Let's discuss some of the hydraulic components that are used in ordnance equipment. We will cover common system components: reservoirs, filtering devices, pressure regulators, pressure accumulators, and pumps and hydraulic power drives.

Figure 4-14.-Transmitting force through a small pipe.

Every hydraulic system has the same basic requirements. It must have a tank to store an adequate supply of fluid, a pump, and a device for removing impurities from the fluid. Most systems also have a mechanism for regulating the system output pressure and a flask for storing fluid under pressure.

Reservoirs

The reservoir (fig. 4-16) is a basic component of any hydraulic system. Inmost systems, the reservoir is a separate component. It may also be used as a housing with the hydraulic pump inside submerged in fluid. Although its primary function is to provide storage space for the fluid of the system, it may also perform several other functions. Reservoirs may be used to dissipate heat, to separate air from the system, and to remove contamination.

Reservoirs dissipate heat by radiation from the external walls. Some are constructed with external radiating devices, such as cooling coils or fins. The separation of air from the system is accomplished by the design of the reservoir. Baffles are used to slow the fluid as it returns to the reservoir. Air bubbles have a greater chance of escaping to the surface when the fluid is moving at a slow velocity. The tank is fitted with a device that allows the air bubbles to escape while not permitting contamination to enter. The separation of contamination from the fluid requires some form of filter, or strainer.

Figure 4-15.-Multiplication of forces.

Figure 4-16.-A fluid reservoir.

Filtering Devices

Most malfunctions in a hydraulic system can be traced to some type of contamination in the fluid. Foreign matter in the system can cause excessive wear, increased power loss, and clogged valves, which increase maintenance costs. For this reason, every effort must be made to prevent contaminants from entering the system. Contaminants that do make their way into the system must be removed before they can cause damage. Filtration devices perform this function.

The filtering devices used in hydraulic systems are most commonly referred to as strainers and filters. Since they share a common function, the terms strainer and filter are often used interchangeably. As a general rule, devices used to remove large particles are called strainers, and those used to remove small particles are called filters.

A strainer will most often be found on the end of the pipe used to supply fluid to a pump from the reservoir. There it can remove any large particles that could clog or damage the pump. Filters can be placed anywhere in the system but are usually located between the pump and the pressure control device. Pumps do not normally have small orifices, which could easily clog. Pressure control devices, however, use very small passages and pistons that must be kept clear for proper operation.

Filters are classified as either full-flow or proportional-flow. In the full-flow type of filter, all the fluid passes through the filtering element. In the proportional-flow type, only a portion of the fluid is passed through the filter. Because of the complex nature of ordnance equipment, most systems use the full-flow type of filter. Figure 4-17 shows a full-flow filter device (view A) and a common micronic filter element (view B). This type of element is designed to prevent the passage of 99 percent of solids greater than 10 microns in size. The element is usually made of disposable paper and is required to be replaced at regular intervals. Notice that the full-flow filter device is equipped with a bypass valve. Should the filter become clogged, the bypass valve opens, allowing unfiltered fluid to enter the system. This triggers an indication to the system operator that the filter is clogged. The system should be secured and the filter replaced immediately. The system does not secure itself under these conditions since the falters could clog in the heat of battle.