Pumping system

Abstract

A pumping system 100 comprises a booster pump 104 with a booster pump inlet 114 and a booster pump outlet 116, and a primary pump 106 with a primary pump inlet 120 and a primary pump outlet 122. The b

Description

FIELD OF THE INVENTION The present invention relates to a pumping system comprising a booster pump and a primary pump. BACKGROUND 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. Roughing or backing pumps (i.e., the primary pump) are typically those that work efficiently at atmospheric pressure. 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. SUMMARY OF THE INVENTION For a 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 03 07 25 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.lmbar 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. 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. Aspects provided herein provide a pumping system comprising small and / or compact booster and primary pumps which tend to provide a high compression ratio, low cost, and tends to enable significant net power saving. In an aspect, there is provided a pumping system comprising a booster pump comprising a booster pump inlet and a booster pump outlet, and a primary pump comprising a primary pump inlet and a primary pump outlet. The booster pump outlet is fluidly coupled to the primary pump inlet. A maximum capacity of the booster pump is less than or equal to 40m3 / hr. A maximum capacity of the primary pump is less than or equal to 5m3 / hr. The maximum capacity of the booster pump may be less than or equal to 30m3 / hr. The maximum capacity of the booster pump may be between 10m3 / hr and 30m3 / hr. The maximum capacity of the primary pump may be less than or equal to 3m3 / hr. The booster pump is a claw pump. The booster pump may be a claw pump selected from the group of claw pumps consisting of: a double claw pump; and a single claw pump. 03 07 25 The primary pump may be a vacuum pump selected from a group of vacuum pumps consisting of: a diaphragm pump; a scroll pump; a piston pump; and a rotary vane pump. The booster pump may comprises at least one rotor. The at least one 5 rotor may be formed from a 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; glass fibre-reinforced PPS. The booster pump may comprise a housing defining a pump chamber of 10 the booster pump. 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 15 100mm, the height being in a radial direction that is perpendicular to the width. The pumping system may further comprise a motor arranged to drive the booster pump, 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. The motor may have a 20 motor voltage of less than or equal to 48V. The 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. 25 A ratio between the maximum capacity of the booster pump and the maximum capacity of the primary pump may be at least 3:1. A ratio between the maximum capacity of the booster pump and the maximum capacity of the primary pump may be at least 5:1, or at least 8:1, or at least 10:1. The booster pump may be a multi-stage pump having an inlet stage. The 30 pumping system may further comprise a recirculation valve disposed across the inlet stage of the booster pump. 03 07 25 The pumping system may further comprise a bypass valve disposed between the primary pump inlet and a primary pump outlet. A power consumption of the primary pump may be 150W or less. A power consumption of the primary pump may be about 60W. 5 A power consumption of the booster pump may be 150W or less. The pumping system may further comprise a common enclosure enclosing both the booster pump and the primary pump. The pumping system may further comprise a secondary pump, wherein the primary pump is arranged as a backing pump for the secondary pump. The 10 secondary pump may be a turbopump. In a further aspect, there is provided a method of pumping a fluid, the method comprising: providing the pumping system of any preceding aspect; driving the booster pump and the primary pump, thereby to pump the fluid into the booster pump inlet, then from the booster pump outlet to the primary pump 15 inlet, and then out of the primary pump outlet. The booster pump may be driven by a motor with a continuous output shaft power of less than or equal to 150W. The continuous output shaft power of the motor may be less than or equal to 100W. 20 BRIEF DESCRIPTION OF THE DRAWINGS 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; Figure 3 is a process flow chart showing certain steps of a method of 25 pumping a fluid; Figure 4 is a schematic illustration (not to scale) showing a pump system; and Figure 5 is a schematic illustration (not to scale) showing a further pump system. 03 07 25 DETAILED DESCRIPTION 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 5 system. The vacuum system 100 comprises a chamber 102, a booster pump 104, a primary pump 106, and a secondary pump 108. The chamber 102 is a chamber of a mass spectrometer from which a fluid (in this embodiment, a gas) is to be evacuated. 10 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. The booster pump 104 comprises a booster pump inlet 114 coupled to 15 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. In this embodiment, the booster pump 104 is a small booster pump. More 20 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 25 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 30 capacity of the booster pump 104 may be less than or equal to 10m3 / hr, e.g. 03 07 25 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. The primary pump 106 comprises a primary pump inlet 120 and a 5 primary pump outlet 122. The booster pump outlet 116 is fluidly coupled to the primary pump inlet 120 via the intermediate line 118. 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 10 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. 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 15 of less than or equal to about 5m3 / hr, e.g. between 1m3 / 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 20 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 1m3 / hr, about 1.5m3 / hr, about 2m3 / hr, about 2.5m3 / hr, or about 3m3 / hr. 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 25 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 30 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 03 07 25 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. 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. 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 1mbar, e.g. about O.lmbar. The secondary pump 108 may be, for example, a turbopump. 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. 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. 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 03 07 25 second motor 142 may have a motor voltage of less than or equal to 48V, e.g. 48V or 24V. The first motor 140 and the second motor 142 may be driven by a single drive. 5 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 10 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 104may be between 10W and 40W, e.g. about 10W, about 20W, about 30W, or about 40W. The power consumption of the primary pump 106 depends on the type of 15 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 20 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 25 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. In this embodiment, the booster pump 104 and the primary pump 106 are 30 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. 03 07 25 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 sound-5 dampening or soundproofing to reduce noise and / or vibration. Figure 2 is a schematic illustration (not to scale) showing a cross section of the booster pump 104. 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 10 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. 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 15 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. 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 20 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. 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 25 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. In this embodiment, the second rotor 208 comprises a pair of opposing 30 claw portions, namely a third claw portion 224 projecting in a third radial 03 07 25 direction, and fourth claw portion 226 projecting in a fourth radial direction opposite to the third radial direction. The third claw portion 224 defines a first recess 228. The fourth claw portion 226 defines a second recess 230. 5 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. 10 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. 15 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 110. The small clearances advantageously tend to prevent or oppose back flow within the pump chamber 210, thereby improving efficiency. As discussed above with reference to Figure 1, a maximum capacity of 20 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. 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 25 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. In this embodiment, a distance between the pair of parallel shafts 202, 30 204 in a radial direction is less than or equal to about 50mm. For example, the 03 07 25 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 5 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 31mm, about 32mm, about 33mm, about 34mm, about 35mm, about 36mm, about 37mm, about 38mm, about 39mm, or about 40mm. 10 The height of the rotors may be between 3mm and 40mm, for example about 15mm. The booster pump 104 further comprises a housing 236 defining the pump chamber 210. Preferably, the housing 236 has a width w of less than or equal to about 15 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, 20 about 91mm, 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. Preferably, the housing 236 has a height h of less than or equal to about 25 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 61mm, about 62mm, about 63mm, about 30 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 03 07 25 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 5 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 161mm, about 162mm, about 163mm, about 164mm, or about 165mm. The length of the housing 236 10 may be dependent on the shaft separation d. For example, the length may be about 5 x d. The housing 236 may be comprised of any appropriate material, such as a metal e.g. aluminium or an aluminium alloy. As an example for the booster pump 104, the swept volume per 15 revolution of the rotors 206, 208 may be 2,850mm3 for a 15m3 / hour pump at a shaft speed of 200Hz. For such a booster pump 104, the distance d may be 32mm. 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 20 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. 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 25 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. 30 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 03 07 25 102. 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 5 primary pump outlet 122. Backflow of the pumped gas along the roughing line 110 is opposed or prevented by the roughing valve 113. 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 10 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 15 outlet 122. Backflow of the pumped gas along the backing line 112 is opposed or prevented by the backing valve 134. 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 20 210. 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 25 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. As the rotors 206, 208 rotate past the booster pump inlet 114, gas is 30 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 03 07 25 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, 5 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 10 the booster pump outlet 116. 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 15 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. Typically, the primary pump 106 (e.g. diaphragm or small scroll pump) 20 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. 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 25 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 30 opposed or prevented by the high vacuum valve 126. Thus, a method for pumping fluid is provided. 03 07 25 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 5 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 10 pump, and thus otherwise the booster pump may have poor performance. 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 15 the booster pump. Such pre-compression tends not to be performed by a Roots mechanism. Advantageously, the double claw booster pump tends to have good inlet conductance. This tends to provide a good filling efficiency, even at low pressures. 20 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. 25 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. Advantageously, the combination of small booster and primary pump 30 provided herein tends to provide for reduced the power requirement at all 03 07 25 operating inlet pressures. The arrangement involves a dry exhaust or primary pump in combination with a compact high-efficiency dry booster. The present disclosure provides various combinations of a booster and a primary pump that tend to substantially reduce the power required the pump 5 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 10 will tend to satisfy a high proportion of small pump applications. 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 15 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 20 consumption of the primary pump may be about 60W, giving a total power consumption of about 80W. 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 25 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. In some embodiments, a recirculation valve may be implemented. Figure 4 is a schematic illustration (not to scale) showing a pump system 400 30 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- 03 07 25 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 5 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 10 404 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. In this embodiment, the first pressure threshold (i.e. a cracking pressure 15 of the recirculation valve 402) may be between about 20mbar and about 100mbar, e.g. about 20mbar, about 30mbar, about 40mbar, about 50mbar, about 60mbar, about 70mbar, about 80mbar, about 90mbar, or about 100mbar. The recirculation valve 402 may be integrated with the booster pump 104, or may be a separate component. 20 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 25 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 30 122 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 03 07 25 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 5 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. In some embodiments, a pump system may comprise both the 10 recirculation valve 402 and the by-pass valve 502. 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 15 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. 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. 20 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 25 and reduced capacity. 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. 30 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 03 07 25 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 5 pumping stage. 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 10 different supply voltage. Examples of appropriate supply voltages for motors include but are not limited to 24V, 48V, 110V and 230 V. In the above embodiments, the booster pump is a double claw pump. However, in other embodiments, the booster pump is a different type of pump. Examples of appropriate booster pumps that may be used include, but are not 15 limited to, a Roots, a single claw pump, a scroll pump, and a screw pump. Examples 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 20 pump is a single stage booster pump. Option Booster pump capacity (m3 / hr) Capacity ratio Primary (exhaust) pump capacity (m3 / hr) 1 3 2 1.5 2 6 4 1.5 3 9 6 1.5 4 12 8 1.5 5 15 10 1.5 6 6 2 3 7 12 4 3 8 18 6 3 9 24 8 3 10 30 10 3 11 12 2 6 12 18 3 6 13 24 4 6 14 30 5 6 Table 1 Table 2 below provides a non-exhaustive list of example combinations of 5 booster and primary pumps. For the combinations given in Table 2, the booster pump is a two stage booster pump. Option Booster pump stage 1 capacity (m3 / hr) Stage ratio Booster pump stage 2 capacity (m3 / hr) Capacity ratio Primary (exhaust) pump capacity (m3 / hr) 1 6 2 3 2 1.5 2 13.5 3 4.5 3 1.5 3 24 4 6 4 1.5 4 30 4 7.5 5 1.5 5 12 2 6 2 3 6 T1 3 9 3 3 7 24 2 12 2 6 8 30 2.5 12 2 6 Table 2 10 03 07 25 Reference numeral list 100 - vacuum system 102 - chamber 104 - booster pump 5 106 - primary pump 108 - secondary pump 110 - roughing line 112 - backing line 113 - roughing valve 10 114 - booster pump inlet 116 - booster pump outlet 118 - intermediate line 120 - primary pump inlet 122 - primary pump outlet 15 124 - high vacuum line 126 - high vacuum valve 128 - secondary pump inlet 130 - first secondary pump outlet 132 - second secondary pump outlet 20 134 - backing valve 140 - first motor 142 - second motor 150 - enclosure 202 - first shaft 25 204 - second shaft 03 07 25 206 - first rotor 208 - second rotor 210 - pump chamber 211,212 - directions of rotation 5 220 - first claw portion 222 - second claw portion 224 - third claw portion 226 - fourth claw portion 228 - first recess 10 230 - second recess 232 - plane 236 - housing 238 - compression pocket 300 - method 15 s302-s306 - method steps 400 - pump system 402 - recirculation valve 404 - inlet stage 406 - second stage 20 408 - outlet 500 - pump system 502 - by-pass valve 03 07 25

Claims

1. A pumping system comprising:a booster pump comprising a booster pump inlet and a booster pump outlet; and5 a primary pump comprising a primary pump inlet and a primarypump outlet; whereinthe booster pump outlet is fluidly coupled to the primary pump inlet;a maximum capacity of the booster pump is less than or equal to10 40m3 / hr; anda maximum capacity of the primary pump is less than or equal to 5m3 / hr, andwherein the booster pump is a claw pump.15 2. The pumping system of claim 1, wherein the maximum capacity ofthe booster pump is less than or equal to 30m3 / hr.

3. The pumping system of claim 2, wherein the maximum capacity of the booster pump is between 10m3 / hr and 30m3 / hr.

204. The pumping system of any preceding claim, wherein the maximum capacity of the primary pump is less than or equal to 3m3 / hr.

5. The pumping system of any preceding claim, wherein the booster25 pump is selected from the group of claw pumps consisting of:a double claw pump; anda single claw pump.03 07 256. The pumping system of any preceding claim, wherein the primary pump is a vacuum pump selected from a group of vacuum pumps consisting of:a diaphragm pump;a scroll pump;5 a piston pump; anda rotary vane pump.

7. The pumping system of any preceding claim, wherein:the booster pump comprises at least one rotor; and10 the at least one rotor is formed from a polymer.

8. The pumping system of claim 7, wherein the polymer is a polymer selected from a group of polymers consisting of polyether ether ketone, PEEK; polyphenylene sulphide, PPS; a fibre-reinforced polymer; fibre-reinforced PPS;15 glass fibre-reinforced PPS.

9. The pumping system of any preceding claim, wherein the booster pump comprises a housing defining a pump chamber of the booster pump, the housing having one or more dimensions selected from a group of dimensions 20 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; and25 a height of less than or equal to 100mm, the height being in aradial direction that is perpendicular to the width.03 07 2510. The pumping system of any preceding claim, further comprising a motor arranged to drive the booster pump, wherein an output shaft power of the motor in typical continuous use is less than or equal to 150W.5 11. The pumping system of claim 10, wherein the output shaft powerof the motor in typical continuous use is less than or equal to 100W.

12. The pumping system of claim 10 or 11, wherein the motor has a motor voltage of less than or equal to 48V.1013. The pumping system of any preceding claim, wherein the 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 15 stage is less than that of the first pumping stage.

14. The pumping system of any preceding claim, wherein a ratio between the maximum capacity of the booster pump and the maximum capacity of the primary pump is at least 3:1.2015. The pumping system of any preceding claim, wherein a ratio between the maximum capacity of the booster pump and the maximum capacity of the primary pump is at least 5:1, or at least 8:1, or at least 10:1.25 16. The pumping system of any preceding claim, wherein the boosterpump is a multi-stage pump having an inlet stage, and the pumping system further comprises a recirculation valve disposed across the inlet stage of the booster pump.03 07 2517. The pumping system of any preceding claim, further comprising a bypass valve disposed between the primary pump inlet and a primary pump outlet.5 18. The pumping system of any preceding claim, wherein a powerconsumption of the primary pump is 150W or less.

19. The pumping system of claim 18, wherein a power consumption of the primary pump is about 60W.1020. The pumping system of any preceding claim, wherein a power consumption of the booster pump is 150W or less.

21. The pumping system of any preceding claim, further comprising a 15 common enclosure enclosing both the booster pump and the primary pump.

22. The pumping system of any preceding claim, further comprising a secondary pump, wherein the primary pump is arranged as a backing pump for the secondary pump.2023. The pumping system of claim 22, wherein the secondary pump is a turbopump.

24. A method of pumping a fluid, the method comprising:25 providing the pumping system of any preceding claim; anddriving the booster pump and the primary pump, thereby to pump the fluid into the booster pump inlet, then from the booster pump outlet to the primary pump inlet, and then out of the primary pump outlet.

Images