CENTRIFUGAL PUMP MODIFICATION
NOTE: The blue links do not work on this
version of the tutorials. They work only on the CD
If you find that your present centrifugal pump
is not satisfying your application and running as trouble free as
you'd like, and you've checked:
- All of the internal tolerances are correct.
- There is no excessive pipe strain.
- The open impeller has been
adjusted to the volute or backplate
after the pump came up to operating temperature.
- The pump to driver alignment
- The rotating parts were dynamically balanced.
- The wear ring clearance
is within manufacturers specifications.
- The pump is running at the correct speed, in the right
direction, with the correct size impeller.
- There is no evidence of cavitation.
- There is no evidence of corrosion.
Then you may have to purchase a different centrifugal pump, or you
might want to consider modifying the existing pump to get the
performance and reliability you are looking for.
Here are a few modifications and pump upgrades you can
- Modifying the impeller
diameter could get you closer to the best efficiency point. The
affinity laws will predict the
affect the trimming will have on the pump's head, capacity, net
positive suction head required (NPSHR),
and horsepower requirement.
- Converting to an impeller with a different specific
speed number will change the shape of the pump curve, power
consumption and the NPSH required.
- Changing to a heavy duty power end can stop a lot of shaft
deflection, and with some pump manufacturers give you the pilot
diameter you need to install a "C or D" frame
adapter to eliminate pump alignment.
- Converting from a sleeved to a solid, corrosion resistant
shaft will often reduce or stop shaft deflection
problems caused by operating off the best efficiency point
- If you're using
mechanical seals be sure that you are using the type that prevents fretting corrosion. Most original
equipment manufactured (OEM) seals damage shafts, and that is one
of the main reasons they supply a sacrificial sleeve.
- Reducing the overhung shaft length can solve many shaft
deflection problems. You should
be able to get the L3/D4 number
down to less than 60 (2,0 metric) by either
reducing the shaft length or increasing the shaft diameter.
- Changing the wet end to a double volute
configuration will allow the pump to operate in a larger window
without the danger of deflecting the shaft too much.
- You can drill a hole in the end of the stuffing box, at the
top, to increase stuffing box
- Change the flushing or recirculation connection from the top
lantern ring connection to the bottom of the stuffing box to
insure a better fluid flow through the stuffing box. Try to get
close to the seal faces.
- Enlarging the inside diameter of the stuffing box, or going to
an oversize stuffing box can
solve some persistent seal problems.
- Converting the wet end of the pump to a centerline
design might solve some pipe strain problems by compensating for
radial thermal growth.
- Increasing the impeller to cutwater clearance, could stop a
- Installing a sight glass in the bearing case can help you
maintain the correct oil level and prevent overheating problems in
- Replacing the bearing case grease
or lip seals with either labyrinth
or positive face seals for
bearings will keep moisture out of the bearing case and eliminate
a lot of premature bearing failure.
- Converting the radial bearing retention snap
ring to a more rugged holding device will eliminate many of he
problems associated with axial movement of the shaft.
- Converting the packed pump to
a good mechanical seal will reduce power consumption and product
- Converting solid mechanical seals to split
mechanical seals can reduce the time it takes to change seals and
eliminate the need for re-alignment. It will also prevent the need
for other trades to become involved in the process of
disassembling the pump and bringing it to the shop.
For information about my
CD with over 600 Seal & Pump Subjects
Link to Mc Nally home page