Figure 1-16.Pressure regulator.
Figure 1-17.Typical pressure control with a differential
from 0 to 10 pounds.
To secure the fuel-burning equipment when the
pressure reaches a predetermined cutout
To start the fuel-burning equipment when the
pressure drops to the cut-in point
There are two settings on the pressure controlthe
cut-in point and the differential. To find the cut-out point,
you add the differential to the cut-in pressure; for example,
when you were operating a boiler with a cut-in pressure of
90 pounds and a differential of 13 pounds, the cut-out
pressure should be 103 pounds. When excessive vibrations
are encountered, you should mount the pressure control
remotely from the boiler on a solid mounting with a
suitable piping connection between them. When a mercury
type of switch control is used, be sure that it is mounted
level and that the siphon (pigtail) has the loop extending in
the direction of the back of the control and at a 90-degree
angle to the front, as shown in figure 1-18. This position
prevents expansion and contraction of the siphon from
affecting the mercury level and accuracy of the control.
Additionally, when you install any pigtail, ensure the tube
is filled with water. The water will prevent hot steam from
contacting the control.
The pressure control can be mounted either on a tee
along with the pressure gauge on the pressure-gauge
tapping, as shown in figure 1-18, or it can be mounted on
the low-water cutout provided by some manufacturers.
In either case, be sure that the pipe dope does NOT enter
the control. The procedure you should follow is to apply
the dope to the male threads, leaving the first two threads
Figure 1-18.A typical steam gauge installation.