Subject: Pump and driver alignment
In the pump business, alignment means that the centerline of the
pump shaft is aligned with the centerline of the driver shaft. Although this
alignment was always a consideration with packed pumps, it is
critical with sealed pumps, especially if you're using rotating seal
designs where the springs or bellows rotates with the shaft.
A little misalignment at the power end of the pump is a lot of
misalignment at the wet end, and unfortunately that's where the seal
is located in most pump applications.
Misalignment will cause many problems:
- It can cause rotating mechanical seals to move back and forth
axially two times per revolution. The more the seals move the more
opportunity for the lapped faces to open
- Packing could support a misaligned shaft. A mechanical seal
- Misalignment will cause severe shaft or sleeve fretting if you
use spring loaded Teflon® as a secondary seal in your
mechanical seal design.
- The pump bearings can become overloaded.
- The misalignment could be severe enough to cause contact
between stationary and rotating seal components:
- The wear rings can contact.
- The shaft can contact the restriction bushing often found at
the end of the stuffing box.
- The shaft or sleeve can contact the stationery face of the
- The shaft can contact the disaster bushing in an API (American
Petroleum Institute) gland.
- The impeller could contact the volute or back plate.
Regardless of the alignment method you select, you must start with
a pump and driver in good repair. A perfectly aligned piece of junk
is still a piece of junk. You should also check the following:
- A straight shaft that has been dynamically balanced.
- Good wear rings with the proper clearance.
- The correct impeller to volute, or backplate clearance.
- The elimination of "soft foot".
- Eliminate all pipe strain.
- Good bearings installed on a shaft with the proper finish and
- A good mechanical seal set at the proper face load. The closer
the seal is to the pump bearings the better off you are going to
All pump to driver alignments consist of
- You must level the pump and driver. If the pump is aligned
without being level, the oil level will be incorrect and you will
develop bearing problems.
- You then take a series of radial and axial measurements to see
where the pump is located in respect to its driver (motor).
- You make calculations to see how far the driver must be moved
to align the centerline of the pump to the centerline of the
driver. These calculations must consider that the pump and driver
operating temperature will probably be very different than the
ambient temperature when you are taking the readings.
- Most pump manufacturers should be able to supply you with the
proper readings for a hot alignment. They are the only people that
know how their unit expands and contracts with a change in
- You must now shim and move the driver to get the alignment.
Most of the small pump designs are not equipped with "jack bolts"
so this will be the most difficult part of the alignment
procedure. You cannot move the pump because it is connected to the
I see lots of pumps that have never been aligned properly. When
you talk to the people that should be concerned, you get the
- Alignment is not important. I've been working with pumps for
years and we never do it at this facility. And we do not do
dynamic balancing of the rotating assembly either!
- There is no time to do an alignment. Production wants the unit
back on line, and they will not allow me the time to do it
- We purchase good couplings. The coupling manufacturer states
that their coupling can take a reasonable amount of
It turns out that there are at least three methods of getting a
good pump to driver alignment, and a good coupling is not one of
them. The coupling is used to transmit torque to the shaft and
compensate for axial thermal growth, nothing else. You install a good
coupling after you have made the pump to driver alignment, not
instead of making the alignment.
Here are some acceptable methods:
reverse indicator method is an acceptable method, but it does
take a great deal of time. There are plenty of schools that teach
this method if you are interested in learning how to do it:
- Very accurate especially for small diameter flanges
- Not affected by axial float.
- Can be used with a flexible coupling in place.
- You have to rotate both shafts
The laser is the latest method. It is also the most popular. There
are lots of people that can teach you to use the equipment, once you
have made the purchase.
"C or D" frame adapter is probably the easiest method of all
and available from most quality pump manufacturers It solves most of
the problems with thermal expansion.
You use a machined, registered fit to insure the alignment.
shaft to coupling spool method:
- The best method when there are big distances between the shaft
- A simple method to use.
- Most people rotate both shafts
- Use this method if one of the shafts cannot be rotated.
- An excellent method for large shaft diameters (8 inches or
200mm or greater) or if the diameters are equal to, or greater
than the span from the bracket location to the face and rim
location where the readings are to be taken.
- Not too good a method if there is axial float from sleeve or
a choice I would select the C or D frame every time.
- The "C frame" is for inch sizes The "D frame" for metric
- Automotive people use the same concept to align an automobile
transmission to the engine. They call the adapter a "bell
- The concept was originally developed for the marine industry
where it would be impossible to bolt the motor and pump to the
deck of the ship, and then do an alignment. The hull flexes making
any conventional alignment ineffective. The same logic applies to
off shore drilling rigs.
- The adapter does a better job of equalizing the heat transfer
between the pump and the driver. It does not all have to conduct
through the shaft.
- The adapter is available for all quality end suction
centrifugal pumps. Check with your supplier for the availability
of one for your pump
- When given a choice, select a ductile rather than a cast
- Up to about thirty-horse power (22 KW) you hang the motor on
the pump. Above thirty-horse power (22 KW) you hang the pump on
- The adapter solves the problem of "there is no time to do an
- If your motor does not have a "C or D" end bell, one can be
installed when the motor is rewound. Some, but not all explosion
proof motors are available with a C or D frame end bell. Check
with your supplier.
If you do not have a C or D frame adapter you will be involved in
the last three steps of the four-step procedure.
the pump driver.
Once you have made all the measurements, put in the recommended
compensation for thermal expansion, and figured out all the
calculations for how much to move the driver, and in which direction;
now comes the fun part; moving the driver.
You can hit the motor with a big hammer, but small dimensions are
hard to get with this method.
Some people use an adjusting wheel that attaches to shims. This
will give you a very precise movement that is necessary for a proper
Another method is to use an adjusting wheel that slips over the
motor hold down bolts. Many mechanics make there own tools and these
units also work very well for precise motor movement.
How concerned should you be about alignment? You do it on your
automobile when you notice uneven tire wear or the car drifts to one
side of the road when you loosen your grip on the wheel, and have no
problem justifying the cost and time involved. It's the same logic
you use towards the added cost and time spent balancing the tires and
wheels of your car.
We do not always apply the same logic to our very expensive
rotating equipment in the shop, but we should. A mechanical seal
should run trouble free until the carbon sacrificial face has worn
away. When we inspect the seals we remove from leaking pumps we find
that in better than 85% of the cases there is plenty of carbon face
left on the seals. The seals are leaking prematurely and the seal
movement caused by pump to motor misalignment is a major contributing
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