The present invention relates to a chemical dosing sensor for measuring the level of a chemical in a sample, particularly for measuring the level of a corrosion inhibitor in a central heating and/or cooling system circuit.

BACKGROUND TO THE INVENTION

Corrosion inhibitor is added to central heating system water to prevent or reduce corrosion of system components such as radiators, pipework, and heat exchangers. Corrosion can cause premature failure of heating systems firstly if it results in a leak (for example, a pinhole leak in an aluminium heat exchanger which can effectively end the useful life of a boiler), and secondly because it leads to particles, especially iron oxide particles, becoming entrained in the system water. These particles can collect in radiators, reducing heat output and reducing system efficiency, can damage pumps, and can clog heat exchangers.

Various inhibitor chemicals are used in proprietary formulations, but often include an amine, sodium molybdate, and/or sodium gluconate.

In theory, the inhibitor dosed into a sealed system can remain stable, and protect the system, for many years. However, if the system is topped up for some reason, by adding water from the mains supply, the inhibitor will become diluted. Components of inhibitors often work by reacting with oxygen in the water, to reduce the oxygen concentration in the water and therefore the oxidation reactions which can occur to corrode metals in the system. If oxygen is allowed to continually enter the system (as is the case in an open-vented system) then the inhibitor will become “used up” over time.

It is therefore difficult to estimate the length of time for which a dose of inhibitor will remain effective in a particular heating system. There is a risk that the system will either be under-dosed, resulting in ineffective protection from corrosion, or over-dosed, which is a waste of expensive chemicals.

An optical testing device has been proposed in GB2565061. The testing device includes a testing chamber in the form of a syringe, so that a sample of water can be drawn into the testing chamber, tested, and then released back into the central heating system. During testing, the sample is isolated from the central heating system to reduce turbulence in the sample chamber which may interfere with the optical test. This is achieved by means of a sealing element integrated into the piston, extending from the piston crown on a necked-down section. When testing is not in progress, the piston is extended so that the sample chamber is empty. This is important to keep the sample chamber clean, as dirty walls would interfere with the optical testing. However, one consequence of this is that the necked-down section in front of the piston crown, which is inside the sample chamber during testing, is outside the sample chamber and exposed to moving water when testing is not in progress, which is most of the time. This can result in corrosion on the surface of the necked-down section, which changes its optical properties and thus interferes with the optical test.

It is an object of the present invention to provide an improved and miniaturized optical chemical dosing sensor for a central heating system, which addresses the above problems.

STATEMENT OF INVENTION

The present invention relates to various aspects of a chemical dosing sensor for use in a heating and/or cooling system, the chemical dosing sensor comprising: a fitment having an inlet and an outlet for connection to the heating / cooling system circuit, and a flow passage to carry system water from the inlet to the outlet; a sample tube for holding a sample of water to be tested, the sample tube being connected to the flow passage to allow fluid to pass between the heating / cooling system circuit and the sample tube; optical testing apparatus including a light source and a detector, for measuring an optical property of the sample of system water isolated within the sample tube; a piston for controlling filling of the sample chamber with system water from the system circuit, and emptying of the sample chamber, the piston being movable to a retracted position for drawing water out of the system circuit into the sample chamber, and to an extended position for emptying the sample chamber, the piston having a piston crown, a rod extending in front of the piston crown, and a sealing element at the end of the rod, the sealing element isolating the sample tube from the flow passage when the piston is in the retracted position, and the rod in the extended position extending into the flow passage in an interface portion of the flow passage. In a first aspect, a flow deflector is provided in the flow passage, between the inlet and the interface portion, the flow deflector being positioned to divert flow of system water around the rod in the extended position.

The flow deflector protects the rod from surface damage which could result from the rod being left in the flow passage, in the path of fast-flowing fluid. The flow diverter diverts flow around the rod, to reduce the velocity of fluid flow which is actually incident on the rod.

Preferably, the flow passage widens in the interface portion. This further reduces the flow velocity in the vicinity of the rod. Widening the flow passage also compensates for the restriction introduced by the flow diverter and reduces the static pressure drop across the inlet and outlet. This avoids overworking a system pump.

The flow diverter preferably has a tapered profile, with a narrow end facing towards the inlet and a wide end facing towards the interface portion. This provides a barrier wide enough to protect the rod from fast-flowing fluid, while also reducing eddies in the vicinity.

In another aspect, the rod of the piston includes a bore, the bore being open to the front side (facing out of the sample tube) of the sealing element, and a guide rod is provided, fixed within the interface portion of the flow passage. The guide rod fits into the bore of the piston and the piston can slide along the guide rod in a “telescoping” manner. Preferably the guide rod is sufficiently long that it always extends at least partially into the bore, even with the piston in the fully-retracted position.

The guide rod stabilises the piston while in the extended position, and reduces vibration caused by the flow of system water acting on the piston rod. The guide rod is especially of benefit during the travel of the piston between extended and retracted positions. In intermediate positions between extended and retracted positions, the piston crown will be inside the sample tube and the sealing element will be in the flow passage. Forces applied to the sealing element by the movement of water in the flow passage have the potential to cause, via the rod as a lever, forces between the piston crown and the sample tube. The sample tube is preferably made from borosilicate glass, and these forces have the potential to crack the sample tube. It is therefore advantageous to reduce these forces as much as possible.

In another aspect, a recess is provided in an interior wall of the flow passage, in an interface portion of the flow passage, the recess being positioned to receive the sealing element when the piston is in the extended position. This protects the sealing element, which is wider than the rod, from flow in the flow passage.

The sealing element preferably includes an O-ring seal on a curved cylindrical surface of the sealing element. The O-ring seal seals either against a side wall of the sample tube, or a side wall of an extension of the sample tube (for example, there may be a plastic extension of the glass sample tube), when the piston is in the retracted position. The O-ring seal also helps to locate the sealing element and stabilise it in the recess, when the piston is in the extended position.

The recess provides an anchor point at the end of the rod. This stabilises the rod which is then supported at both ends when in the extended position - by the piston crown at the sample tube end, and by the sealing element in the recess in the interface portion of the flow passage.

One or more slots may be provided as extensions to the recess, at the edge of the recess. The slots prevent hydraulic lock and allow the sealing element to move into and out of the recess with minimum force applied.

In another aspect, the sample tube is mounted on elastomeric mounts. The sample tube may be a short tube, for example around 30mm long, and open at both ends. One end is open to the flow passage (but can be closed using the sealing element) and the other end is open to allow the piston operating mechanics to pass into the tube. The sample tube is preferably made from borosilicate glass, which has good optical properties and stays clean, even when the system water is sometimes contaminated with materials which may foul the surface. Borosilicate glass also provides good sealing against the piston components.

The elastomeric mounts may comprise one or more O-rings surrounding the tube. Preferably, two O-rings are provided, one close to either end of the tube. The O-rings are made from a soft elastomeric material, for example rubber or synthetic rubber (such as EPDM). Hence the tube is able to move slightly - it is held in a “floating” position in relation to other components. This protects the tube from damage which may be caused by forces on the tube from the piston crown and/or the sealing element.

A substantially rigid cage may be provided, which surrounds a central section of the tube. Where O-rings are provided, the rigid cage may surround a central section, between the O-rings. The O-rings may contact ends of the cage. An interior bore through the cage may be slightly larger than an exterior diameter of the tube, allowing the tube to move within the cage. The cage may have apertures to allow the optical testing components to “see” into the tube.

Elastomeric mounts may comprise one or more sealing elements having an L-shaped profile, and placed against an end wall and part of the side wall of the tube. The L- shaped profile may extend in a ring, around the circumference of the tube. The outer surface of the ring may have flat portions, for locating and rotationally fixing the ring in relation to surrounding housing components.

In another aspect, the piston crown includes a first seal and a second seal for sealing against the inner wall of the sample tube, the first seal being made from a relatively flexible material and the second seal being made from a relatively inflexible material, and the first seal being disposed at the front end of the piston crown, between the second seal and the rod.

The first seal may be an elastomeric O-ring, for example made from rubber, EPDM or polyurethane. The second seal may be made for example from PTFE. The second seal is a relatively hard “scraper seal”. It is found that using a double seal in this arrangement not only provides for very reliable sealing, preventing any water from leaking out of the back end of the sample tube, but also effectively keeps the walls of the sample tube clean and dry between tests.

The syringe crown may be assembled in two parts, for example fixed together by a screw thread, and with at least the second seal clamped between the two parts. This allows for a hard seal to be used, which would not be possible to deform to fit over the outside of a pre-assembled piston crown. In some embodiments, both the first and second seals may be clamped between the two parts of the piston. In some embodiments, the first and second seals are placed against each other.

In another aspect, the piston may be driven, i.e. moved between the extended and retracted positions, by means of a leadscrew and motor drive. Preferably, a bearing is provided between the piston crown and the leadscrew, allowing the leadscrew to rotate without rotating the piston crown. As the leadscrew rotates, the piston crown is driven axially in an extending / retracting direction. The rotational bearing protects the glass sample tube from torsional forces, and also reduces torque on the motor, especially at start up. This may allow a smaller motor to be used and also improves motor lifetime and battery life. Preferably, position sensors are provided for detecting one or more positions of the leadscrew. The position sensor(s) may be provided as, for example, non-contact optical sensors or as microswitches. Preferably, there are two sensors for sensing a fully extended position and a fully retracted position. The sensor(s) may feed into a control circuit to stop the motor running when the full extent of the syringe in either direction is reached.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which:

Figure 1 is a cross section through part of a chemical dosing sensor according to the invention, with the piston in a retracted position;

Figure 2 is a cross section through the chemical dosing sensor of Figure 1, with the piston in an extended position;

Figure 3 is a perspective view of a fitment, forming part of the chemical dosing sensor of Figure 1;

Figure 4 is a cross section showing the result of a computer simulation of fluid flow through the fitment of Figure 3;

Figure 5 is a close-up of part of Figure 1, showing in particular the mounting of the sample tube of the chemical dosing sensor;

Figure 6 is an exploded view of the sample tube and related mounting / sealing components;

Figure 7 is an exploded view of a syringe, forming part of the chemical dosing sensor;

Figure 8 is a perspective view of the chemical dosing sensor, showing in particular the mounting positions of electronics and batteries;

Figure 9a is a plan view showing the motor, leadscrew, and a PCB forming part of the chemical dosing sensor, when the syringe is in the extended position, and Figure 9b is the same plan view with the syringe in the retracted position; and Figure 10 is a perspective view of a fully-assembled chemical dosing sensor, including an outer casing.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figure 1 and Figure 2, part of a chemical dosing sensor is indicated generally at 10. The chemical dosing sensor comprises a fitment 12 and a sensor support housing 14. The sensor support housing 14 provides a base for all the moving parts of the chemical dosing sensor 10, and is removably attached to the fitment 12. The support housing 14 also provides a light-tight enclosure for the optical testing components and sample tube.

The fitment could in some embodiments be integrated with the rest of the chemical dosing sensor 10.

The fitment 12 has an inlet 16 and an outlet 18. The inlet and outlet in this embodiment are in-line, so that the dosing sensor 10 can be fitted in a straight section of central heating system pipework, by cutting out a length of pipework to leave two open pipe ends, and then fitting the fitment 12 between the two open pipe ends. The fitment 12 is fitted into the system by any suitable means. In this embodiment threads are provided on the inlet 16 and outlet 18, and the dosing sensor 10 may be fitted to the pipework via valves (see Figure 10).

The fitment includes a flow passage between the inlet and the outlet. The flow passage includes an interface portion 20, which is a region of the flow passage into which a syringe 22 may extend.

The flow passage has an aperture in its wall at the interface portion 20, to allow entry of the syringe 22. A spigot 24 surrounds the aperture. The sensor support housing 14 seals against the inside walls of the spigot 24 with a double O-ring seal 26.

A flow diverter 28 is provided in the flow passage. The purpose of the flow diverter 28 is to reduce flow velocity directly against components of the syringe 22, when the syringe is in the interface portion 20 of the flow passage. The interface portion 20 is wider than the rest of the flow passage which also serves to reduce flow velocity in the interface portion.

A sample tube 30 is housed in the sensor support housing 14. The sample tube 30 is made from borosilicate glass, and it is a substantially cylindrical tube with two open ends. One open end faces towards the interface portion 20 of the flow passage of the fitment 12.

The syringe 22 includes a syringe crown 32, a rod 34 extending from in front of the syringe crown 32 (downwards in Figure 1) and a sealing element 36. The syringe crown 32, rod 34 and sealing element 36 all move together to extend or retract the syringe into / out of the sample chamber 30. In Figure 1 , the syringe 22 is shown in a retracted position, in which the syringe crown 32 is at a back end (i.e. the end facing away from the fitment 12) of the sample tube. In this position, the sealing element 36 seals the front end of the sample tube, so that the sample tube 30 is isolated from the interface portion 20 of the flow passage.

In an extended position, as shown in Figure 2, the syringe crown 32 is at the front end of the sample tube 30. As the syringe 22 extends from the retracted position (Figure 1) to the extended position (Figure 2), fluid is forced out of the sample tube, leaving the sample tube empty. In the extended position the syringe crown 32 seals the entrance to the sample tube, isolating the sample tube from the interface portion 20 of the flow passage.

As the syringe 22 moves from the extended position (Figure 2) to the retracted position (Figure 1), water from the interface portion 20 of the flow passage is drawn into the sample tube 30, to fill the sample tube. At the end of the travel of the syringe, the sealing element 36 then isolates the sample tube from the flow passage.

Optical testing may then take place on the isolated sample, held in the sample tube. The optical testing components (a light source and a detector) are not shown in Figure 1 or Figure 2 but would typically be provided on the outside of the sample tube 30, facing into the sample tube 30. The sample tube is transparent (for example made from borosilicate glass) so that optical tests can be done using components on the dry side. Further details of the types of optical testing which may be employed are found in GB2565061 , the disclosure in which is incorporated by reference.

In particular, a fluorescent tracer chemical may be added to a corrosion inhibitor, and the optical tester may measure the level of corrosion inhibitor indirectly by measuring the level of the fluorescent tracer chemical. The fluorescent tracer chemical is excitable by UV radiation, and then emits radiation of a particular wavelength. This can be detected and the concentration of tracer chemical in the system water thereby estimated. The syringe 22 is driven forwards and backwards, to extend / retract it to / from the sample tube 30, by means of a leadscrew 38 driven by a motor 40. The leadscrew passes through the motor and extends from the front of the motor into the syringe, and from the rear of the motor into a free space provided for the leadscrew when the syringe is in the retracted position. Position sensors may be provided to detect the position of the leadscrew, and the position sensors may be located behind the motor as described in more detail below with reference to Figure 9a and Figure 9b.

A circular recess 42 is provided in a wall of the flow passage, opposite the aperture through which the syringe 22 enters into the interface portion 20. The circular recess 42 is sized to receive the sealing element 36 of the syringe 22, when the syringe is in the extended position (Figure 2). Slots 44 (one slot is visible in the cross section of Figure 1) are provided as extensions of the circular recess 42. The slots 44 prevent hydraulic lock as the sealing element 36 moves in or out of the recess.

The rod 34 of the syringe 22 has a bore running substantially centrally along its length. The bore is open on a front face of the sealing element 36. A corresponding guide rod 46 is fixed to the base of the circular recess 42. The syringe 22 is therefore supported by the guide rod as it moves between extended and retracted positions. In the fully extended position, the location of the sealing element 36 in the circular recess 42 provides an anchor point for the syringe 22, which is then supported at both ends. This reduces vibration as a result of flow past the syringe 22.

Figure 3 is a perspective view of the fitment 12, in which the interface portion 20 of the flow path can be seen through the aperture surrounded by spigot 24. Figure 4 is a cross section from the other side, i.e. looking from “inside” the fitment out of the aperture. In these drawings, the arrangement of the flow diverter 28 is clearly seen. The flow diverter 28 is wedge-shaped, with a narrow end facing the inlet and a wide end facing the interface portion 20. Figure 4 is generated by a particle-based fluid flow computer simulation and shows how the flow of fluid is diverted around the centre of the interface portion 20. The interface portion 20 is a wider part of the flow passage, so there is space for the diverted flow around the sides of the syringe 22, and the widening also helps to slow down the flow through the interface portion 20.

For most of the lifetime of the device, the rod 34 of the syringe 22 is in the interface portion 20 of the flow passage. This is the case whenever optical testing is not actually in progress. Keeping the syringe 22 in this position when the device is not in use keeps the sample tube 30 empty of system water, and this reduces the possibility of the walls of the sample tube becoming dirty or discoloured, which could impact on the optical testing process. However, this also means that the rod 34 is exposed to fluid flow for most of the time. Since the rod 34 is positioned in the sample tube when testing takes place, the optical properties of the surface of the rod 34 need to not to interfere with the optical testing. The rod may be made for example from black anodised aluminium. This is a rigid, lightweight and stable material. However, surface damage from constant exposure to fluid flow over a long period of time can change the optical properties of the surface and make it more reflective. This has the potential to disrupt the optical testing and lead to inaccurate measurements. The flow diverter 28 and widened interface portion 20 mitigate this problem.

It can also be seen that mechanical forces incident on the sealing element 36 of the syringe have the potential to cause a reaction, via the rod 34 as a lever, between the piston crown 32 and the inside of the sample tube. Since the sample tube is made from glass, a brittle material, this could crack the sample tube. Locating the sealing element 36 in the recess prevents this while the syringe 22 is in the extended position. The guide rod 46 also helps prevent such forces while the syringe is moving between positions.

Referring now to Figure 5 and Figure 6, the mounting of the sample tube 30 will be described. To protect the glass sample tube, it is provided in a “floating” mount, i.e. the sample tube is able to move slightly while remaining sealed. This helps to mitigate against forces which may be applied due to vibration and due to the flow of fluid acting on the syringe.

A substantially rigid plastic cage 48 surrounds the sample tube 30. The cage 48 has an interior bore which is slightly larger than the exterior diameter of the sample tube 30. The cage includes apertures through which the optical components (i.e. the light source and detector) can transmit and receive light / UV / other radiation to and from the sample tube.

Two O-rings 50 are provided. Each O-ring is fitted around the outside wall of the sample tube 30. The O-ring provides an elastomeric buffer between the side of the sample tube and the housing 14. This allows for slight movement of the sample tube. The amount of movement may be, for example, less than one millimetre, but sufficient to protect the sample tube from forces which could arise from the flow acting on the syringe, bearing in mind that the syringe and other components will be subject to manufacturing tolerances and therefore all components may not be precisely concentric.

Two end seals 52 are provided. Each end seal is in the form of a ring having an L- shaped section. The overall shape of the seal is similar to a union nut - having a short substantially cylindrical shell and an inwardly extending flange portion. The end seals 52 fit over each end of the sample tube 30. They provide an elastomeric buffer in an axial direction, and also ensure fluid-tight sealing.

The end seals 52 may have flat faces around their outer circumference. This assists with seating the end-seals non-rotatably within the housing 14.

Referring now to Figure 7, the construction of the syringe 22 is shown in more detail. The syringe 22 is in two parts which screw together. The sealing element 36, rod 34 and part of the crown 32 form one part, and the rest of the crown 32 forms the other part. In addition, various seals are assembled onto the syringe 22.

The two parts are preferably made from a rigid material, for example anodized aluminium.

The sealing element 36 is a substantially cylindrical section, having a diameter just smaller than an interior diameter of the sample tube 30. An annular recess is provided around the circumference of the sealing element 36, and an O-ring 54 is held within the annular recess to seal against the inside of the sample tube 30, or against the inside of an extension to the sample tube 30 (which may be made from a different material from the sample tube).

The rod 34 is of smaller diameter than the sample tube 30, so that the rod can be positioned within the sample tube 30 while optical testing is in progress, with room for fluid being tested around the outside of the rod 34.

The syringe crown 32 includes two seals. An O-ring 56 may be similar to O-ring 54. The O-ring 56 is the frontmost seal (i.e. closest to the rod 34) of the syringe crown 32. The O-ring 56 is made from a soft elastomeric material.

A further seal 58 is a “scraper seal”. The scraper seal 58 is made from a harder material, for example PTFE. The scraper seal 58 fits behind the elastomeric seal 56. The harder scraper seal 58 helps to clear any dirt from the inside of the sample tube 30, when the sample tube 30 is emptied after optical testing is complete. The seals 56, 58 of the syringe crown 32 are both in the form of rings, and are held in place between the two screw-together parts of the syringe 22. A rear part (upper part in Figure 7) has a projection, and a screw thread at the end of the projection. The seals 56, 58 fit over the projection and the rear part is then screwed into the front part of the syringe.

A bearing 60 is provided to rotatably mount the syringe to the leadscrew 38. The leadscrew 38 rotates to move the syringe axially, but the bearing 60 prevents the syringe 22 itself from rotating with the leadscrew. The bearing is provided in the form of a KLM retaining clip which acts to retain the leadscrew 38 to the piston 22. A groove is machined into the end of the lead screw and the clip 61 clips onto the groove, and retains the leadscrew to the part indicated at 60. The clip 61 transmits linear forces between the piston and the leadscrew whilst simultaneously preventing torque from being transmitted.

Figure 8 is a perspective view from behind the support housing 14, additionally showing PCBs 62 which mount control and communication electronics, and batteries 64 (four AA cells) to power the device. Two PCBs 62 are provided, spaced apart by standoffs 66. The leadscrew 38 extends between the two PCBs, centrally of the motor 40. Figures 9a and 9b are plan views, with one of the two PCBs hidden. The leadscrew 38 is thus visible above the bottom PCB 62. The PCB 62 has a slot corresponding to the travel of the leadscrew. The other PCB, not shown, may also have a corresponding slot. A flag 68, i.e., a part which extends through the slot, is provided at the end of the leadscrew.

Two position sensors 70, 72 are provided, mounted to the PCB. The position sensors 70, 72 in this embodiment are optical break-beam sensors, but could alternatively be microswitches or any other type of sensor, which indicates when the flag 68 has reached a particular position. The position sensors correspond with fully-extended and fully-retracted positions of the syringe. The position sensors can be used to control the motor 40, to stop the motor when the syringe is at the end of its travel. This avoids the need to sense an increase in motor torque, and importantly also avoids the motor ever running against resistance at the end of the travel. This increases the lifetime of the motor and also increases battery life.

Figure 10 shows a fully-assembled chemical dosing sensor 10, including an outer casing 74 which encloses the electronics. Valves 76, 78 may be provided, connecting the fitment 12 to a central heating system circuit and allowing the dosing sensor 10 to be isolated if necessary.

The chemical dosing sensor 10 can monitor the level of a corrosion inhibitor in a central heating system, and alert a householder or another party when a top-up is required. The results of the tests and/or alerts can be sent for example by wireless internet. Preferably a wireless module is included in the device, to connect to a home WiFi network. Information may be sent to a server on the internet and from there, any number of follow-on actions may be triggered, for example text messages, emails, or an entry into a maintenance task database. In some embodiments, unprocessed data from the optical sensors may be sent to an external server for processing to determine the level of chemical in the system. However, it is envisaged that such processing will normally be fairly straightforward and can be carried out in electronics within the device itself.

The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.