Controls. MIL-HDBK-1003/12, Boiler Controls, provides design
criteria for plant controls. Paragraph 8.10 provides guidelines for selecting
the type of control.
Combustion Controls for Forced Circulation Generators with Steam
a) Provide for continuous modulating control of firing, since
interruption of firing may cause a loss of pressurization in hot temperature
b) For generator outputs up to 10,500,000 Btu per hour (3077 kW),
use the water outlet temperature from each boiler to control the firing rate
of the generator.
c) For generator outputs under 30,000,000 Btu per hour (8790 kW),
provide a water outlet temperature regulator on each generator to control the
firing rate on that generator and a master pressure controller on the
expansion drum to override the individual temperature regulators when
necessary to average out the total load among the generators carrying the
d) For generator outputs over 30,000,000 Btu per hour (8790 kW),
regulate the firing rate of each generator by the temperature difference
between outlet and inlet water temperatures. This difference must be measured
directly in order to avoid compounding instrument errors. Provide a master
pressure controller on the expansion drum to override the individual
temperature regulators when necessary.
e) As in steam boilers, draft controls shall be suited to the
furnace draft arrangement, whether pressurized or balanced.
Combustion Controls for Forced Circulation Generators with Inert
Gas-Pressurized Systems. Use the same controls as on a steam-pressurized
system, except omit the master pressure regulator on the expansion tank.
Water Flow Control for Steam-Pressurized HTW Systems with Forced
Plants with Combination System and Boiler Circulating Pumps
a) Measure water flow at each generator inlet so that all
generator flows can be equalized.
b) Place an automatic control valve (incorporating a manual three-
valve bypass) in bypass piping between the pump discharge header and return
line from the distribution system. Use generator flow measurements to
regulate the automatic bypass control valve to assure constant design water
flow through each generator, regardless of load conditions.