Pump with a resilient seal

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application is a continuation of U.S. application Ser. No. 13/265,510 filed Oct. 20, 2011, now pending, which, in turn, is the U.S. national phase of PCT Appin. No. PCT/GB2010/000798 filed Apr. 21, 2010, which claims priority to Great Britain application GB 0906768.7 filed Apr. 21, 2009, the disclosures of which are incorporated in their entirety by reference herein.

TECHNICAL FIELD

0002The invention relates to pumps.

BACKGROUND

0003A known form of pump comprises a housing with an inlet for connection to a source of fluid and an outlet for pumped fluid with the inlet and the outlet being spaced apart around a path of a rotor within the housing. The rotor includes at least one surface forming, with the housing, a closed chamber travelling around the housing to convey fluid around the housing. In this specification, the term “fluid” includes both gases and liquids.

0004A pump of this kind is disclosed in WO 2006/027548 in which a seal is provided in the housing between the inlet and the outlet to seal against the rotor. A first problem with pumps of this kind is that the housing and the seal are formed separately and then fitted together. As described in WO 2006/027548, the housing may be injection moulded and the seal fixed in the housing using an adhesive. Alternatively, the seal may be moulded with the housing in a 2-shot injection moulding process. This is a problem when there are two or more chambers because, any mismatch at the join between the housing and the seal can cause a leakage between adjacent chambers, particularly at higher pressure differences between the inlet pressure and the outlet pressure and where the apices of the rotor are positioned pressing into the seal. This leakage causes inaccuracy of flow rate of the pump and may allow unwanted backflow through the pump when stopped or at low flow rates.

0005According to a first aspect of the invention, there is provided a pump comprising a housing, the housing having an interior defining a rotor path, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, at least one first surface formed on the rotor and sealing against said rotor path of the housing, at least one second surface formed on said rotor circumferentially spaced from said first surface and forming a chamber with the rotor path that travels around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal formed in one piece with the housing, located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the first rotor surface seals with, and resiliently deforms, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal.

0006A further problem with such a pump arises if there is a mismatch between, first, the force required to form a seal between the rotor and the housing and, secondly, the pressure of the fluid at either the inlet or the outlet. At higher pressures, a greater sealing force is required but, if such a higher force is used at lower pressures, then frictional forces are unnecessarily increased and the torque required to drive the rotor is unnecessarily high. If a lower sealing force is used at higher pressures, then there can be leakage between the seal and the rotor and higher outlet pressures cannot be achieved.

0007According to a second aspect of the invention, there is provided a pump comprising a housing, the housing having an interior defining a rotor path, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, at least one first surface formed on the rotor and sealing against said rotor path of the housing, at least one second surface formed on said rotor circumferentially spaced from said first surface and forming a chamber with the rotor that travels around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the rotor surface seals with, and resiliently deforms, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal, the seal having an under surface opposed to a surface of the seal contacted by the rotor, a passage being provided to supply said fluid to said under surface at a pressure that acts to urge the seal against the rotor.

0008In WO2006/027548, the rotor is provided with one or more chambers with each chamber having a circumferential length that is shorter than the circumferential distance between the inlet port and the outlet port. This limits the volume of fluid that can be pumped.

0009According to a third aspect of the invention, there is provided a pump comprising a housing, the housing having an interior defining a rotor path, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, one first surface formed on the rotor and sealing against said rotor path of the housing, said first surface having a circumferential length longer than the circumferential length between the inlet and the outlet, a single second surface formed on said rotor circumferentially spaced from said-first surface, having a circumferential length longer than the circumferential length between the inlet and the outlet and forming a chamber with the housing travelling around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the first surface and the single second surface seal with, and resiliently deform, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal.

0010In pumps of this kind, the rotor and the chamber of the housing have a generally cylindrical shape with the cylinder of the rotor fitting into and rotating within the cylindrical chamber. The required tightness of fit between the parts is determined during manufacture and is difficult to adjust during assembly or in use.

0011According to a fourth aspect of the invention, there is provided a pump comprising a housing, a rotor path defined by the housing and within the housing, an inlet formed in the housing at a first position on said rotor path, an outlet formed in the housing at a second position on said rotor path spaced from said first position, a rotor rotatable in said housing, at least one first surface formed on the rotor and sealing against said rotor path of the housing, at least one second surface formed on said rotor circumferentially spaced from said first surface and forming a chamber with the rotor path that travels around said rotor path on rotation of the rotor to convey fluid around the housing from the inlet to the outlet, a resilient seal located on said rotor path and so extending between the outlet and the inlet in the direction of rotation of said rotor that the rotor surface seals with, and resiliently deforms, the seal, as the rotor rotates around the rotor path within the housing to prevent fluid flow from said outlet to said inlet past the seal, the rotor path being frustoconical and the first surface of the rotor being frustoconical and being a mating fit with the rotor path.

0012In this case, the relative positions of the rotor and the housing may be axially adjustable.

BRIEF DESCRIPTION OF THE DRAWINGS

0013The following is a more detailed description of some embodiments of the invention, by way of example, reference being made to the accompanying drawings, in which:

0014<figref idref="DRAWINGS">FIG. 1</figref> is a schematic cross-section through a known pump as disclosed in WO 2006/027548 including a housing provided with an inlet and outlet and a rotor rotatable within the housing and sealing against a seal provided by the housing, the rotor being shown in a first angular position;

0015<figref idref="DRAWINGS">FIG. 2</figref> is a similar view to <figref idref="DRAWINGS">FIG. 1</figref> but showing the rotor of the known pump rotated by about 30° from the position shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0016<figref idref="DRAWINGS">FIG. 3</figref> is a similar view to <figref idref="DRAWINGS">FIG. 1</figref> but showing the rotor of the known pump rotated by about 60° from the position shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0017<figref idref="DRAWINGS">FIG. 4</figref> is a schematic cross-section through a pump according to the invention including a housing provided with an inlet and outlet and a rotor rotatable within the housing and sealing against a seal formed in one piece with the housing;

0018<figref idref="DRAWINGS">FIG. 5</figref> is a similar view to <figref idref="DRAWINGS">FIG. 4</figref> but showing a modified form of the pump in which a port is provided leading from a point adjacent the outlet to behind the seal;

0019<figref idref="DRAWINGS">FIG. 6</figref> is a similar view to <figref idref="DRAWINGS">FIGS. 1 to 3</figref> and showing a pump according to the invention including a rotor provided with a single chamber;

0020<figref idref="DRAWINGS">FIG. 7</figref> is a longitudinal cross-section through a pump of the general kind shown in <figref idref="DRAWINGS">FIGS. 1 to 3</figref> but with a rotor and housing having a frusto-conical shape;

0021<figref idref="DRAWINGS">FIG. 8</figref> is a longitudinal cross-section of a pump of the general kind shown in <figref idref="DRAWINGS">FIG. 7</figref> but with a second form of frusto-conical rotor and housing;

0022<figref idref="DRAWINGS">FIG. 9</figref> is a similar view to <figref idref="DRAWINGS">FIG. 8</figref> but showing the provision of a spring to allow axial adjustment of the position of the rotor relative to the housing;

0023<figref idref="DRAWINGS">FIG. 10</figref> is a side elevation of a cap with a serrated end for use as a spring in the embodiment of <figref idref="DRAWINGS">FIG. 9</figref>;

0024<figref idref="DRAWINGS">FIG. 11</figref> is a similar view to <figref idref="DRAWINGS">FIG. 7</figref> but showing the provision of a spring between the rotor and the housing at the larger diameter end of the rotor, and

0025<figref idref="DRAWINGS">FIG. 12</figref> is an end view of the rotor of <figref idref="DRAWINGS">FIG. 11</figref>.

DETAILED DESCRIPTION

0026As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

0027Referring first to <figref idref="DRAWINGS">FIGS. 1 to 3</figref>, the known pump of WO 2006/027548 is formed by a housing indicated generally at <b>10</b> which may be formed by a plastics moulding of, for example, polyethylene or polypropylene. The housing <b>10</b> is formed with an inlet <b>11</b> for connection to a source of fluid and an outlet <b>12</b> for pumped fluid. The interior of the housing <b>10</b> is cylindrical. The portion of the interior of the housing <b>10</b> between the outlet <b>12</b> and the inlet <b>11</b>, again in clockwise direction as viewed in <figref idref="DRAWINGS">FIGS. 1 to 3</figref>, carries a seal <b>14</b> that will be described in more detail below.

0028The housing <b>10</b> contains a rotor <b>15</b>. The rotor <b>15</b> may be formed of a metal such as stainless steel or as a precision injection moulded plastics part formed from a resin such as acetal. As seen in the Figures, the rotor <b>15</b> is generally- of circular-cross-section and includes four recessed surfaces <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c </i>and <b>16</b><i>d </i>of equal length equiangularly spaced around the rotor and interconnected by apices <b>17</b><i>a</i>, <b>17</b><i>b</i>, <b>17</b><i>c </i>and <b>17</b><i>d </i>formed by unrelieved portions of the rotor <b>15</b>. Accordingly, each apex is rounded with a curvature that matches the curvature of the cylindrical housing surface <b>13</b> so that the rotor <b>15</b> is a close fit within the cylindrical housing surface <b>13</b> that forms a rotor path for the rotor. As a result, each recessed surface <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c </i>and <b>16</b><i>d </i>forms a respective chamber <b>18</b><i>a</i>, <b>18</b><i>b</i>, <b>18</b><i>c </i>and <b>18</b><i>d </i>with the cylindrical housing surface <b>13</b> as each surface <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d </i>travels around that rotor path <b>13</b>. If the housing <b>10</b> is formed from a resilient plastics material that deforms under load, the rotor <b>15</b> may be arranged to distend slightly the housing <b>10</b>, so ensuring a fluid-tight seal around each surface <b>16</b><i>a</i>, <b>16</b><i>b</i>. <b>16</b><i>c</i>. <b>16</b><i>d. </i>

0029The rotor <b>15</b> is rotated in a cloclca4se direction in <figref idref="DRAWINGS">FIGS. 1 to 3</figref> by a drive (not shown in the Figures).

0030The seal <b>14</b> is formed by a block of elastomeric material that is compliant, flexible and resilient such as that sold under the trade mark Hytrel. The seal <b>14</b> is connected to the housing <b>10</b> to prevent fluid passing between the seal <b>14</b> and the housing <b>10</b>. This may be by use of an adhesive. Alternatively, the seal <b>14</b> could be moulded with the housing <b>10</b> in a 2-shot injection moulding process. In this latter case, the material of the seal <b>14</b> must be such that it welds to the housing to prevent leakage. The seal <b>14</b> has a first axial edge <b>19</b> adjacent the inlet <b>11</b> and a second axial edge <b>20</b> adjacent the outlet <b>12</b>. The seal <b>14</b> has a rotor engaging surface <b>21</b> that has a length between the first and second edges <b>19</b>, <b>20</b> that is generally equal to the length of each of the recessed surfaces <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c </i>and <b>16</b><i>d </i>between the associated apices <b>17</b><i>a</i>, <b>17</b><i>b</i>, <b>17</b><i>c</i>, <b>17</b><i>d </i>and is shaped to match the shape of each recessed surface <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d</i>. The axial extent of the seal <b>14</b> is that at least the same as the axial extent of the recessed surfaces <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d</i>. The seal <b>14</b> projects into the space defined by an imaginary cylinder described by a continuation of the cylindrical surface <b>13</b> between the inlet <b>11</b> and the outlet <b>12</b>. The seal <b>14</b> may be flexed between the first and second axial edges <b>19</b>, <b>20</b> so that it bows outwardly relatively to the seal <b>14</b> towards the axis of the rotor <b>15</b> where the recessed surfaces <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d </i>are concave.

0031The natural resilience of the material will tend to return the seal <b>14</b> to the undistorted disposition after distortion by the rotor <b>15</b> and this may be assisted by a spring (not shown) acting on the outer end of the seal <b>14</b>.

0032The operation of the known pump described above with reference to <figref idref="DRAWINGS">FIGS. 1 to 3</figref> will now be described. The inlet <b>11</b> is connected to a source of fluid to be pumped and the outlet <b>12</b> is connected to a destination for the pumped fluid. The rotor <b>15</b> is rotated in a clockwise direction as viewed in <figref idref="DRAWINGS">FIGS. 1 to 3</figref>. In the position shown in <figref idref="DRAWINGS">FIG. 1</figref>, the rotor surface <b>16</b><i>a </i>engages resiliently the seal surface <b>21</b>. In this way, the space between the housing <b>10</b> and the rotor <b>15</b> is closed in this zone mad the passage of fluid from the outlet <b>12</b> to the inlet <b>11</b> is prevented. In this position, the apex <b>17</b><i>a </i>is aligned with the inlet <b>11</b> while the rotor surfaces <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d </i>form respective sealed chambers <b>18</b><i>b</i>, <b>18</b><i>c</i>, <b>18</b><i>d </i>with the cylindrical housing surface <b>13</b>. As a result of earlier revolutions of the rotor <b>15</b>, these chambers <b>18</b><i>b</i>, <b>18</b><i>c </i>and <b>18</b><i>d </i>are filled with fluid in a manner to be described below.

0033Referring next to <figref idref="DRAWINGS">FIG. 2</figref>, on rotation of the rotor <b>15</b> by about 30°, the chamber <b>18</b><i>d </i>is now connected to the outlet <b>12</b>. The associated apex <b>17</b><i>d </i>contacts the seal surface <b>21</b> and seals against that surface. Accordingly, the rotating rotor <b>15</b> forces fluid from the chamber <b>18</b><i>d </i>out of the outlet <b>12</b>. In addition, the apex <b>17</b><i>a </i>previously aligned with the inlet <b>11</b>, moves away from the inlet <b>11</b> and allows the rotor surface <b>16</b><i>a </i>to separate from the sealed surface <b>21</b> to begin to form a chamber <b>18</b><i>a </i>(<figref idref="DRAWINGS">FIG. 3</figref>) with the cylindrical housing surface <b>13</b>- and with the apex <b>17</b><i>d </i>against the seal surface <b>21</b>.

0034Referring next to <figref idref="DRAWINGS">FIG. 3</figref>, a further rotation of the rotor <b>15</b> by about 60° from the position shown in <figref idref="DRAWINGS">FIG. 1</figref>, results in the rotor surface <b>16</b><i>d </i>that previously formed the chamber <b>18</b><i>d </i>adjacent with outlet <b>12</b> begins to contact the seal surface <b>21</b> and sealing against that surface <b>21</b>. Thus, the chamber <b>18</b><i>d </i>reduces in volume until zero and fluid from that chamber is forced through the outlet <b>12</b>. At the same time, the rotor surface <b>16</b><i>a </i>formerly in contact with the seal surface <b>21</b> is now clear of that surface <b>21</b> and forms a chamber <b>18</b><i>a </i>with the cylindrical housing surface <b>13</b> and the chamber <b>18</b><i>a </i>receives fluid from the inlet <b>11</b>. The apex <b>17</b><i>d </i>between the surfaces <b>16</b><i>a </i>and <b>16</b><i>d </i>moves out of engagement with the seal surface <b>21</b> and starts to align with the inlet <b>11</b>.

0035The rotor <b>15</b> then moves to a position equivalent to the position shown in <figref idref="DRAWINGS">FIG. 1</figref> and pumping continues. In this way, fluid is pumped between the inlet <b>11</b> and the outlet <b>12</b>.

0036It will be appreciated that the rate of flow of liquid is proportional to the rate of rotation of the rotor <b>15</b> and the volumes of the chambers <b>18</b><i>a</i>, <b>18</b><i>b</i>, <b>18</b><i>c </i>and <b>18</b><i>d</i>. Although the rotor <b>15</b> is shown as having four surfaces <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d</i>, it could have any number of surfaces such as one or two or three surfaces or more than four surfaces. The surfaces <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d </i>may be planar, or may be, for example, convexly o1″ concavely curved. They may be shaped as indentations formed by the intersection with the rotor <b>15</b> of an imaginary cylinder having its axis at 90° to the axis of the rotor and offset to one side of the rotor axis. As described above, the rotor engaging surface <b>21</b> of the seal <b>14</b> may be shaped to complement the shape of the surfaces <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, <b>16</b><i>d. </i>

0037At all times, the seal-<b>14</b> acts to prevent the formation of a chamber between the outlet <b>12</b> and the inlet <b>11</b> in the direction of the rotor <b>15</b>. The resilience of the seal <b>14</b> allows it always to fill the space between the inlet <b>11</b> and the outlet <b>12</b> and the portion of the rotor <b>15</b> in this region. As the pressure differential between the inlet <b>11</b> or the outlet <b>12</b> increases, there is an increased tendency for fluid to pass between the seal <b>14</b> and the rotor <b>15</b>. The use of a spring acting on the seal <b>14</b>, as described above, will decrease that tendency and so allow the pump to operate at higher pressures. Thus, the force applied by the spring determines the maximum pump pressure. Pumps are known in which the outlet and the inlet are separated by a thin vane extending from the housing and contacting the rotor. In such pumps, there is a volume of fluid between the outlet and the inlet and a large pressure gradient across the vane that will increase as the speed of rotation of the rotor if it is driving the fluid through a fixed outlet and the viscosity of the fluid leads to a back pressure that rises with flow rate. As a result, there is an increased liability to leakage across the vane. In the pump described above with reference to the drawings, although there is a pressure differential between the inlet and the outlet, there is a smaller pressure gradient across the barrier between the inlet <b>11</b> and the outlet <b>12</b> as the fluid is gradually squeezed out of the chambers <b>18</b><i>a</i>, <b>18</b><i>b</i>, <b>18</b><i>c </i>and <b>18</b><i>d </i>into the outlet <b>12</b> and then, after further rotation of the rotor <b>15</b>, gradually introduced into a chamber <b>18</b><i>a</i>, <b>18</b><i>b</i>, <b>18</b><i>c </i>and <b>18</b><i>d </i>on the inlet side. This reduces the possibility of leakage and allows the pump to provide an accurate metered flow. The seal <b>14</b> acts as a displacer displacing the fluid between the inlet <b>11</b> and the outlet <b>12</b>.

0038All that is described above with reference to <figref idref="DRAWINGS">FIGS. 1 to 3</figref> is disclosed in WO 2006/027548.

0039Referring next to <figref idref="DRAWINGS">FIG. 4</figref>, parts common to <figref idref="DRAWINGS">FIGS. 1 to 3</figref> and to <figref idref="DRAWINGS">FIG. 4</figref> will be given the same reference numerals and will not be described in detail.

0040In the embodiment of <figref idref="DRAWINGS">FIG. 4</figref>, the separate seal <b>14</b> is omitted. A seal <b>114</b> is formed in one-piece with the housing <b>10</b>. These parts may be formed from a plastics material by a single injection moulding process. The seal <b>114</b> is a thin plastics wall that extends circumferentially from the inlet <b>11</b> to the outlet <b>12</b>. The thickness of the wall may, for example, be 0.15 mm. The material of the housing <b>10</b> and the thickness of the wall are chosen such that the wall can distort when contacted by the apices <b>17</b><i>a</i>, <b>17</b><i>b</i>, <b>17</b><i>c</i>, <b>17</b><i>d </i>of the rotor <b>15</b>. Suitable materials may be polyethylene or polypropylene.

0041In order for the seal <b>114</b> to be flexible enough to follow the contour of the rotor <b>15</b> as it rotates requires that the seal <b>114</b> be moulded with a very thin wall section. This requirement for a thin wall section over a large area is not normally encountered in typical injection moulded parts. By careful processing using high injection pressures, locally hot tooling around the seal area and local venting to eliminate gassing it is possible to achieve seals <b>114</b> with a wall thickness between 0.1 mm-0.3 mm.

0042In a preferred process, the sliding portion of the tool that creates the outer surface of the seal <b>114</b> is controlled hydraulically. The molten plastic is injected into the tool by the injection screw in the conventional manner where the seal wall thickness is approximately twice the design thickness thus allowing the molten material to flow readily across the seal. Instead of using the injection screw to provide the packing pressure whilst the moulding cools and solidifies the sliding portion of the tool is advanced hydraulically to create the desired seal wall thickness and creating the packing pressure at the same time.

0043The use of a suitable flexible material for the seal <b>114</b> may require the moulding of stiffening members such as flanges on the housing <b>10</b> to provide it with sufficient rigidity.

0044In use, the presence of the unitarily formed seal <b>114</b> ensures that there is no leakage between adjacent chambers <b>18</b><i>a</i>, <b>18</b><i>b</i>, <b>18</b><i>c </i>and <b>18</b><i>d </i>at the joint between the housing <b>10</b> and the seal <b>114</b> as an apex <b>17</b><i>a</i>, <b>17</b><i>b</i>, <b>17</b><i>c</i>, <b>17</b><i>d </i>passes the joint, as may occur in the known embodiment of <figref idref="DRAWINGS">FIGS. 1 to 3</figref> particularly at higher pressures. The use of a single shot moulding compared with twin shot or co-moulding processes, reduces the number of processes, has a faster cycle time, requires simpler mould tools and mould machinery and leads to higher manufacturing yield and lower production costs. In comparison with pumps of this kind omitting these features, the pump of <figref idref="DRAWINGS">FIG. 4</figref> may have a longer operational life.

0045Referring next to <figref idref="DRAWINGS">FIG. 5</figref>, parts common to <figref idref="DRAWINGS">FIGS. 1 to 4</figref> and to <figref idref="DRAWINGS">FIG. 5</figref> will be given the same reference numerals and will not be described in detail.

0046In the embodiment of <figref idref="DRAWINGS">FIG. 5</figref>, the seal <b>114</b> is formed in one piece with the housing <b>10</b>, as in <figref idref="DRAWINGS">FIG. 4</figref>. In this embodiment, however, there is provided a resilient displacer pad <b>141</b> that bears against the underside of the seal <b>114</b> to urge the seal against the rotor <b>10</b>. This allows the pump to be used at higher pressures since the additional pressure from the pad <b>141</b> resists the forced passage of fluid between the rotor <b>10</b> and the seal <b>114</b>. The force applied by the pad <b>141</b> is chosen to allow the pump to operate at a lower end of a range of operating pressures for which the pump is designed, for example up to 0.5 bar.

0047In addition, a port <b>101</b> is provided in the outlet <b>12</b> to allow communication between the outlet <b>12</b> and the space behind the seal <b>114</b>. The effect of this is to allow fluid to flow through the port <b>101</b> in operation and apply fluid pressure to a chamber <b>147</b> formed by the under surface of the seal <b>14</b>, a turret <b>145</b> projecting outwardly from the rest of the housing <b>10</b> and a cap <b>146</b> closing the turret <b>145</b>. The force applied by the seal <b>114</b> to the rotor is thus the sum of the force applied by the pad <b>141</b> and the force applied by the fluid. In this way, the applied force varies with the outlet pressure and an increase in outlet pressure results in a corresponding increase in the force applied to the seal <b>114</b> so preventing leakage between the seal <b>114</b> and the rotor <b>10</b> as a result of the increased pressure.

0048It has been found that pumps that have a maximum operating pressure of 1 bar without the port <b>101</b> can be operated at pressures of up to and exceeding 6 bar with the port <b>101</b>. As the pressure applied to the seal <b>114</b> varies automatically with output pressure, a single design of pump incorporating such a port <b>101</b> may be used for a variety of applications requiring a wide range of pressures. In addition, the pump always operates with the minimum torque requirement since the force between the seal <b>114</b> and the rotor <b>10</b> is never unnecessarily high.

0049Since the pad <b>141</b> bears against the under surface of the seal <b>114</b>, it advisable to make the pad <b>141</b> sufficiently resilient that pressure from the outlet <b>12</b> is transmitted to the seal <b>114</b>.

0050The fluid could be provided to the under surface from the inlet <b>11</b> or from any other suitable point within the housing <b>10</b> or supplied via a tube from a remote location in the fluid system, thus enabling the manufacture of a pump with high input pressure or output pressure.

0051Referring next to <figref idref="DRAWINGS">FIG. 6</figref>, parts common to <figref idref="DRAWINGS">FIGS. 1 to 3</figref> and to <figref idref="DRAWINGS">FIG. 6</figref> will be given the same reference numerals and will not be described in detail. In <figref idref="DRAWINGS">FIG. 6</figref>, the housing <b>210</b> is moulded in one-piece as described above with reference to <figref idref="DRAWINGS">FIG. 4</figref>. The housing <b>210</b> has an inlet <b>211</b> and an outlet <b>212</b> that a closely spaced in a circumferential direction. A seal <b>214</b> is formed in one-piece with the remainder of the housing <b>210</b> as described above with reference to <figref idref="DRAWINGS">FIG. 4</figref> and is urged radially inwardly by a resilient pad <b>240</b> acting between seal <b>214</b> and a base <b>241</b> formed on the housing. The space containing the pad <b>240</b> is connected to the outlet <b>212</b> by a port <b>201</b> formed between the seal <b>214</b> and the housing <b>210</b>. This port <b>201</b> operates as described above with reference to <figref idref="DRAWINGS">FIG. 5</figref>.

0052The rotor <b>15</b> is provided with a single recessed surface <b>216</b> with the ends of this surface <b>216</b> interconnected by a single apex <b>217</b> extending axially along the rotor <b>15</b>. The circumferential length of the apex <b>217</b> is longer than the circumferential spacing of the inlet <b>211</b> and the outlet <b>212</b>.

0053The seal <b>214</b> has a radially inwardly projecting rotor engaging surface <b>221</b> urged by the pad <b>240</b> into contact with the surface of the recessed portion <b>216</b>, as the portion <b>216</b> passes over the seal <b>214</b>.

0054The pump of <figref idref="DRAWINGS">FIG. 6</figref> operates generally as descried above with reference to <figref idref="DRAWINGS">FIGS. 1 to 5</figref>. Since, however, the circumferential length of the recessed surface <b>216</b> is greater than the circumferential spacing of the inlet <b>211</b> and the outlet <b>212</b>, the contact between and the surface <b>216</b>, as the surface <b>216</b> passes over the seal <b>214</b>, prevents communication between the inlet and outlet ports <b>211</b>, <b>212</b>.

0055The benefit of the pump of <figref idref="DRAWINGS">FIG. 6</figref> is that the single chamber <b>218</b> formed between the recessed surface <b>216</b> and the chamber <b>13</b> maximises the volume of fluid transferred from the inlet <b>211</b> to the outlet <b>212</b> on each rotation of the rotor <b>15</b>. This is further improved by the decrease in the circumferential separation of the inlet <b>211</b> and the outlet <b>212</b>, so allowing the circumferential extent of the apex <b>217</b> to be reduced and the circumferential extent of the recessed surface <b>216</b> to be correspondingly increased, so increasing the volume of the chamber <b>218</b>.

0056Of course, the pump of <figref idref="DRAWINGS">FIG. 6</figref> could have a separate seal, as described above with reference to <figref idref="DRAWINGS">FIGS. 1 to 4</figref>. In addition, the port <b>201</b> is optional. In addition, in the embodiments of both <figref idref="DRAWINGS">FIGS. 5 and 5</figref>, the ports <b>101</b> and <b>201</b> are shown as leading from the outlet <b>12</b>, <b>212</b> to the under surface of the seal <b>114</b>, <b>214</b>, It is possible, as an alternative, for the ports to lead from the associated inlet <b>11</b>, <b>211</b> to the under surface of the seal <b>114</b>, <b>214</b>.

0057In the embodiments described above with reference to <figref idref="DRAWINGS">FIGS. 1 to 6</figref>, the interior of the housing <b>10</b> and the exterior of the rotor <b>15</b> have complementary cylindrical surfaces. The operating torque and the maximum pumping pressure are affected by the closeness of the fit between these parts and small manufacturing variations can have an adverse effect by increasing the required torque and by reducing the maximum pumping pressure through leakage.

0058Referring next to <figref idref="DRAWINGS">FIG. 7</figref>, parts common to the pump of <figref idref="DRAWINGS">FIGS. 1 to 3</figref> and to the pump of <figref idref="DRAWINGS">FIG. 7</figref> will be given the same reference numerals and will not be described in detail.

0059In the pump of <figref idref="DRAWINGS">FIG. 7</figref>, the housing <b>300</b> has an interior that has a first short smaller diameter cylindrical end <b>350</b> and a second short larger diameter end <b>351</b> inter-connected by a frusto-conical section <b>352</b>. The rotor <b>315</b> has a short smaller diameter cylindrical end <b>353</b> with the body of the rotor <b>354</b> being frusto-conical so that the rotor <b>315</b> fits in, and is rotatable in, the interior of the housing <b>300</b> with the rotor body <b>354</b> mating with the frusto-conical section <b>352</b> of the housing <b>300</b>. The smaller diameter end <b>353</b> of the rotor <b>315</b> carries an annular seal <b>355</b> that seals between the rotor <b>315</b> and the housing <b>300</b>. The seal may be an O-ring, a quad seal or a lip seal and may be moulded in either the housing <b>300</b> or the rotor <b>315</b>

0060The included cone angle of the frusto-conical section <b>352</b> of the housing <b>300</b> and of the rotor body <b>354</b> may be between 2° and 20° and may preferably be between 5° and 15° more preferably 10°

0061The larger diameter end <b>350</b> of the housing <b>300</b> carries a washer <b>357</b> that can be adjusted to move the rotor <b>315</b> axially relative to the housing <b>300</b> to adjust the fit between these parts and to obtain the required interface pressure between the rotor <b>315</b> and the housing <b>300</b> while minimising the torque required to rotate the rotor <b>315</b> via a drive socket <b>356</b> extending axially into the smaller diameter end <b>353</b> of the rotor <b>350</b>. This thus mitigates the potential problem with manufacturing variations affecting the fit between a cylindrical housing interior and mating rotor surface. The contact point between the washer <b>357</b> and the rotor <b>315</b> may be made preferentially near the axis of the rotor <b>315</b> to reduce the torque required to rotate the rotor <b>315</b>.

0062As seen in <figref idref="DRAWINGS">FIG. 7</figref>, rotor <b>350</b> is provided with recessed surfaces, two of which <b>16</b><i>a</i>, <b>16</b><i>c </i>as seen in <figref idref="DRAWINGS">FIG. 7</figref>. In addition, the housing <b>300</b> is provided with a seal <b>14</b> that may be formed in any of the ways described herein with reference to the drawings. A pad <b>141</b> may be provided as described above with reference to <figref idref="DRAWINGS">FIG. 5</figref> and held in place by a cap <b>358</b>.

0063The pressure urging the rotor <b>350</b> against the housing can be carefully controlled so that the interface pressure between the housing and the contact surfaces is set to a desired value. This pressure can be provided in any of the following ways (which may be used individually or in any combination). Firstly, the pressure could be provided by a spring acting on the rotor <b>350</b>. Secondly, the pressure could be provided by modifying the rotor <b>350</b> to crate a flange or lugs during manufacture so that it is held by the smaller diameter end of the housing <b>300</b> at the appropriate position. Thirdly, the pressure could be provided by modifying the larger diameter end of the housing <b>300</b> to hold the rotor <b>350</b> at the appropriate axial position. The modification can be achieved by heating treating the end of the housing <b>300</b> and producing a lip around the circumference (“heat staking”) or by welding a washer to the housing <b>300</b> to form a rim or by moulding a deformable lip on the housing <b>300</b> over which the rotor <b>315</b> snaps into place.

0064Referring next to <figref idref="DRAWINGS">FIG. 8</figref>, in this embodiment, the housing <b>410</b> contains a rotor <b>415</b> with the housing <b>410</b> and the rotor <b>415</b> having mating frusto-conical surfaces, as described above with reference to <figref idref="DRAWINGS">FIG. 7</figref>. In this embodiment, the housing <b>410</b> is formed at a larger diameter end with an L-section annular flange <b>450</b> having a cylindrical inner surface <b>451</b> co-axial with the axis of the housing <b>410</b>. At a smaller diameter end of the rotor <b>410</b>, there is formed inwardly projecting hub <b>452</b> provided with a larger diameter outer cylindrical surface <b>453</b> connected to a smaller diameter outer cylindrical surface <b>454</b> by an angled annular step <b>455</b>.

0065The rotor <b>415</b> is of hollow cylindrical shape and is received within the housing <b>410</b>. The rotor <b>415</b> is formed at its larger diameter end with a radially outwardly directed flange <b>456</b> carrying an axially projecting annular seat <b>457</b> that bears against the inner surface <b>451</b> of the annular flange <b>450</b> of the housing <b>410</b> to form a seal between the parts. At the smaller diameter end of the rotor <b>415</b>, an inner surface <b>451</b> of the rotor <b>415</b> is formed with an annular L-section seal <b>459</b> having a lip <b>460</b> that bears against the larger diameter outer cylindrical surface <b>453</b> of the hub <b>452</b> to form a seal between the parts.

0066A spline is formed on the inner surface of the flange <b>456</b> to transmit drive to the rotor <b>415</b>. Alternatively, gear teeth can be formed to the outer surface of the flange <b>456</b> to transmit drive to the rotor.

0067A cap <b>461</b> has a beveled end surface <b>462</b> and fits over the smaller diameter outer cylindrical surface <b>454</b> of the hub <b>452</b> with the beveled end surface <b>462</b> bearing against the step <b>455</b> and the open end <b>463</b> of the cap <b>461</b> bearing against L-section seal <b>459</b> on the smaller diameter end of the rotor <b>415</b>. The cap <b>461</b> is fixed to the hub <b>452</b> by, for example, welding.

0068This engagement positions the rotor <b>415</b> axially relatively to the housing <b>410</b>. It will be appreciated that by varying the dimensions and/or position of the cap <b>461</b>, the axial position of the rotor <b>415</b> relative to the housing may be so varied as to provide a required interface pressure between the rotor <b>415</b> and the housing <b>410</b>.

0069The pump of <figref idref="DRAWINGS">FIG. 8</figref> has an inlet and an outlet (not shown) and a seal (not shown) and otherwise operates as described above with reference to <figref idref="DRAWINGS">FIGS. 1 to 7</figref>.

0070The pump <b>10</b> need not be made from a metal such as stainless steel or a resin such as acetal, the rotor <b>15</b> could be made from, for example, polyethylene or polypropylene.

0071The seal <b>14</b> need not have a shape to match the shape of each recessed surface <b>16</b><i>a</i>, <b>16</b><i>b</i>, <b>16</b><i>c</i>, and <b>16</b><i>d</i>. The seal <b>14</b> may, for example have a natural shape that is a continuation of the cylindrical surface of the housing <b>10</b> with a spring or resilient pad acting to distort the seal <b>14</b> towards the axis of the rotor <b>15</b>. In practice the seal is formed to the same radius of curvature as the diameter of the cylindrical housing <b>10</b>, but in general it can be moulded to curved shapes which cross the cylindrical volume provided that the join between the housing and the seal is tangential to the cylinder defined by the interior of housing.

0072The rotor <b>15</b> may also be driven in the anti-clockwise direction and the direction of flow will reverse. Where the ports <b>11</b> and <b>12</b> are placed symmetrically with respect to the seal <b>14</b>, the pump will provide the same flow characteristic in both directions. In practice it is found that higher output pressures can be obtained with the output port moved circumferentially slightly away from the seal <b>14</b> as this reduces the tendency for fluid to travel back between the seal <b>14</b> and the rotor <b>15</b> when the apices <b>17</b><i>a</i>, <b>17</b><i>b</i>, <b>17</b><i>c</i>, <b>17</b><i>d </i>are close to the output port. In this case the flow rate in the anti-clockwise direction is lower due to the seal <b>14</b> not being as effective at displacing the fluid from the chamber.

0073Referring next to <figref idref="DRAWINGS">FIG. 9</figref>, parts common to <figref idref="DRAWINGS">FIG. 8</figref> and to <figref idref="DRAWINGS">FIG. 9</figref> will be given the same reference numerals and will not be described in detail.

0074In the pump of <figref idref="DRAWINGS">FIG. 8</figref>, the position of the cap <b>461</b> determines the interface pressure between the rotor <b>415</b> and the housing <b>410</b>. As described with reference to <figref idref="DRAWINGS">FIG. 8</figref>, this force can be adjusted by varying the position and/or the dimensions of the cap <b>461</b>.

0075This adjustment may be required to allow the pump to be used with fluids of differing viscosities or with adverse rheological properties such as shear thickening. For lower viscosity fluids, for example, a smaller gap between rotor <b>415</b> and the housing <b>410</b> is possible without unduly increasing the torque required to turn the rotor <b>415</b>. With higher viscosity fluids such as paint or food sauces, it is advantageous to increase this gap in the bearing area to reduce the torque required to rate the rotor <b>415</b>. Such an increased gap does not lead to leakage of fluid or affect output pressure or accuracy of flow rate but such a larger gap can affect the self-priming ability of the pump (where the pump and its supply lines are empty of fluid at the start of operation).

0076The embodiment of <figref idref="DRAWINGS">FIG. 9</figref> addresses this problem by the provision of a spring <b>470</b> located around the hub <b>452</b> and acting between the cap <b>461</b> and a radially extending annular wall <b>472</b> of the seal <b>459</b>. The effect of the spring <b>470</b> is to urge the rotor <b>415</b> against the housing <b>410</b> and so close the gap between these parts when the pump is empty of fluid. This allows gas to be pumped through the pump when the pump is priming so allowing higher viscosity fluids to be drawn into the pump to prime the system. When such a higher viscosity fluid reaches the pump outlet, the increased outlet pressure and the thin film of liquid that forms between the mating surfaces between the rotor and the housing act on the rotor <b>415</b> to force it away from the housing <b>410</b> by compressing the spring <b>470</b>, so increasing the gap between the rotor <b>415</b> and the housing <b>410</b>. Thus, the axial position of the rotor <b>415</b> relative to the housing <b>410</b> is adjusted in accordance with the pressure of the fluid being pumped to increase the spacing between the rotor <b>415</b> and the housing <b>410</b> with increasing fluid pressure in the pump

0077The spacing between the cap <b>461</b> and the seal <b>459</b> limits the maximum movement of the rotor <b>415</b> away from the housing <b>410</b> and this can be varied as required. In addition, the spring constant may be varied to provide differing rates of compression of the spring <b>470</b> under the action of a pumped fluid.

0078This spring force need not be provided by a coil spring <b>470</b> as shown in <figref idref="DRAWINGS">FIG. 9</figref>. Any suitable form of spring may be used such as a spring metal or a plastics washer. One possible variation is shown in <figref idref="DRAWINGS">FIG. 10</figref>. As seen in this Figure, the cap <b>461</b> is formed of a flexible material and is provided with a serrated open end so that each serration <b>473</b> can flex when compressed. The serrated open end of the cap <b>461</b> presses against the wall <b>472</b> of the seal <b>459</b> so that when the pressure of the rotor <b>415</b> increases as higher viscosity fluid is pumped through the pump, the serrations <b>473</b> flex to allow the spacing between the rotor <b>415</b> and the housing <b>410</b> to increase.

0079A second variation is shown in <figref idref="DRAWINGS">FIGS. 11 and 12</figref>. In these Figures, the pump is constructed as described above with reference to <figref idref="DRAWINGS">FIG. 7</figref> and parts common to that Figure and to <figref idref="DRAWINGS">FIGS. 11 and 12</figref> are given the same reference numerals and are not described in detail.

0080Referring to <figref idref="DRAWINGS">FIGS. 11 and 12</figref>, the larger diameter end of the rotor <b>350</b> is formed with two arcuate cantilevered spring arms <b>370</b>, <b>371</b> extending away from and around the larger diameter end. As seen in <figref idref="DRAWINGS">FIG. 11</figref>, the free ends of the spring arms <b>370</b>, <b>371</b> bear against the washer <b>357</b> and provide a spring force urging the rotor <b>350</b> against the housing <b>300</b> and acting in the manner described above to allow priming of the pump with the rotor <b>350</b> close to the housing <b>300</b> followed by increased spacing as a higher viscosity liquid reaches the outlet.

0081The spring arms <b>370</b>, <b>371</b> may be formed separately from the rotor <b>350</b>. Where the rotor <b>350</b> is moulded, for example, the spring arms <b>370</b>, <b>371</b> may be co-moulded with the rotor <b>350</b>. A preferred material for such moulding is a polyacetal as it has a property of low creep. The benefit of a low creep spring is that it allows a range of viscosities to be pumped with one pump assembly.

0082Of course, the spring arms <b>370</b>, <b>371</b> may be replaced by any other suitable form of spring acting between the rotor <b>350</b> and the housing <b>300</b>, such as a coil spring or a spring washer.

0083In this embodiment, the range of movement is again limited by the spacing between the larger diameter end of the rotor <b>350</b> and the washer <b>357</b> and this can be adjusted or limited as required.

0084While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.