Air Motivators / Air Handlers / Fans
The terms “air motivator,” “air handler” and “fan” are to some degree synonymous. All these devices cause air to move. How they make the air move, whether through blades slicing through the air, or via a “squirrel cage” which gathers and moves the air much like waterwheels powered the Industrial Revolution, is what distinguishes them apart.
There are currently three different types of air motivators, or fans, used in Global Finishing Solutions booths. The three types are:
- Turbo fan (direct-drive, backward-inclined centrifugal blower), used in our Ultra groups and BT-1200 systems.
- Tube axial fan. Tube axial fans appear in our BT-1200 and Expert systems.
- Double-wheel, double-inlet squirrel cage blower, which is used in the Expert system.
Direct-Drive, Backward-Inclined Centrifugal Blower / Turbo Fan
In an Ultra group or a BT-1200 system, the supply air is delivered by our direct-drive, backward-inclined centrifugal blower. In the Ultra group, this turbo fan also serves as the exhaust air motivator.
Direct-drive, backward-inclined fans:
- Maintain consistent air flow, even when the filters load up causing increased resistance. Less expensive fans just can’t stand up to the pressure.
- Deliver higher performance with less horsepower, while consuming far less energy.
- Require much less maintenance because there are no belts, pulleys or bearings to replace.
The current unit is direct drive using a 10 HP open face motor. The blower wheel is directly attached to the motor shaft.
It is approximately 23″ in diameter with 12 blades, each 6″ long. The 7½ HP wheel is the same size, but the blades are only 4 inches long. The wheel is 12¾” wide from the inlet section to the discharge section. The wheel is steel with an aluminum inlet scroll, which meets the NFPA 33 code requirements about ferrous metal to ferrous metal in exhaust fans.
This design will deliver 12,000 CFM of air at 1750 RPM. The construction of the wheel makes it capable of delivering this airflow into a high static pressure situation.
Ture Axial Fan
The main exhaust fan is mounted in a housing, which supports the fan blade in the middle of the duct and contains the motor mounting and belt housing. Fan sizes can range from 17-1/2″ to 40″. Some applications have required fans as large as 60″, or 5 ft. Horsepower can range from 1/2 HP to 10 HP. The diameter of the pulley and the HP of the motor work together to create a specific CFM. On some systems, the speed is controlled by a VFD (variable-frequency drive).
Pulley alignment is very important in this fan. Ordinarily, a misalignment of more than 1/8″ in one foot will adversely affect belt life. Improper pulley alignment produces vibration and uneven wear on one side of the belt. This causes the belt to roll over in the pulley, or throws the entire load on one side of the belt. The latter condition will result in stretching or breaking of cords on the loaded side. Once the pulleys are aligned, the belts also need to be properly tensioned.
The forced dry package uses a variable pitch pulley. The pulley setting should allow the booth to remain balanced. The fan motor is a 2 speed – 2 winding motor.
Double-Wheel, Double-Inlet Squirrel Cage Blower
The supply air is handled by twin 15″ DWDI (double-width, double-inlet) blower wheels mounted on a 4″ tubular shaft. The blower wheels are attached to this shaft via two clamps (one on each side of the wheel). Two 3/8″ socket head screws secure this clamp.
The shaft is hollow except for the end journals. This type of shaft is capable of spanning greater distances between bearings than a solid shaft style. Since this type of shaft can span more distance without whipping, the bearings can be mounted on the external face of the casing
Flange block bearings are used with eccentric locking collars. The bearings require greasing at least once every 6 months.
The drive assembly is made up of two pulleys. The driven pulley is a fixed or non-adjustable type. The driver pulley is a variable or adjustable type. The driver pulleys used on the 10,000 CFM and the 12,000 CFM cure units are identical. The one used on the 12,000 CFM unit is a 9.4 pitch diameter.
Pulley adjustment is only required if the blower speed needs to be changed to balance airflow with the exhaust system. All adjustments to the speed of the blower are done with the variable pulley.
The motor used on the supply blower is 10 HP. The RPM of the motor, depending on the manufacturer, is between 1750 to 1800. These motors are ODP (open drip-proof) style with standard T-frames.
The three-phase motors carry a voltage rating of 200-208/230/460. The 575 volt motor is a single rated motor.
The motor mounts right on the blower housing. Pulley alignment is very important in this fan. Ordinarily, a misalignment of 1/8″ in one foot will definitely affect belt life. When the pulleys are aligned, the belts need to be properly tensioned.
Pressurizing a Booth
Because of the incredible volume of air needed to produce the velocity required for coatings operations, rather than drawing air from the area surrounding the booth, systems are fitted with air replacement or air make-up units so that they draw their air from the atmosphere through intake ducting. While passing through the air make up equipment, the air is not only filtered for atmospheric particulate (down to about 10 microns), but then may also be heated to a temperature specific to the application. This configuration assures even, continuous, filtered, tempered input air.
The term “pressurized” comes from the fact that inside the booth there is a slight “positive pressure”. The dampers are set so that the tendency is for the air to push out of the booth. This prevents particulate in the area surrounding the booth to be sucked into the booth environment by negative pressure each time a door is opened.