Protecting Your Regenerative Blower Investment

Motor Thermistors

In applying your regenerative blower, it is therefore necessary to know the operating conditions for the blower. Most blowers (including APPL’s standard models), include motor winding embedded thermistors for protection of the motor.  On small single phase units, these thermistor leads (in the motor terminal box) should be wired in series with the 115V hot lead supplied to the blower. On larger single phase units (over 15 amp service) and on 3 phase models, the thermistors may be used for pilot duty service only. With these voltages, a motor starter must be used and the thermistor should be wired in series with the contactor control coil circuit. If a VFD is used, an input for is usually provided for a motor fault to which the thermistor could be wired. In addition to the winding embedded motor thermistors, standard starters and VFD’s provide overload protection which will protect the blower motor from an over-current or phase loss condition.protecting your blowerPressure/Vacuum Relief Valves

For applications in which there is a possibility for the blower discharge or inlet to be restricted to levels that may cause low flow conditions, protection should be put in place to prevent overheating of the blower. The performance curve for your blower model should always be consulted when applying the blower, as this curve will provide pressure and vacuum maximum limits which must be complied with. In applying your blower, it will be beneficial to know the level of vacuum or pressure at which the blower will operate to ensure you are within the acceptable limits. A pressure or vacuum gauge is a good investment, and will allow you to monitor any changes in system pressures over time. To ensure that excessive pressure or vacuum levels are not encountered, a pressure or vacuum relief valve should be used in applications where these possibilities exist.  It is especially critical for vacuum applications, as not only will air flow be reduced as the inlet is throttled, but this air is rarified, and will have a lower specific heat value than compressed air. As the air passing through the blower in a vacuum application will have a similar heat load based on pressure differential across the blower, the heat transferred to the rarified air will result in a higher sensible temperature which will cause the blower to run hotter.  Always ensure that you do not exceed the maximum pressure and vacuum levels shown on the performance curve.

Intake Filters

Your blower should always be protected against ingestion of foreign materials and particles. Although small particles in the form of dust may pass through the blower, an accumulation and build-up of these particles in the blower housing or on the impeller over time may result in reduced performance, in-effective cooling and/or overheating, motor overloading, or a combination of all. Larger particles may not be able to pass through the blower’s tighter tolerance areas, and may result in impeller damage. The type of filter installed will depend on user requirements. In fairly clean environments, for protection of the blower from ingestion of larger particles which may damage the impeller, an economical stainless steel strainer-type intake filter may be suitable. For applications in dusty or dirty environments, or in applications where the air is being used for processes requiring clean air, a paper cartridge-type filter may be required. These filters are available with standard elements with a 10 micron filtration rating, but are also available with various element types, including HEPA rating for special applications.  For vacuum applications, in-line filters are available with either paper elements or polyester elements. Polyester elements, although more expensive, provide the advantage of being washable, and are moisture resistant. It is not recommended that regenerative blowers be subjected to high intake moisture loads, and continual ingestion of free liquids or droplets on the inlet side of the blower may result in damage to the blower. It is recommended that close attention be paid to the condition of the filter over time. As intake filters become dirty, a restriction to air flow will occur, and this could result in insufficient air flow through the blower for cooling purposes.  A strict filter maintenance schedule or a filter pressure differential gauge or an alarm switch may benefit your application, and prevent future problems or failure.