about 94mm, about 95mm, about 96mm, about 97mm, about 98mm, about 99mm, or about 100mm. The width w of the housing 236 may be dependent on the shaft separation d. For example, the width w may be about 3 x d.

[0080] Preferably, the housing 236 has a height h of less than or equal to about 100mm, e.g. about between about 40mm and about 100mm. The height h is in a radial direction perpendicular to the width w. More preferably, the height h is less than or equal to about 80mm, such as between about 40mm and about 80mm, or between about 60mm and about 80mm, or between about 60mm and about 70mm e.g. about 60mm, about 61 mm, about 62mm, about 63mm, about 64mm, about 65mm, about 66mm, about 67mm, about 68mm, about 69mm, or about 70mm. The height of the housing 236 may be dependent on the shaft separation d. For example, the height may be about 2 x d. Preferably, the housing 236 has a length I of less than or equal to about 250mm, e.g. about between about 100mm and about 250mm. The length I is in a direction perpendicular to both the width w and the height h. More preferably, the length I is less than or equal to about 200mm, such as between about 100mm and about 200mm, or between about 120mm and about 200mm, or between about 155mm and about 165mm e.g. about 155mm, about 156mm, about 157mm, about 158mm, about 159mm, about 160mm, about 161 mm, about 162mm, about 163mm, about 164mm, or about 165mm. The length of the housing 236 may be dependent on the shaft separation d. For example, the length may be about 5 x d.

[0081] The housing 236 may be comprised of any appropriate material, such as a metal e.g. aluminium or an aluminium alloy.

[0082] As an example for the booster pump 104, the swept volume per revolution of the rotors 206, 208 may be 2,850mm3for a 15m3 / hour pump at a shaft speed of 200Hz. For such a booster pump 104, the distance d may be 32mm.

[0083] Figure 3 is a process flow chart showing certain steps of an embodiment of a method 300 of pumping a fluid. The method 300 is for pumping fluid, e.g. a gas, within the vacuum system 100. In this embodiment, the primary pump 106 works as a backing or roughing pump for the secondary pump 108, i.e. the primary pump 106 “backs” the secondary pump 108.

[0084] It should be noted that certain of the process steps depicted in the flowchart of Figure 3 and described below may be omitted or such process steps may be performed in differing order to that presented below and shown in Figure 3. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally.

[0085] At s302, the booster pump 104 and the primary pump 106 pump gas from the chamber 102, thereby to establish a “rough vacuum” in the chamber 102. At this stage, the gas is pumped (by the booster pump 104 and the primary pump 106) from the chamber 102 via the roughing line 110 and the backing line 112 to the booster pump 104, from the booster pump 104 to the primary pump 106 via the intermediate line 118, and out of the primary pump 106 via the primary pump outlet 122. Backflow of the pumped gas along the roughing line 110 is opposed or prevented by the roughing valve 113.

[0086] At s304, the booster pump 104 and the primary pump 106 pump gas from the secondary pump 108, thereby to establish a “rough vacuum” in the pumping chamber of the secondary pump 108. Steps s304 may be performed simultaneously or at least overlapping to some extent temporally with step s302. At this stage, the gas is pumped (by the booster pump 104 and the primary pump 106) from the secondary pump 108 via the backing line 112 to the booster pump 104, from the booster pump 104 to the primary pump 106 via the intermediate line 118, and out of the primary pump 106 via the primary pump outlet 122. Backflow of the pumped gas along the backing line 112 is opposed or prevented by the backing valve 134.

[0087] In this embodiment, operation of the booster pump 104 (i.e. at s302 and s304) comprises the first motor 140 rotating the shafts 202, 204 of the booster pump 104, and thereby rotating the rotors 206, 208 within the pump chamber 210. The rotation of the rotors 206, 208 causes the first claw portion 220 to enter the first recess 228, e.g. proximate a central portion of the pump chamber 210. This state is illustrated in Figure 2. Continued rotation of the rotors 206, 208 causes the first claw portion 220 to move out of the first recess 228, e.g. towards an upper portion of the pump chamber 210. Continued rotation of the rotors 206, 208 causes the second claw portion 222 to enter the second recess 230, e.g. proximate a central portion of the pump chamber 210. Continued rotation of the rotors 206, 208 causes the second claw portion 222 to move out of the second recess 230.

[0088] As the rotors 206, 208 rotate past the booster pump inlet 114, gas is drawn into the pump chamber 210 at the booster pump inlet 114. Continued rotation of the rotors 206, 208, moves this gas through the pump chamber 210, from the booster pump inlet side of the plane 232 to the booster pump outlet side of the plane 232. On the booster pump outlet side of the plane 232, a compression pocket 238 is formed; the compression pocket 238 is defined or surrounded by the pair of rotors 206, 208 and the walls of the pump chamber 210. As the rotors 206, 208 rotate in the directions of the arrows 211 , 212, respectively, the volume of the compression pocket 238 decreases progressively, and the gas in the compression pocket 238 is compressed correspondingly. Continued rotation of the rotors 206, 208 causes the compression pocket 238 to become in communication with the booster pump outlet 116, and the gas in the compression pocket 238 is discharged through the booster pump outlet 116.

[0089] In this embodiment, the shafts 202, 204 of the booster pump 104 are rotated at a speed of less than or equal to 20,000rpm. For example, the shafts 202, 204 are rotated at a speed of between 10,000rpm and 20,000rpm. In this embodiment, the booster pump 104 is operated such that its swept volume per unit time is less than or equal to 30m3 / hr, e.g. between about 5m3 / hr and about 30m3 / hr, or less than or equal to 20m3 / hr, or between about 5m3 / hr and about 20m3 / hr, or less than or equal to 10m3 / hr, or between about 5m3 / hr and about 10m3 / hr.

[0090] Typically, the primary pump 106 (e.g. diaphragm or small scroll pump) may be operated with a speed that pumps the fluid at a rate of less than or equal to 5m3 / hr, or more preferably less than or equal to 3m3 / hr.

[0091] At s306, once the rough vacuum conditions have been established in the chamber 102 and the pumping chamber of the secondary pump 108 by the booster pump 104 and the primary pump 106, the secondary pump 108 pumps gas from the chamber 102, thereby to establish lower pressure conditions (e.g., a high vacuum or ultra high vacuum) in the chamber 102. At this stage, the gas is pumped (by the secondary pump 108) from the chamber 102 via the high vacuum line 124, and out of the secondary pump 108 via the second secondary pump outlet 132. Backflow of the pumped gas along the high vacuum line 134 is opposed or prevented by the high vacuum valve 126.

[0092] Thus, a method for pumping fluid is provided.

[0093] In the above-described embodiments, the pumping system implements a double claw rotor pump as a small-size booster pump as opposed to, for example, a Roots rotor pump. The double claw pump advantageously tends to provide a valving action; specifically, the rotors of the double claw pump provide a seal between the pump inlet and pump outlet for much of the time during operation. Thus, the compression ratio of the booster pump tends to be improved compared to conventional booster pumps, such as Roots pumps. This tends to be particularly important as the small scale of the booster pump means that clearance leakage may be high relative to the swept volume of the pump, and thus otherwise the booster pump may have poor performance.

[0094] The double claw booster pump advantageously tends to compress the fluid passing therethrough between the inlet and the outlet. This precompression before the fluid reaches the primary pump tends to improve the efficiency of the booster and tends to reduce power and heat generation within the booster pump. Such pre-compression tends not to be performed by a Roots mechanism.

[0095] Advantageously, the double claw booster pump tends to have good inlet conductance. This tends to provide a good filling efficiency, even at low pressures.

[0096] The use of polymer parts, such as the rotors, in the above-described small-size double claw booster pump tends to reduce the costs and difficulty in fabricating the pump. Furthermore, the weight of the pump tends to be reduced. This tends to make the use of small booster pumps a viable option with small primary pumps.

[0097] In the above-described systems, small vacuum pumps having maximum capacities of 30m3 / hr and below are provided with motors that tend to be capable of maintaining full pump speed at all potential inlet pressures from atmosphere to vacuum.

[0098] Advantageously, the combination of small booster and primary pump provided herein tends to provide for reduced the power requirement at all operating inlet pressures. The arrangement involves a dry exhaust or primary pump in combination with a compact high-efficiency dry booster.

[0099] The present disclosure provides various combinations of a booster and a primary pump that tend to substantially reduce the power required the pump combination at some or all inlet pressures. Conventionally, a typical “single” pump pumping 12m3 / hr of gas may require more than 300W at ultimate. In contrast, the provided combinations of a booster and a primary pump tend to use less than 100W at ultimate. Although the pump combination may have lower speed at higher inlet pressures, such as above 50 mbar, the capabilities will tend to satisfy a high proportion of small pump applications.

[0100] By way of example, in embodiments provided herein, the primary pump tends to be of sufficiently low capacity to reduce power consumption to 60W or less. The booster pump runs at much higher speed compared to the primary pump, which tends to allow for substantially reduced size and power consumption of the primary pump. The power consumption of the booster pump may be, for example, about 20W. As an example, a booster pump arranged to pump about 8 m3 / hr of fluid may be used in combination with a primary or exhaust pump arranged to pump about 1.5 m3 / hr of fluid. The power consumption of the booster pump may be about 20W, and the power consumption of the primary pump may be about 60W, giving a total power consumption of about 80W.

[0101] In the above embodiments, there is preferably a high capacity ratio of at least 3:1 between the booster pump and the primary pump. This tends to achieve both high system inlet speed and low power. The capacity ratio can be higher than 3:1 , for example 5:1 , 8:1 or 10:1 . For higher capacity ratios, such as those above 8:1 , a two-stage booster may be implemented to improve the compression ratio and booster inlet speed.

[0102] In some embodiments, a recirculation valve may be implemented. Figure 4 is a schematic illustration (not to scale) showing a pump system 400 comprising the booster pump 104 and a recirculation valve 402. In this embodiment, the booster pump 104 is a multi-stage pump (specially, a two- stage pump) comprising a first or inlet stage 404, and a second stage 406 downstream of the inlet stage 404. The recirculation valve 402 is arranged in parallel with the booster pump inlet stage 404 and coupled between the backing line 112 and an outlet 408 of the inlet stage 404. The recirculation valve 402 acts to relieve pressure (i.e. reduce a pressure differential) across the booster pump inlet stage 404. Specifically, when the pressure differential across the booster pump inlet stage 404 is greater than a first pressure threshold (i.e. a cracking pressure of the recirculation valve 402), the recirculation valve 402 opens thereby allowing gas to travel back from the outlet 408 of the inlet stage 404 to the booster pump inlet 114. This reduces the pressure differential across the booster pump inlet stage 404. The recirculation valve 402 advantageously tends to maintain shaft and pump speed of the booster pump 104, for example when motor power of the first motor 140 is limited.

[0103] In this embodiment, the first pressure threshold (i.e. a cracking pressure of the recirculation valve 402) may be between about 20mbar and about 10Ombar, e.g. about 20mbar, about 30mbar, about 40mbar, about 50mbar, about 60mbar, about 70mbar, about 80mbar, about 90mbar, or about 10Ombar.

[0104] The recirculation valve 402 may be integrated with the booster pump 104, or may be a separate component.

[0105] In some embodiments, a by-pass valve may be implemented. Figure 5 is a schematic illustration showing a pump system 500 comprising the booster pump 104 and the primary pump 106 coupled together as described in more detail earlier above with reference to Figure 1. In this embodiment, the pump system 500 further comprises a by-pass valve 502 arranged in parallel with the primary pump 106 and coupled between the intermediate line 118 and the exhaust line from the primary pump outlet 122. The by-pass valve 502 acts to relieve over pressure (e.g. pressure above atmospheric pressure) between the booster pump 104 and the primary pump 106. Specifically, when the pressure differential between the primary pump inlet 120 and the primary pump outlet 122 is greater than a second pressure threshold (i.e. a cracking pressure of the by-pass valve 502), the by-pass valve 502 opens thereby allowing gas to bypass the primary pump 106, travelling from intermediate line 118 to the exhaust line without passing through the primary pump 106. This reduces the pressure differential across the primary pump 106. The by-pass valve 502 is opened when the first motor 140 has sufficient power to enable the booster pump 104 to exhaust the gas to the atmosphere. This by-pass valve arrangement tends to deliver higher pump speed at high inlet pressures, for example compared to the recirculation valve arrangement of Figure 4. In this embodiment, the second pressure threshold (i.e. a cracking pressure of the by-pass valve 502) may be a low pressure value such as 20mbar or less.

[0106] In some embodiments, a pump system may comprise both the recirculation valve 402 and the by-pass valve 502.

[0107] In the above embodiments, the pump system comprising the booster pump and the primary pump is implemented in the vacuum system for evacuating the chamber of a mass spectrometer. The booster pump and the primary pump back a turbopump (i.e. the secondary pump). However, in other embodiments, the pump system comprising the booster pump and the primary pump is implemented in a different type of vacuum system, and / or for a different pumping application other than backing a turbopump.

[0108] In the above embodiments, the booster pump is a double claw pump. That is to say, each rotor of the claw pump has exactly two claw portions. However, in other embodiments, one or more rotors of the claw booster pump has a different number of claw portions. For example, in other embodiments, each rotor of the claw pump has exactly one or exactly three claw portions. Preferably, each rotor of the claw pump has two or more claw portions. Typically, a higher number of claw portions tends to result in improved sealing and reduced capacity.

[0109] In the above embodiments, the booster pump is a single-stage pump. However, in other embodiments, the booster pump is a multi-stage pump. Use of a multi-stage booster pump may increase the gas speed at the inlet to the primary pump. For example, the booster pump may be a 2-stage booster pump. The booster pump (which may be a claw pump) may be a multi-stage pump having at least a first pumping stage and a second pumping stage. A maximum capacity of the first pumping stage may be less than or equal to 30m3 / hr. A maximum capacity of the second pumping stage may be less than that of the first pumping stage. In the multi-stage booster pump, a maximum capacity of each subsequent pumping stage may be less than that of the preceding pumping stage.

[0110] In the above embodiments, the motors that drive the booster pump and primary pump are low voltage / low power motor which may be run on a low- voltage DC supply, less than or equal to 48V, e.g. 48V or 24V. However, in other embodiments, one or more of the motors may be configured to run on a different supply voltage. Examples of appropriate supply voltages for motors include but are not limited to 24V, 48V, 110V and 230 V.

[0111] In the above embodiments, the small-sized or small-capacity claw pump is used as a booster pump of a primary pump. However, in other embodiments, the claw pump is used for a different application. For example, in some embodiments the motor driving the claw pump has sufficient power to enable the claw pump to evacuate a chamber (e.g. to create a “rough” vacuum) and to exhaust the pumped gas to the atmosphere. Thus, in such embodiments, the primary pump may be omitted.

[0112] Examples

[0113] Table 1 below provides a non-exhaustive list of example combinations of booster and primary pumps. For the combinations given in Table 1 , the booster pump is a single stage booster pump.

[0114] Table 1 Table 2 below provides a non-exhaustive list of example combinations of booster and primary pumps. For the combinations given in Table 2, the booster pump is a two stage booster pump.

[0115] Table 2

[0116] In some embodiments the booster pump is formed as a modular pump that uses a common base architecture allowing it to be constructed in several capacities ranging from 6 m3 / h to 50 m3 / h by attaching different pump sections onto the base assembly. This reduces manufacturing costs and simplifies assembly and service logistics.

[0117] Embodiments provide a common booster pump base assembly on which a range of booster capacities can be fitted. Both single-stage and two-stage pumps are possible on the common base. All parts associated with the motor, bearings, seals, gears and oil system are common and can be pre-assembled. The inlet flange and end cover assembly is also made from common parts on all pump variants and can be pre-assembled. Common shafts can be used for two-stage pumps and large single stage pumps. Shorter shafts are required for low capacity single stage versions.

[0118] Figure 6 shows a modular booster pump at an early stage of assembly. It shows the base assembly module 148 that contains the bearings 147 for mounting the shafts 202 and 204, the gears 145 and the motor 140 for driving the shafts. The shafts 202 and 204 extend out of the base assembly module 148 ready to receive the rotor slices.

[0119] Figure 7 shows various configurations of the booster pump in its modular form whereby the rotors are mounted on respective shafts 202 and 204 in the form of rotor slices, a first rotor slice 207 and a second rotor slice 209. In the first embodiment Figure 7a the pump forms a single stage pump with one rotor slice forming the claw rotor mounted on each shaft.

[0120] Figure 7b shows a two-stage version of the booster pump 104 with an inlet stage 404 and a second stage 406. The pump inlet 114 admits gases into the inlet stage 404 and they are pumped to the outlet stage 406 and then out through an exhaust. In this embodiment, the inlet stage is formed of two rotor slices 207 and 209 while the second stage is formed of a single rotor slice. As can be appreciated by forming the rotor of rotor slices, different sized rotors to form pumps of different pumping capacities can be provided from the same basic components. The rotor slices may be formed of polymers, allowing for ease of moulding of several identical components which can then be stacked on top of each other where a thicker rotor is required.

[0121] Figure 7C shows a single stage higher capacity booster pump with several rotor slices 207, 209 stacked on top of each other to form a thicker rotor. This embodiment shows the cross pins 205 which hold the rotor slices in place and attach them to the shaft. These cross pins provide not only the fixing to the shaft but provide good alignment allowing the rotor slices to form the desired shape.

[0122] Figure 8 shows a flow chart schematically showing steps in a method 310 of manufacturing a modular booster pump according to an embodiment. The method 310 comprises a first step S311 where the desired capacity of the claw booster pump is determined. At step S312 a number of rotor slices that are required for that capacity of pump are determined and at step S313 the lengths of the pair of shafts required for this number of rotor slices and capacity of pump is determined. At step S314 the rotor slices are mounted on the pair of rotor shafts using cross pins to fix them in place. A pump chamber housing is then arranged around the rotor and affixed to the base assembly module that contains the motor gears and bearings.

[0123] Reference numeral list

[0124] 100 - vacuum system

[0125] 102 - chamber

[0126] 104 - booster pump

[0127] 106 - primary pump

[0128] 108 - secondary pump

[0129] 110 - roughing line

[0130] 112 - backing line

[0131] 113 - roughing valve

[0132] 114 - booster pump inlet

[0133] 116 - booster pump outlet

[0134] 118 - intermediate line

[0135] 120 - primary pump inlet

[0136] 122 - primary pump outlet

[0137] 124 - high vacuum line

[0138] 126 - high vacuum valve

[0139] 128 - secondary pump inlet

[0140] 130 - first secondary pump outlet

[0141] 132 - second secondary pump outlet

[0142] 134 - backing valve

[0143] 140 - first motor

[0144] 142 - second motor

[0145] 145 - gears

[0146] 147- bearings

[0147] 148 - base assembly module

[0148] 150 - enclosure

[0149] 202 - first shaft

[0150] 204 - second shaft

[0151] 205 cross pins

[0152] 206 - first rotor

[0153] 207 -first rotor slices

[0154] 208 - second rotor

[0155] 209 - second rotor slices 210 - pump chamber

[0156] 211 , 212 - directions of rotation

[0157] 220 - first claw portion

[0158] 222 - second claw portion

[0159] 224 - third claw portion

[0160] 226 - fourth claw portion

[0161] 228 - first recess

[0162] 230 - second recess

[0163] 232 - plane

[0164] 236 - housing

[0165] 238 - compression pocket

[0166] 300 - method s302-s306 - method steps 310 - method of manufacture S310 - s316 method steps 400 - pump system

[0167] 402 - recirculation valve

[0168] 404 - inlet stage

[0169] 406 - second stage

[0170] 408 - outlet

[0171] 500 - pump system

[0172] 502 - by-pass valve

Claims

CLAIMS1. A claw booster pump comprising: a pair of parallel shafts arranged to rotate in opposite directions to each other; a pair of rotors secured to the pair of shafts, respectively, the pair of rotors including a first rotor having a claw portion projecting in a radial direction and a second rotor having a recess into which the claw portion enters in use; a pump chamber accommodating the pair of rotors; an inlet formed in the pump chamber on one side of a plane containing axes of the pair of shafts; and an outlet formed in the pump chamber on another side of the plane; wherein a maximum capacity of the claw booster pump is less than or equal to 40m3 / hr.

2. The claw booster pump of claim 1 , wherein the claw booster pump is a double claw pump.

3. The claw booster pump of claim 1 or 2, wherein the maximum capacity of the claw booster pump is less than or equal to 30m3 / hr.

4. The claw booster pump of claim 3, wherein the maximum capacity of the claw booster pump is between 10m3 / hr and 30m3 / hr.

5. The claw booster pump of any preceding claim, wherein at least one rotor of the pair of rotors is formed from a polymer, and wherein the polymer is preferably selected from a group of polymers consisting of polyether ether ketone, PEEK; polyphenylene sulphide, PPS; a fibre-reinforced polymer; fibre-reinforced PPS; glass fibre-reinforced PPS.

6. The claw booster pump of any preceding claim, wherein a distance between the pair of parallel shafts in the radial direction is less than or equal to 50mm, preferably less than or equal to 40mm.

7. The claw booster pump of any preceding claim, further comprising a housing defining the pump chamber, the housing having one or more dimensions selected from a group of dimensions consisting of: a length of less than or equal to 250mm, the length being in a direction parallel to the axes of the pair of shafts width height; a width of less than or equal to 150mm, the width being in a radial direction between the pair of shafts; and a height of less than or equal to 100mm, the height being in a radial direction that is perpendicular to the width.

8. The claw booster pump of any preceding claim, wherein the claw booster pump is a multi-stage pump having at least a first pumping stage and a second pumping stage, wherein a maximum capacity of the first pumping stage is less than or equal to 40m3 / hr, and a maximum capacity of the second pumping stage is less than that of the first pumping stage.

9. The claw booster pump of any preceding claim further comprising: a module comprising a motor, gears, and bearings, for mounting and driving the pair of parallel shafts, the pair of parallel shafts extending out of said module into the pump chamber portion.

10. The claw booster pump of any preceding claim, wherein the pair of rotors are each formed of multiple rotor slices mounted on and fixed to the respective shafts.11 . The claw booster pump according to claim 10 when dependent on claim 8, wherein the multiple stages comprise rotor sections with different numbers of rotor slices.

12. The claw booster pump of claim 10 or 11 , wherein the rotor slices are aligned and fixed to the respective shafts with cross pins.

13. The claw booster pump of claim 9 or claims 10 to 12 when dependent on claim 9, wherein an output shaft power of the motor in typical continuous use is less than or equal to 150W, preferably less than or equal to 100W.

14. A method of manufacture of a claw booster pump according to any one of claims 10 to 12 when dependent upon claim 9, comprising mounting a pair of shafts within and extending out of a drive module comprising a motor, gears and bearings; mounting at least one slice of a claw rotor onto each of said pair of shafts; fixing said slices of rotor in place; and arranging a pump chamber housing around said rotor.

15. The method of manufacture of claim 14, further comprising initial steps of: determining a capacity of said claw booster pump; and selecting a number of rotor slices to mount on said pair of shafts.

16. The method of manufacture of claim 15, comprising a further initial step of selecting a length of said pair of shafts in dependence upon said determined capacity.

17. The method of manufacture according to claim 15 or 16 wherein the determined capacity lies between 6 and 40 m3 / hr, preferably between 10 and 40 m3 / hr.

18. A pumping system comprising: a claw booster pump, the claw booster pump being in accordance with any of claims 1 to 13; and a primary pump, wherein the outlet of the claw booster pump is fluidly coupled to an inlet of the primary pump.

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