Howden Roots Metric Series, Installation, Operation And Maintenance Manual

ISRB_2002 GEA 19171 Roots URAI 

Page 7 of 32

Pipe flanges or male threads must meet the unit 

connections accurately and squarely. DO NOT attempt 

to correct misalignment by springing or cramping the 

pipe. In most cases this will distort the unit casing and 

cause impeller rubbing. In severe cases it can prevent 

operation or result in a broken drive shaft. For similar 

reasons, piping should be supported near the unit to 

eliminate dead weight strains. Also, if pipe expansion is 

likely to occur from temperature change, installation of 

flexible connectors or expansion joints is advisable. 
Figure 3 represents an installation with all accessory 

items that might be required under various operating 

conditions. Inlet piping should be completely free of 

valves or other restrictions. When a shut-off valve 

cannot be avoided, make sure a full size vacuum relief is 

installed nearest the unit inlet. This will protect against 

unit overload caused by accidental closing of the shutoff 

valve. 
Need for an inlet silencer will depend on unit speed and 

pressure, as well as sound-level requirements in the 

general surroundings. An inlet filter is recommended, 

especially in dusty or sandy locations. A discharge 

silencer is also normally suggested, even though 

WHISPAIR* units operate at generally lower noise levels 

than conventional rotary blowers. Specific 

recommendations on silencing can be obtained from 

your local Howden Roots distributor. Discharge piping 

requires a pressure relief valve, and should include a 

manual unloading valve to permit starting the unit under 

no-load conditions. Reliable pressure/vacuum gauges 

and good thermometers at both inlet and discharge are 

recommended to allow making the important checks on 

unit operating conditions. The back-pressure regulator 

shown in Figure 3 is useful mainly when volume 

demands vary while the unit operates at constant output. 

If demand is constant, but somewhat lower than the unit 

output, excess may be blown off through the manual 

unloading valve. 
In multiple unit installations where two or more units 

operate with a common header, use of check valves is 

mandatory. These should be of a direct acting or free 

swinging type, with one valve located in each line 

between the unit and header. Properly installed, they will 

protect against damage from reverse rotation caused by 

air and material back-flow through an idle unit. 
After piping is completed, and before applying power, 

rotate the drive shaft by hand again. If it does not move 

with uniform freedom, look for uneven mounting, piping 

strain, excessive belt tension or coupling misalignment. 

DO NOT

 operate the unit at this time unless it has been 

lubricated per instructions. 
 

ISRB_2002 GEA 19171 Roots URAI.indd   7

17/09/2015   12:52