Heating Info From Warmair.net
Aquastats
Aquastats have numerous applications. If mounted on a boiler, it will control
the temperature range that the boiler operates and the working
temperature for the circulators. A thermostat transformer, relay,
and circulator switch will sometimes be encased within the aquastat
control on a boiler. Hydro-air systems use an aquastat to turn
the fan on during heating mode. Some hot water heaters use an
aquastat to regulate the water temperature.
Designs differ by application and manufacturer. Clip-on aquastats are common
in air handlers for hydro-air heating. Well-type aquastats are
used on boilers and some hot water makers. Strap-on aquastats
have universal application and can be used for circulators, hydro-air
fan controlling, and hot water makers.
Most aquastats use a bulb sensor and capillary tube. A seal copper bulb about
the size of a pencil is attached to a diaphragm by a thin copper
tube. The bulb is kept in contact with the heat source in order
to function. As the bulb warms up, the gas inside expands through
the tubing and into the diaphragm. Expansion of the diaphragm
triggers a switch to control the intended device. The switch can
be double acting. It can open a circuit to shut off the appliance
(e.g. stop the heating action in a boiler or hot water maker)
or close a circuit and turn an appliance on (turn the blower on
for a fan coil heater). The switching contacts can be fixed at
a predetermined temperature setting or adjustable, depending on
the application. When handling the sensor bulb and capillary tubing,
caution must be taken not to kink or rupture the copper or it
will fail to operate. Some clip-on aquastats use a bi-metal strip
and contacts that function the same as a thermostat. They have
a fixed setting and are limited in application.
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