Backwardly Inclined



The Robinson backward curve unit is designed to give quiet, highly efficient, stable operation through a wide performance range with the protection of absolute non-overloading characteristics.

Both the airflow principles and structural design feature incorporated are based on 60 years in the fan design application and manufacturing business.

The heart of the unit is a 12 blade rotor of shrouded design. The 12 blades are welded to a heavy back plate. The hub assembly is in turn attached to the back plate on most sizes through a second heavy plate approximately one-half wheel diameter. A fabricated steel cone is used to ensure squareness of the hub to the back plate and to complete the assembly. All rotors are statically and dynamically balanced to G-2.5 on special equipment to ensure smooth operation at operating speed. The rotor is mounted on machined shafting of extra-heavy size which in turn is carried on bearings as described in later pages.

Housings are fabricated throughout with electric welding except when specifically requested otherwise. Material gauges meet or equal all standards in the various classes. Bracing in excess of required standards is furnished on all size units.

The spun inlet piece is the final major component. Designed to give desirable flow conditions to the unit and manufactured to close tolerances to maintain minimum running clearances, it ensures the excellent operating characteristic as illustrated on the accompanying curve.

Robinson Fans, Inc. has furnished all welded construction in fan equipment of all classes, wherever possible, since 1925. Experience has proven it the most desirable type of construction where access area can accommodate the size of the units thus formed. It gives extra strength, increased rigidity, and cleaner appearance.

Classes and Construction

Type J Fan

This bulletin covers class I and class II equipment. Type J fans are also produced in the class III and class IV range and, by contacting your nearest representative or the home office, proper sizes and performance can be supplied for any desired performance in these ranges. Our company, after 110 years of experience as custom fan builders, feels than when operating conditions in excess of class II requirements are encountered, a better job can be done for the customer by dealing individually with his application.

Class I equipment is designed for operation against a maximum 3-3/4″ water gauge total pressure when handling air of a density of .075 pounds per cubic foot and a maximum wheel tip speed of 10,000 feet per minute.

Class II equipment is designed for operation against a maximum of 6-3/4″ water gauge total pressure when handling air of a density of .075 pounds per cubic foot and a maximum wheel tip speed of 13,000 feet per minute.

All fans are furnished with fixed housings as standard, universal housings optional for sizes 12″ – 36-1/2″. Fan discharges are available to the locations indicated in the dimension sheets for either the standard fixed housing or the optional universal housing.

Split housings are available as an option. All welded construction standard. Bolted construction can be furnished if requested. All standard discharges furnished. Other discharges are available on request.


Anti-Friction Bearings

Heavy series, grease-lubricated, self-aligning, ball bearing pillow blocks, such as illustrated will be furnished as standard equipment on shaft sizes up to and including 3-15/16″.

Spherical roller, self-aligning pillow blocks, as illustrated, will be furnished as standard equipment on shaft sizes 4-7/16″ and larger.

Timken Roller pillow blocks are available on all sizes at a slightly higher cost.


Sleeve bearings furnished are the Dodge self-aligning Sleevoil pillow block. This is a babbitt-lined, ring-oiling, self-aligning lock with special seals specifically designed for fan work. Oil lubricated, it can be piped for remote indication and filling through a site glass provided on the unit. Collars for thrust loads can be installed within the bearing housing.

This bearing can be provided with water-cooled features for high-temperature operation.

Arrangement No. 2 – Ball Bearing Pillow Block

Ball bearing fan and blower pillow block equipped with two precision, single-row, deep-groove ball bearings. The inner race is locked to the shaft through set screws so that both radial and thrust load carrying capacity are provided. Bearing effectively sealed for grease lubrication.

A bronze bushed fan and blower pillow block will be furnished. Pillow blocks are fitted with two bronze bushings of high lead content and two “T” section oil rings. Two steel thrust collars adjustable from the outside are used. Piston ring seals keep oil chamber sealed. Oil gauge can be placed on either side of the pillow block and can be piped to extended distances. Oil indication and filling through site glass gauge.

Optional Extras

Outlet Dampers

Outlet dampers of the multi-leaf, airfoil blade design are offered. Generous shafts mounted in ball bearings, bolted to set-out plates for temperature operations are interconnected for operation by a single lever. Quadrant locking device furnished if requested. Positive air seal at shaft is ensured by design. Bolting flanges both sides to attach to fan outlet flange and duct.

Inlet Dampers

Inlet dampers are of the multi-leaf type, made of a set of pivoted radial blades suitable for power saving where wide operating range is encountered. Operating mechanism is outside of the air stream. Bolting flanges are located on both faces. Single lever control for automatic operation or quadrant locking, as requested, and may be interconnected on double-inlet installations.

Inlet Screens

Inlet screens of heavy mesh, double crimp wire with outside frame for bolted attachment and ease of removal can be provided.

Inspection Doors

Inspection doors of the bolted design are provided. Set-out doors can be provided on casings where insulation of the casing is contemplated. Quick-opening inspection doors can be supplied on special request at extra cost.


Belt guards and coupling guards of fabricated steel and expanded metal can be provided where necessary to ensure protection from moving components.

Bearing Pedestals

Independent bearing pedestals of heavy welded steel construction are available on arrangement No. 3, single inlet and double inlet, at extra cost.

Isolation Bases

Isolation bases of various designs can be supplied to eliminate transmission of vibration from operating unit to mounting floor. Units can be fabricated to receive both fan and driving motor for isolation of complete unit.

Special Construction Features

Units can be furnished in stainless steel, aluminum and other special alloy materials.

Coatings of Neoprene sheet vulcanized to steel, rubber sheet vulcanized to steel, Baked Phenolic or other special coatings of this nature can be furnished.

Other features, such as standard and custom shaft seals, blade liners, temperature and vibration detectors, stuffing boxes, special paints and drain openings are available for all sizes of equipment.

Primary Industries Served

  • Steel
  • Mining
  • Cement
  • Ceramic
  • Chemical
  • Woodworking

Typical Air-Moving Applications

  • Building ventilation
  • Fume removal
  • Dust removal
  • Dust collection
  • Pneumatic conveying
  • Oven and dryer exhaust
  • Combustion air
  • Incinerators
  • Heat recovery