Economical to use because it’s powered by air–there is no need to buy cartridges.  Easy maintenance.  There are only 7 major components and just eight O-rings.  An air compressor, tool balancer, and an air filter lubricator are all that is needed.  This knocker operates effectively at only 180 P.S.I., a reasonable pressure range that does not cause excessive parts wear.  Comes complete with an operator’s guide, safety glasses and safety sign.  Spanish signs/literature available upon request.