Model DFS–221 is an airflow proving
switch designed for duct heater, oven,
and other HVAC or Energy Management
applications where an open-mounted,
nonadjustable switch is desirable. It is especially suitable for surface-mounting in
areas where internal access is limited. It
can be used to sense positive, negative,
or differential air pressure. The DFS–221
is equipped with a convenient barbed
sample line connector that accepts flexible tubing.