MPH COLUMBIA BOILER COMPANY
21
HOT WATER BOILERS
Aquastat
®
Controllers
All Columbia water boilers and indirect water heaters are controlled by both operating and safe-
ty limit Aquastat
®
Controllers. The safety limit should always be adjusted higher than the oper-
ating limit under normal operating conditions. If for any reason the water temperature would
exceed the operating limit and not trip the control, the safety limit should break the circuit to the
burner.
The operating Aquastat
®
consists of an adjustable thermostatic control and separate tempera-
ture sensing immersion well. The immersion well mounts either in the boiler’s coil plate or in the
3/4" tappings on rolled tube units. Adjust the indicating dial to set the maximum operating tem-
perature. The differential wheel setting is subtractive from the operating limit indicating the refire
temperature. This differential set point should be adjusted above the required water tempera-
ture for the system. The differential wheel can be adjusted for 3 to 5F .
The safety limit like the operating Aquastat
®
, consists of an adjustable thermostatic control and
separate temperature sensing immersion well. This controller has a manual reset switch which
must be depressed in the event that the operating circuit reached and shut off on safety.
For additional information on either controllers, see the Publication following this booklet.
Low Water Cut-off
Hot water boilers utilize the
McDonnell & Miller 750-MT-120 Probe Type Low Water Cut-Off
with
Remote Sensor. The 750-MT-120 has a test feature that allows this control to meet CSD-1
requirements. Similar to the Warrick 26C1C1C, this control breaks the control circuit in the event
of a low water condition and must be manually reset once the proper water level is restored.
For additional information on the
McDonnell & Miller 750-MT-120 Probe Type Low Water Cut-
Off with Remote Sensor see McDonnell & Miller
Bulletin MM-212(A) and Installation and Main-
tenance Instructions MM-213(C).
Relief Valve
Relief valves are a safety devices to relieve boiler water pressure. Like safety valves, relief
valves should be piped so any discharge cannot cause injury to people or damage property.
See the “Safety Valve” description in the Control Descriptions, Steam Boiler section of this book-
let.
