Backlash is unintended movement between two coupled shafts that can cause mechanical problems and impede the alignment process. It is a common problem during pump and motor alignments and can occur between any two mated components.
Backlash happens when two coupled shafts are not moving in perfect sync with each other. When one shaft rotates, there’s sometimes a slight delay before the other shaft moves, too. It can also create unintended angular motion between two coupled shafts. Loose couplings or pre-existing alignment issues can cause backlash.
It’s hard to completely avoid backlash in pump alignment. In very small degrees, backlash is harmless. Technicians measure backlash by calculating the angle at which a shaft can move in any direction without causing the rest of the mechanical system to move along with it. When that degree exceeds the limit (typically two degrees or more), then you have too much backlash and need to correct it.
Controlling Backlash
Backlash can make it almost impossible to get repeatable readings during the alignment process. Today’s leading laser alignment tools – like the RotAlign Touch – use software to automatically correct alignment measurements and account for backlash. But it’s still a good idea to follow common-sense procedures that control backlash.
How do you control backlash? In a nutshell, let gravity rotate the shafts as much as possible.
During the backlash pump alignment process, rotate the moveable half of your shaft coupling first, and then let gravity move the other half into place. This process is called pre-loading. Always rotate the shafts in the direction that the machine normally rotates. This minimizes the distance and angle between the two halves of the shaft coupling. Following these simple practices can protect you from backlash in pump alignment.
How to Correct Pump Misalignment
Even with the best precautions, pump misalignment can happen. The best way to correct misalignment is by using a single laser alignment tool.
Laser alignment systems use laser beams to measure the degree of alignment between two components. Since lasers create perfectly straight, sag-free lines, they’re the ideal way to check whether two shafts are collinear. You can use a laser alignment tool to measure pump misalignment.
Older tools, like dial indicators, can also check for pump alignment. However, those tools are not as precise as laser alignment tools. Today’s assets often require a high level of precision to perform at their best, which means that precision alignment should be a priority for every plant.
Tools like dial indicators and feeler gauges also require more training and mathematical insight to use correctly. If your crew does not have extensive training on these legacy tools, they may not be the best option.
How Do You Align Between Pump and Motor?
It’s best practice to perform backlash pump alignment regularly, since assets can gradually become misaligned over time.
You should align your pump and motor during installation, and you should realign them every time you make repairs. It’s also a good idea to check alignment about once a year.
When you align your pump and motor, start by controlling backlash to avoid the problems associated with backlash in pump alignment. You should also use a laser alignment tool to achieve the precision alignment that can keep your plant running smoothly and prevent unplanned downtime.
How To Check a Pump for Coupling Alignment
Start the alignment process with a thorough inspection of the pump and couplings. Look for excess wear and tear and check for obvious signs of damage on the bolts and couplings.
If you’re using dial indicators, you’ll also need to perform a pre-alignment or “rough” alignment. During this stage, do a basic alignment check and move your pump and motor shafts closer to correct alignment. Otherwise, if you’re using a single laser alignment tool like RotAlign, you can skip this process.
RotAlign’s adaptive alignment technology automatically adjusts for backlash, so that you don’t need to worry about backlash in pump alignment. The device’s touchscreen interface walks users through the whole process, so even inexperienced crews can get precise, accurate measurements right away.
What is the Backlash Clearance of a Gear Pump?
Clearance is another commonly used way to refer to backlash. You may also see it called “play” or “slop.” All of these words refer to the gap or angle that’s created when there’s movement in the gear shaft that doesn’t correspond to movement in the motor shaft.
When left uncorrected, backlash can cause major headaches during the alignment process. Fortunately, the best laser alignment tools, like the RotAlign Touch, come with built-in adaptive technology that can correct for backlash and ensure that you always get precise, accurate, and repeatable readings.