A governor is a feedback device that is used to provide automatic control of speed, pressure, or temperature. A constant-pressure pump

Figure 9-17.-Constant-pressure pump governor.

governor maintains a constant discharge pressure, regardless of pump capacity or output. Most constant-pressure pump governors used in the Navy control steam-driven pumps, both rotary and centrifugal types.

The constant-pressure pump governor (sometimes referred to as pressure-regulating) consists essentially of an automatic throttling valve installed in the steam supply line to the pump's driving unit. A pipeline connects the governor to the pump's discharge line. Variations in discharge pressure, or in pressure differential, actuate the governor, causing it to regulate the pump speed by varying the flow of steam to the driving unit.

A constant-pressure pump governor for a lubricating oil service pump is shown in figure 9-17.  The governors used on fuel oil service pumps and on main feed pumps are of the same type. The size of the upper diaphragm and the amount of spring tension vary on governors used for different services. You will find detailed information concerning the operation and adjustment of governors in chapter 503 of the NSTM.

VALVES

A valve is any device used to control fluids in a closed system. In this section we will discuss valve construction and the most common types of valves you will use in the day-to-day operation and maintenance of the various shipboard engineering systems. Valves are typed or classified according to their use in a system.

VALVE CONSTRUCTION

Valves are usually made of bronze, brass, cast or malleable iron, or steel. Steel valves are either cast or forged and are made of either plain steel or alloy steel. Alloy steel valves are used in high-pressure, high-temperature systems; the disks and seats (internal sealing surfaces) of these valves are usually surfaced with a chromiumcobalt alloy known as Stellite. Stellite is extremely hard.

Brass and bronze valves are never used in systems where temperatures exceed 550F. Steel valves are used for all services above 550F and in lower temperature systems where internal or external conditions of high pressure, vibration, or shock would be too severe for valves made of brass or bronze. Bronze valves are used almost exclusively in systems that carry salt water. The seats and disks of these valves are usually made of Monel, a metal that has excellent corrosion- and erosion-resistant qualities.

Most submarine seawater valves are made of an alloy of 70 percent copper to 30 percent nickel (70/30).