Electrical salinity indicating cells fig. 11-25 are installed throughout distilling plants to maintain a constant check on the distilled water. An electrical salinity indicator consists of a number of salinity cells in various locations in the plant. For example, an electrical salinity indicator might consist of salinity cells placed in the evaporators, the condensate pump discharge, and the air-ejector condenser drain. These salinity cells are all connected to a salinity indicator panel.

Since the electrical resistance of a solution varies according to the amount of ionized salts in the solution, it is possible to measure salinity by measuring the electrical resistance. The salinity indicator panel is equipped with a meter calibrated to read directly, either in equivalents per million (epm) or grains per gallon (gpg).

NOTE: Other dissolved solids, in addition to ionized salt, may change the electrical resistance of water. To be safe, always assume that any resistance change is caused by ionized salt.

TORQUE WRENCHES

At times, you will need to apply a specific force to a nut or bolt head. At these times, you will use a torque wrench. For example, equal force must be applied to all the head bolts of an engine. Otherwise, only one bolt may bear the brunt of the force of internal combustion, ullimately causing engine failure. A torque wrench will allow you to apply the specifically required force.

The three most commonly used torque wrenches are the deflecting beam, the dial-indicating, and the micrometer-setting types . When using a deflecting-beam or dial-indicating torque wrench, you visually read the torque on a dial or scale mounted on the handle of the wrench. The micrometer-setting torque wrench, however, indicates the torque value by sound.

To use the micrometer-setting torque wrench, you unlock the grip and adjust the handle to the desired setting on the scale; then, relock the grip. Next, install the required socket or adapter to the square drive of the handle. Place the wrench assembly on the nut or bolt and pull in a clockwise direction, using a steady, smooth motion. (A fast or jerky motion results in an improperly torqued unit.  When the torque applied reaches the required torque value, a signal mechanism automatically issues an audible click; and the handle will release or break, moving freely for a short distance. The release and free travel are easily felt. his feature indicates that the torquing process is complete.

You should use a torque wrench that reads about mid-range for the amount of torque to be applied. Manufacturers' and technical manuals generally specify the amount of torque to be applied. To make sure the correct amount of torque is applied to the fasteners, you must use the torque wrench according to the specific manufacturer's instructions.

CAUTION

Be sure the torque wrench has been calibrated before you use it.

Remember, the accuracy of torque measuring depends on how the threads are cut and the cleanliness of the threads. Make sure you inspect and clean the threads. If the manufacturer specifies a thread lubricant,

Figure 11-26.-Torque wrenches.

use it. When using deflecting-beam or dial-indicating wrenches, hold the torque at the desired value until the reading is steady.

Torque wrenches are delicate and expensive tools. When using them, always follow these precautions:

When you use the micrometer-setting type, do not move the setting handle below the lowest torque setting. However, place it at its lowest setting before you return it to storage.

Do not use the torque wrench to apply greater amounts of torque than its rated capacity.

Do not use the torque wrench to break loose bolts that have been previously tightened.

Do not drop the wrench. If a torque wrench is dropped, its accuracy will be affected.

Do not apply a torque wrench to a nut that has been tightened. Back off the nut one turn with a nontorque wrench and retighten it to the correct torque with the indicating-torque wrench.

Calibration intervals have been established for all torque tools used in the Navy. When a tool is calibrated by a qualified calibration activity at a shipyard, tender, or repair ship, a label showing the next calibration due date is attached to the handle. Before you use a torque tool, check this date to make sure the tool is not overdue for calibration.

SUMMARY

Only a few of the many types of instruments used by Navy personnel have been covered in this chapter. For the operating principle of individual systems, you should consult the specific equipment technical manuals and the NSTM, chapter 504.

Just as we monitor automobile instruments (oil pressure gauge/light, fuel tank level indicator, water temperature gauge, and so forth) to determine how an automobile is operating, we use instruments to determine how the engineering plant is operating. In addition to the use of visual indicating equipment in an engineering plant, audible alarms warn operating personnel of actions required or of unsafe conditions that are approaching. You may avoid machinery damage, personnel injury, and expensive and time-consuming repairs by taking proper operator action. However, proper operator actions can take place only when the instruments (temperature indicators, pressure gauges, and so forth) are properly calibrated and properly interpreted by operating personnel.