Component & System Guide - Hurst Boiler

H U R S T B O I L E R S E R I E S “ M H ”
Operation of the feed water pumps (on/off or variable speed) is controlled by a pump
control --- this is a pump control not a flow control. The pump control is located on
the side of the boiler at normal boiler water level --- a sight glass is attached to allow a
visual indication of level. The control has an internal float which senses changes in
water level and mechanically actuates switches that start and stop --- it supplies the
control voltage for the pump motor starter --- the designated pump as the boiler level
dictates. Each pump is protected electrically by thermal overloads located in the motor
starters and a three-phase circuit breaker or fuses.
When flow modulation (protects the boiler from thermal shock) with a constant
running feed water pump is desired a proportioning valve is installed in the main feed
Figure 12 HBC's Oxymiser Deaerator (removes dissolved O2 in feed water, used in high make-up water applications)
line before the boiler check valve. The valve has gate-type isolation valves on either
side, to allow for removal, and a globe type by-pass valve, to allow for throttling in the
event the valve should fail. Units operating below 250 PSI use a similar control,
however, rather than actuate on/off switches the float is connected to a slide-wire
potentiometer that controls the proportioning valve. Units operating beyond 250 PSI
are fitted with a Hurst manufactured water column and a water level transmitter
connected to the PLC which ultimately provides the control signal to the
proportioning valve. Before the discharge isolation valve, the pump discharge lines are
fitted with recirculating lines containing pump-matched orifices to assure minimum
flow through the pump regardless of boiler load.
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