Pumps and Meters • Liquid Fill Systems  • What's New at ACI

Why Positive Displacement over Centrifugal?

• If liquid viscosity is too high
• Constant flow is needed over varying differential pressure
• Suction lift or high vapor pressure liquid involved

Common Application Parameters for Positive Displacement Pumps

• Most require some modification to run at higher viscosity
• Reduced speed
• Increased clearances
• Larger ports
• Most require some modification to run at higher temperatures
• Change in materials
• Increased clearances
• Most need to be slowed down with shear sensitive liquids
• All needs overpressure protection

Applying Positive Displacement Pumps

A successful application results when the following are known and understood:

• Characteristics of the liquid pumped
• Piping and system design
• Pump design

Positive Displacement Pump Design

• Individual pump principal and design is important in applying a pump
• Understanding a pump principal and design helps in determining application limits

Positive Displacement Pump Types

Internal Gear Pump

Advantages Disadvantages Only two moving parts Only one shaft to seal Non-Pulsating flow Bi-Directional Low NPSHr Easy to maintain Adjustable end clearance Flexible design offers application customization Larger pumps usually requires requires reduced speeds At least one bearing runs in the product pumped Overhung load on the rotor shaft

External Gear Pump

Advantages Disadvantages High speed High pressure capacity No overhung bearing loads Design accommodates wide variety of materials Sections can be stacked for multiple inlets and outlets Bi-Directional Four bushings in liquid area No solids allowed Fixed end clearances

Lobe Pump

Advantages Disadvantages Pass medium solids No metal-to-metal contact Superior clean-in-place and steam-in-place capabilities Positive suction, nonpulsing with thin liquids discharge Bi-directional Requires timing gears Requires two seals Overhung load on shafts Reduced suction capability

Vane Pump

Advantages Disadvantages Sliding contact of vanes make this pump good for thin liquids Pump normally has one seal chamber Can have two seal chambers Not suitable for high pressures Not good with abrasives Failure mode is catastrophic when vanes fail (unless metal vanes are used)

Progressive Cavity Pumps

Advantages Disadvantages Very good on liquids with solids Can handle dry material Does not require modification for change in viscosity Can be staged for high pressure Cannot run dry Temperature limited to 350 degrees F Requires sealed universal joint Large footprint

Two Screw Pump

Advantages Disadvantages Runs at motor speed High pressure capability Broad flow range Requires timing gears Two to four shaft seals required Will not tolerate solids Expensive

Three Screw Pump

Advantages Disadvantages Runs at motor speed High pressure capability Broad flow range Not well suited for thin liquids Not well suited for non-lubricating liquids Not well suited for abrasives

Hydraulically Actuated Diaphragm Pump

Advantages Disadvantages Only two moving parts Only one shaft to seal Non-Pulsating flow Bi-Directional Low NPSHr Easy to maintain Adjustable end clearance Flexible design offers application customization Larger pumps usually requires reduced speeds At least one bearing runs in the product pumped Overhung load on the rotor shaft