Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 609 of 707

(CPVC), polypropylene, or other molded plastic piping for permanent installa- tion is becoming more common. Some plastics are available with socket-type fit- tings, which are joined with solvents. Their chemical inertness and temperature capabilities are excellent. Iron piping, lined with either rubber or plastic, is ide- al but usually limited to use on a larger tank capable of justifying the investment. It should be pointed out that whenever permanent piping can be used in and out of the tank a more reliable installation will exist, since there is no shifting to loosen fittings, and collapsing or sharp bending of hoses is eliminated. The suction should be located away from anode bags, to avoid their being drawn into the line and causing cavitation. Strainers on the suction are always advisable. It is also desirable to drill a small opening into the suction pipe below the nor- mal solution operating level on permanent installations so that, should any damage occur to the system, the siphon action or suction of the pump will be broken when the level reaches the hold (Fig. 8). This provides added safety dur- ing unattended operation. Whenever automatic equipment is operated, some provision must be made to protect against unforeseeable events that could cause severe losses. This includes some form of barrier or removable strainer to pre- vent the suction of parts into the pump. The addition of a pressure gauge is strongly recommended to determine the initial pressure required to force the solution through the filter and also to determine when the filter media needs to be replaced. When starting up a new filter system, or after servicing an existing system, it is advisable to completely close the valve on the downstream side of the fil- ter; in this way, the pump will develop its maximum pressure, and one can immediately determine whether the system is secure. Sometimes filtration systems are tested on a cold solution and, in turn, will leak on a hot solution and vice versa. Therefore, a further tightening of cover bolts, flange bolts, and so on may be necessary after the filter has been operating at production temperature and pressure. If pump curves are not available, one may wish to check the flow at different pressure readings to determine a reasonable time for servicing the equipment before the flow rate has dropped too low to accomplish good dirt removal. 608

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