There have been numerous questions asking the differences of impellers and casings when there is an “H” or “G” following the pump size. For example:

  • 3×4-10 and 3×4-10H
  • 3×4-8 and  3×4-8G
  • 4×6-10, 4×6-10H and 4×6-10G
  • 8×10-15 and 8×10-15G

What do these letters indicate? The letters specifically by themselves don’t explain anything to you, except that the style is different.

Take the previous example of the 3×4-10 and the 3×4-10H. Casings have a 3 inch discharge port and both have a 4 inch suction port. The impellers are both 10 inches in diameter. Without getting into the “nitty-gritty” foil design equations, the difference is the impeller vane profile. Best shown visually below:

impeller_compair3x4-10Please note, the casings are also different between the 3×4-10 and 3×4-10H to fit these profiles. You cannot interchange a 3×4-10 impeller into a 3×4-10H casing and vice-versa.

As you can see some of the differences for each vane:

  • Entry angle of the fluid (angle of attack)
    • Also depends on RPM and volumetric flow rate
  • Camber (curvature)
  • Chord line (tip to tail line)
  • Leading and trailing edges
  • Max foil thickness
  • Surface geometries of the high and low pressure sides
  • Vane height or capacity of each vane

All these attributes affect the performance of the pump in just about all aspects: capacity, head, NPSHr, required horsepower and efficiency. The curves for the 3×4-10 and the 3×4-10H are shown below. Take notice of all the performance aspects and imagine how the impeller profile differences affect the performance. The most obvious being the vane height and the difference in the pump capacity.


3×4-10 Pump Curve


3×4-10H Pump Curve

There are differences in “H” and “G” versions of pumps and are very important to take notice of when ordering. Any further questions please feel free to contact your local distributor if you have any further questions regarding impeller style differences.