Specifications

LWLCWH COLUMBIA BOILER COMPANY REV. 13106

CONTROL DESCRIPTIONS

STEAM BOILERS

Pressure Controls

All Columbia steam boilers are controlled by both operating and safety limit Pressure Control. Both

devices are adjustable and use pressure actuated mercury switches. These switches open when

pressure reaches the main scale set point value, cycling the boiler off.

The operating Pressure Control also has an adjustable differential feature. Differential settings values

are subtractive from the main scale set point value, indicating the change in pressure for when the

boiler will refire. Always adjust the differential set point above the required steam pressure for the sys-

tem. Make the differential value as large as possible to prevent short cycling.

The safety limit Pressure Control does not have an adjustable differential, and has a manual reset fea-

ture. The safety limit Pressure Control breaks the control circuit if the operating Pressure Control

becomes inoperable, and steam pressure continues to climb. The burner will not start until the exces-

sive pressure situation is corrected and the reset button is pushed.

Adjust the safety limit value higher than the operating limit under normal operating conditions. This

setup allows the operating control to function properly and reduces the need to reset the control cir-

cuit constantly. Set the safety limit value less than the error margin of the safety relief valve, so the

Pressure Control can safely control boiler pressure.

Make set point value adjustments by turning the adjusting screws found on top of the Pressure

Control casing.

For additional information on either Pressure Control, see the Danfoss Publication following this book-

let.

Low Water Cut-offs

Low water cut-offs safely control boiler operation in the event of a low water condition. The standard

LWCO for steam applications is a McDonnell & Miller #767. If an installation needs a CSD-1 require-

ment, an additional Warrick 26C1C1C probe type LWCO is supplied. Other optional equipment used

in place of, or in addition to, one of the aforementioned LWCO s includes water feeders and combi-

nation LWCO/ feeders.

The McDonnell & Miller #767 is a float operated control consisting of a large sediment chamber with

its own spring closing blow-off valve. The float actuated low water switch opens in a low water con-

dition. In the same instance, the McDonnell & Miller #767 has an extra set of contacts that close with

a drop in water level. If necessary, this set of contacts could be used to activate an additional water

feeder.

A Warrick 26C1C1C “Probe” type LWCO is used only as a Secondary low water cut-off device. Its

primary function is to protect the boiler against low water situations where the primary LWCO fails to

break the control circuit. The probe mounts in the top head of the boiler and has a rod length lower