Figure 5 - Relationship of Specific Gravity to Transfer of Sulphate From Electrolyte to Plates

Figure 7 - Specific Gravity Temperature Correction Valves

TM-5-3820-256-24-4 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
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BATTERY more sulfate in the plates than in the electrolyte. Note that the hydrometer float sank lower and lower in the electrolyte as the specific gravity became lower. Figure 5 - Relationship of Specific Gravity to Transfer of Sulphate From Electrolyte to Plates Table 1 illustrates typical specific gravity values for a cell in various stages of charge. A fully charged specific gravity of 1.265 corrected to 26.70C (800F) is assumed. TABLE 1 Specific Gravity State of Charge 1.265 100% charged 1.225 75% charged 1.190 50% charged 1.155 25% charged 1.120 Discharged HOW TO USE A HYDROMETER Figure 6 illustrates the correct method of reading a hydrometer. The barrel must be held vertically so the float is not rubbing against the side. The electrolyte should be drawn in and out of the hydrometer barrel a few times to bring the temperature of the hydrometer float and barrel to that of the acid in the cell. Draw an amount of acid into the barrel so that with the bulb fully expanded, the float will be lifted free, touching neither the side, top nor bottom stopper of the barrel. When reading the hydrometer, your eye should be on a level with the surface of the liquid in the hydrometer barrel. Disregard the curvature of the liquid where the surface rises against the float stem and the barrel due to surface tension. Keep the float clean. Make certain it is not cracked. Never take a hydrometer reading immediately after water is added to the cell. The water must be thoroughly mixed with the underlying electrolyte, by charging, before hydrometer readings are reliable. If a reading is being taken immediately after the battery has been subjected to prolonged cranking, it will be higher than the true value. The water formed in the plates during the rapid discharge has not had time to mix with the higher specific gravity acid above the plates. MT-23240 Figure 6 - Correct Method of Reading Hydrometer (Eye on Level With Liquid Surface) Because there are many different types of battery hydrometers available, always follow manufacturer’s instructions. TEMPERATURE CORRECTION Hydrometer floats are calibrated to give a true reading at one fixed temperature only. A correction factor must be applied for any specific gravity reading made when the electrolyte temperature is not 26.7°C (80°F). A temperature correction must be used because the electrolyte will expand and become less dense when heated. The float will sink lower in the less dense solutions and give a lower specific gravity reading. The opposite occurs if the electrolyte is cooled. It will shrink in volume, becoming more dense. The float will rise higher and read too high. A correction factor of .004 specific gravity (sometimes referred to as 4 "points" of "gravity") is used for each 5.5°C (10°F) change in temperature. Four "points of gravity" (.004) are added to the indicated reading for each 5.50C (100F) increment above 26.7°C (80°F) and four points are subtracted for each 5.5°C (10°F) increment below 26.70C (800F). This correction is important at extremes of temperature because it can become a substantial value. CTS-4111B - Page 6

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