Auxiliary Low Level Cut-Off - Vulcan-Hart MHB24E Service Manual

VHX SERIES STEAMER - ELECTRICAL OPERATION

Auxiliary Low Level Cut-Off

This control serves as a safety backup to the main
water level control (WLC) board to meet CSD-1 code
requirements. The operation of the auxiliary control
board is identical to the low level cut-off (LLCO)
function of the main WLC board but performs a
single function: 1) Provide auxiliary low level cut-off
protection to shut off the heat source in case the
water level drops below the auxiliary low level cut-off
(Aux LLCO) probe. A single Aux LLCO probe,
identical to the LLCO probe on the main WLC board,
is connected to the auxiliary control.
The auxiliary control board has input voltage
(120VAC) across terminals 11 and 12 which powers
the primary side of the transformer. On one side of
the transformer secondary, power is provided to the
control by a series path through chassis ground
(terminal 10). The other side of the transformer
secondary (12VAC) is attached to the Aux LLCO
probe that directs power to the other side of the
auxiliary control board relay (LLCO). As water enters
the boiler, it becomes part of the auxiliary water level
control's circuit. When the water level in the boiler
reaches the Aux LLCO probe, the circuit is
completed.
When the main power switch is turned on, power is
supplied to the auxiliary control board but no
switching occurs. Also, the low water level indicator
light (amber) on the boiler base control panel comes
on.
When the water level reaches the auxiliary low level
cut-off (Aux LLCO) probe, the LLCO relay is
energized (LLCO-1 close) and the LLCO LED lights
up. The LLCO relay will remain energized and its
LED will stay lit until the water level in the boiler
drops below the Aux LLCO probe.
When the boiler stops filling, press the manual reset
switch on the boiler base control panel. This turns off
the low water light and energizes the heat source.
F25154 (February 2004) Page 30 of 48