GB2100410A - Safety systems for gas water heaters - Google Patents

Abstract

In a gas water heater with a thermocouple (7) sensitive to the heat of a pilot flame (2) and operative to cut-off the gas supply to the heater if pilot flame (2) is extinguished, there is provided a safety system having a pressure-sensitive valve (11) fitted to a passage (8) in the main waterway whereby, when the pressure in passage (8) exceeds a certain level, water is vented and directed by duct (12) onto thermocouple (7). This rapidly quenches the thermocouple and thereby turns off the gas supply more quickly than conventional interruptors. The operating pressure of valve (11) is adjustable by moving screw (16) so as to vary the compression of spring (15). <IMAGE>

Description

SPECIFICATION Safety systems for gas water heaters The present invention relates to safety systems for gas-fired water heaters and in particular for gas fired instantaneous water heaters.

A gas fired instantaneous water heater includes a burner of gas which heats water flowing through the system and a control valve system which is responsive to the flow of water at a preset rate to control the gas flow.

A known fault in such water heaters is that the automatic gas valve, which should close when water flow ceases, may fail in the open position, for which one reason may be inadequate maintenance.

Such a failure may have two results. If the waterways are not completely sealed, the heat from the gas burner boils away the contents of the heat exchanger and then destroys it. This generally results in total loss of the appliance.

Alternatively the waterways may be sealed by turning off the outlet tap since as a result of water regulations the water inlet cock or control is generally fitted with a loose jumper washer thus creating a non-return valve. In that event when the failure occurs the heat from the burner and subsequent boiling of the water in the heat exchanger causes a large increase in the water pressure. The rise in the water pressure can be very rapid, having been observed to reach 1000 p.s.i. in a few seconds. Such a rise can be expected to cause the metal work to burst explosively and create flooding and other damage.

Methods have been devised for protecting appliances from this danger. One such known safety method takes advantage of a flame failure device which is already fitted to the appliance.

This examines the presence of a pilot flame by means of a thermocouple and holds open an additional gas valve by means of a solenoid energised by the current from the thermocouple.

A switch, sensitive to the temperature of the heat exchanger can be included in this thermocouple circuit and can then be arranged to break the circuit and close the valve if the temperature exceeds a preset limit. However, it is found that this may not provide complete protection since the pressure may rise so rapidly that bursting can occur before the temperature sensitive switch can respond.

There is a known protection against high pressures which is the provision of a pressure sensitive valve in the waterway. The contents are then voided at pressures lower than those which do damage. The flames then continue until the temperature sensitive device turns off the gas flow.

This is not, however, found to be completely satisfactory and it is an object of this invention to provide an improved safety system.

According to the invention there is provided a safety system for a gas fired water heater having a thermocouple sensitive to the heat of a pilot flame and operative to cut-off the gas supply to the heater if the pilot flame is extinguished, the safety system including means for venting water from the heater if the pressure of the water exceeds a set level and means for directing the vented water onto said thermocouple to quench said thermocouple and thereby more rapidly to cut off the gas supply in response to the said excess pressure.

In order that the invention may be more clearly understood and readily carried into effect it will now be described by way of example, with reference to the single figure of the accompanying drawing which shows a pilot flame arrangement for an instantaneous water heater and a safety system incorporated therewith.

In the figure there is shown a pilot device 1 which produces a pilot flame 2 protected by a pilot hood 3 which serves to shield the flame and partly to direct and stabilise it. Gas for the pilot is provided at a gas pipe 4 connected to the gas supply to the main burner in a manner not shown.

The pilot device is mounted on a bracket 5 fixed to the heater at an appropriate place, the bracket also supporting a conventional piezoelectric ignitor electrode 6. As described so far this is a conventional pilot burner arrangement.

Also mounted on the bracket 5 for the known pilot protection system is a thermocouple 7 which intrudes into the pilot flame 2. The thermocouple output is used to hold open a solenoid valve, not shown, in the gas supply to the main burner. If the pilot flame goes out the consequent cooling of the thermocouple allows this solenoid valve to close and thus cuts-off the gas supply.

In combination with this conventional pilot system there is illustrated a safety system in accordance with the present invention. This is fitted to a passage 8 in the main waterway, through which water being heated passes in the direction shown at 9.

In an aperture 10 in the water passage 8 there is provided a pressure sensitive valve 11 having a duct 12 through which water is vented when the pressure in the passage 8 exceeds a certain level.

In this example the valve comprises a ball 13 urged into contact with a seating 14 by a spring 1 5, the compression of which determines the release pressure, and an adjusting screw 1 6 to adjust the spring compression and thereby vary the release pressure. Part of this is also shown to a larger scale in the inset detail. The duct 12 extends sufficiently to direct water 1 7 released by valve 11 onto the thermocouple 7.

In operation should the main gas valve stick in the open position with the waterway sealed, the pressure in the water passage 8 rises until the pressure operates the valve 11 and is vented thereby. The vented water 1 7 directed onto the thermocouple 7 rapidly quenches the thermocouple and thereby turns off the gas supply more quickly than does a conventional temperature sensitive thermocouple interruptor.

It will be appreciated that the invention is not limited to the specific pilot installation shown but may readily be adapted to other arrangements in accordance with the principle of the invention.

Claims (filed 7 June 82) 1. A safety system for a gas fired water heater having a thermocouple sensitive to the heat of a pilot flame and operative to cut-off the gas supply to the heater if the pilot flame is extinguished, the safety system including means for venting water from the heater if the pressure of the water exceeds a set level and means for directing the vented water onto said thermocouple to quench said thermocouple and thereby more rapidly to cut off the gas supply in response to the said excess pressure.

2. A safety system according to Claim 1, wherein the venting means comprises a pressure sensitive valve in communication with a duct along which the water is vented.

3. A safety system according to Claim 2, wherein the valve comprises a closure member normally urged, by a compression spring, against a seating to thereby close an aperture communicating with a water pipe of the heater.

4. A safety system according to Claim 2 or 3, comprising means to vary the pressure sensitivity of the valve.

5. A safety system for a gas fired water heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

6. A gas fired water heater having a thermocouple sensitive to the heat of a pilot flame and operative to cutoff the gas supply to the heater if the pilot flame is extinguished and a safety system according to any one of Claims 1 to 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. may readily be adapted to other arrangements in accordance with the principle of the invention. Claims (filed 7 June 82)

1. A safety system for a gas fired water heater having a thermocouple sensitive to the heat of a pilot flame and operative to cut-off the gas supply to the heater if the pilot flame is extinguished, the safety system including means for venting water from the heater if the pressure of the water exceeds a set level and means for directing the vented water onto said thermocouple to quench said thermocouple and thereby more rapidly to cut off the gas supply in response to the said excess pressure.

2. A safety system according to Claim 1, wherein the venting means comprises a pressure sensitive valve in communication with a duct along which the water is vented.

3. A safety system according to Claim 2, wherein the valve comprises a closure member normally urged, by a compression spring, against a seating to thereby close an aperture communicating with a water pipe of the heater.

4. A safety system according to Claim 2 or 3, comprising means to vary the pressure sensitivity of the valve.

5. A safety system for a gas fired water heater substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

6. A gas fired water heater having a thermocouple sensitive to the heat of a pilot flame and operative to cutoff the gas supply to the heater if the pilot flame is extinguished and a safety system according to any one of Claims 1 to 5.