It’s all in the connections

This step-by-step guide will make your next pump installation easy

by John Lambert

They are everywhere.

We each have one, the cars we drive have at least three and, according to the Guinness Book of Records, after the electric motor they are the most used item in our industrial world. They are pumps. They come in all shapes, sizes and price ranges, and supply the lifeblood to our industries.

Try to imagine how many pumps are used in the chemical industry alone. Other large users of pumps are steel mills, paper mills and mines. A typical paper mill might have more than 600 pumps.

Not surprisingly, the industry that manufactures and supplies pumps is large and complex. It takes plenty of highly skilled people to design, manufacture, market and technically support the pumps that suppliers sell. The cost of all this is in the pump’s purchase price. If you were involved in acquiring a pump recently, you know that they are not inexpensive. However, the cost of maintaining a pump can be much higher than its original pricetag.

The greatest influence on the amount of maintenance required for a new pump is not the amount or type of pumping it is doing but rather how it is installed. In fact, it comes right down to how you connect the pump and to what you connect it.

If you think about it, a pump that is sized properly and made out of the correct material for the job should pump forever. The majority of pump repairs aren’t made because of a worn-out impeller. Instead, it’s because of a leaking seal. Pump bearings do fail, mainly due to misalignment and contamination, but the pump is usually pulled because of a seal leak. (And at that point, many of you probably think you might overhaul the pump as well, while you have it out). This is why the bearings get replaced. This is obvious overmaintenance.

The mounting connection
Pumps are great workhorses, but it’s what you connect them to that creates problems. The first connection is to the base. You can either make your own or buy a base designed for the pump. The latter usually will be very well-made and likely very expensive, but there is no guarantee that it won’t have soft foot, which has a huge influence on premature pump failure.

If we bolt a base to an inadequate foundation, it will take on the same characteristic as the foundation. If the foundation is not flat, the base won’t be flat. A twisted base can create internal misalignment between the bearings of a pump or motor. It can also deflect the shaft, which will influence the alignment. The base and foundation are critical to long service life, as they are the cornerstone of your pumping unit. They both must be flat and free of defects.

The piping connection
Piping is the next connection. If you have spent money on a new pump base, there will probably not be much left over for buying a flexible joint to fit between the pump and the pipework. However, doing so is a great investment. One benefit is that if you use a flexible joint, you will have to support the pipe. Nobody leaves a flexible joint supporting a pipe, but they will allow a pump alone to support a pipe. Pumps aren’t designed to handle this kind of load.

Piping can be very heavy, especially when it is full of product. Unsupported, it has a detrimental effect on the longevity of the pump.

Another benefit of flexible joints is that they eliminate pipe strain. Many of us have seen instruments such as pry bars, wrecking bars and come-alongs used to move pipes into position so they can be bolted to the pump. After the pipe is released, the strain has a significant impact on pump life. If you don’t think so, try placing a magnetic-base dial indicator under the pump shaft before you release the come-along. You may be surprised at what you see, as it will prove there is strain on the pump.

The coupling connection
The coupling is the next connection. Before we even attempt to connect it, we must be sure there is no soft foot or pipe strain, because both of these can cause shaft deflection. If the shaft deflects, we won’t be able to achieve the results we need.

The recommended tolerance used should be that of the pump manufacturer, not the coupling manufacturer. These tolerances are designed so you get the optimum efficiency out of the pump.

While some skilled tradespeople talk about “coupling alignment,” what they actually mean is “shaft alignment.” It’s the center line of the shaft that we are trying to align, not the outside edge of the coupling.

Unfortunately, this is a mistake many people still make. If the coupling and shaft are not concentric and you align the coupling edges, you will never get the shafts aligned. You must check the runout of the coupling even if you are doing shaft-to-shaft alignment. This will determine if the coupling is out of alignment and also if the shaft is bent (it does happen).

The coupling’s job is to transmit the power from one shaft to the other, as well as compensate for a small amount of misalignment. That’s because the chances of getting the shaft center lines collinear (in a straight line) at operating conditions range between slim and none.

There are a wide variety of couplings to choose from, and the chances that the style installed is the same as what you keep on the shelf also are between slim and none. But the coupling is a very important part of the machine unit, so choose it wisely. You can use mechanical styles such as gear, chain or grid. Perhaps a metal membrane (disc) type or an elastomer style will be effective for you.

Your choice should be influenced by how much horsepower, torque and speed the coupling can handle, not on how much misalignment it can tolerate. Coupling manufacturers usually state the tolerances of fatigue limits of couplings. This has nothing to do with the tolerance of the equipment it is driving.

Just because a coupling has a high tolerance does not mean it is the best coupling for your application. For example, you may have a high-speed pump, complete with a balanced impeller and shaft. You wouldn’t want to install a heavy, unbalanced cast-iron coupling just because it had a rubber tire for an insert.

Shaft alignment
Shaft alignment is the easy part of the job, as long as you have the right tools. The right tools are not straight edges, as they only get you a close alignment, but not close enough. The right tools do not include homemade bracket sets that have excessive bar sag, nor are they old, loose, mag-based dial indicators.

The proper tool should be either a laser system or a dial system designed for shaft alignment. You wouldn’t do pipe work without a pipe wrench, and it should be the same for alignment work. It’s the price you pay to do the job right the first time.

If you have done all the other preparation work, you’ll find alignment is a simple process.

Conclusion
You are now connected, except for the power, but as long as you don’t have an electrician who decides to move the motor closer to his cable, you should be all right. Start the pump and see how it runs. It’s best to use a vibration meter to check it. Use a simple little instrument that is similar to a digital vernier gauge. Instead of measuring the size of an object, this measures the movement.

Follow these techniques, and your pump will be up and running and within specifications. The only other thing that could affect the pump is dynamic movement, but that will have to be the topic for a future article.

John Lambert is president of Benchmark Maintenance Services Inc., an Ontario firm specializing in proactive maintenance products and training. To learn more, e-mail info@withinspec.com, call 800-598-1117 or visit www.withinspec.com.

This article appeared in the June/July 2003 issue of MRO Today magazine. Copyright 2003.

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