Understanding Pump Rotation

rtexer
Aug 14
3 min read

It may seem like a simple concept, but determining the direction your pump is intended to rotate can be a little confusing sometimes. This post explores how you can have confidence in the intended operation of your motors and pumps.

Why is Pump Rotation Important?

For any Piston Pump, such as Rotary Power "C-range" or Rexroth A2/A7 pumps, the pump is intended to pull fluid in from one direction, and push it out in another. When pump rotation is reversed, the pump will try to pull fluid from upstream and push it backward into the supply line. This often leads to the pump being starved of fluid. In turn, the wear surfaces (pistons, control plate, barrel) heat up significantly, leading to premature pump failure.

Rexroth A2VK Piston Operation — Piston Pump Operation

You can also view this video to understand basic operation of a piston pump:

Clockwise vs. Anti-Clockwise:

First we need to establish standard nomenclature. When talking about pump rotation, the rotation direction is always determined when looking at the pump shaft. The diagram below illustrates this:

Two Scenarios:

You may have a pump in operation and you are wondering in what direction the pump is rotating. We will explore this case in Scenario 1 below.
You may not be sure what rotation direction your pump is set up for. This is most often the case when setting up a new line or finding a pump on a shelf. We will explore this case in Scenario 2 below.

Scenario 1: My pump is currently running. How do I determine which way it's rotating?

The best way to determine your current pump rotation is to look at the electrical motor driving the pump, from the back of the motor. There should be a fan shroud on the back of the motor. Observe the direction the fan is spinning to determine the rotation. You may need to stop the pump and observe the fan direction while the motor is decelerating. You will note that looking at the back of the motor is the same as looking directly at the pump shaft, as mentioned above.

Motor Rotation — From the back of the motor, fan rotation is the same as pump rotation

Scenario 2: How do I determine what direction my pump is set up for?

The best way to determine how your pump is configured is to examine the model code.

For Rexroth A2VK Pumps:

For Rexroth A7VK Pumps:

For Rotary Power C-Range Pumps:

What if I don't have the pump tag? (It's damaged or missing)

The pump rotation can still be determined. How easy that is depends on the manufacturer.

For Rotary Power Pumps, it's as easy as looking for this arrow on the pump casing. If it is pointing at the "CW" - you've got a clockwise oriented pump. If it is pointed at the "ACW" it is oriented Anti-Clockwise (or Counter-Clockwise).

Unfortunately for Rexroth A2 or A7 pumps, the pump would need to be disassembled to determine which direction it is configured to rotate.

In Summary:

In most cases pump rotation can be easily determined. Review the Scenarios above if you're still not sure about your specific situation, or reach out to us at MHR and we can walk you through it!

Finally, MHR maintains stock of most Rotary Power and Rexroth pump models, ready to ship. We also rebuild Rexroth pumps back to like-new condition. Reach out to us if you need a new or spare pump!