GB2258295A

GB2258295A - Improvements in boilers

Info

Publication number: GB2258295A
Application number: GB9116505A
Authority: GB
Inventors: Malcolm Robert Snowball
Original assignee: MOORWOOD VULCAN Ltd
Current assignee: MOORWOOD VULCAN Ltd
Priority date: 1991-07-30
Filing date: 1991-07-30
Publication date: 1993-02-03
Also published as: GB9116505D0

Abstract

In a liquid heater cold water is supplied from a solenoid inlet valve 20 through conduits 18 and 22 to a chamber below an anti-mixing baffle 24 enclosing a heater 26 and separating cold liquid from heated liquid above. An outlet 32 with a tap is provided. Three liquid depth sensors 26, 28 & 30 extend from a lid 14. A steam trap or condenser 38 (Fig 3, not shown) comprises four discs (40a, b, c, d) extending from the turned over end of the conduit 18 to close enough to the conduit 22 to allow a meniscus to form which condenses steam passing through conduit 22 by holes (42) above the liquid level. The liquid is heated in stages from an empty tank by filling to the bottom of probe 26 energising the heater until a set temperature is reached, supplying further liquid and heating to the set temperature and repeating the supply of quantities of liquid until the tank is full then controlling the heater by a thermostat 34. <IMAGE>

Description

IMPROVEMENTS IN BOILERS.

This invention relates to boilers and concerns boilers suitable for heating water for use in catering, the home and the like.

An embodiment of a boiler according to one aspect of the invention may comprise a vessel, means for supplying a liquid to a lower portion of the vessel, heating means for heating liquid in said vessel and anti-mixing means so positioned in the vessel as to tend to restrict unheated liquid to said lower portion. Thus, the anti-mixing means tends to prevent mixing of newly introduced cold liquid with heated liquid.

The anti mixing means may be in the form of a plate positioned and arranged substantially horizontally and substantially at the interface between the lower and upper portions of the vessel.

Preferably, the heating means is positioned in the lower portion of the vessel Another embodiment of a boiler according to another aspect of the invention may comprise a vessel, means for supplying liquid to said vessel, heating means for heating liquid in said vessel, a first liquid detector located in the vessel and so positioned as to define a lower portion of said vessel (the interface between the lower and upper portions), a second liquid detector for defining the upper limit of liquid in the vessel, a third liquid detector arranged intermediate said first and second detectors, a temperature control means, and boiler control means, the arrangement being such that, in operation, when the vessel is charged initially the liquid supply means is opened until the liquid fills said lower portion and the first detector detects the presence of liquid and then said heating means is arranged to heat the liquid until the temperature of the liquid reaches a predetermined value, determined by said temperature control means when the heating means may be de-energised and the liquid supply means is opened to introduce more liquid into said lower portion until a predetermined value has been introduced or until the temperature of the liquid in the lower portion has dropped to a predetermined value, when the liquid supply means is closed and the heating means heats or is energised to heat the liquid in the lower portion to said first predetermined value, the sequence continuing until the liquid reaches the upper limit level at which it is detected by the second liquid level detector.

When the liquid attains said upper level the liquid supply means is maintained closed and the heating means is energised and de-energised under the control of said temperature control means to maintain the temperature of the liquid between predetermined limits.

The third liquid level detector may be arranged, in use, to define a lower working level for the liquid intermediate the upper limit level and the level of the lower portion, such that when it detects that the liquid level has fallen below said lower level it causes the water supply means to open and the heating means to be energised sequentially until the liquid level attains the said upper level. The vertical distance between said second and third detectors may depend upon the use to which the boiler is to be put, but the greater the distance the fewer the operation cycles of the liquid supply means, the heating means and the temperature control means with a concomitant reduction in wear, maintenance and replacement costs.

An embodiment of the boiler according to another aspect of the invention may comprise a vessel, means for supplying a liquid to the vessel, heating means for heating liquid in the vessel, a vapour condenser arranged above an upper limit level of the liquid in the boiler, the condenser having an inlet for receiving liquid vapour, means for condensing a substantial amount of said vapour and an external outlet.

The, or some of the condensed liquid can fall back into the liquid in said vessel.

As all or a substantial amount of the vapour is condensed, the gas, such as air, in the vessel or the gas with only a relatively small proportion of liquid vapour is exhausted by way of the outlet.

The vapour condenser may be in the form of a heat exchanger cooled by the liquid supplied to the vessel.

In one embodiment of the boiler the vapour condenser may comprise a first tube extending into a second tube and in spaced relation thereto, said tubes being arranged substantially vertically and means for supplying a cooling fluid to said first tube, a heat exchanger arranged in the space between the first and second tubes and in heat exchange relationship with said first tube, the heat exchanger having at least one portion terminating in relation to the second tube where it is capable of maintaining a miniscus between it and the inner surface of the second tube, said liquid-vapour inlet being provided in said second tube below said heat exchanger.

The heat exchanger may comprise a plurality of discs, plate, fins or a secondary tube of heat conducting material arranged in spaced relation, in thermal contact with said first, inner tube, extending towards said second tube, a substantial peripheral portion of each said disc, plate or fin terminating at a position at which it is capable of maintaining a miniscus between the inner peripheral portion and said second tube.

The means for supplying a cooling fluid is preferably the liquid supply means.

The second tube may be secured around its upper periphery to an aperture in the upper part of the vessel to provide the only outlet apart from selectively operable outlets such as a liquid-dispensing means and a drain means.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. -1 is a cross-sectional view of one embodiment of a boiler according to the invention taken on the line 1-1 of Fig.2.

Fig. 2 is a cross-sectional view of the boiler of Fig.

1 taken on the line 2-2.

Fig. 3 is a cross-sectional view of am embodiment of a vapour condenser according to the invention.

Fig. 4 is a circuit diagram of a control circuit for use with the boiler of Fig.l Referring to the drawings there is shown a water boiler 10 comprising a rectangular vessel 12 having a cover 14, a heating element 16 and a water supply conduit 18 provided with a solenoid-operated valve 20. The conduit 18 enters the vessel 12 through the cover 14 and extends into a tube 22 which is fixedly secured to the inner surface of the cover 14 to be substantially co-axial with the conduit 18.

The conduit 18 and tube 22 are arranged vertically in the vessel 12 with the lower, open end of tube 22 terminating in a lower portion of the vessel 12.

A substantially horizontal plate 24 is arranged in the vessel above the heater 16 and is provided with an aperture 24a through which the tube 22 protrudes. The plate 24 extends over a substantial portion of the superficial area of the boiler.

A liquid detector 26 in the form of a probe extends through the cover 14 and its active end terminates just above the baffle plate 24. The detector 26 acts as the primary water detector in the sense that it enables the opening of the solenoid valve 20 if it detects an absence of water and enables energisation of the heater 16 when water is detected.

A second liquid detector 28 extends through the cover 14 and its active end terminates at a position near the top of the vessel 12 and serves to define the upper limit of water.

A third liquid level detector 30 extends through the cover 14 and its active end terminates at a position below that of the second detector 28 and serves to define a lower working level such when the water level drops to this level the solenoid valve 20 is opened to recharge the vessel and the heater 16 is energised in sequence.

A water outlet 32 is provided in a longer wall of the vessel 12 and this can be provided with a tap (not shown), conduit or the like depending upon the application.

A thermostat 34 is secured in a wall of the vessel with its active end positioned intermediate the heater 16 and outlet of the water supply tube 22 to ensure a rapid response to the inrush of cold water into the vessel.

A drain outlet 36 is provided in the bottom surface of the vessel 12.

Referring now to Fig. 1 and 3, there is shown a vapour condenser in the form of a steam trap 38 which is arranged in the vessel 12 above the upper water level defined by the position of the detector 28.

The steam trap 38 comprises four annular metal discs 40 a - d welded at spaced points around their periphery to the conduit 18 in spaced parallel relationship and extend towards the tube 22, the gaps between the peripheral edges of the discs 40 and the inner surface of tube 22 being sufficient to maintain a miniscus therebetween, say less than lmm. The disc 40d is provided with a depending peripheral wall 41. Some or all of the other discs 40a to 40c could be provided with a wall 41.

A steam inlet in the form of apertures 42 about 3mm to 5mm diameter is provided in the tube 22 at a position below the lowermost disc 40d and the upper limit of the water level.

The tube 22 is open to atmosphere but is surrounded by an open topped "overflow" tray 44.

Typical dimensions for the components of the steam trap are: conduit 18 external diameter 10 - 15 mm tube 22 internal diameter 35.5mm disc 40 diameter 34.0mm distance between discs 17.0mm height of wall 41 4. Omm In use, cold water flowing through conduit 18 into the receptacle 12 cools the conduit 18 and hence the discs 40. When water vapour and steam passes through the inlet apertures 42 and impinges on the discs it condenses to water and forms a miniscus between the peripheral edges of the discs 40 and the inner surface of the tube 22 effectively creating a seal.

As the temperature of the water rises, giving off more steam, or water is introduced into the vessel, the pressure in the closed vessel 12 rises just above atmospheric pressure so that the mixture of air and steam overcomes the surface tension of the miniscus and "bubbles" through the miniscus, the steam condensing on the discs continuously to renew the miniscus and the relatively dry air exhausting to atmosphere.

As water in the vessel is reduced the pressure in the vessel is also reduced and if it goes below atmospheric pressure air "bubbles" down through the steam trap 38.

The steam trap is self maintaining in the sense that, in operation, steam continuously condenses on the discs to replenish the miniscus, any excess condensed water falling back into the vessel 12 in the form of droplets.

The conduit 18 can be in two parts connected by a spring clip 46 which facilitates descaling of the boiler 10.

To descale the boiler it is merely necessary to bring the water to the boil, remove the conduit 18 by releasing the spring clip 46, add de-scaling material, top-up the vessel 13 with water, replace the conduit 18, allow the mixture to stand for the period recommended by the manufacturer of the descaling material and then drain the boiler 10 by way of the drain plug 36.

Boilers according to the invention can find a variety of applications including, for example, the provision of hot water in domestic, hotel and catering industry, the preparation of hot beverages, as urns, coin-operated equipment and the like.

The boiler can be manufactured from stainless steel, or polypropylene plastics or other potable water grade materials or both if it is required to meet E.E.C. Water Regulations.

Referring to Fig. 4, there is shown a circuit diagram 50 of a control circuit for the boiler 10 of Fig. 1 As the boiler can be controlled in a variety of ways the description of the circuit will be limited to an explanation sufficient to give a broad understanding of its operation with the boiler.

A 240 volt a.c. supply is coupled to the primary winding 54a of a transformer 54 having secondary windings 54b and 54c. Winding 54b is coupled to a bridge rectifier circuit and provides 24 volt and 15 volt d.c. supplies to the circuit 50. The winding 54c provides a 24 a.c.

supply to the three detectors 26, 28, 30.

The three detectors 26, 28, 30, coupled to inputs 52a to c respectively, and energised with the 24 a.c. supply which in the absence of water and when converted to a d.c. signal represents a logic "1" signal. The vessel 12 is earthed and in the presence of water and the d.c.

signal derived from a detector is shorted to earth is representative of logic level '0'.

When the boiler is first put into operation the vessel 12 is empty, and the heater 16 and solenoid valve 20 are de-energised.

The output of the prime detector 26 rectified by diode 56 provides a logic level '1' signal to the input of a gate 58 which provides an output at logic level '0' which is coupled by way of gates 60, 62, and 64 to cause transistor 66 to conduct and energise the solenoid valve 20. Water flows into vessel 12 to cover the heating element 16 and then cover the bottom end of the detector 26.

The vessel is earthed and as the water touches the detector 26 the output of the detector provides a 'O' signal at the input of gate 58. The output of gate 58 changes to level '1' to switch off the water solenoid 20.

The temperature responsive device 34 such as a thermistor has a high resistance when cold and causes pin 1 of integrated circuit 68 to be at logic level '1'. This logic '1' is coupled to gates 70 and 72, which are connected in a latch configuration, and causes a transistor 74 to conduct and hence to energise the heater 16.

As the water temperature rises the resistance of the thermistor decreases causing output 7 of integrated circuit 68 to go to logic level '1'. The logic level '1' is coupled to pin 9 of gate 72 to cause a delayed de-latch of the latch 70, 72 by way of resistor 76, capacitor 78 and diode 80 and to cause transistor 66 to conduct and energise the water solenoid 20 by way of gates 62 and 64.

The output of gate 62 is at level '1' because the low and high level detectors 28, 30 have not yet been covered by the water and gates 82 and 62 are connected in a latch configuration.

The delayed de-latch of the latch 70, 72 causes the tank to continue filling without switching off the heaters.

Cold water enters the vessel 12 directly on the thermistor 34 which causes a rapid cooling and hence a corresponding rapid rise in resistance of the thermistor which, in turn, switches off the water solenoid valve 20 and removes the de-latch signal from the water latch circuit 70, 72.

The vessel 12 continues to fill with water until it reaches the high level detector 28; as the low level detector 30 is covered with water. This does not have any effect as gates 82, 62 are connected in latch configuration.

When water covers the distal end of detector 28 the latch 82, 62 is unlatched by way of gate 84 and the removal of the signal from input 37, the circuit reverts to a maintenance of water temperature mode.

As water is removed from the boiler the high level detector 28 is uncovered and the '1' signal is restored to input 57. The output of gate 84 reverts to logic level '0' enabling latch 82, 62 to be latched. However, as the low level detector 30 is still covered by water the latch 82, 62 cannot be latched. Eventually the low level detector 30 is uncovered and the latch 82, 62 latches causing the water solenoid 20 to be energised and the cycle continues.

Gates 86, 88 are connected as a latch which provided that the vessel 12 is primed with water, the water is up to the required temperature, and the low level detector 30 has been covered by water, then the "water ready light" 90 is illuminated.

Gate 92 provides a conditioning signal which ensures that all of the latches are unlatched when the circuit is initially switched on.

Gate 94 ensures that the charge in the capacitor 96 is fully discharged when the "water on" signal is fed to latch 70, 72.

Claims

CLAIMS:

1. A boiler comprising a vessel, means for supplying a liquid to a lower portion of the vessel, heating means for heating liquid in said vessel and anti-mixing means so positioned in the vessel as to tend to restrict unheated liquid to said lower portion.

2. A boiler according to claim 1, wherein the anti mixing means is in the form of a plate positioned and arranged substantially horizontally and substantially at the interface between the lower and upper portions of the vessel.

3. A boiler according to claim 1 or 2, wherein the heating means is positioned in the lower portion of the vessel.

4. A boiler comprising a vessel, means for supplying liquid to said vessel, heating means for heating liquid in said vessel, a first liquid detector located in the vessel and so positioned as to define a lower portion of said vessel (the interface between the lower and upper portions), a second liquid detector for defining the upper limit of liquid in the vessel, a third liquid detector arranged intermediate said first and second detectors, a temperature control means, and boiler control means, the arrangement being such that, in operation, when the vessel is charged initially the liquid supply means is opened until the liquid fills said lower portion and the first detector detects the presence of liquid and then said heating means is arranged to heat the liquid until the temperature of the liquid reaches a predetermined value, determined by said temperature control means when the heating means may be de-energised and the liquid supply means is opened to introduce more liquid into said lower portion until a predetermined value has been introduced or until the temperature of the liquid in the lower portion has dropped to a predetermined value, when the liquid supply means is closed and the heating means heats or is energised to heat the liquid in the lower portion to said first predetermined value, the sequence continuing until the liquid reaches the upper limit level at which it is detected by the second liquid level detector.

5. A boiler according to claim 4, so arranged that when the liquid attains said upper level the liquid supply means is maintained closed and the heating means is energised and de-energised under the control of said temperature control means to maintain the temperature of the liquid between predetermined limits.

6. A boiler according to claim 4 or 5 wherein, the third liquid level detector is arranged, in use, to define a lower working level for the liquid intermediate the upper limit level and the level of the lower portion, such that when it detects that the liquid level has fallen below said lower level it causes the water supply means to open and the heating means to be energised sequentially until the liquid level attains the said upper level.

7. A boiler comprising a vessel, means for supplying a liquid to the vessel, heating means for heating liquid in the vessel, a vapour condenser arranged above an upper limit level of the liquid in the boiler, the condenser having an inlet for receiving liquid vapour, means for condensing a substantial amount of said vapour and an external outlet.

8. A boiler according to claim 7, wherein the vapour condenser is in the form of a heat exchanger cooled by the liquid supplied to the vessel.

9. A boiler according to claim 7 or 8, wherein the vapour condenser comprises a first tube extending into a second tube and in spaced relation thereto, said tubes being arranged substantially vertically and means for supplying a cooling fluid to said first tube, a heat exchanger arranged in the space between the first and second tubes and in heat exchange relationship with said first tube, the heat exchanger having at least one portion terminating in relation to the second tube where it is capable of maintaining a miniscus between it and the inner surface of the second tube, said liquid-vapour inlet being provided in said second tube below said heat exchanger.

10. A boiler according to claim 7, 8 or 9 wherein the heat exchanger comprises a plurality of discs, plate, fins or a secondary tube of heat conducting material arranged in spaced relation, in thermal contact with said first, inner tube, extending towards said second tube, a substantial peripheral portion of each said disc, plate or fin terminating at a position at which it is capable of maintaining a miniscus between the inner peripheral portion and said second tube.

11. A boiler according to claim 9 or 10 wherein the means for supplying a cooling fluid is the liquid supply means.

12. A boiler according to claim 7, 8, 9, 10 or 11 wherein the second tube is secured around its upper periphery to an aperture in the upper part of the vessel to provide the only outlet apart from selectively operable outlets such as a liquid-dispensing means and a drain means.