| OCR Text |
Show 4 3. Principle of measuring control 3.1 Conventional air ratio control system The following three methods (1) ~ (3) have mainly been applied to air ratio contro I of the burner, but any of these methods had some demer its and I imi tat i on in realizing highly accurate combustion control. (1) Mechanical linkage system Mechanical linkage system, which uses butterf I y va I ve on the air I i ne and adjustable port valve on the gas I i ne is shown in Fig. 2. However thi s system has some demerits as fo I lows. 1) Skilled personnel are required for linkage adjustment. 2) Even in use of variable-port valve, its performance characteristic does not match perfect I y that of butterf I y va I ve. Due to th i s reason, the range i n wh i ch constant air ratio can be maintained is limited. 3) Difficult to apply to fluctuation of preheated air temperature. (2) Pressure equalizing valve system Pressure equalizing valve system, which uses butterfly valve on the air Iine and pressure equalizing valve on the gas I i ne is shown i n Fi g. 3. However, this system has some demerits as fol lows. Fig.3 Pressure equalizing valve system 1) Even if gas and air burner inlet pressures are simply retained equals, there is no means to verify achievement of optimum air ratio in case of gas to air i nterference. 2) At low flow rate condition, following ability and reproducibility become worse because inlet pressure is very fine. 3) Even if correct ion dev ice is used for preheated a i r, the accuracy i s limited. ButterflyValve Air II Gas II Control Motor -a^C- • ^ < H f A Adjustable Port Valve Fig. 2 Mechanical Linkage System Butterfly Valve Gas II - S i -~, 0- Control Motor ~~I ^ Q Equalizing V < I alve |
