GB2130357A - Apparatus for flow ratio control - Google Patents

Abstract

Apparatus for controlling the air/ gas mixture to a burner comprises a gas line 1 to which gas is supplied from a domestic gas meter at a constant pressure and an airline 2 to which air is supplied by a fan. The fan may deliver air at fluctuating pressures and the purpose of the apparatus is to smooth out these fluctuations. Lines 1,2, meet in a common outlet 3 which leads to a burner. Each line 1,2, comprises a valve 4,5, the valves being interlinked by a mechanical linkage 6 so that the valve opening areas are adjustable simultaneously. Gas line 1 incorporates a non-return valve 7. Airline 2 incorporates a fluid flow regulator valve 8 which responds to the air pressure upstream of the valve 5 via a tapping line 9 to maintain across the valve 5 a constant differential pressure. Valve 8 opens in response to decreased air pressure upstream of the valve 5 to increase air flow through the valve 8 and closes in response to increase air pressure upstream of the valve 5 to reduce air flow through the valve 8. Thus upstream air pressure fluctuations are smoothed out leading to the maintenance of a constant air/gas ratio. <IMAGE>

Description

SPECIFICATION Apparatusforflow ration control The present invention relates to apparatus for controlling the flow offluids in a predetermined ratio by volume in a first system to which fluid isto be supplied at a substantially constant pressure and in a second system to which fluid is to be supplied at a pressure which may fluctuate.

The apparatus is particularly, although not exclusively, intended for use as a so-called air/gas ratio controller in supplying a mixture of air and gas to a burner in,for instance, a domestic appliance such as central heating boiler, particularly a condensing-type gas boiler, or a heat pump.

Itiswell known thatsuch burners only operate at maximum efficiency when the percentage of excess airsupplied isataminimum value. In practicefor safety reasons, a small amount of excess air is supplied to these burners but it is particularly impor tantthattheair/gas ratio is held constant at all gas heat inputs despite any performance deterioration ofthe components making up the apparatus.

UK Patent Specification No. 1027042 describes an apparatus for controlling the ratio of air/gas flowing in two separate systemsto a burner, one system carrying air,theothercarrying gas. Each system includes a valve with a variable opening area.

Upstream of each valve is a differential pressure governor which determines the pressure upstream of the valve and each governor is back-loaded by pressure downstream ofthe valve so as to maintain a substantially constant differential pressure across the valve. The valves are mechanically linked forsimul taneous variation so that underthe respective constant differential pressures across the valves the flows in the systems are in the predetermined ratio.

This apparatus is adequate for industrial applica tions where the size of the apparatus components is not criticai. However, in domestic applications where the size ofthe components is critical, it is important thatthe components, particularly the differential pressure governors, are as small as possible so asto be as unobtrusive as possible, orso as to be incorporated into an appliance. So far asthe gas supply is concerned there is no problem since domestic gas is supplied at a relatively constant low pressurefrom the outletside of the gas meterwhich incorporates its own governor.However, since the air to the appliance will normally be supplied by a motor operated fan there is a real possibility of air pressure fluctuations occuring due to wear ofthe fan or due to the build up of lint and other detritus in the apparatus.

These air pressure fluctuations must be smoothed out to enable a constant air/gas ratio to be maintained but the use of an apparatus incorporating a differential pressure governorforthis purpose is impractical because to provide accurate control atthe relatively low air pressures prevailing in domestic applications, the governorwould tend to be unacceptably large.

It is therefore an object of the present invention to provide an apparatusfor controlling the ratio of air/gas particularly for a domestic appliance and obviating the need for a large differential pressure governor in the air system.

According to the present invention, apparatus is providedforcontrolling aflowoffluids in a predetermined ratio by volume in two systems, to a first of which fluid isto be supplied at a substantially constant pressure and to a second of which fluid is to be supplied at a pressure which may fluctuate, the apparatus comprising in each system, a valve, the area ofthe opening ofwhich is variable, and in the second system, a fluid flow regulating valve for maintaining a substantially constant differential pressure acrossthevariable opening valve in that system,thevariableopening valves being linked for simultaneous variation and their valve opening areas aftervariation being so related that with fluid being supplied at a substantially constant pressure to the first system and with a constant differential pressure maintained across the variable opening valve in the second systemtheflows in the systems are in a predetermined ratio.

An embodiment ofthe invention will now be particularly described with reference to the accompanying drawings in which: Figure 1 shows a schematic view of a circuit diagram incorporating apparatus suitablefor controlling the ratio of air/gas for supplyto the burner of a domestic appliance, Figure 2 is a sectional view of the linked valve assembly, Figure 3 is a plan view ofthefluidflow regulator and Figure 4 is a sectional view of the fluid flow regulator along the lines IV-IV of Figure 3.

Referring to Figure 1, the circuit includes two lines 1,2, respectivelyforsupplying gas and airtoa common outlet junction 3. The pressure ofthe gas supply is maintained substantially constant by a conventional pressure governor housed within the domestic gas meter. The air line 2 is connected to a suitable small fan (not shown) which may be of the conventional electrically driven type for supplying air under pressureto the line 2.

While a reliable fan will, when new, supply air at a relatively constant pressure even the most reliable fan will tend from time to time to deliverthe air a fluctuating pressures. But as the fan performance deteriorates with use and as lint accumulates within the air line 2, these pressures will tend progressively to vary undesirably and these fluctuations must be smoothed out ifthe air/gas ratio is to be held at its predetermined value.

Each ofthe lines 1 and 2 incorporate valves 4 and 5 which are mechanically linked by a linkage 6 and which have openings whose areas are variable. These will be described subsequently in greater detail with reference to Figure 2.

Downstream of valve 4 and upstream of the outlet 3 in line 1 there is located a conventional non-return valve 7 to prevent air entering the gas supply line at anytime.

Downstream ofthevalve 5 in line 2, and upstream of the outlet3there is located a fluid flow regulator valve 8which can be of conventional design (such as the "Flostat"type manufactured by GA. Platon Ltd) but is preferably of the type shown in Figure 3. This will also be described in more detail subsequently. The air line upstream ofthe valve is tapped off as shown and is connected to the regulator valve 8 by a tapping line 9.

As will be subsequently shown, the air pressure upstream ofthe valve 5 serves to vary the opening in the regulatorvalve 8 in orderto maintain a substantial ly constant differential pressure across the valve 5.

Referring to Figure 2 the linked valve assembly comprises a valve housing 10 with a gas inlet duct 11, an air inlet duct 12 and a linkage housing 13 intermediatetheductsll and 12.

The gas inlet duct 11 comprises a hollow body with a conically tapering inlet end 14which is internally threaded for connection to a suitablythreaded gas supply pipe (not shown). The other cylindrical end 15 ofthe duct 11 is externally flanged at 16 for connection (as by welding or screw connection) to the linkage housing 13. Within the cylindrical end 15 of the duct 11 ,there is provided an annular seating 17 forthe gas valve head 18. The valve head 18 is in the form of a cone. the conical wall of which is sprung loaded into engagementwiththeseating 17 by means of a compression spring 19.One end ofthe spring 19 is located againstthe base of the valve head 1 8while the other end is located against an externally threaded washer 20 which is fitted within the threaded end 14 of the duct 11. Athreaded outlet port 21 is provided in the wall ofthe cylindrical portion 15 of the duct 11. This is connected to the suitably threaded end of a gas pipe (incorporating the non-return valve 7 shown in Figure 1).

The air inlet duct 12 comprises a generally tubular body having an externallyflanged inlet end 22 for connection to an air supply pipe (not shown) or directlyto a suitable fan casing (not shown). The duct 12 also has an externallyflanged end 23 opposite the inlet end 22 for connection (as by welding or screw connection) to the linkage housing 13. The duct 12 is provided with an internal recess so that the duct bore widensfrom a neck portion 24atthe inletsideofthe duct 12to a body portion 25. The shoulders 26 intermediatethe portions24,25formannularseating forthevalve head 27 which is in the form of a truncated cone whose side walls engagethe seating 26.

Upstream ofthe seating 26 there is provided in the ductwall, a threaded tapping point 28 for connection togthethreaded end of a pipe (not shown) which is to be connected to the regulatorvalve 8 (as shown in Figure 1).

Downstream ofthe seating 26, there is provided in the duct wall, a threaded outlet port 29 which is connected to a suitablythreaded end of a pipe (not shown) fordirectconnection to the regulatorvalve 8.

The linkage housing 13 comprises a box to the side walls 30,31 of which the ducts 11 and 12 are secured as previously slated. Extending through the walls 30, 31 ofthe housing 13 by means of corresponding apertures is a valve spindle 32 serving to link or connectthe respective valve heads 18 and 27 together.

The spindle 32 is connected to the apex ofthe valve cone 18 and to the base ofthe valve cone 27. The spindle 32 is caused to move lengthways in either axial direction by a gear or similartype device (not shown) engagingsuitableteeth 33 on the spindle32.

The gear may be motor driven or manually operable.

There is also provided within the housing 13 a flexible diaphragm 34through a central aperture of which the spindle 32 extends. The diaphragm 34 servesasaseal preventing anygaswhich may leak into the housing enclosure 35 byway of the spindle 32 and the side wall 30from entering the housing enclosure 36. Likewise the diaphragm prevents any air leaking into enlcosure 36 from entering enclosure 35.

The valves 4 and 5 are such that their openings are simultaneously adjustable via the spindle 32 to provide a preset or predetermined flow ratio of air/gas byvolumeformixing atthe outlet3.

Referring to Figure 3 and 4, the airflow regulator8 comprises a casing 37 having a generally cylindrical main wall 38,atopwall 39 and a bottom wall 40.

Extending tangentiallyfrom the main wall 38 is an air inlet pipe41.This pipe 41 is, in use, connected to the pipe which extends from the outletport29 (Figure 2) and therefore receives air issuing through the air valve 5.

The casing 37 encloses a cylindrical sleeve 42 which is axially slidable in the casing 37 and movable under the action of a resilient annular diaphragm 43.

The top wall 39 is a discforming an uppermost closureto the casing 37.

The bottom wall 40 is in the form of an annulas formed with a threaded outlet port44which, in use, is connected to a pipe which leads to the common outlet 3(Figure 1).

Extending inwardly from the main wall 38 ofthe casing 37 are two flat annularwalls 45 and 46 which are spaced vertically from each other and are separated bythediaphragm 43.

Extending downwardly from the wall 46 is an annular wall 47 which with the main wall 38, the bottom wall 40 and the flat annularwall 46 forms an annular chamber 48. The main wall 38 is provided with threaded port 49 for communicating with the chamber48. The port49 is, in use, connected to the tapping point 28 upstream of the air valve 5 (Figure 2).

Extending upwardly from the wall 45 is an annular wall 50 which terminates short of a radial flange 51 extending radially inwardlyfrom the main wall 38 of the casing 37 at a point us a eta pointjustabovethetangential inlet 41. The flange 51 is conically chamfered to form a seat forthe sleeve 42 which is slidable on the internal casing walls 47 and 50. Afurther generally annular chamber 52 is thus formed between the main wall 38 of the casing 37, the annularwall 45, the vertical wall 50 and theflange 51 and including part ofthe tangential inlet41.

The chamber 52 communicates, in use, with the internal bore ofthe sleeve 42 by way ofthe variable opening formed, in use, between the sleeve 42 and the flange 51 to allow airto escapefrom the valve 8.

The chambers 48 and 52 lead to opposite sides of the diaphragm 43 which is secured to the sleeve 42 and to the main wall 38 ofthe casing 37 and therefore separates the chambers.

Located in the walls 45 and 46 are annular porous plugs 53 and 54 of sintered metal, the air passing through the plugs to the diaphragm 43.

Air passing along the sleeve bore leaves the valve 8 byway ofthe outlet port 44 at a rate controlled by the annular opening between the sleeve 42 and the flange 51.

It will be noted that air enters the chamber 52 tangential to the diaphragm 43 to avoid direct impact therewith.

The porous plugs 53,54 meanwhile ensure that pressure changes are not communicated too rapidly tothediaphragm to aid stability.

In operation of the apparatus, the openings of valves 4and 5 are first adjusted so asto provide the desired flow ratio of air/gas by volume. After initially adjusting the gas valve 4there is no need for any further adjustment since the gas inlet pressure to the valve 4 will be constant.

So far as the air line 2 is concerned, air pressure upstream ofthevalve 5 is fed by way of the tap line 9 into the chamber 48 oftheflow regulator 8 and thence to the lower sidle of the diaphragm 43. This causes the diaphragm to flex upwardly to move the sleeve 42 upwardly. This causes the annular opening between the sleeve 42 and the flange 51 to close and restrict the flow rate ofairthrough the regulatorvalve 8.

Meanwhile air downstream of the valve 5 is supplied to the chamber 52 through the inlet pipe 41 and causes the diaphragm tofiex downwardlyto move the sleeve 42 downwardly. Downward movement ofthe sleeve 42 causes the annular opening to increase and thus increase the flow rate of air from the chamber 52 through the opening, along the sleeve bore and out through the outlet port 44. The net effect ofthis is that a constant differential pressure is maintained across th e valve 5. Should the air pressure upstream ofthe valve 5 increase for any reason, the sleeve 42 will move upwards with the diaphragm to restrict the annular opening and reduce the airflow rate through the regulatorvalve 8. This will tend to maintain a constant differential pressure across the valve 5.

Similarly, should the air pressure upstream of the valve 5 decrease for any reason, the sleeve 42 will move downwardswith the diaphragm to increasethe annular opening and the airflow rate through the regulatorvalve 8. Again this will tend to maintain a constant differential pressure across the valve 5.

Consequently pressure fluctuations upstream of the air valve 5 are smoothed out to maintain the ratio of the flow rates constant as initially set by the positions of the two valves 4 and 5.

Whilethefluid flow regulatorvalve8 performs basically the same function as a differential pressure governor, it can successfully smooth out even very small pressure fluctuations yet be of relatively small size in comparison to the size of a governor giving an equivalent performance.

Claims (11)

1. Apparatus for controlling the flow offluids in a predetermined ratio by volume in two systems, to a first ofwhich fluid isto be supplied at a substantially -constant pressure and to a second of which fluid is to be supplied at a pressure which may fluctuate, the apparatus comprising in each system, a valve,the area of the opening of which is variable, and in the second system, a fluid flow regulating valve for maintaining a substantially constant differential pressure across the variable opening valve in that system, the variable opening valves being linked for simultaneous variation and their valve opening areas aftervariation being so related that with fluid being supplied at a substantially constant pressure to the first system and with a constant differential pressure maintained across the variable opening valve in the second system the flows in the systems are in the predetermined ratio.

2. Apparatus as claimed in Claim 1 in which the fluid flow regulating valve is downstream of the variable opening valve.

3. Apparatus as claimed in Claim 2 in which the opening in the regulating valve is variable in response to pressure upstream ofthevariable opening valve.

4. Apparatus as claimed in Claim 3 in which the valve includes a closure device movable by a resilient elementtoaclosed position in responsetofluid pressure upstream ofthe variable opening valve and to an open position by fluid pressure downstream of the variable opening valve.

5. Apparatus as claimed in Claim 4 in which the closure device comprises a sleeve movable to close offfluid through the regulating valve and adapted to provide an axial flowforfluid discharging from the regulating valve.

6. Apparatus as claimed in Claim 4 or Claim 5in which the resilient element is a diaphragm.

7. Appartus as claimed in any of claims 4to 6 in which the fluid downstream ofthe variable opening valve is arranged to enter the regulating valve in a direction parallel to the element to avoid direct impact therewith.

8. Apparatus as claimed in any of Claims4to 7 in which fluid is caused to travel towards opposite sides of the element by way of porous plugs.

9. Apparatus as claimed in any of the preceding claims in which the systems meet at a common outlet.

10. Apparatus as claimed in any of the preceding claims in which the first system includes a non-return valve downstream of the variable opening valve.

11. Apparatus substantially as hereinbefore described with reference to the drawings.