Figure 1-26.-Purity meter

correct flow rate through the flowmeter. The high of a flow rate can damage the cartridges. If the flow rate cannot be increased to the proper rate with the inlet supply valve fully open, you should check to ensure that the outlet valve is fully open. The submicron filter is used to remove small particles from the coolant flow having a size greater than 0.5 micron. If the filter becomes clogged, it also reduces the flow of coolant. This necessitates a change of the filter cartridge or filter sheet (membrane). To change the filter, the demineralize valves must be properly positioned. If the filter cartridge or membrane continually becomes clogged (about one-half hour or less after replacement), the usual cause in the distilled water system is the presence of bacteriological impurities, Bacteriological impurities introduced into the secondary liquid cooling system using distilled water may exist in the demineralize cartridges and/or the whole secondary cooling system. If the bacteriological impurities are in the whole secondary cooling system, the growth rate in a warm water environment could be of a magnitude that exceeds the capability of the demineralize. You will have to determine the source and magnitude of contamination. However, it should be noted that bacteriological contamination in a secondary cooling system that uses distilled water and ethylene glycol is highly improbable. Improper handling or storage of the cartridges could cause the cartridge to be a source of contamination. You should always store the cartridges in a cool, dry area. Exposure to heat hastens the growth of any biological contaminates that may have entered the cartridges. You will encounter three different types of cartridges. The first cartridge is the organic removal cartridge. It contains granulated activated charcoal (carbon) that removes large organic molecules and chlorine by adsorption. It is always installed in the first exchanger (if required) to prevent organic molecules from fouling the remaining cartridges. The second cartridge is the oxygen removal cartridge. It is composed of anion resins that remove oxygen from the water by ion exchange of sulfite ions to sulfate ions. By conducting a standard oxygen test (or if the cooling system has an oxygen analyzer installed), the quality of the outlet water from the demineralize can be tested for oxygen content so that you will know when to replace an oxygen cartridge. When the oxygen cartridge is near exhaustion, it will have a urine odor, which is given off by the sulfate. The third cartridge is the mixed-bed cartridge. It is filled with cation (positive charge) and anion (negative charge) resins, which remove solids, dissolved metals, and carbon dioxide. The charged resins exchange ions with the contaminates, thereby removing them and leaving pure deionized coolant. You should replace the mixed-bed cartridge when the purity meter indicates a low outlet purity. As indicated in figures 1-25 and 1-26, two conductivity cells monitor the coolant through the demineralize. The first cell measures the purity of the coolant as it enters the demineralize. The second purity cell is used to measure the purity of the coolant as it leaves the demineralize. The conductivity cell consists of two electrodes immersed in the coolant flow path. The electrodes measure the conductivity of the coolant, which varies with the amount of ionized salts dissolved init. If the impurity content increases in the coolant, the purity meter indicates higher conductance. On some purity meters, the purity of the coolant is displayed as resistivity. In this type of meter, an increase in the impurity of the coolant causes the meter to indicate a low resistivity. Conductance is the reciprocal of resistance, and is measured in micromhos/cm. Resistivity is measured in megohms/cm. You can convert from conductivity to resistivity by taking the reciprocal of conductivity. Similarly, the reciprocal of resistivity is equal to the conductivity. A comparison of both ways of measuring the purity of the coolant is Figure 1-26.-Purity meter. 1-21