Figure 1-14.Boiler accessory equipment.
Figure 1-15.Float controller.
Pressure regulating is the process of maintaining a
difference of pressure between two points in a system.
One type of pressure regulating maintains a definite
pressure in one part of the system, while the other part
fluctuates or changes within certain limits. An example
of this type of control is a pressure-regulator valve (fig.
1-16) that maintains a definite pressure on the discharge
side of the valve by controlling the flow of steam, air, or
gas through the valve.
A second type of regulator maintains a definite
difference in pressure between two points and also
controls the flow. This type of regulator is often applied
to a boiler feeding to maintain a fixed difference between
the pressure of water supplied at the feed valve and the
pressure in the boiler steam drum. The pressure regulator
may consist of a self-contained device that operates the
regulating valve directly, or it may consist of a
pressure-measuring device, such as a Bourdon-tube
gauge, that operates a pilot or relay valve. The valve
positions the regulating valve or mechanism to maintain
the desired conditions.
Pressure controls (fig. 1-17) are designed primarily
for steam-heating systems but are also available for
controlling air, liquids, or gases that are not chemically
injurious to the control. The function of the pressure
control is as follows:
To control the pressure in the boiler