Howden Roots 412 HPT, Installation, Operation & Maintenance Manual

3

ISRB-2009, Rev. 02_17.

Safety Precautions 

It is important that all personnel observe safety precautions 

to minimize the chances of injury. Among many  

considerations, the following should be particularly noted:
•  Blower casing and associated piping or accessories 

may become hot enough to cause major skin burns  

on contact.

•  Internal and external rotating parts of the blower and 

driving equipment can produce serious physical injuries. 

Do not reach into any opening in the blower while it is 

operating, or while subject to accidental starting.  

Protect external moving parts with adequate guards.

•  Disconnect power before doing any work, and avoid 

bypassing or rendering inoperative any safety or  

protective devices.

•  If blower is operated with piping disconnected, place a 

strong coarse screen over the inlet and avoid standing 

in the discharge air stream. 

• 

CAUTION: Never cover the blower inlet with your  

hand or other part of body.

•  Stay clear of inlet and discharge openings.
•  Stay clear of the blast from pressure relief valves and 

the suction area of vacuum relief valves.

•  Use proper care and good procedures in handling,  

lifting, installing, operating and maintaining the  

equipment.

•  Casing pressure must not exceed 25 PSI (1725 mbar) 

gauge. Do not pressurize vented cavities from an  

external source, nor restrict the vents without first 

consulting Roots.

•  Do not use air blowers on explosive or hazardous 

gases.

•  Other potential hazards to safety may also be  

associated with operation of this equipment.  

All personnel working in or passing through the area  

should be trained to exercise adequate general  

safety precautions.

Operating Limitations 

A Howden Roots blower must be operated within certain 

approved limiting conditions to enable continued satisfactory 

performance. Warranty is contingent on such operation.
Maximum limits for pressure, temperature and speed are 

specified in TABLE 1 for this truck application blower. 

These limits apply to this blower of normal construction, 

when operated under standard operating conditions.  

Be sure to arrange connections or taps for instruments  

used to measure temperature, pressure and vacuum at 

or near the inlet and discharge connections of the blower. 

These, along with tachometer will enable period checks of 

operating conditions.

Pressure 

The pressure rise, between inlet and discharge, must not 

exceed the figure listed in TABLE 1. 

• 

The term “intermittent operation” is defined as operation 

for no longer than 10 seconds at maximum pressure list 

in TABLE 1, provided that the inlet restriction (filter 

pressure drop, etc.) does not exceed 20” (508 mm)  

of water.

•  Also, in any system where the blower inlet is at a 

positive pressure above atmospheric, a maximum 

case rating of 25 PSI gauge (1725 mbar) should not 

be exceeded. Never should the maximum differential 

pressure be exceeded.

Temperature 

Blowers are approved only for installations where following 

temperature limits can be maintained in service. 
•  Measured temperature rise must not exceed listed 

values when inlet is at ambient temperature. Ambient 

temperature is considered as the general temperature 

of the space around the unit. This is not outdoor  

temperatures unless unit is mounted outdoors.

•  If inlet temperature is higher than ambient, the listed 

allowable temperature rise values must be reduced by 

2/3 of the difference between the actual measured inlet 

temperature and the ambient temperature. Example: 

Tinlet = 150 °F and Tambient = 60 °F; Temperature rise 

limit, ∆Tnew = 350 – 2/3(150-60) = 290 °F.

•  The ambient temperature of the space the blower/ 

motor is installed in should not be higher than  

120 °F (49 °C).

Speed 

This blower may be operated at speeds up to the maximum 

listed in TABLE 1. Blower may be direct coupled to suitable 

constant or variable speed driver if pressure/temperature 

conditions are also within limits. At low speeds, excessive 

temperature rise may be a limiting factor.
Special Note: The listed maximum temperature rise may  

occur well before its maximum pressure is reached. This 

may occur at high altitude, low vacuum or at very low 

speed. The blower operating limit is always determined by 

the maximum rating reached first. It can be any one of the 

three: Pressure, Temperature or Speed.