National Oilheat Research Alliance 35
Pressure reducing valve (PRV)—an
isolation valve (globe, ball or gate), backflow
prevention device and PRV should be installed
into a tee under the air elimination device. The
PRV should be connected at the same point as
the expansion tank so that it senses and reacts
to the pressure of the tank.
Expansion tank—if a diaphragm type tank
is used, it should be connected into the bottom
of the tee as shown in Figure 4. It is a recommended
that an isolation valve be installed to
simplify service of the tank. Note that diaphragm
tanks should never be installed upright
or sideways as the diaphragm tends to dry out
in those positions.
If a steel compression tank is used, there
should not be an automatic air vent installed;
the tank should be connected to a ¾" tapping in
the top of the separator.
Circulator—the circulator should be connected
so that it “pumps away” from the “point
of no pressure change”—the expansion tank.
This means that the suction side of the circulator
should be as close as possible to the expansion
tank.
Isolating flanges or isolation valves are recommended
to simplify service.
Figure 4