Troubleshooting Fan Problems

At Canadian Buffalo we resolve fan problems. If your current fan system is acting up, please check our list of the most common industrial fan problems and probable causes.

At Canadian Buffalo, our engineers and technicians understand rotating equipment. If your current fan system requires repairs or replacing, we can provide service technicians to carry out performance testing, troubleshooting, vibration analysis, field supervision. Our offerings include custom heavy duty fans, ventilation fans, process compressors, fluid drives, process pumps, rotary air heaters, and process fan application solutions.


NOISE
Source Probable Cause

IMPELLER HITTING INLET OR HOUSING

a. Impeller not centered in inlet or housing.
b. Inlet or housing damage.
c. Crooked or damaged impeller.
d. Shaft loose in bearing.
e. Impeller loose on shaft.
f. Bearing loose in bearing support.
g. Bent shaft.
h. Misaligned shaft and bearings.

IMPELLER HITTING CUTOFF

a. Cutoff not secure in housing.
b. Cutoff damaged.
c. Cutoff improperly positioned.

DRIVE

a. Sheave not tight on shaft (motor or fan).
b. Belts hitting belt tube.
c. Belts too loose. Adjust for belt stretching after 48 hours operating.
d. Belts too tight.
e. Belts wrong cross-section.
f. Belts not 'matched' in length on multi-belt drive.
g. Variable pitch sheaves not adjusted so each groove has same pitch diameter (muiti-belt drive).
h. Misaligned sheaves.
i. Belts worn.
j. Motor, motor base or fan not securely anchored.
k. Belts oily or dirty.
l. Improper drive selection.
m. Loose key.

COUPLING

a. Coupling unbalanced. misaligned, loose or may need lubricant.
b. Loose key.

BEARING

a. Defective bearing.
b. Needs lubrication.
c. Loose on bearing support.
d. Loose on shaft.
e. Seals misaligned.
f. Foreign material inside bearing.
g. Worn bearing.
h. Fretting corrosion between inner race and shaft.
I. Bearing not sitting on flat surface.

SHAFT SEAL SQUEAL

a. Needs lubrication.
b. Misaligned.
c. Bent shaft.
d. Bearing loose on support.

IMPELLER

a. Loose on shaft.
b. Defective impeller. Do not run fast. Contact the manufacturer.
c. Unbalance.
d. Coating loose.
e. Worn as result of abrasive or corrosive material moving through flow passages.
f. Blades rotating close to structural member.
g. Blades coinciding with an equal number of structural members.

HOUSING

a. Foreign material in housing.
b. Cutoff or other part loose (rattling during operation).

MOTOR

a. Lead-in cable not secure.
b. AC hum in motor or relay.
c. Starting relay chatter.
d. Noisy motor bearings.
e. Single phasing a 3 phase motor.
f. Low voltage.
g. Cooling fan striking shroud.

SHAFT

a. Bent
b. Undersized. May cause noise at impeller, bearings or sheave.

HIGH AIR VELOCITY

a. Ductwork too small for application.
b. Fan selection too large for application.
c. Registers or grilles too small for application.
d. Heating or cooling coil with insufficient face area for application.

OBSTRUCTION IN HIGH VELOCITY GAS STREAM MAY CAUSE RATTLE, OR PURE TONE WHISTLE

a. Dampers.
b. Registers.
c. Grilles.
d. Sharp elbows.
e. Sudden expansion in ductwork.
f. Sudden contraction in ductwork.
g. Turning vanes.

PULSATION OR SURGE

a. Restricted system causes fan to operate left of peak.
b. Fan too large for application.
c. Ducts vibrate at same frequency as fan pulsation.
d. Rotating stall.
e. Inlet vortex surge.
f. Distorted inlet flow

GAS VELOCITY THROUGH CRACKS, HOLES OR PAST OBSTRUCTIONS

a. Leaks in Ductwork.
b. Fins on Coils.
c. Registers or Grills.

RATTLES AND/OR RUMBLES

a. Vibrating Ductwork.
b. Vibrating cabinet parts.
a. Vibrating parts not isolated from building

INSUFFICIENT AIR FLOW
Source Probable Cause

FAN

a. Impeller installed backwards.
b. Impeller running backwards.
c. Improper blade angle setting.
d. Cutoff missing or improperly installed.
e. Impeller not centred with inlet collar(s).
f. Fan speed too slow.
g. Impeller/inlet dirty or clogged.
h. Improper running clearance.
i. Improper inlet cone to wheel fit.
j. Improper set inlet vane or damper.

DUCT SYSTEM

a. Actual system is more restrictive (more resistance to flow) than expected.
b. Dampers closed.
c. Registers closed.
d. Leaks in supply ducts.
e. Insulating duct liner loose.

FILTERS

a. Dirty or clogged.
b. Replacement filter with greater than specified pressure drop.

COILS

a. Dirty or clogged.
b. Incorrect fin spacing.

RECIRCULATION

a. Internal cabinet leaks in bulkhead separating fan outlet (pressure zone) from fan inlets (suction zone).
b. Leaks around fan outlet at connection through cabinet bulkhead.

OBSTRUCTED FAN INLETS

a. Elbows, cabinet walls or other obstructions restrict air flow. Inlet obstructions cause more restrictive systems but do not cause increased negative pressure readings near the fan inlet(s). Fan speed may be increased to counteract the effect of restricted fan inlet(s). CAUTION! Do not increase fan speeds beyond the manufacturer's recommendations.

NO STRAIGHT DUCT AT FAN OUTLET

a. Fans which are normally used in duct systems are tested with a length of straight duct at the fan outlet. If there is no straight duct at the fan outlet, decreased performance may result. If it is not practical to install a straight section of duct at the fan outlet, the fan speed may be increased to overcome this pressure loss. CAUTION! Do not increase fan speeds beyond the manufacturer's recommendations.

OBSTRUCTION IN HIGH VELOCITY AIR STREAM

a. Obstruction near fan outlet or inlet.
b. Sharp elbows near fan outlet or inlet.
c. Improperly designed turning vanes.
d. Projections, dampers or other obstruction in a part of the system where air velocity is high.

CFM HIGH — TOO MUCH AIR FLOW
Source Probable Cause

SYSTEM

a. Oversized ductwork.
b. Access door open.
c. Registers or grilles not installed.
d. Dampers set to by-pass coils.
e. Filter(s) not in place.
f. System resistance low.

FAN

a. Fan speed too fast.
b. Improper blade angle setting.

STATIC PRESSURE WRONG
Source Probable Cause

SYSTEM, FAN OR INTERPRETATION OF MEASUREMENTS

GENERAL DISCUSSION:
The velocity pressure at any point of measurement is a function of the velocity of the air or gas and its density. The static pressure at a point of measurement in the system is a function of the system design (resistance to flow), air density and the amount of air flowing through the system. The static pressure measured in a 'loose' or oversized system will be less than the static pressure in a 'tight' or undersized system for the same air flow rate. In most systems, pressure measurements are indicators of how the installation is operating. These measurements are the result of air flow and as such are useful indicators in defining system characteristics- Field static pressure measurements rarely correspond with laboratory static pressure measurements unless the fan inlet and fan outlet conditions of the installation are exactly the same as the inlet and outlet conditions in the laboratory.

STATIC PRESSURE LOW, CFM CORRECT
Source Probable Cause

GAS DENSITY

Pressures will be less with high temperature gases or at high altitudes.

STATIC PRESSURE LOW, CFM HIGH
Source Probable Cause

SYSTEM

System has less resistance to flow than expected. This is a common occurrence. Fan speed may be reduced to obtain desired flow rate. This will reduce power (operating cost).

STATIC PRESSURE LOW, CFM LOW
Source Probable Cause

SYSTEM

Fan inlet and/or outlet conditions not same as tested.

FAN

a. Impeller installed backwards.
b. Impeller running backwards.
c. Improper blade angle setting.
d. Cutoff missing or improperly installed.
e. Impeller not centered with inlet collar(s).
f. Fan speed too slow.
g. Impeller/inlet dirty or clogged.
h. Improper running clearance.
i. Improper inlet cone to wheel fit.
j. Improperly set inlet vane or damper.

STATIC PRESSURE HIGH, CFM HIGH
Source Probable Cause

DUCT SYSTEM

a. Actual system is more restrictive (more resistance to flow) than designed
b. Dampers closed.
c. Registers closed.
d. Insulating duct liner loose.

FILTERS

a. Dirty or clogged.
b. Replacement filter with greater than specified pressure drop.

COILS

a. Dirty or clogged.
b. Fin spacing too close.

POWER HIGH
Source Probable Cause

FAN

a. Backward inclined impeller installed backwards.
b. Fan speed too high.
c. Forward curve or radial blade fan operating below design pressures.
d. Blade angle not set properly.

SYSTEM

a. Oversized ductwork.
b. Face and by-pass dampers oriented so coil dampers are open at same time by-pass dampers are open.
c. Filter(s) left out.
d. Access door open.

NOTE: The causes listed pertain primarily to radial blade, radial tip and forward curve centrifugal fans, i.e., fans that exhibit rising horsepower curves. Normally, backward inclined, backward curve or backward inclined airfoil centrifugal fans and axial flow fans do not fall into this category.

GAS DENSITY

a. Calculated horsepower requirements based on light gas (e.g. high temperature) but actual gas is heavy (eg. cold start up).

FAN SELECTION

a. Fan not selected at efficient point of rating

FAN DOES NOT OPERATE
Source Probable Cause

ELECTRICAL OR MECHANICAL

Mechanical and electrical problems are usually straightforward and are normally analyzed in a routine manner by service personnel. In this category are such items as:
a. Blown fuses.
b. Broken belts.
c. Loose pulleys.
d. Electricity turned off.
e. Impeller touching housing.
f. Wrong voltage.
g. Motor too small and overload protector has broken circuit.
h. Low voltage, excessive line drop or inadequate wire size.
i. Load inertia too large for motor.
j. Seized bearing.

PREMATURE FAILURE
Source Probable Cause

BELTS, BEARINGS, SHEAVES, IMPELLERS, HUBS, ETC.

General Discussion: Each fan component is designed to operate satisfactorily for a reasonable life time. Fans intended for heavy duty service are made especially for that type of service. For example, Class I fans are intended for operation below certain limits of pressure and outlet velocity. Class II fans are designed for higher operating limits.

COUPLINGS

a. Coupling unbalanced. misaligned, loose or may need lubricant.
b. Loose key.

SHAFT

a. Bent.
b. Undersized.



DISCLAIMER This information has been reproduced in part from Air Movement and Control Association, Inc.(AMCA) manual (publication 202-88). The information contained herein has been derived from many sources and is believed to be accurate. Please note that the recommendations contained herein do not necessarily represent the only methods or procedures appropriate for the situation discussed, but rather are intended to present consensus opinions and practices of the air movement and control industry which may be helpful, or of interest, to those who design, test, install, operate or maintain fan-duct systems. Thus, Canadian Buffalo disclaims any and all warranties, express or implied, regarding the accuracy of the information contained herein and further disclaims any liability for the use or misuse of this information

For technical assistance, parts or new fan inquiries contact our sales office.

Canadian Buffalo
465 Laird Road
Guelph, ON Canada N1G 4W1
Telephone: (519) 837-1293
Fax: (519) 837-2380
Toll-free: (866) FAN-GUYS (326-4897)
Email: sales@canadianbuffalo.com