FR2614385A1 - IMPROVEMENTS TO SAFETY DEVICES FOR GAS VALVES - Google Patents

Abstract

THIS IS A SAFETY DEVICE ASSOCIATED WITH THE FUEL GAS VALVE 3 OF THE BURNER 1 OF A HEATER EQUIPPED WITH A PILOT LIGHT 13, SAID VALVE COMPRISING A VALVE 5 CAPABLE OF BEING ARMED WITH THE HAND IN ITS OPENING POSITION, THIS VALVE BEING ASSOCIATED WITH AN ELECTROMAGNETIC COIL 10 SO THAT MAINTAINING IN THE OPEN ARMED POSITION OF THE VALVE IS PROVIDED BY CIRCULATION IN THE COIL OF ELECTRIC CURRENT GENERATED BY THE SIMPLE HEATING OF A THERMOCOUPLE 12 THE PILOT LIGHT, THE SEARCHED SAFETY IS OBTAINED BY OPENING AN ELECTRIC SWITCH 16 MOUNTED ON THE CIRCUIT THAT CONNECTS THE THERMOCOUPLE TO THE COIL. THE ELECTRICAL SWITCH 16 IS CONSTITUTED BY A MOS TYPE TRANSISTOR HAVING A VERY LOW DRAIN-SOURCE RESISTANCE IN THE CONDUCTIVE STATE.

Description

Improvements to safety devices for

qaz valves.

  The invention relates to safety devices associated with gas supply valves

  burnable burners fitted to heating appliances

  such as water heaters, bath heaters, boilers, ...

equipped with a pilot.

  More specifically, among these provisions,

  tifs, those which include a gas valve capable of being cocked by hand in its open position, this valve being associated with an electromagnetic coil so that the maintenance in the open or armed position of the valve is ensured by circulation in the coil of electric current generated by the simple heating of a

thermocouple by the pilot.

  In the known embodiments, these arrangements

  safety devices include an electric switch

  that mounted on the circuit that connects the thermocouple to the

coil.

  As the potential difference generated by

  the thermocouple is relatively weak, namely from the

  dre of a few tens of mV, it is important that the resistance

  overall electrical tance of the circuit considered either

  even very weak, generally know less than 100

milli-ohms (min).

  Such a requirement has hitherto excluded in practice the use of semiconductor junctions for the establishment of electrical switches

  considered, due to the relative internal resistance-

ment of these Junctions.

  So we used these switches

mechanical contacts.

  The latter had to present during their closings very low electrical resistances,

2624385 .;

  only a few minutes, and the very low value

  ble of these contact resistances had to be retained

in time.

  In practice, this conservation was very difficult to obtain owing in particular to the oxidation of the contacts under consideration, their soiling, due in particular to dust, the vibrations to which the heating appliances are subjected during their operation, etc. The invention aims, above all, to remove

these latter drawbacks.

  To this end, the safety devices of the gen-

  re in question according to the invention are essentially characterized in that their electrical switches

  as defined above consist of tran-

  MOS type sistors with very low resistance

  this drain-source in the conducting state, this resistance

  preferably being less than 30 min.

  The invention includes, apart from this arrangement

  main tion, certain other provisions which

  preferably use at the same time and which will be

  more explicitly question below.

  In the following, a preferred embodiment of the invention will be described with reference to

  drawing appended hereto in a way of course not limited to

tive.

  Figures 1 and 2 of this drawing show a diagram

  a safety device established according to the

  vention respectively in operation, pilot

  on, and at rest, pilot off.

  The security device considered is associated

  to a burner 1 capable of being supplied with gas

  bustible from line 2 through succes-

  a safety valve 3 and a gas valve

nal 4.

  The purpose of the device is to exercise

26,243% 5

  safety from certain dangers (pollution of

  the atmosphere, fouling of a duct, breakdown of ventilation

  lation, lack of water, etc.) by automatically closing valve 3 as soon as predetermined thresholds are crossed by appropriate parameters representative of these dangers. By extension we can also consider that the

  indicated automatic closing of valve 3 either

  triggered by phenomena which are not particularly dangerous but which are interesting to consider in

  certain circumstances, such as a temperature (

  ambient temperature, circulating water temperature

  in a central heating circuit ...).

  The safety valve 3 is composed of a 'bou-

  magnetic chon itself comprising a gas valve 5 adapted to cooperate with a seat 6 and integral with a rod 7 having at one of its ends a pallet

  magnetic 8 suitable for closing the field lines ma-

  genetics of a magnetic circuit 9 in U on which is

wound a wound 10.

  The coil 10 of the electromagnet thus formed is supplied with direct current, via a circuit 11, from a thermocouple 12 capable

  to be placed in the flame 13 of a pilot.

  This pilot light 13 is itself supplied by the combustible gas taken, downstream from the valve 3, in a section of pipe 14 connecting this valve to the

gas valve 4.

  In addition, it is arranged so as to ignite the burner 1 when the latter is supplied with gas successively through the open control members 3 and 4.

both.

  The electric current i generated by the thermo-

  torque 12 when it is heated by the pilot 13

is very weak.

  But if the overall electrical resistance of the circuit

  cooked 11 is itself sufficiently weak, namely by

  example less than 100 min, the circulation of this cou-

  rant j in the coil 10 generates on the magnetic pallet

  tick 8 and therefore on the valve 5 a force F sufficient to overcome the return force R of a light spring

  urging said valve 5 towards its closed position

  for which it is applied against the seat 6.

  It is on circuit 11 that an inter-

  electric switch 16 of "safety" normally closed and suitable for being opened when the "danger" appears

  against whom you want to be protected.

  As indicated above, this switch was constituted by a mechanical contact in the previously known embodiments: such an embodiment seemed inevitable due to the extreme smallness required for

  the internal electrical resistance of the contact in question.

  The plaintiff has found that there is

  now on the market some electro- switches

  niques with extremely low internal resistance under certain conditions and that it was therefore

  possible to use them in the framework described above

  above: this is the case of pre-MOS type transistors

  feeling an extremely low drain-source resistance in the conductive state, that is to say as soon as their base is supplied with a very low minimum voltage, for example of the order of 2.5 V.

  Therefore, according to the invention, such a tran

  MOS sistor to constitute the electrical contact 16 of the

circuit 11.

  As we know, the MOS transistor is a tran

  field effect sistor whose grid or base is iso-

  bonded by a very insulating layer of silicon oxide.

  An example of such a transistor having given all satisfaction, and given purely by way of illustration, is that distributed under the reference SN P 60 NO 5 in shoemaker 26243b5

  TO 220 AB by SILICONIX: resistance

  dull drain-source of this transistor is 20 min alone-

  when a low voltage is applied to its base. - We have schematized on the drawing by the rectangle 17 a device suitable for detecting the parameter (degree

  pollution, temperature, ...) whose progression

  beyond a predetermined threshold must automatically trigger

only closing the valve 3.

  This device is arranged so as to develop a low amplitude direct voltage which is applied

  based on transistor 16 as long as the threshold in question

  tion is not crossed, said tension canceling out automatically

  matically upon crossing said threshold.

  The operation of the safety device which

  just described is as follows.

  As long as the above threshold is not crossed

  by the parameter considered, transistor 16 is conduct-

  tor, its internal resistance is very low and its pre-

  sence in circuit 11 practically does not affect the intensity of the current j when this current is generated

by the thermocouple 12.

  As soon as the magnetic plug is armed, obtained by

  manual press (arrow A) on a button 18 provided for ex-

  end, of rod 7, opposite to pallet 8, gas

  crosses valve 3 and reaches pilot 13, la-

  which ignites, in particular due to the production of sparks from a piezoelectric igniter or the like. The current j is then generated in the circuit 11 and the resulting force F slightly outweighs the restoring force R of the spring 15, so that the valve 3 is maintained in its armed opening position, even when the arming pressure on button 18

  ceases; similarly the pilot light 13 then remains on.

  The burner 1 then ignites automatically as soon as the gas valve 4 is opened, this opening being

  controlled for example by drawing hot water

  shut up in the case of a water heater or bath heater.

  The burner 1 then goes out as soon as said gas valve 4 is closed. If the pilot light 13 goes out, for example & following a gale or an air discharge, the

  thermocouple 12 is no longer heated, the current i generates

  dré by heating this thermocouple is canceled and it is the same for the force F: the restoring force R of

  spring 15 then closes valve 3 by applying the

pet 5 against his seat 6.

  It is an analogous effect which is produced as soon as the threshold defined above is crossed by the parameter

to which security is subject.

  Indeed, this crossing, detected at 17, results in the cancellation of the voltage applied to the base of transistor 16, which immediately gives the internal resistance of this transistor a value much higher than that of coil 10: the current j is - no longer sufficient to generate the force F and the balance previously established between this force F and the restoring force R is broken in favor of the second,

  which causes the valve 3 to close.

  Following this, and whatever the embodiment adopted, a safety device for valve & gas is finally obtained, the constitution and the

  operation result sufficiently from the above.

  This device has a number of advantages.

  compared to those previously known, in part

  particular as regards the reliability and longevity of the safety contact 16 because it is made by static semiconductor elements much less vulnerable than the mechanical contacts to

moving parts.

  As it goes without saying, and as it results from

  their already from the above, the invention is not limited

  in no way & those of its modes of application and implementation

  sation which have been more especially envisaged, it embraces, on the contrary, all the variants.

Claims (2)

  1. Safety device associated with the fuel gas supply valve (3) of the burner (1) of a heating appliance equipped with a pilot light (13), said valve comprising a valve (5) capable of being armed by hand in its open position, this valve   being associated with an electromagnetic coil (10) so   lesson such that maintaining the valve in the open open position is ensured by circulation in the coil of the electric current generated by the simple heating of a   thermocouple (12) by the pilot, the security sought   chée being obtained by opening an electric switch   plate (16) mounted on the circuit which connects the thermo   torque at the coil, characterized in that the electrical switch (16) is constituted by a MOS type transistor having a very low drain-source resistance at the driver state.   2. Safety device according to claim 1, characterized in that the drain-source resistance in the conductive state of the transistor (16) is less than 30 min.