Howden Roots Metric Series, Installation, Operation And Maintenance Manual

ISRB_2002 GEA 19171 Roots URAI 

Page 10 of 32

Operation 

Before operating a blower under power for the first time, 

recheck the unit and the installation thoroughly to reduce 

the likelihood of avoidable troubles. Use the following 

procedure check list as a guide, but consider any other 

special conditions in the installation. 



  Be certain that no bolts, tools, rags, or debris have been 

left in the blower air chamber or piping. 



  If an outdoor intake without filter is used, be sure the 

opening is located so it cannot pick up dirt and is 

protected by a strong screen or grille. Use of the 

temporary protective screen as described under 

INSTALLATION is strongly recommended. 



  Recheck blower levelling, drive alignment and tightness 

of all mounting bolts if installation is not recent. If belt 

drive is used, adjust belt tension correctly. 



  Turn drive shaft by hand to make sure impellers still 

rotate without bumping or rubbing at any point. 



  Ensure oil levels in the main oil sumps are correct. 



  Check lubrication of driver. If it is an electric motor, be 

sure that power is available and that electrical overload 

devices are installed and workable. 



  Open the manual unloading valve in the discharge air 

line. If a valve is in the inlet piping, be sure it is open. 



  Bump blower a few revolutions with driver to check that 

direction of rotation agrees with arrow near blower shaft, 

and that both coast freely to a stop. 
After the preceding points are cleared, blower is ready 

for trial operation under “no-load” conditions. The 

following procedure is suggested to cover this initial 

operation test period. 

a. Start blower, let it accelerate to full speed, then 

shut off. Listen for knocking sounds, both with 

power on and as speed slows down. 
b. After blower comes to a complete stop, repeat 

above, but let blower run 2 or 3 minutes. Check for 

noises, such as knocking sounds. 
c. After blower comes to a complete stop, operate 

blower for about 10 minutes unloaded. Check oil 

levels. Observe cylinder and headplate surfaces for 

development of hot spots such as burned paint, 

indicating impeller rubs. Be aware of any noticeable 

increase in vibration. 

Assuming that all trials have been satisfactory, or that 

necessary corrections have been made, the blower 

should now have a final check run of at least one hour 

under normal operating conditions. After blower is 

restarted, gradually close the discharge unloading valve 

to apply working pressure. 
At this point it is recommended that a pressure gauge or 

manometer be connected into the discharge line if not 

already provided, and that thermometers be in both inlet 

and discharge lines. Readings from these instruments 

will show whether pressure or temperature ratings of the 

blower are being exceeded. 
During the final run, check operating conditions 

frequently and observe the oil levels at reasonable 

intervals. If excessive noise or local heating develops, 

shut down immediately and determine the cause. If 

either pressure rise or temperature rise across the 

blower exceeds the limit specified in this manual, shut 

down and investigate conditions in the piping system. 

Refer to the TROUBLESHOOTING CHECKLIST for 

suggestions on various problems that may appear. 
The blower should now be ready for continuous duty 

operation at full load. During the first few days make 

periodic checks to determine whether all conditions 

remain steady, or at least acceptable. This may be 

particularly important if the blower is supplying air to a 

process system where conditions can vary. At the first 

opportunity, stop the blower and clean the temporary 

inlet protective screen. If no appreciable amount of 

debris has collected, the screen may be removed. See 

comments under INSTALLATION. At this same time, 

verify levelling, coupling alignment or belt tension, and 

mounting bolt tightness. 
Should operating experience prove that blower capacity 

is a little too high for the actual air requirements, a small 

excess may be blown off continuously through the 

manual unloading or vent valve. Never rely on the 

pressure relief valve as an automatic vent. Such use 

may cause the discharge pressure to become 

excessive, and can also result in unsafe operation of the 

valve itself. If blower capacity appears to be too low, 

refer to the TROUBLESHOOTING CHECKLIST. 

Vibration Assessment Criteria 

With measurements taken at the bearing locations on 

the housings, see chart below for an appropriate 

assessment guide for rotary lobe blowers rigidly 

mounted on stiff foundations. 
In general, blower vibration levels should be monitored 

on a regular basis and the vibration trend observed for 

progressive or sudden change in level. If such a change 

occurs, the cause should be determined through 

spectral analysis. 
As shown on the chart below, the level of all pass 

vibration will determine the need to measure discrete 

frequency vibration levels and the action required. 
 
 

ISRB_2002 GEA 19171 Roots URAI.indd   10

17/09/2015   12:52