Metal Finishing Guide Book


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there is no filtering action, and the contaminated solution passes through. To prime a centrifugal pump, if a hose is used on the suction side of the pump (without a slurry tank), liquid may be introduced through the hose and pump into the filter chamber. The filter need not be filled completely, but most contain a sufficient volume of liquid so that, as the hose is lowered to approximately the same height as liquid in the chamber, the hose will gradually fill with solution. Shake the hose to make certain any air trapped in the top of the pump or in other high points is completely expelled. When the liquid level completely fills the hose, keep the tip of the hose at the same position, but close the valve between the pump and the filter chamber. Now insert the hose in the tank (since the valve is closed, virtually no liquid will run out of the hose if a gloved hand is cupped over the end). Start the motor and wait until the motor has reached its proper speed; then slowly open the valve to the filter. This is a further precaution, which will enable the pump to create enough suction to handle the small amount of air that may still be in the line. When transfer pumping out a tank, it is advisable to connect a 90O hose barb or a strainer to the suction end of the hose so that it may be lowered as solution level drops. This prevents cavitating the pump, which could occur if the end of the hose rested flat on the bottom or against the side of the tank. If the hose has a tendency to curl, insert a length of straight, corrosion-resistant pipe into the end to accomplish the preceding purpose. Since the most difficult time to prime a pump is after most of the solution has been removed from the tank, operators often dump this remaining heel, which is a needless waste of solution. Plating tanks with sumps at one end minimize this loss when solution transfer is necessary. Small self-priming pumps, such as drum pumps, may be used to salvage the heel left in the plating or treatment tank. 757

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