Pneumatic ratio controller

0001The invention relates to a control device for maintaining an at least almost always the same ratio between the pressure of a first, in particular gaseous fluid, preferably a fuel gas, and the pressure of a second, in particular gaseous fluid, preferably from air, just before merging into a mixture room, preferably in a combustion chamber of a gas burner independent of the pressure prevailing in the mixture space with respect to the pressures of the two fluids, with a main line leading into the mixing space for the first fluid and with a pressure regulator, which adjusts the prevailing in the main inlet pressure of the first fluid as a function of the required pressure ratio.

0002Such adjusting device has become known for example from DE 25 47 075 C3.

0003For controlling the combustion gas and combustion air supply to gas combustion systems, gas / air composite regulators are known which ensure that the gas / air pressure ratio deviates as little as possible from a value desired for optimal combustion in the entire performance range of the gas combustion system. The amount of the gas firing supplied gas / air mixture depends on the currently required heating power, which can vary in large areas.

0004Composite regulators are already known in which the gas metering depends on the pressure loss at a throttle point.

0005In the so-called "mechanical gas-air network" to change the power, the cross sections of gas and air alike changed. The disadvantage of this, however, is the great technical effort.

0006In the so-called "zero pressure control", the pressure loss at a gas nozzle is chosen to be about the same as the pressure loss at an air nozzle. This makes the mixing ratio independent of throughput. However, here the gas pressure must be chosen quite low, resulting in greater inaccuracies and a small power range.

0007In order to change the performance, in the so-called "pneumatic composite regulator", the pressure of the gas is changed based on the pressure loss at a throttle point in order to always achieve the same mixing ratio. For ratio formation usually two membranes and a comparison scale lever are required. Common to all pneumatic composite regulators is also the possibility of taking into account the pressures in the combustion chamber of the gas furnace, so that the decisive for the mass flow from the burner into the furnace pressure difference in the gas mixture composition can be considered.

0008The operation of such a pneumatic composite regulator, as known for example from the aforementioned DE 25 47 075 C3, based on the equilibrium between the two moments of the forces on the air membrane times lever arm of the air side and the forces on the gas membrane times the lever side of the gas side Balance lever, wherein both the air membrane and the gas membrane counteracts the pressure in the furnace. According to the position of the balance lever, the gas supply is adjusted by means of a gas valve provided in the gas line. By adjusting the support point of the balance beam along the balance beam, the gas / air pressure ratio can be adjusted mechanically, which is very expensive to construct.

0009The present invention is based on the object of developing a control device of the type mentioned in that the desired always the same pressure ratio between the first fluid (fuel gas) and the second fluid (air) just before the common mixing space (combustion chamber) as simple as possible few components can be adjusted.

0010This object is achieved in that of the main line downstream of an actuating element of the pressure regulator is also branched into the mixing chamber bypass line with two throttles arranged behind each other, wherein the prevailing between the two throttles arranged, reduced pressure of the first fluid to the pressure regulator as a controlled variable is supplied.

0011This control device allows a low-cost metering of the fuel gas in almost always the right proportion to the incoming combustion air in gas burners or generally in devices or machines that require a specific mixture of a first and a second fluid. This control device enables this correct metering in a large operating load range in a non-mechanical manner with few components and in a particularly small space.

0012The regulated pressure of the first fluid flows through the two throttles (eg Nozzles) in the mixing space. Due to the fact that, in the stationary state, the same mass flow passes through both throttles, a fixed pressure ratio between the throttles is established, which is determined only by the ratio of their throttle cross sections. Through the first throttle, the fluid pressure prevailing upstream of the actuating element is reduced in the desired ratio as a controlled variable to the pressure regulator. As a result, the pressure regulator does not regulate - as usual - eg to zero pressure, but to a higher pressure, which is determined by the ratio of the pressure losses at the two throttles. By this ratio of the throttle cross sections, the desired pressure ratio of the two fluids is determined.

0013In particularly preferred embodiments of the invention, the ratio of the throttle cross-sections of the two throttles arranged one behind the other can be changed in order to be able to adjust the same control device to a different pressure ratio of the two fluids if required. For example, throttles having different cross sections may be interchangeable.

0014In a particularly advantageous development of this embodiment, the throttle cross-section of at least one throttle is continuously adjustable in order to adjust the pressure ratio arbitrarily within certain limits. As a continuous-action throttle, for example, an adjusting screw which can be screwed into the flow cross-section can be provided.

0015Furthermore, the throttle cross-section of at least one throttle can also be changed by switching on or switching over one or more further throttles.

0016In preferred embodiments of the invention, the pressure regulator on a control diaphragm, one side of which is acted upon by the reduced pressure of the first fluid and the other side with the pressure of the second fluid, so that the actuator of the pressure regulator, the pressure of the first fluid according to the pressure difference between the reduced pressure of the first fluid and the pressure of the second fluid.

0017For this purpose, the control element of the pressure regulator adjusting the input pressure prevailing upstream of the bypass line can be in driving connection with the regulating diaphragm. For example, actuator and control diaphragm may be rigidly connected together.

0018Preferably, the control element of the pressure regulator against the force of gravity and the upstream input pressure of the first fluid kra tbeaufschlagt, in particular spring-loaded, so that according to the set over the throttle cross sections pressure ratio, a resultant force acts, which controls the first fluid flow control element only against eg the force a spring opens more or less wide.

0019In very particularly preferred embodiments of the invention, the pressure regulator is a zero-pressure regulator. The starting point can be a conventional zero-pressure regulator whose pressure measuring point is not located, as usual, directly at the outlet of the first fluid, but the pressure of the first fluid passes through the first throttle in the desired ratio reduced as a controlled variable to the pressure regulator. As a result, the zero pressure regulator does not regulate the pressure difference between air and gas pressure to zero, as usual, but to a higher pressure, which is determined by the ratio of the pressure losses at both throttles.

0020Preferably, the zero pressure regulator has a zero pressure adjustment. By changing, for example, a spring preload on the pressure regulator (zero pressure adjustment), a performance-dependent change in the mixing ratio can be achieved. It preferably influences the lower power range.

0021The pressure regulator can also be designed as a servo pressure regulator. In this case, the control element of the servocontroller adjusting the input pressure prevailing upstream of the bypass line can be actuated via the first fluid in accordance with the difference between the reduced pressure of the first fluid and the pressure of the second fluid.

0022The throttles can already be integrated in the pressure regulator, in particular in the case of new appliances, or can also be provided in a separate throttle part, which can be connected to a conventional pressure regulator.

0023The invention also relates to a separate throttle member having at least two throttles arranged one behind the other for the control device described above, wherein the throttle member is connectable to a conventional Druc kregler. Through the throttle part, the pressure measuring point of the first fluid, for example in a conventional zero pressure regulator is not as usual directly applied to the pressure of the first fluid but is reduced by the first throttle in the desired ratio reduced to the actuator of the pressure regulator. As a result, the gas pressure regulator does not regulate to zero pressure, as usual, but to a higher pressure, which is determined by the ratio of the pressure losses at the two throttles. This throttle part may be the above-described adjustable, interchangeable or um- or have switchable throttles.

0024Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those listed further in accordance with the invention can each be used individually for themselves or for several in any desired combinations. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

0025It shows:<dl id="dl0001"><dt>Fig. 1</dt><dd>a schematic representation of a fan burner, which is supplied by means of a control device according to the invention fuel gas and air in always correct pressure ratio independently of the respective power range of the fan burner;</dd><dt>Fig. 2</dt><dd>a section through a first embodiment of a control device according to the invention with pneumatic pressure ratio formation for a gas / air composite; and</dd><dt>Fig. 3</dt><dd>a section through a second embodiment of a control device according to the invention with pneumatic pressure ratio formation for a gas / air composite.</dd></dl>

0026In Fig. 1 is with <b>1</b> a control device according to the invention for automatically setting the correct pressure ratio between a fuel gas (first fluid<b>2</b> and air (second fluid) <b>3</b> just before they are separated from each other in a common firebox (mixing room) <b>4</b> a gas burner <b>5</b> be initiated.

0027The over a gas line <b>6</b> supplied fuel gas 2 flows after passing two safety valves <b>7</b> into a main line <b>8th</b> a, from which it has a gas nozzle <b>9</b> in the firebox 4 exits. In the firebox 4 is by means of a blower<b>10</b> a negative pressure (furnace backpressure) p_F generated so that the fuel gas 2 and atmospheric air 3 are sucked. The power of the gas burner 5 is determined by different speeds of the fan motor, ie by a modified negative pressure p_F set. About an actuator<b>11</b> in the main 8, the part of a pressure regulator <b>12</b> is, in the main line 8 in front of the gas nozzle 9 prevailing fuel gas pressure p_br be set.

0028Of the main 8 is between actuator 11 and 9 gas nozzle a bypass line <b>13</b> branched off, which also leads into the firebox 4. In the bypass line 13 are two throttles behind each other<b>14</b> and <b>15</b> arranged between which a reduced fuel gas pressure p_red prevails. This reduced fuel gas pressure p_red is via a located between the throttles 14, 15 line <b>16</b> supplied to the pressure regulator 12 as a controlled variable, which corresponds to the pressure ratio p_L/ p_br between the air pressure p_L at the gas burner 5 and the reduced fuel gas pressure p_red via the control element 11, for example via a gas valve, the fuel gas pressure p_br in the main 8 sets. For this purpose, the actuator 11 is in drive connection with a control diaphragm<b>17</b> in the pressure regulator 12, on one side of the reduced fuel gas pressure p_red and on the other side the air pressure p_L acts. A restoring force of the control membrane 17 can be achieved by changing the bias of the rule diaphragm 17 kraftbeaufschlagenden spring<b>18</b> be set (zero pressure adjustment). The pressure regulator 12 is set at approximately zero pressure, so that an actuation of the actuating element 11 only pneumatically by the applied pressures, p_L and p_red, he follows. That is, the actuating element 11 is opened or closed more and more, until no longer acts on the control diaphragm 17 pressure difference.

0029The fuel gas 2 in the main line 8 flows in addition to the gas nozzle 9 via the two throttles 14, 15 in the combustion chamber 4 a. Since the same mass flow passes through both throttles 14, 15, a fixed pressure ratio arises between the two throttles 14, 15, which is determined only by the ratio of their throttle cross-sections. Between the two throttles 14, 15 prevails in the stationary operating point in about p_Lie <maths id="math0001" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>red</mtext></mrow></msub><msub><mrow><mtext> = p</mtext></mrow><mrow><mtext>L</mtext></mrow></msub></mrow></math><img file="EP0907052A2_D0001.tif" /></maths>because the pressure regulator 12 otherwise the gas pressure p_br still have to correct.

0030Thus, the gas pressure p_br formed according to the following simplified equation:<maths id="math0002" num=""><math display="block"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>br</mtext></mrow></msub><msub><mrow><mtext> - p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><msub><mrow><mtext> = (n + 1) x (p</mtext></mrow><mrow><mtext>L</mtext></mrow></msub><msub><mrow><mtext> - p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP0907052A2_D0002.tif" /></maths> where n indicates the aspect ratio between the first throttle 14 and the second throttle 15. In the following, throttle throttles of the same size (n = 1) are assumed and pressure values ​​are given as relative pressures with respect to the absolute air pressure.

0031If in the firebox 4 a pressure of <maths id="math0003" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><mtext> = -10 mbar</mtext></mrow></math><img file="EP0907052A2_D0003.tif" /></maths> and in the main 8, a pressure of <maths id="math0004" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>br</mtext></mrow></msub><mtext> = 10 mbar</mtext></mrow></math><img file="EP0907052A2_D0004.tif" /></maths> prevail, is the reduced pressure between the throttles 14, 15 <maths id="math0005" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>red</mtext></mrow></msub><mtext> = 0 mbar</mtext></mrow></math><img file="EP0907052A2_D0005.tif" /></maths>, Since at the regulator membrane 17 no pressure difference between<maths id="math0006" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>L</mtext></mrow></msub><mtext> = 0 mbar</mtext></mrow></math><img file="EP0907052A2_D0006.tif" /></maths> and p_red is present, the stationary state is reached, and for the pressure ratio applies: <maths id="math0007" num=""><math display="inline"><mrow><msub><mrow><mtext>(p</mtext></mrow><mrow><mtext>br</mtext></mrow></msub><msub><mrow><mtext> - p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><msub><mrow><mtext>) / (P</mtext></mrow><mrow><mtext>L</mtext></mrow></msub><msub><mrow><mtext> - p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><mtext>) = 2</mtext></mrow></math><img file="EP0907052A2_D0007.tif" /></maths>,

0032If now the power of the fan burner 5 is reduced by a lower speed of the blower 10, the pressure in the combustion chamber 4 is reduced, for example <maths id="math0008" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><mtext> = -5 mbar</mtext></mrow></math><img file="EP0907052A2_D0008.tif" /></maths>, As in the main 8 is still a fuel gas pressure<maths id="math0009" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>br</mtext></mrow></msub><mtext> = 10 mbar</mtext></mrow></math><img file="EP0907052A2_D0009.tif" /></maths> and thus between the throttles 14, 15 a reduced pressure <maths id="math0010" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>red</mtext></mrow></msub><mtext> = 2.5 mbar</mtext></mrow></math><img file="EP0907052A2_D0010.tif" /></maths> prevail, due to this also on the control diaphragm 17 prevailing pressure difference of the pressure regulator 12, the control element 11 close so far until <maths id="math0011" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>red</mtext></mrow></msub><mtext> = 0 mbar</mtext></mrow></math><img file="EP0907052A2_D0011.tif" /></maths> is reached. This stationary state for the lower power adjusts when the fuel gas pressure p_br by the actuator 11 in the main line 8 <maths id="math0012" num=""><math display="inline"><mrow><msub><mrow><mtext>p</mtext></mrow><mrow><mtext>br</mtext></mrow></msub><mtext> = 5 mbar</mtext></mrow></math><img file="EP0907052A2_D0012.tif" /></maths> is reduced. Even then applies to the pressure ratio<maths id="math0013" num=""><math display="inline"><mrow><msub><mrow><mtext>(p</mtext></mrow><mrow><mtext>br</mtext></mrow></msub><msub><mrow><mtext> - p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><msub><mrow><mtext>) / (P</mtext></mrow><mrow><mtext>L</mtext></mrow></msub><msub><mrow><mtext> - p</mtext></mrow><mrow><mtext>F</mtext></mrow></msub><mtext>) = 2</mtext></mrow></math><img file="EP0907052A2_D0013.tif" /></maths>,

0033In Fig. 2 is a conventional zero pressure regulator <b>20</b> shown, whose control membrane <b>21</b> not as usual with the downstream of the actuator <b>22</b> in the main <b>23</b> prevailing gas pressure p_brbut via the bypass line <b>24</b> with the through the two throttles <b>25</b>. <b>26</b> in the desired ratio reduced gas pressure p_red is charged. On the other side of the control membrane 21, the air pressure p acts_L, and the actuator 22 is provided with a diaphragm plate <b>27</b> the control membrane 21 rigidly connected. The throttles 25, 26 are in a separate throttle part<b>28</b> provided, wherein the bypass line 24 and the conduit <b>29</b> the throttle member 28 to corresponding external terminals <b>30</b>. <b>31</b> of the zero pressure regulator 20 are connected. A force acting on the diaphragm plate 27 spring<b>32</b> serves to compensate for the gravity and acting on the actuator 22 upstream gas inlet pressure.

0034As described above, this zero pressure regulator 20 does not regulate, as usual, to zero pressure, but to a higher pressure, which is determined by the ratio of the pressure losses at the two throttles 25, 26. The pressure ratio may be variable using different throttles or an adjustable throttle.

0035In Fig. 3 is a servo pressure regulator 40 with a control diaphragm <b>41</b> shown, whose lower working space <b>42</b> not as usual with the downstream of the actuator <b>43</b> in the main <b>44</b> prevailing gas pressure p_brbut via the bypass line <b>45</b> with the through the two throttles <b>46</b>. <b>47</b> in the desired ratio reduced gas pressure p_red is charged. On the other side of the control membrane 41, the air pressure p acts_L A membrane plate 41 connected to the diaphragm <b>48</b> regulates according to the ratio p_red/ p_L and the bias by the spring <b>49</b> the outflow of the fuel gas within an opening into the lower working chamber 42 servo line <b>50</b>, This servo line 50 is upstream of the actuator 43 from the gas line<b>51</b> branched off and via a throttle <b>52</b> reduced pressure with the lower working space <b>53</b> a control membrane <b>54</b> connected, whose other upper working space <b>55</b> via a relief well <b>56</b> is connected to the main line 44. A membrane plate<b>57</b> the control diaphragm 54 is, by a spring <b>58</b> biased, rigidly connected to the actuator 43. The throttles 46, 47 are in a separate throttle part<b>59</b> provided, wherein the bypass line 45 and the lower working space 42 leading line <b>60</b> of the throttle portion 59 to corresponding external ports (not shown) of the servo pressure regulator 40 are connected.

0036As described above, this servo pressure regulator 40 also does not regulate, as usual, to zero pressure, but rather to a higher pressure, which is determined by the ratio of the pressure losses at the two throttles 46, 47. With the help of trained as a set screw second throttle 47, the throttle cross-section is continuously adjustable and thus the pressure ratio within certain limits adjustable.