Governors for diesel engines used by the Navy can be divided into two general classes- MECHANICAL and HYDRAULIC. Both types of governors serve to regulate engine speed by controlling the fuel injected and are referred to as SPEED-REGULATING GOVERNORS. The mechanical governor is usually simple in design, contains few parts, and is relatively inexpensive. It is frequently used as a speed-limiting device or when extremely sensitive operation is not required. (See fig. 9-26.) The hydraulic governor is more complex in design and contains more parts than the mechanical governor. However, it is more sensitive to speed variations, quicker acting, and more accurate because of the reduction of friction and the small mass of moving parts. Due to the forces exerted by the hydraulic system, it

Figure 9-27.-Hydraulic governor with a compensating device.

is possible to use a smaller, more compact governor to operate the fuel mechanism of large engines than would be possible with a mechanical governor. (See fig. 9-27). Both mechanical and hydraulic governors will be discussed in greater detail later in this chapter.

Governors may also be classified according to the function or functions they perform, the forces they use in operation, and the means by which they operate the fuel control mechanism. The function of a governor on a given engine is determined by the load on the engine and the degree of control required. Governors are classified according to their function as constant-speed, variable-speed, speed-limiting, and load-limiting. Some installations require a constant engine speed from a no-load condition to a full-load condition. Governors that maintain one speed, regardless of load, are called CONSTANT-SPEED governors. Governors that maintain any desired engine speed over a wide speed range and that can be set to maintain a desired speed in that range are classified as VARIABLE-SPEED governors. Speed-control devices that serve to keep an engine from exceeding a specified maximum speed and from dropping below a specified minimum speed are classified as SPEED-LIMITING governors. Some speed-limiting governors limit maximum speed only. Some engine installations need a control device to limit the load that the engine will handle at various speeds. Such devices are called LOAD-LIMITING governors. Some governors are designed to perform two or more of these functions.