Construction | Differential Pressure Ratio Regulator
CONSTRUCTION Body: cast iron
There are three basic methods of air/fuel ratio control:
1. Area Control --normally done with linked valves in air and gas lines, maintaining constant upstream pressures. The valve combination is opened or closed to accomplish flow changes. With fixed port valves, desired ratio usually can be realized at only two points. Adjustable port valves enable closer matching of flow characteristics. But Area Control is crude, not considered satisfactory for the great majority of industrial combustion installations. 2. Pressure Balance --a cross-connected regulator matches its outlet gas pressure to air pressure. Thus, as an air control valve modulates (in an air primary system), gas pressure to the burner follows air pressure. Pressure Balance ratio control is used on most industrial furnaces, kilns, and ovens. It overcomes the need to match valve areas and flow characteristics, and it compensates for reasonable variations in upstream pressures. However, it aggravates ratio variations caused by increased resistance in the downstream air line.
Diaphragm cases: cast aluminum
Internals: brass, steel, stainless steel, aluminum (for gases cor- rosive to brass, consult North American.
Diaphragms: silicone rubber
Maximum pressure: 3 psi (shock loads to 4 psi)
Minimum Temperature: -20°F
Maximum temperature: 180°F ambient
Available spring bias: +0.7"w.c. to –0.7"w.c.
NOTE: 7288 Regulators should be installed horizontally with spring on bottom.
3. Flow Balance --described herein for the 7288 Regulator.
Note: Flue gas analysis is rarely used as the primary method of ratio control. Some sophisticated installa- tions use flue gas oxygen readings to “trim” a Pres- sure Balance or Flow Balance system.
Bulletin 7288 Page 3
Made with FlippingBook flipbook maker