Pumping World News Blog

Is Your Trailer Pump Impeller Installed Correctly?

Posted by Elizabeth Kaiser on Wed, Feb 08, 2012 @ 08:02 AM

By Travis Stroh, SRS Crisafulli Applications Specialist

Over the years trailer pumps get modified, parts get replaced and sometimes one of those parts is a new impeller. Here are some tips for inspection, removal and installation to make sure your impeller gets installed correctly.

To avoid expensive repairs and downtime, take a minute and verify that your impeller is rotating in the right direction. Problems you might see if your impeller is installed backwards:

  • Pump does not deliver water
  • Insufficient flow delivered
  • Insufficient pressure developed
  • Pump requires excessive power

backwards impeller resized 600An impeller installed backwards

The impeller in this picture was installed backwards. When looking at the impeller from the back of the pump, make sure the blades are backhanding the water and not cupping it.

Operation of the pump with the impeller rotating in the wrong direction will result in greatly reduced performance and increased wear.  Check the impeller assembly to make sure the vanes curve backward from the hub out in direction of rotation as shown in the figure below.  If incorrect, the impeller is installed backwards and must be reversed on the shaft. 

impeller drawing resized 600

Warning: Before performing maintenance, disconnect the power source and take any necessary precautions to assure that power to the pump will not be engaged while work is being done.

Note:  Ridding the shaft of paint with paint remover, cleaning and sanding the shaft with an emery cloth, and oiling the shaft may assist in impeller removal and installation.


  1. Remove the nuts from the bolts on the casing back door (6-18 nuts depending on pump size).
  2. If water-lubricated bearings are used, no loosening of set screws on the bearing eccentric collar is necessary prior to back door removal.  This type of bearing is assembled to slide over the shaft.  However, if sealed bearings are used, loosening of the set screws on the bearing eccentric collar is necessary to allow the bearing to slide over the shaft.  (See note below.)
  3. Remove the casing back door.  Mark the casing and casing back door so reassembly will be to the same bolt pattern.  Tapping the back door around the bolts may be necessary for removal due to adhesive glue or gasket holding the back door to the casing.
  4. Loosen the impeller hub set screws.
  5. Slide the impeller off of the shaft.
  6. Remove key stock from shaft and inspect for wear or damage.


  1. Clean the impeller hub and shaft to assure both surfaces are clean, smooth, and free of paint, burrs, sharp gouges, etc.
  2. Place key stock in the shaft keyway
  3. Apply anti-seize lubricant to shaft and key.
  4. Slide impeller onto the shaft and over the keyway.  Check the impeller for correct vane curvature as discussed above.
  5. Center the impeller in the volute. The impeller is set equally spaced between front and back cases of pump to allow it to spin free.  The tolerance between inside the pump case and impeller is generally about 1/8".
  6. Block the impeller to prevent rotation.
  7. Tighten the impeller set screws which hold the impeller to the shaft.  Do not lubricate the set screws.
  8. Slide the back door and bearing over the shaft.  Align the back door to the proper bolt holes and install two or three nuts.  Turn the shaft and check the
  9. If the impeller is rubbing the casing, remove back door, adjust the impeller, reassemble and recheck for proper clearances.
  10. Once the impeller is centered properly, slide the back door a few inches away from the casing and spread gasket cement around the back door where contact is made with the casing.  This will prevent leakage from the pump and will improve overall performance.
  11. Bolt the back door to the casing.
  12. If water lubricated bearings are used, no set screw adjustment is needed.  Tighten the eccentric lock collar to the bearing by use of a punch and then tightened to the shaft by set screws.
  13. Remove any impeller blocking devices.  Turn the shaft to check alignment; shaft should turn freely by hand.  If binding of the shaft occurs, adjust bearings and recheck alignment.


Watch SRS Crisafulli's how to video How to Install Discharge Tubing.

Watch SRS Crisafulli's Trailer Pump video.

Watch SRS Crisafulli's Slurry Trailer Pump video.

Watch SRS Crisafulli's pump slideshow.

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Topics: crisafulli, srs crisafulli, Product Information, agriculture, pumps and power units, Replacement Part, Spare Parts

Trailer Pump Operation and Performance (Part 1 of 3)

Posted by Elizabeth Kaiser on Thu, Dec 15, 2011 @ 10:12 AM

By Isaiah Helm, SRS Crisafulli Applications Engineer

Crisafulli pumps are naturally robust, and capable of handling a variety of unscreened water-borne debris and slurry mixtures.  The following table lists the maximum sizes of spherical solids each model can pass without clogging.


Impeller (in)

Solid Size (in)
















Occasionally the pump's speed will have to be changed to get more or less flow and pressure.  A small change in speed can result in a large change in power required.  Increasing the speed by a factor of 2 increases the horsepower requirement by a factor of 8 (2 cubed).  This can be estimated with the Affinity Laws below, taken from the Cameron Hydraulic Data Book (Flowserve Corporation):

Crisafulli Pump Curve 

H = Heads in feet

Q = Capacities in gallons per minute

S = Speeds in revolutions per minute

BHP = Brake Horsepower

Subscript 1 is for original design conditions.

Subscript 2 is for new design conditions.

Note: The Affinity Laws lose accuracy with larger speed variations.  Consult with the factory when considering speed changes of more than 20%.

A pump's impeller may need to be changed in order to get more flow and pressure or to require less horsepower with resulting less flow and pressure.  SRS Crisafulli offers up to three different impeller styles for each pump size.  They are referred to as Regular Lift, Intermediate Lift, and High Lift impellers.  The difference is their diameter.  For a change from a 16 inch Regular Lift impeller to a 21 inch High Lift impeller, the flow would increase by a factor of 1.3, the pressure by a factor of 1.7, and the power by a factor of 2.2.  This effectively doubles the horsepower requirements without changing the pump speed.

While Affinity Laws exist for diameter changes, they are only accurate for small changes of 5%-10%.  The best way to understand this relationship is to view the pump performance curves for the various impellers offered by SRS Crisafulli.


Request a consultation with one of our Applications Engineers/Specialists.

Watch a Crisafulli Trailer Pump Video.

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Topics: crisafulli, srs crisafulli, Product Information, agriculture, slurry trailer pumps, Equipment Dealers, pumps and power units, mining, Replacement Part

SRS Crisafulli Product Spotlight: Slurry Trailer Pump

Posted by Elizabeth Kaiser on Mon, Jul 25, 2011 @ 15:07 PM

slurry pumpToday's SRS Crisafulli Slurry Pumps are the latest versions of a 40-year tradition - i.e., building highly efficient, rugged long lasting slurry pumps for use in agricultural waste pits.

SRS Crisafulli Slurry Pumps also work well for refineries, municipalities and geothermal plants.

Discover the versatility and productivity of SRS Crisafulli Slurry Pumps when used to remove viscous wastes from your ponds and lagoons.

See Video of Slurry Trailer Pump in action here.


Topics: agriculture, Announcements, Press Release, slurry trailer pumps