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Sanitary PD Pump Rotor Clearances

March 29, 2019

In today’s post, we are going to look at the different clearance options that are available on a Waukesha Cherry-Burrell Universal 1, 2, & 3 PD Pump.

As you may know, the Waukesha Alloy 88 is the standard rotor material for the Universal 1, 2, & 3 PD pumps. This alloy was developed to provide the advantage of excellent corrosion resistance and close operating clearance requirements. The clearance between rotating parts (rotor) and stationary parts (pump head) is very important in limiting slip and maximizing efficiency.

 

Slip

Slip is proportional to clearance to the 3rd power

 

Here is a summary of the different clearance options for a U1 & U2 PD pump:

 

“Standard” and “Wine” clearance rotors may be used with liquid temperatures up to 180°F (82°C).

However, between 160°-200°F (71°-93°C), it is best to consider other application factors such as:

  • Speed of operation
  • Differential pressure
  • Lubricating properties of liquid being pumped
  • Product viscosity

If these factors trend toward a difficult application (high speed, high pressure, non-lubricating) then “Front Face” or “Hot” clearance rotors are recommended. Wine clearance rotors (same operating parameters as listed for standard rotors) provide additional clearance between the rotor hub and the cover bore area only. They give extra protection against contact in this area.

“FF” (Front Face) clearance rotors provide additional clearance in the front face area only. They are recommended for use with liquid temperature between 180°F (82°C) to 200°F (93°C). They give better pumping efficiency (less slip) than “Hot” clearance rotors when used with low viscosity liquids. Do not use “FF”, however, rotors if they will be subjected to temperature shock (extreme, rapid temperature change.)

“Hot” clearance rotors are recommended for use with liquid temperatures between 180°F (82°C) to 300°F (149°C). They provide additional clearance in the front face area plus rotor to body areas. Because of this additional clearance there is more slip (inefficiency) with low viscosity liquids, which the pump must overcome with higher operating speed (rpm.) VHP (viscous horsepower) is slightly lower when using hot clearance rotors. Hot clearance rotors are also used when the product viscosity is above 200 CPS.

“316SS” clearance rotors are used with rotors made from 316 stainless steel material (in place of standard non-galling alloy 88) and recommended for use at temperatures up to 200°F (93°C). These rotors provide additional clearance all around (more than Hot clearance alloy 88 rotors) to insure no running contact between the 316 SS rotors and other 316 SS pump components. Because of this additional clearance there is more slip (inefficiency) with low viscosity liquids, which the pump must overcome with higher operating speed (rpm). VHP (viscous horsepower) is slightly lower when using “316SS” clearance rotors.

Some models in some series have a “316SS Hot” clearance rotor option for temperature above 200°F (93°C).

NOTE: Consult Holland Technical Services for applications near 300°F or above 200°F with 316 SS rotors.

“Extra Hot” clearance rotors are recommended for use with products such as chocolate, which tend to “plate out” and build up on rotor surfaces. These rotors require special selection procedures. Contact SPX FLOW Technical Services for assistance.

 

The model U3 pump uses slightly different nomenclature and clearance options:

“Low Viscosity” rotors are similar to the U1 & U2 “standard” clearance rotors in that they may be used with liquid temperatures up to 180°F (82°C). Between 160° (71°C) and 200°F (93°C), other application factors must be considered such as; speed of operation, differential pressure, lubricating properties of liquid being pumped, and product viscosity. If these factors trend toward a difficult application (high speed, high pressure, non-lubricating) then “Standard” clearance rotors are recommended.

“Standard” clearance rotors are recommended for use with liquid temperatures between -40°F (-40°C) and 300°F (149°C). They provide additional clearance in the front face area plus rotor to body areas. Because of this additional clearance there is more slip (inefficiency) with low viscosity liquids, which the pump must overcome with higher operating speed (rpm.) VHP (viscous horsepower) is slightly lower when using standard clearance rotors. Standard clearance rotors are also used when the product viscosity is above 200 CPS.

There are many factors to consider when sizing a PD pump for a specific application. The different rotor clearance options available on the Waukesha Universal series positive displacement pumps allow our Holland Sales Engineers to size a pump that will maximize pump performance. Contact a Holland Sales Engineer today with your next sanitary pump application.

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