Howden Roots 412 HPT, Installation, Operation & Maintenance Manual

ISRB-2009, Rev. 02_17.

6

Operation

Before operating blower under power for 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 special conditions in the 

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

left in the blower air chamber or piping.

•  Recheck blower leveling, drive alignment and tightness 

of all mounting bolts if installation is not recent.

•  Turn drive shaft by hand to make sure impellers still 

rotate without bumping or rubbing at any point.

•  Ensure oil levels in main sump are correct.
•  Bump blower a few revolutions with driver to check that 

direction of rotation agree with arrow near blower shaft, 

and that both coast freely and come 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.
•  Start blower, let it accelerate to full speed slowly, than 

shut off. Slowly engage the power take off and never 

pop the clutch on engagement. Listen for knocking 

sounds, both power-on and as speed slows down.

•  After blower comes to complete stop, repeat above but 

let run 2 to 3 minutes. Check for noises, such as  

knocking sounds.

•  After blower comes to complete stop, operate blower for 

about 10 minutes unloaded. Check oil levels. Observe 

cylinder and head plate surfaces for development of hot 

spots such as burnt paint, including 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 final check run of at least one hour under normal 

operating conditions. After blower is stated, gradually close 

the inlet for vacuum service, or the discharge for pressure  

service. At this point it is recommended that pressure gauge 

be connected into the discharge line if not already provided, 

and that temperature gauge be installed on inlet and  

discharge. 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 TABLE 

1, shut down and investigate conditions in the piping system. 

Refer to trouble shooting check list for suggestions on various 

problems that may appear. 
When the blower vacuum or pressure  is at a maximum 

intermittent value for over 10 seconds, stop the blower and 

remove the line blockage manually.  Otherwise the blower 

might seize due to excessive operating temperature and  

pressure.

Always start blower slowly with power take off and never 

pop the clutch on engagement.
Never operate blower above 25 PSI (1.72 bar) pressure rise 

on gauge at immediate blower discharge.
Do not operate blower with defective pressure relief valve.
  

See Table 1, for maximum pressure limits when operating 

below maximum speed or above sea level conditions.
See Table 2, for unit internal clearances.

Vibration Assessment Criteria

With measurements taken near the bearing locations on  

the housing, see chart below for an appropriate assessment 

guide for blower mounted rigidly. In general, blower vibration 

levels should be monitored on a regular basis and the  

vibration trend observed for progressive or sudden change 

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

vibration will determine need to measure discrete frequency 

vibration levels and the action required.

Lubrication

Blower efficiency and life depend on the quality of 

maintenance the blower receives. Maintenance must be 

done regularly and with care. A clean work space, tools, 

solvents, and wiping rags are necessary to avoid transfer 

of dirt into the unit. A maintenance chart listing each blower 

and scheduling regular checks of the unit is valuable.
Any premium grade, non-detergent industrial grade oil with 

rust, oxidation and foam inhibitors will be adequate for 

use for most applications. Example: Mobile DTE grade oil. 

Because of blower design features, the oil temperature will 

remain below 220 °F (104 °C) even at maximum blower 

operating temperature rise and ambient temperatures of up 

to 120 °F (49 °C). Oil life for mineral base oil is 2000 hours if 

operating below 180 °F (82 °C). General rule of thumb: Oil 

life at 200 °F (93 °C), would be only 1000 hours and at 220 

°F (104 °C) would be only 500 hours. Therefore, if expected 

to run at the maximum continuous pressure operation or in 

elevated ambient conditions, such as inside enclosure or in 

warm environments, consider reduction in oil life and change 

with more frequency. When oil temperature does reach 

above 180 °F (82 °C), also good synthetic grade oil, such as 

Roots synthetic can be used to increase oil life by factor of 

3X that of mineral base oils.

Oil sump is shared for both ends of the blowers and oil fill 

can be accomplished by removing breather (item 60) on 

drive end cover and filling to the center of sight glass (item 

59) on the side of the reservoir on drive end of blower. Oil 

sump capacity is approximately 96 fluid ounces (2.85 liters).

Grade of oil to use is based on blower discharge 

temperature. See TABLE 3 for recommended oil grades.
NOTE: 
Blower discharge temperature of 250 °F, can typically  

be achieved ≥ 15 PSI (1000 mbar) pressure rise. 

However, can be reached sooner if operating blower  

at any of following conditions:
a.  higher altitude operation,
b.  high ambient temperature, 

c.  excessive vacuum (inlet filter pressure drop high), 

d.  lower blower operating speeds.  
For operation at temperatures below 10 °F (-12 °C), the  

use of heat tracing and synthetic lubricants is recommend.  

The pour point should be at least 5 to 10 °F (3 to 5 °C) 

below the minimum expected ambient temperature.
For adequate lubrication to the blower internal components, 

maximum allowable tilt and roll of the truck is 7.5 degrees 

for each direction or in combination.