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V. CATALYST POISONS Certain elements and compounds of these elements significantly shorten or end the production life of any catalyst. These elements include: lead, silicon, mercury, arsenic, zinc, copper, antimony, nickel, iron, phosphorus and sulphur. Contaminants other than phosphorus and sulphur should not singularly exceed 1 ppm and collectively exceed 5 ppm. Phosphorus should not exceed 1 ppm and sulphur should not exceed 25 ppm. These elements will shorten catalyst life by poisoning the catalyst and completely rendering it useless or will fully or partially "blind" the active sites of the catalyst. For "blinded" catalyst, cleaning methods will be recommended. For a poisoned catalyst, replacement with new catalyst material is the only method of restoring performance. VI. MAINTENANCE The MAXIM catalytic silencer is virtually a maintenance-free unit. A periodic check of the catalyst basket to insure no loss of the catalyst pellets is basically all that is required. When replacement is required, the catalyst pellets can be removed and replaced with new pellets. If the catalyst's pellets cannot be removed due to bridging, the engine can be turned on for a few minutes to blow the pellets out. Insertion of a small rod into the evacu- ation port can also be used to help remove the pellets. To refill the catalytic silencer, the evacuation ports are replaced, the renewal ports on top of the unit are removed and fresh catalyst is poured into the basket. There is no need to disassemble or remove a horizontal unit or to handle fragile and expensive 'monolithic catalyst assemblies. A vertical unit may require removal to facilitate evacuation of the old catalyst pellets. The vertical unit can then be filled and reinstalled. The catalyst may be cleaned in order to remove oil, grease or carbon which may be masking the active surface area and reducing the effectiveness of the catalyst. The catalyst should be removed from the chamber and cleaned by recommended cleaning methods only. VII. RECOMMENDED CLEANING METHODS 1. Heat Treatment Remove the catalyst via the evacuation ports on the bottom of the unit and spread the pellets out, not more than three inches deep, on a perforated steel tray. Clean for approximately 20 minutes by passing 1100OF air at low velocity through the catalyst. This method vaporizes oil and grease and incinerates carbon (soot) which combines with excess oxygen to form carbon dioxide (CO2). Heat treatment should remove submicron sized particles on the catalyst surface. 1 Bell, "Catverter 4.76mm 3/16 Catalyst Cleaning Methods" C/23