Many installations on board naval ships still use lockwashers to prevent threaded fasteners from loosening. If loosening has not been a problem, you may replace worn lockwashers with an identical type; however, if loosening has been a problem, you should use self-locking fasteners instead of lockwashers.

The most common lockwasher used is the helical spring washer. Other types are the conical and toothed tab.

Helical Spring Lockwashers

The helical spring lockwasher (split ring) (fig 9-70) is flattened when the bolt is torqued down, When torqued, it acts as a flat washer contributing normal friction for locking the screw or bolt and the working surface; it also maintains the tension on the bolt. Because of the helical spring lockwashers small diameter, it is usually not used on soft materials or with oversized or elongated holes.

Curved or Conical Spring Lockwashers

Curved or conical spring lockwashers have almost the same properties as the helical spring lockwasher. They provide a constant tension on the bolt or screw when loosened. The tension produced is usually less than that produced by the helical spring lockwasher. Like any locking device relying on tension, spring lockwashers may loosen on shock loading. When the bolt stretches more

Figure 9-70.-Helical spring lockwasher.

Figure 9-71.-Toothed lockwashers.

than the spring distortion from the shock loading, the washer serves no further purpose. Recheck the washer, where possible, when shock is sufficient to suspect loosening. Some spring lockwashers have teeth on the outer edge. These teeth do not aid in locking, but they prevent side slippage and turning.

Toothed Lockwashers

Toothed lockwashers fig 9-71 have teeth that are twisted or bent to prevent loosening. Cutting edges engage both working surfaces on the nut and bolt or screw. Some have teeth on the inner diameter for applications where teeth projecting beyond the nut are not desired, The most common type have teeth on the outer diameter. Washers with teeth on both inside and outside diameters are used for soft materials and oversize holes. The teeth are twisted, so as the nut is installed and torqued down, the rim of the washer supports the pressure. Any backing off of the nut or bolt releases tension that allows the teeth to dig into the working surfaces of the nut and bolt.

INSULATION

The purpose of insulation is to retard the transfer of heat FROM piping that is hotter than the surrounding atmosphere or TO piping that is cooler than the surrounding atmosphere. Insulation helps to maintain the desired temperatures in all systems. In addition, it prevents sweating of piping that carries cool or cold fluids. Insulation also serves to protect personnel from being burned by coming in contact with hot surfaces. Piping insulation represents the composite piping covering, which consists of the insulating material, lagging, and fastening. The INSULATING MATERIAL offers resistance to the flow of heat; the LAGGING, usually of painted canvas, is the protective and confining covering placed over the insulating materials; and the FASTENING attaches the insulating material to the piping and to the lagging.

Insulation covers a wide range of temperatures, from the extremely low temperatures of the refrigerating plants to the very high temperatures of the ship's waste heat boilers. No one material could possibly be used to meet all the conditions with the same efficiency.