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The Importance of Proper Adjustment of Electromagnetic Impact Rappers

by TRK Engineering Services, Inc.

The importance of the mechanical adjustment of an Electromagnetic Rapper is too often overlooked. A rapper system utilizing Electromagnetic Gravity Impact Rappers is generally controlled by a microprocessor sequence control. These controls are capable of adjusting the rapping frequency and intensity with great accuracy. To achieve this the rapper must be mounted properly and the piston (slug) insertion in the coil must be adjusted to deliver rapping forces that can be achieved consistently.

An electromagnetic rapper consists of a DC electrical coil in a sealed housing assembly and a steel piston. When the coil is energized, the piston is lifted. Rapping impact occurs when the coil is deenergized and the piston falls under the influence of gravity to strike a rapper shaft. The weight of the piston and the distance it falls after being released from the influence of the energized coil (lift height) determine the rapping intensity. Several factors determine the lift height; the ON time programmed by the rapper controller, the piston penetration into the coil, and ambient temperature. In order to achieve consistent, repeatable rapping it is important to follow the precipitator manufacturers recommendations regarding initial rapper mounting and adjustment. Many specify the visible piston exposure between the rapper rod and the bottom of the rapper in order to assure the desired piston penetration in the coil housing. Tolerances are generally tight in order to produce consistent, repeatable rapper lift. The rapper must also be mounted correctly and plumb.

Typical symptoms of electromagnetic rappers that are not properly adjusted, or inconsistently adjusted, are material buildups caused from lack of rapping, or opacity spiking due to over-rapping. Obviously, this will have an adverse effect on precipitator performance. The effects may vary from season to season with the change in temperature. Extreme variations in piston lift may also lead to damage to internal components from over-rapping. The proper mechanical adjustment of Electromagnetic Impact rappers insures that consistent rapping forces are achieved to effectively clean the collecting and discharge electrodes.

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Last updated: May 10, 2009.
Copyright 1997 TRK Engineering Services, Inc. All rights reserved.
For more information contact: TRK Engineering Services - 95 Clarks Farm Road - Carlisle, MA 01741 - Telephone: 978-287-0550 - Fax: 978-287-0569 - email: