GB2576050A

GB2576050A - Pressure fill system

Info

Publication number: GB2576050A
Application number: GB1812694.6A
Authority: GB
Inventors: Lambden Peter; Burgess Steven; Manning Paul
Original assignee: Stuart Turner Ltd
Current assignee: Stuart Turner Ltd
Priority date: 2018-08-03
Filing date: 2018-08-03
Publication date: 2020-02-05
Anticipated expiration: 2038-08-03
Also published as: GB2576050B; GB201812694D0

Abstract

A pressure fill unit having a fluid storage tank and a pump 120 fluidly connected to a tank outlet 129, the pump being mounted directly to and supported by the tank. The tank acts as a break tank which is fed from a supply e.g. fluid reservoir or mains. Fluid is pumped out of the tank and into the fluid circuit, supplying the required pressure to the circuit. There may be multiple pumps connected to a manifold 123, a pressure transducer 125 and a controller 105, also mounted directly to the tank, and working with level sensors 150a,b,c to maintain pressure in the circuit without letting the pumps run dry of cycling on and off too frequently. Variable rate pumps may be used. The tank itself acts as the frame to support all the components of the unit, so there is no additional framework to support the other components, and a large tank volume can be achieved for a given unit size. The unit may also be used to fill the fluid circuit. Also claimed is a circuit in combination with the unit.

Description

Pressure fill system

The invention relates to pressure fill units and systems, also referred to as auto-fill pressurization units. In particular, the invention relates to such units with a storage tank and one or more pumps to supply pressurized fluid from the tank to a fluid circuit.

Pressure fill units are used to provide, control and maintain pressure within a fluid circuit such as those typically used in large pressurized heating systems or chilling systems (e.g. chilling systems for freezer cabinets in supermarkets). Such fluid circuits can have a high capacity, typically ranging from 5,000 litres to 60,000 litres or more. The fluid circuit is sealed and in a perfectly functioning system should not lose pressure overtime. However, in practice, pressure in the circuit will vary, e.g. pressure may be lost due to fluid loss through small leaks or through volume changes with temperature etc. For example a pressure increase due to a temperature rise may result in excess pressure being vented. A subsequent drop in temperature will result in an under-pressurized system. If the system pressure drops below a certain level, the pressure fill unit is required to top it up and repressurize the system.

Pressure fill units are usually designed to include a small break tank that separates the fluid circuit from the main source of fluid for refilling (which may be another tank or may be mains water if the circuit is a water circuit). The break tank holds enough fluid to repressurize the system in most cases, but is often too small to be ideal for extended fluid supply to the circuit. The main limitation of a small break tank is that if the fluid supplying the break tank cannot keep up with the rate at which fluid is pumped out of the break tank then the pump(s) will run dry and will require repriming which is an inconvenient maintenance requirement. Some units are fitted with a mechanism to prevent the pump(s) running dry (e.g. a fluid level sensor or a timer or flow sensor to monitor fluid supply) which can stop the pump(s) until the tank is refilled. However, repeated starting and stopping of the pumps is not ideal for pump health and therefore normally pressure fill units are not rated for initial filling of the fluid circuit, e.g. upon installation or after a full drain down. The system is instead normally filled via a separate valve and a direct connection to a large fluid

-2supply reservoir (e.g. mains water) before the pressurization unit is attached for final pressurization and ongoing pressure monitoring and maintenance.

The break tank is normally kept small so as to reduce the size of the pressure fill unit and also reduce the weight. It is often desirable for pressure fill units to be wall-mountable. In such cases large break tanks would add significantly to the weight and size of the unit to be mounted and therefore these wall-mountable units have a restricted size and capacity of water tank in order to reduce weight and keep the unit compact. Alternatively floor standing units are also available which are typically larger to allow for greater water capacity to supply larger systems. Also, a large break tank is not required throughout the vast majority of the unit’s normal working life and therefore a small break tank is generally preferred as it is all that is required to meet the system design requirements.

However, while pressure fill units are not normally designed to be used for filling the fluid circuit, there can sometimes be problems when a maintenance worker either does not realize this or does not care. As discussed above, many pressure fill units will self-protect against run-dry situations by cycling the pumps on and off. While this is not good for the pumps, it will in the long run result in a filled fluid circuit, thus achieving the aim of the maintenance worker without having to go to the trouble of setting up and operating a separate system fill.

According to a first aspect, the invention provides a pressure fill unit for pressurizing a sealed fluid circuit, the unit comprising: a fluid storage tank; and a pump fluidly connected to a tank outlet, the pump being mounted to and supported by the tank.

The tank can act as a break tank which is fed from a supply such as a large fluid reservoir or mains water. It will be appreciated that the fluid stored in the tank may be water or it may be another fluid useful for heating or cooling systems. For example some cooling systems use an ethylene glycol/water mix as the operational fluid. The pumps are arranged to pump fluid out of the tank and into the fluid circuit, supplying the required pressure to the fluid circuit.

As the pump is mounted directly to the tank and is supported by the tank, the tank itself acts as the frame of the pressure fill unit. Thus there is no need for an

- 3additional framework to support the other components of the system. The pump (or more than one pump in some cases), the manifold, the pressure transducer and the controller may all be mounted directly to the tank. By using the tank as the frame to which all other components are mounted, the tank can conveniently be made larger in volume without adversely affecting the overall size of the pressure fill unit. It also avoids the need for a separate frame, thus reducing the component count and simplifying the assembly process. The increased size of the tank allows the pumps to run for longer with reduced risk of running dry, even if the fluid supply that feeds the tank cannot keep up with the rate of supply to the pressurized fluid circuit. With a larger size of tank, the pressure fill unit can be used to fill the fluid circuit from empty, as the pump(s) can be allowed to run for longer periods of time, thus reducing the impact of cycling. This means that the pressure fill unit can be rated for initial fill of the fluid circuit making initial installation and subsequent maintenance much simpler for the installation/maintenance engineer as a separate fill process can be avoided.

The pressure fill unit preferably further comprises a pressure transducer arranged to measure a pressure at an outlet of the unit and supply that measurement to a controller. A pressure transducer is distinct from a simple pressure switch which can only represent a binary state (on/off). A pressure switch is used in certain simple fluid systems to switch a pump or other component on or off at a certain threshold pressure, but that threshold pressure cannot easily be set or reset without some physical adjustment of the switch. A pressure transducer on the other hand measures the pressure and outputs a pressure value across its operational range, thus allowing much easier calibration of pressure thresholds for more complicated systems. Pressure transducers are more complicated and expensive and generally require a more complex controller to perform setup and calibration for each particular installation. For example, in a multi-floor heating system, the threshold pressures for operation will depend on the overall capacity of the system as well as the number of floors being supplied and the heights of those floors. This is specific to each installation, requiring a pressure transducer and suitable calibration.

As discussed above, preferably the controller is mounted to the tank (i.e. not to a separate frame) such that the tank acts as the main support frame of the pressure fill unit.

- 4A single pump is sufficient for many pressure fill units, particularly as the pumping requirements after filling are typically minimal. Indeed such a system will typically only need its pump to operate for a few seconds each time a repressurization is required. A well-sealed system with no leaks may not require repressurization for many months at a time. In fact, it is for this reason that a plurality of pumps are often provided, i.e. for redundancy. A pump that remains inoperational for a long time may seize such that it is not operational when required. Providing two (or more) pumps reduces this possibility. Other anti-seize measures may also be employed such as periodic running of the pumps, even when not required, just to ensure that free movement of the impellers is maintained. Thus the pressure fill unit preferably comprises a plurality of pumps, each mounted to and supported by the tank, the plurality of pumps being fluidly connected to the same outlet. Thus both (or all) pumps can be mounted directly to the tank, again requiring no further framework to support the pumps. The pumps may each have a separate connection to the tank or they may be connected together and share a connection to the tank.

The plurality of pumps are preferably connected to a manifold, the manifold being connected to an outlet of the unit, and the manifold comprising a pressure transducer arranged to measure a pressure at the outlet and supply that measurement to a controller. As discussed above, the pressure transducer can be used to measure the system pressure and detect when the system pressure is outside acceptable limits. The acceptable limits will typically depend on the particulars of a given installation and may be set during a configuration or setup process at the time of installation or maintenance. The controller takes the pressure measurement from the transducer and compares the measurement against thresholds (e.g. upper and lower pressure thresholds) to determine what action, if any, should be taken, e.g. operating one or more pumps to repressurize the system.

The pressure fill unit preferably has one or more fluid level sensors arranged to sense the level of fluid in the tank. In many cases a single sensor is sufficient, e.g. to detect when the fluid level drops below a certain minimum level so that the pumps can be switched off to avoid running dry. However, with the larger tank it is

- 5preferred that the tank comprises a plurality of fluid level sensors arranged to detect a plurality of fluid levels within the tank. By detecting more than one fluid level, the rate of tank emptying or tank filling may be detected, allowing more sophisticated control of the unit. For example, it may be possible to determine the severity of a leak, or the approximate difference between rate of fluid supply to the tank and rate of fluid draw from the tank, which can in turn be used to determine the risk of cycling the pumps too often. This may be used to determine whether or not the pressure fill unit is currently capable of performing a complete system fill from empty.

The fitting of level sensors can also ensure that the tank replenishes adequately between pump cycles. For example, if the pump(s) are stopped to avoid running dry, a traditional pump design might restart the pumps as soon as fluid is available again, but this can lead to rapid cycling and wear. With level sensors in the tank, the pumps can be stopped from running until the tank has replenished to a certain level, thus ensuring that there is a good supply of water for the pumps and preventing rapid cycling, even in cases where the pumps draw fluid from the tank at a higher rate than the tank replenishes from the supply. This arrangement makes the system much more suitable for performing an initial fill of a large system without significant risk of damage to the pressure fill unit in the process.

In some preferred arrangements the sensors are arranged to sense two fluid levels, being a lower level and an upper level. The lower level can be used to sense that water supply from the tank is approaching an insufficient level and can be used to stop the pumps to avoid running dry. The upper level can be used to detect that the tank has replenished to an adequate level that will be able to supply the pumps for a significant period of time, thereby reducing rapid cycling. It will be appreciated that in situations where the supply to the tank is low, the pump(s) will still cycle, but the number and rate of cycles will be reduced, thereby reducing wear and damage to the pumps.

The plurality of fluid level sensors may be individual sensors each located at a particular height in the tank and each outputting a signal representative of the presence or absence of fluid at that height. This may be done by detecting conductance at that height in the tank (with fluid normally being conductive and air

- 6not being conductive). Each sensor may be a self-contained pair of electrodes, but in preferred embodiments the fluid level sensors comprise a single common fluid level sensor at a lowest fluid level and each other fluid level sensor then being used to detect conductivity between that fluid level sensor and the common fluid level sensor. This arrangement reduces the number of electrodes required and thus simplifies manufacture and reduces cost.

As discussed above, the controller is preferably arranged to control the pump (or plurality of pumps) based on outputs of the fluid level sensors to prevent the pump (or pumps) running dry. In more sophisticated control arrangements, the starting and stopping times of the pumps could be optimized based on the sensed levels, e.g. pumps could be used in alternation, or if variable speed pumps are used, the pump speed and thus fluid transfer rate could be adjusted to match the fill rate, thus avoiding a run-dry situation.

The connection between the pump and the tank outlet may be made by any suitable connection, e.g. by a screw connection. However, for ease of installation and maintenance, it is preferred that the pump (or each pump) is arranged to connect to the tank outlet via a push-fit connection. This allows a pump to be installed or replaced easily from the front of the unit without requiring difficult connections (such as nuts) to be made in the constrained space at the back of the unit which may be small due to the larger size of the tank. Avoiding the need for large tools such as a wrench or spanner to be used in such a small space is advantageous. The push-fit connection may be formed from two tubes with a fluid seal that seals between them, e.g. a male connector tube that is inserted into a female connector tube with a fluid seal (such as an O-ring) sealing circumferentially around the male tube in the space between the two. The tank outlet may comprise a shut off valve which may be an automatic valve that engages upon removal of the pump, or may be a simple manual valve operated by lever or small wheel to block flow through the outlet during installation or maintenance. Although this will be located at the back of the recess, it can be operated easily so long as the installer can reach a hand past the pump to turn the valve on or off. Again there does not need to be space for a large tool to reach the valve, so the pumps can be housed in a smaller space, thus increasing the usable volume of the tank.

- 7The pump (or pumps) is (are) preferably mounted in a recess (or recesses) formed in the fluid storage tank. Mounting the pump in a recess formed in the tank reduces the overall volume and dimensions of the unit as a whole as the pump does not need to be installed alongside the tank. This is particularly advantageous for wall mountable units where size and weight are ideally kept to a minimum, while still having a relatively large volume of tank. By providing a tank outlet at the rear of the recess, the amount of pipework (or the space required for pipework) to connect the tank to the pump can be reduced as the pump can be inserted into the recess and into direct engagement with the tank outlet. The tank outlet is preferably a gravity outlet (i.e. water from within the tank flows out of the outlet under its own weight due to gravity).

The recess is preferably formed such that fluid is stored in the tank above the pump; and on both sides of the pump and/or behind the pump. While the recess could be formed on one side of the tank (e.g. open to one side, but with stored water on the other side) it is preferred to arrange the tank to store water on both sides. The mass of stored water partially surrounding the pump reduces vibration and provides a barrier that reduces the transmission of noise which is beneficial when the unit may be installed in a confined space, as well as being a good thermal regulator which helps to regulate the temperature of the pump, improving lifespan and reducing maintenance costs.

The recess is preferably formed such that fluid is stored below the pump. Water above and/or below similarly insulates for noise and temperature. Although the extension of the tank volume underneath the recess is not generally usable, the provision of this volume, connecting the side volumes (i.e. the water storage volumes to the sides of the recess) gives better dimensional consistency and stability of the tank whose sides might otherwise splay outwards when floor mounted.

The tank may have a cavity (or inset region) formed at the rear of the tank (the cavity being external to the tank) and extending along the width of the tank for accommodating pipework (such as horizontal pipe runs that feed fluid (e.g. mains water) to the tank or supply fluid from the tank to the fluid circuit). This cavity may be a channel of fixed height (i.e. with usable tank volume above and below it) or it

- 8may extend from the base of the unit to a given height (i.e. with usable tank volume above, but not below it). The latter arrangement is useful for pipe runs that are often situated at a standard height. It is preferred not to require the installer to alter the height of existing pipework when installing the unit.

The pressure fill unit is preferably mountable to a wall. The pressure fill unit preferably comprises a mounting plate fixable to a wall and the tank is preferably removably mountable to the mounting plate. The pressure fill unit can then be used in either a floor-mounted configuration or a wall-mounted configuration. The mounting plate allows the pressure fill unit to be removed from the wall easily for cleaning or maintenance, simply by disconnecting the fluid inlet and fluid outlet connections. As the pumps are directly mounted to the tank and the tank is directly mounted to the mounting plate, the pumps do not separately need to be disconnected to remove the unit from the wall, while at the same time, there is no separate frame part that is mounted to the wall.

The pressure fill unit preferably further comprises a display operationally connected to a controller and arranged to display a pressure at the output of the pressure fill unit. The pressure at the output is preferably the pressure sensed by the transducer as discussed above.

The pressure fill unit may further comprise a decorative front plate, removably mountable to the tank and arranged to cover the pumps. The front plate preferably hides or conceals the pumps from view, but provides a viewing aperture for viewing a display screen which can provide status information such as system pressure and pump status.

As discussed above, the pressure fill unit preferably has a tank larger than typical break tanks in pressure fill units. Thus the pressure fill unit preferably has a tank with a volume of at least 5 litres, preferably at least 8 litres, more preferably at least 10 litres. However, in order to be wall-mountable and to reduce the size of the unit (and the weight when full), it is also preferred that the tank has a volume less than 50 litres, preferably less than 30 litres, more preferably less than 20 litres.

- 9The tank (which provides the structural support for the other system components) is preferably formed from plastics. This makes for a lightweight construction which reduces the weight of the pressure fill unit and makes for easy mounting. In particular, as the unit can be mounted in an empty state, the plastics tank can be significantly lighter than traditional pressure fill units with a metal frame or box support structure. In some particularly preferred embodiments the tank is rotational moulded which is a cost effective way to produce a tank with the required shape and structure for mounting the various components thereto.

The invention also extends to a heat transfer system comprising: a heat transfer fluid circuit; and a pressure fill unit as described above, optionally including any of the optional or preferred features also described above, the unit arranged to pressurize fluid in the heat transfer fluid circuit.

Further, as discussed above, the pressure fill unit is preferably arranged to fill the heat transfer fluid circuit from an empty state. The larger tank and the fluid level sensors in particular make this feasible without putting undue strain on the pumps.

Certain preferred embodiments of the invention will now be described, by way of example only and with reference to the accompanying drawings in which:

Fig. 1 shows a first embodiment of a pressure fill unit

Fig. 2 shows the first embodiment with cover removed;

Fig. 3 is a rear view of the first embodiment;

Fig. 4 shows a wall mounting bracket;

Figs. 5a and 5b show mounting of a pump in the first embodiment;

Fig. 6 shows a detail of a level sensor;

Fig. 7 shows a second embodiment of a pressure fill unit;

Fig. 8 shows the second embodiment with cover removed; and

Fig. 9 shows an alternative wall mounting bracket.

Figure 1 shows a first embodiment of a pressure fill unit 100. The pressure fill unit has a removable front panel 101 with a window 102 through which the display 103 and control buttons 104 of the electronic controller 105 can be seen. The

- 10removable front panel 101 is mounted to a tank 110 which forms the main body and support structure of the unit 100.

At the rear of the tank 110 a cavity 112 is formed in the shape of a cut-out, i.e. a portion where the rear of the tank is stepped inwards, reducing the depth of the tank at the lower portion thereof. This cavity 112 extends across the full width of the tank 110 (as shown in Fig. 3) and is sized to accommodate a fluid supply pipe 113 that supplies fluid to fill the tank 110. The cavity 112 allows the main rear surface 115 of the tank 110 to sit flush against a wall, thus making efficient use of space, while still allowing easy routing of pipework. An overflow pipe 114 is also shown near the top of the tank.

Figure 2 shows the tank 110 of Figure 1 with the front panel 101 removed so that the other components of the unit 100 can be seen.

Two pumps 120 are shown in this embodiment, although the unit does not require both pumps 120 in order to function properly. Two pumps 120 provide redundancy in case one pump fails and can also be used advantageously to increase the fluid supply rate or to alternate during supply thereby sharing the load and reducing individual pump wear.

For each pump 120, the outlet 121 is connected via conduit 122 to a manifold 123. An outlet 124 of the manifold supplies fluid to the system that is to be filled and pressurized. A pressure transducer 125 is also connected to the manifold 123 to sense the pressure within the manifold 123 and thus the output pressure of the pressure fill unit 100 (and thereby the current fill pressure of the external system). The pressure transducer measures the pressure and provides the measured pressure via electrical wire 126 to the electronic controller 105 which can use this pressure together with other inputs and/or stored data to control the pump(s) 120 and the display 103. For example the current output pressure is typically shown on the display 103 for maintenance personal to check and monitor.

As can be seen from Fig. 2, the pumps 120 are mounted directly to the tank 110 so that the tank 110 acts as the frame and support structure for the whole unit 100. All other components are mounted directly to the tank 110. Pumps 120 are mounted

- 11 to the tank 110 via a mounting plate 130 and mounting screw 131. The mounting plate 130 also sits on a shelf 132 that is integrally moulded as part of the tank 110 to support the pumps 120 on the tank 110. In an alternative embodiment the pumps 120 themselves may rest on the shelf 132. The pump inlet 127 of each pump 120 is connected via conduit 128 to a tank outlet 129 whereby fluid from the tank 110 is fed to the pump 120.

The manifold 123 is also mounted to the tank 110. The electronic controller 105 is mounted directly to the tank 110 via screws 140.

Three fluid level sensors 150a, 150b, 150c are also mounted directly to the tank 110. Each sensor is simply an electrical contact that passes through the wall of the tank through a grommet so as to make contact with fluid inside the tank if there is fluid at the appropriate level. The lowest of these sensors 150a is a common sensor and is used together with each of the lower level sensor 150b and the upper level sensor 150c to detect when the fluid level is at least at the level of the lower level sensor 150b and when the fluid level is at least at the level of the upper level sensor 150c. When the fluid in the tank 110 is at the appropriate level (lower level or upper level), an electrical connection is made between the sensor at that level and the common sensor 150a. Thus when the fluid is below the lower level sensor, no electrical connections will be made, when the fluid is between the lower level sensor and the upper level sensor, an electrical connection will be made between the common sensor 150a and the lower level sensor 150b, but not between the common sensor 150a and the upper sensor 150c. When the fluid level in the tank is above the upper fluid level, electrical connections will be made between the common sensor 150a and both the lower sensor 150b and the upper sensor 150c. These sensors 150a, 150b, 150c can therefore be used to determine to some degree how full the tank 110 is and the controller 105 can use this information to control the pumps 120 appropriately as well as display information on display 103 as required. Again, it may be noted that each sensor 150a, 150b, 150c is directly mounted to the tank 110.

It can be seen from the location of the tank outlets 129 that in this embodiment these are located above the pumps and therefore above the level of the lower side regions 170 of the tank 110. Therefore fluid stored within the lower side regions

- 12170 is not usable tank volume for the purposes of determining the amount of fluid that the pumps 120 can withdraw between cycles. However, the fluid within these side regions 170 is still useful for reducing noise and damping vibrations from operation of the pumps 120 as they encase the pumps 120. These side regions 170 also provide a strong and stable support structure in case the unit 100 is to be floor mounted, while keeping the unit 100 light weight when not filled so that it is easy to mount on a wall if desired.

Supports 160 serve to hold the removable front panel 101 at a suitable distance from the pumps 120, manifold 123, etc.

Figure 3 shows the unit 100 from a rear side and shows the rear cavity 112 as a channel across the full width of the unit 100. This allows pipework to be supplied to the unit 100 easily from either direction, thus making the unit 100 versatile. In Figure 3 a fluid supply pipe 113 is shown feeding into the cavity 112 from one side, and running up a vertical channel 180 in the middle of the unit so as to feed fluid into the inside of the tank 110 at the top of the tank 110. The vertical channel 180 is inset into the rear wall 115 of the tank 110 so as to allow the tank 110 to sit flush against a wall for good space efficiency.

Figure 3 also shows a support bracket 200 for fixedly mounting to a wall so as to provide a support for the unit 100. The unit 100 can then be mounted on the wall simply by hooking it onto the bracket 200. Similarly the unit 100 can be dismounted easily. In figure 3 the support bracket 200 is shown at the top of the rear of the tank 110 with the unit 100 mounted thereon. Figure 4 shows the bracket 200 separate from the tank 110 and showing how the tank 110 is mounted to the bracket 200. The bracket 200 is fixed to a wall via mounting holes 201. The bracket 200 has a horizontal support platform 202 for supporting the tank 110, the support platform 202 having two hooks 203 for retaining the tank 110 against the wall. A single retaining screw 204 is used to hold the tank 110 in secure contact with the bracket 200 simply to hold the tank on the bracket 200 securely against knocks or vibrations. The screw 204 is mounted through washer 205 and vibration damping grommet 206.

- 13Figures 5a and 5b show how a pump 120 is mounted to the tank 110. Only one pump 120 is shown in these figures, but as can be seen, there are two recesses 300 in the tank 110, each capable of accommodating a pump 120. Each pump 120 is mounted to a mounting plate 130 which extends horizontally across the recess 300 and is designed to rest on shelf 132. Shelf 132 is integrally moulded with the tank 110 and supports the weight of the pump 120 in use. The shelf 132 and mounting plate 130 allow the pump 120 to be mounted simply by sliding it into the recess 300 from the front side of the unit 100. The pump inlet 127 with fluid conduit 128 can readily be connected to the tank outlet 129 on the front side of the tank 110 via a push-fit connection. The mounting plate 130 is held securely in place by a single screw 131 which secures the mounting plate 130 directly to the tank 110 via a washer and vibration damping grommet. The pump 120 can be removed easily for repair or replacement without disconnecting the tank 110 from the supply pipe 113 and without having to take the tank 110 off the wall if it is wall mounted. With the front panel 101 removed, both pumps 120, the transducer 125 and the electronic controller 105 are all readily accessible. As these are the components most likely to require maintenance or replacement, the unit 100 is overall very easy to maintain or repair, without first having to dismount the unit 100 from the wall. If the unit does need to be removed from the wall, it is only the inlet pipe 113 and outlet pipe 135 that need to be disconnected before the tank 110 is unhooked from the wall.

Figures 5a and 5b also show one of the level sensors 150b in exploded view. This is shown in close up in Figure 6. Figure 6 also shows the arrangement of the there level sensors 150a, 150b, 150c clearly. The common sensor 150a is positioned at the lowest level of the tank with sensor 150b higher up (to measure the lower level of the tank state) and sensor 150c even higher (to measure the upper level of the tank state). Sensor 150b comprises a sensor body 400 that extends from outside the wall of the tank 110 to inside the tank 110 and provides an electrical connection through the tank wall. An O-ring 401 seals around the sensor body 400 to prevent leakage of fluid from the tank 110. A conductive connector 402 is provided on the outside end of sensor body 400 and is electrically connected thereto. Connector 402 provides a convenient surface for connecting to the sensor 150b for sensing the presence of fluid inside the tank. This arrangement makes use of the fact that the fluid inside the tank 110 is expected to be electrically conductive. Therefore as

- 14the fluid level within the tank 110 rises, it will make an electrical connection firstly between sensor 150a and sensor 150b and secondly between sensor 150a and sensor 150c. Sensor 150a is common to these two measurements while sensors 150b and 150c provide indications of the lower and upper fluid level respectively. Electrical connection to the sensors 150a, 150b, 150c are made via connectors 402 by connecting wires from the electronic controller 105 to the connectors 402 so that the controller 105 can use the sensed information about fluid level to control the pumps 120.

In this embodiment, the lower level sensor 150b is arranged at a slightly higher level than the tank outlet(s) 129 so that when the fluid drops below this level (and the connection between sensors 150a and 150b is broken), the pump(s) 120 can be stopped so as to avoid running dry. The upper level sensor 150c is arranged near the top of the tank, just below the overflow outlet 114 to indicate that the tank is full, indicating to the controller that the tank 110 is at maximum capacity and the pumps 120 can be run for a relatively long time without risk of running dry (thus reducing the pump cycling frequency).

Figures 7, 8 and 9 show a second embodiment of a pressure fill unit 100. The second embodiment operates in substantially the same manner, although with some minor differences. The second embodiment is smaller in that it has a smaller tank 110 and is more compact. No fluid level sensors are shown in the second embodiment although it will be appreciated that they could easily be added and used in the same manner as described above in relation to the first embodiment. The pumps 520 of the second embodiment are different from the pumps 120 of the first embodiment in that they are reciprocal piston pumps rather than centrifugal pumps. However, this does not affect the overall functioning of the pressure fill unit as described above. In particular, the manifold 123, transducer 125 and controller 105 operate in substantially the same manner to control the pumps 520 in order to control fluid delivery through outlet 124 and to fill and maintain pressure within the external system. The piston pumps 520 are mounted to the tank 110 in a different manner. Instead of being supported on a shelf, the pumps 520 are each supported on an elastomeric tube 521 that connects the tank outlet 129 (not visible, but located in the upper surface of the shelf 522 of tank 110) to the pump inlet 523. The elastomeric tube 521 also doubles as a vibration damping mount that absorbs

- 15vibrations from the pump 520 reducing the noise as a result. As the tank outlets 129 close to the bottom of the tank 110 in this embodiment, the tank 110 has a greater usable height and thus can be made less deep while still maintaining a good size of tank.

Figure 9 shows an alternative mounting arrangement for mounting the tank 110 to the bracket 200. The bracket 200 of this second embodiment has two slanted flanges 210 that support the weight of the tank 110 and centre it with respect to the bracket 200. The two flanges 210 make an acute angle with the main face of the bracket 200 so that they also act as hooks to retain the tank 110 adjacent to the bracket 200 and the wall to which it is mounted. The tank 110 can be fixed to the bracket by a single screw attaching to mounting hole 211 located between the two flanges 210. It will be appreciated that the two mounting arrangements of the first and second embodiments can be interchanged if desired.

A further difference between the first and second embodiments, as can be seen in Figures 7 and 8 is that the second embodiment does not have a cavity 112.

Instead, the supply pipe 113 and the overflow pipe 114 are mounted directly to the tank 110. While this removes the flexibility of being able to connect from either side, this arrangement takes up less space, thus allowing more usable space for the tank 110 and allowing the overall product size to be reduced.

Claims

1. A pressure fill unit for pressurizing a sealed fluid circuit, the unit comprising: a fluid storage tank; and a pump fluidly connected to a tank outlet, the pump being mounted to and supported by the tank.

2. A pressure fill unit as claimed in claim 1, further comprising a pressure transducer arranged to measure a pressure at an outlet of the unit and supply that measurement to a controller.

3. A pressure fill unit as claimed in claim 2, wherein the controller is mounted to the tank.

4. A pressure fill unit as claimed in any preceding claim, comprising a plurality of pumps, each mounted to and supported by the tank, the plurality of pumps being fluidly connected to the same outlet.

5. A pressure fill unit as claimed in claim 4, wherein the plurality of pumps are connected to a manifold, the manifold is connected to an outlet of the unit, and the manifold comprises a pressure transducer arranged to measure a pressure at the outlet and supply that measurement to a controller.

6. A pressure fill unit as claimed in any preceding claim, wherein the tank comprises a plurality of fluid level sensors arranged to detect a plurality of fluid levels within the tank.

7. A pressure fill unit as claimed in claim 6, wherein the plurality of fluid level sensors comprises a single common fluid level sensor at a lowest fluid level and each other fluid level sensor being used to detect conductivity between said fluid level sensor and the common fluid level sensor.

8. A pressure fill unit as claimed in claim 6 or 7, wherein a controller is arranged to control the pump based on outputs of the fluid level sensors to prevent the pump running dry.

9. A pressure fill unit as claimed in any preceding claim, wherein the pump is arranged to connect to the tank outlet via a push-fit connection.

10. A pressure fill unit as claimed in any preceding claim, wherein the tank outlet comprises a shut off valve.

11. A pressure fill unit as claimed in any preceding claim, wherein the pump is mounted in a recess formed in the fluid storage tank.

12. A pressure fill unit as claimed in claim 11, wherein the recess is formed such that fluid is stored above the pump; and on both sides of the pump and/or behind the pump.

13. A pressure fill unit as claimed in any preceding claim, wherein the recess is formed such that fluid is stored below the pump.

14. A pressure fill unit as claimed in any preceding claim, wherein the tank has a cavity at the rear of the tank and extending along the width of the tank for accommodating pipework.

15. A pressure fill unit as claimed in any preceding claim, comprising a mounting plate fixable to a wall and wherein the tank is removably mountable to the mounting plate.

16. A pressure fill unit as claimed in any preceding claim, further comprising a decorative front plate, removably mountable to the tank and arranged to cover the pumps.

17. A pressure fill unit as claimed in any preceding claim, further comprising a display operationally connected to a controller and arranged to display a pressure at the output of the pressure fill unit.

18. A pressure fill unit as claimed in any preceding claim, wherein the tank has a volume less than 50 litres, preferably less than 30 litres, more preferably less than 20 litres.

5

19. A heat transfer system comprising:

a heat transfer fluid circuit; and a pressure fill unit as claimed in any preceding claim, arranged to pressurize fluid in the heat transfer fluid circuit.

10

20. A heat transfer system as claimed in claim 19, wherein the pressure fill unit is arranged to fill the heat transfer fluid circuit from an empty state.