Motors and Drives

Parr Geared Drive mounted to a Model 4553 Stirred Reactor System
Parr Geared Drive mounted to a Model 4553 Stirred Reactor System

Torque vs. Stirring Speed

The standard, open-type, variable speed motor installed on each Parr reactor will produce stirring speeds from zero to between 600 and 800 rpm with a torque adequate to drive the installed impellers in average viscosity mixtures. Higher horsepower motors and special stirrers can be provided for higher viscosities.  Alternate drive pulleys are available to produce higher stirring speeds, but several basic rules must be considered when changing any of these components.

The highest torque from any motor is obtained at lower stirring speeds. Increasing the stirring speed reduces the torque in inverse proportion to the speed. For operations involving high viscosity mixtures, the motor size, the type of impeller and the stirring speed must be matched to provide an effective mixing system.

As a general rule, the magnetic coupling installed on each Parr reactor will have a torque rating considerably higher than the torque obtainable from the motors offered for use with that apparatus. The goal is to make the motor the weak link so that the magnetic stirrer will be protected. Reference torque rating for applicable magnetic drive.

Explosionproof Motors

Explosionproof motors designed for Class I, Groups C and D and Class II, Groups F and G with variable speed control can be furnished for most Parr reactors.

Flameproof “d” Motors

ATEX certified AC Flameproof Motors designed for use with group IIC gases are available for all of Parr’s stirred reactors.  These inverter duty motors are available with simple variable frequency drives for control of the stirring speed.  Please consult Parr for any specific ATEX certification related requirements.


Air Motors

Air-driven motors can be installed on most reactors. The horsepower rating, torque, and available speed are all dependent upon the pressure and available volume of the driving air source. Maximum torques are delivered at relatively slow speeds and maximum horsepower is delivered at high speed.

Geared, Direct Drive Motors

A geared, direct drive motor can be installed on most fixed head floor stand reactors. This is an attractive arrangement for handling heavy stirring loads. Any 1/4 hp or larger, variable-speed standard or explosionproof motor can be used. Gear box drives are available with ratios of 3:1, 5:1 and 10:1. The 1700 rpm maximum speed will be reduced in an amount determined by the reduction ratio of the gear box, and the associated torque values from the table will be increased in the same ratio.

Stirrer Drive Motors
Standard PulleyOptional Pulley
Motor DesignationHP (kW)  RatingHazardous Location*Variable SpeedType Max Speed, RPM**Max Torque, in-lbMax Speed, RPM**Max Torque, in-lb
-VS.121/16 (0.05)NoYesPMDC6006.7517002.25
-VS.251/4 (0.18)NoYesPMDC60027 17009
-XP.251/4 (0.18)Class I, Div. 1&2 Groups C&D, E&FYesPMDC60027 17009
-XP.25X1/4(0.18)Ex 2G de IIC T4YesInverter Duty Constant Torque AC45033135011
-AM.25**1/4(0.18)***Ex II 2 GD c T4YesAir1000***30  ___ ___
-VS.501/2 (0.37)NoYesPMDC60054170018
-XP.501/2 (0.37)Class I, Div. 1&2, Groups C&D, E&FYesPMDC60054170018
-XP.50X1/2(0.37)Ex 2G Ex de IIC T4YesInverter Duty Constant Torque AC45066135022
-AM.50**1/2 (0.37)***Ex II 2 GD c T4YesAir1000***66*** ___ ___
-VS.753/4 (0.55)NoYesPMDC60081170027
-XP.753/4 (0.55)Class I, Div. 1&2, Groups C&D, E&FYesYes60081170027
Values represented are nominal.                                                                                                                  *For more information on Hazardous Locations information see Tech Note 230.
**Maximum speed values based on “no load”.
***HP, RPM, and torque values for air motors are based on a 40 psi supply capable of 34 cfm for the AM.50 and 10 cfm for the AM.25.


Gear Box Torques
3:1 Gear Box5:1 Gear Box10:1 Gear Box
Motor HP RatingMax. Speed RPMMax. Torque in-lbMax. Speed RPMMax. Torque in-lbMax. Speed RPMMax. Torque in-lb
3/460081360135Not Recommended
Contact Parr for ATEX Gear Box.


Magnetic Drive
DescriptionMaximum Torque, in-lb
General Purpose16
Footless General Purpose16
Heavy Duty60
Footless Heavy Duty60
Extra Heavy Duty120
Footless Extra Heavy Duty120

We'll help you configure a system that meets all of your research needs.