Subject: Pump and driver alignment 14-3

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:

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:

All pump to driver alignments consist of four parts:

I see lots of pumps that have never been aligned properly. When you talk to the people that should be concerned, you get the following comments:

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:

The 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:

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.

The "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.

The shaft to coupling spool method:

Face and rim method:

Given a choice I would select the C or D frame every time.

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.

Moving 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 alignment

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 factor.

 

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