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 control - the 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 bare.

Figure 1-18. - A typical steam gauge installation.