When we install a pump, we have to notice the pump rotation and ensure to run the pump is in the right direction. The wrong direction will affect regular use, even damaged pumps. But some pumps can rotate reverse and reduce trouble, so are rotary lobe pumps reversible?
Yes, rotary lobe pumps can be reversed continuously. It has a symmetric and valveless structure, so we can quickly reverse a lobe pump by changing the direction of the engine’s rotation.
Next, we will explain some topics related to this question, contains what causes the reverse, how to reverse a lobe pump, which pumps can reverse, and what happens when a centrifugal pump rotates reverse.
How to reverse a rotary lobe pump?
It is simple. Rotary lobe pumps are valveless; you do not need to alter anything but reverse the engine. But please ensure the pipe is available for reverse.
Reasons why reverse a pump
The most common reason is a power failure; the engine rotates reverse. It is essential to run the engine in the right direction for your system. Please check the manual of the machines or contact the manufacturers.
Another common reason is the check valve is not work or uninstall. When a pump stop, the liquid may back down and cause the pump to reverse. A check valve is necessary to protect the pump from backflow, and it also can keep fluid in the pump and prevent the dry run. For more details of dry run, please read this article (Can rotary lobe pumps run dry?).
And the last reason is operational need. Some specific tasks require pumps to run in both rotations, like loading and unloading tanks. For those systems, a reversible pump is necessary. So which pumps can reverse?
Which pumps can reverse?
Most PD pumps (positive displacement pumps) can. But there are some exceptions, like gear pumps with built-in relief valves, which cannot reverse before modifying the valve.
Most centrifugal pumps won’t be allowed to reverse, because of the built-in valves, so they cannot run in reverse. Some centrifugal pumps will still work but can’t run as usual. Then next, we will explain what happens when a centrifugal pump rotates reverse.
What happens when a centrifugal pump rotates reverse?
In some centrifugal pumps, the impellers are threaded, so they will unthread and be damaged when run in reverse.
For the other centrifugal pumps, when run in reverse, it still works and won’t damage, but the efficiency will be significantly reduced. This is a demo video from Grundfos showing what will happen if the direction of pump rotation is reversed.
FAQs
Q: How do I check pump rotation?
A: Rotation is indicated on the head of the pump; you’ll see an arrow going counter-clockwise.
Q: Can a motor be reversed? And how to reverse it?
A: Yes, motors can run in both directions by switching the wire connections.
Conclusion
Rotary lobe pumps can run in reverse with no harm and without impacting performance. It is an excellent option for those systems that require a pump to run in both flow directions. Other pumps are not that good; they might be damaged or perform poorly. It is necessary to confirm whether your pump can reverse with the manufacturer before installing it.
