Howden Roots Metric Series, Installation, Operation And Maintenance Manual

ISRB_2002 GEA 19171 Roots URAI 

Page 5 of 32

With the mounting plate in place and levelled, set the 

unit on it without bolting and check for rocking. If it is not 

solid, determine the total thickness of shims required 

under one foot to stop rocking. Place half of this under 

each of the diagonally-opposite short feet, and tighten 

the mounting studs or screws. Rotate the drive shaft to 

make sure the impellers turn freely. If the unit is to be 

direct coupled to a driving motor, consider the height of 

the motor shaft and the necessity for it to be aligned 

very accurately with the unit shaft. Best unit 

arrangement is directly bolted to the mounting plate 

while the driver is on shims of at least 1/8 inch (3mm) 

thickness. This allows adjustment of motor position in 

final shaft alignment by varying the shim thickness. 

Aligning 

When unit and driver are factory mounted on a common 

baseplate, the assembly will have been properly aligned 

and is to be treated as a unit for levelling purposes.  

Satisfactory installation can be obtained by setting the 

baseplate on a concrete slab that is rigid and free of 

vibration, and levelling the top of the base carefully in 

two directions so that it is free of twist. The slab must be 

provided with suitable anchor bolts. The use of grouting 

under and partly inside the levelled and shimmed base 

is recommended. 
It is possible for a base-mounted assembly to become 

twisted during shipment, thus disturbing the original 

alignment. For this reason, make the following checks 

after the base has been levelled and bolted down. 

Disconnect the drive and rotate the unit shaft by hand. It 

should turn freely at all points. Loosen the unit foot hold-

down screws and determine whether all feet are evenly 

in contact with the base. If not, insert shims as required 

and again check for free impeller rotation. Finally, if unit 

is direct coupled to the driver, check shaft and coupling 

alignment carefully and make any necessary 

corrections. 
In planning the installation, and before setting the unit, 

consider how piping arrangements are dictated by the 

unit design and assembly. Drive shaft rotation must be 

established accordingly and is indicated by an arrow 

near the shaft.  
Typical arrangement on vertical units has the drive shaft 

at the top with counterclockwise rotation and discharge 

to the left. Horizontal units are typically arranged with 

the drive shaft at the left with counterclockwise rotation 

and discharge down. See Figure 4 for other various unit 

arrangements and possible conversions. 
When a unit is DIRECT COUPLED to its driver, the 

driver RPM must be selected or governed so as not to 

exceed the maximum speed rating of the unit. Refer to 

Table 1 for allowable speeds of various unit sizes. 
A flexible type coupling should always be used to 

connect the driver and unit shafts. 
When direct coupling a motor or engine to a blower you 

must insure there is sufficient gap between the coupling 

halves and the element to prevent thrust loading the 

blower bearings. When a motor, engine or blower is 

operated the shafts may expand axially. If the coupling 

is installed in such a manner that there is not enough 

room for expansion the blower shaft can be forced 
back into the blower and cause the impeller to contact 

the gear end headplate resulting in damage to the 

blower. The two shafts must be in as near perfect 

alignment in all directions as possible, and the gap must 

be established with the motor armature on its electrical 

center if end-play exists. Coupling manufacturer’s 

recommendations for maximum misalignment, although 

acceptable for the coupling, are normally too large to 

achieve smooth operation and maximum life of the 

blower. 
The following requirements of a good installation are 

recommended. When selecting a coupling to be fitted to 

the blower shaft Howden Roots recommends a taper 

lock style coupling to insure proper contact with the 

blower shaft. If the coupling must have a straight bore 

the coupling halves must be fitted to the two shafts with 

a line to line thru .001” interference fit. Coupling halves 

must be warmed up per coupling manufacturer’s 

recommendations. Maximum deviation in offset 

alignment of the shafts should not exceed .005" (.13 

mm) total indicator reading, taken on the two coupling 

hubs. Maximum deviation from parallel of the inside 

coupling faces should not exceed .001" (.03 mm) when 

checked at six points around the coupling.  
When a unit is BELT DRIVEN, the proper selection of 

sheave diameters will result in the required unit speed. 

When selecting a sheave to be fitted to the blower shaft 

Howden Roots recommends a taper lock style sheave to 

insure proper contact with the blower shaft. This 

flexibility can lead to operating temperature problems 

caused by unit speed being too low. Make sure the drive 

speed selected is within the allowable range for the 

specific unit size, as specified under Table 1. 
Belt drive arrangements usually employ two or more V-

belts running in grooved sheaves. Installation of the 

driver is less critical than for direct coupling, but its shaft 

must be level and parallel with the unit shaft. 

The driver 

should be mounted on the inlet side of a vertical unit 

(horizontal piping) and on the side nearest to the 

shaft on a horizontal unit. SEE PAGE 6 - Acceptable 

ISRB_2002 GEA 19171 Roots URAI.indd   5

17/09/2015   12:52