Most boilers have old mechanical linkage systems with one “foot-mounted” actuator to position both air and fuel at the same time. A linkageless fuel/air ratio control system replaces this single actuator with separate direct-coupled actuators for the air, fuel, and flue gas recirculation (FGR), if required.

Linkageless systems are easy to set up and eliminate the mechanical wear that normally occurs on ball joints over time. In general, “hysteresis” or drift increases with the number of joints. O2 level generally has to be set higher to compensate, and this results in inefficiency and increased fuel costs.

Linkageless systems are especially useful for dual fuel applications. Mechanically linked systems typically require readjustment of combustion air when switching fuels, compromising maximum efficiency for either fuel profile. Linkageless systems allow for two independent fuel curves.

A linkageless system provides:

• Closer and more precise firing rate control over the entire firing rate of the burner
• Increase turndown ratio from 3:1 to 6:1
• Improved 4-20 mA controller operation over old 135 ohm slide wire controls
• Can incorporate optional “Low Fire Hold“ to prevent short cycling and boiler thermal shock
• Password protected to prevent unauthorized readjustment
• Safe shutdown if a positioning error is found
• Easy setup with a step-by-step menu driven commissioning process

Case Study: Medical Research Facility

Webinar: Boiler Efficiency Improvement Through Linkageless Control

Honeywell Controlinks