Do you know what charge pumps are and how they can affect your final drive when they start wearing out? Read on to find out!

Here are a few other blog posts you might find of interest:

• Hydraulic Pump Failure
• Hydraulic Motor Wear and How to Minimize It
• Maintenance is Always Cheaper Than Repairs

What Are Hydraulic Charge Pumps For?

The charge pump is separate from the main pump in your hydraulic system. Charge pumps serve several purposes as part of the hydrostatic transmission for your machine.

For one, they replenish the hydraulic fluid lost due to internal leaking of the pumps and motors on your machine. Keep in mind that some level of internal leakage is inevitable. However, wear of components such as piston shoes and the barrel in the rotator group of your final drive will lead to additional internal losses.

Wear within the rotator group, including components such as the pistons, piston shoes, and manifold, will lead to the type of internal leaking that charge pumps replenish. 

Charge pumps also provide backpressure and lubrication for the rotating groups within your pumps and motors. And in some cases, they may be used for supplying pilot pressures.

When used as part of the hydraulic braking system, charge pumps provide back pressure to help prevent freewheeling and provide the needed pressure to release the brakes. And this is where they have the most significant impact on your track drives -- but we’ll talk about that more in a moment.

What Kind of Pumps Are Used for Charge Pumps?

Most charge pumps will be gear pumps with either fixed or variable displacement. Gear pumps increase pressure by forcing hydraulic fluid between the teeth of rotating gears. These rotating gears operate on different centers. Mobile hydraulic equipment usually has an internal gear meshing with an external gear -- and are known as external gear pumps.

What Happens When a Charge Pump Starts to Fail?

If your machine has a hydraulic braking system, a weak or failing charge pump won’t be able to provide enough back pressure to release the brake. This will also cause your final drives to seem weak and generate some interesting noises as they try to turn against the brake. If this issue is neglected long enough, the braking system can suffer severe damage. Here’s a summary of what to look for:

• High pitched squealing coming from the final drive motors
• Resistance to controls
• Eventually, the machine will no longer move

And by the time your machine won’t move either forward or backward, the damage is most likely irreparable.

Here's an example of what it can sound like when you have a weak charge pump. In this instance, there really wasn't anything wrong with the final drive (yet).

How Do I Check Charge Pump Pressure?

If you need to check the charge pump pressure to see if it’s still functioning as it should, we strongly recommend that you go to the service manual for your machine. If you don’t have a copy, track one down or borrow one. Look for the section dealing with either the gear pump, charge pump, or hydraulic charge pump pressure. There you should find the steps needed to check the pressure and what the pressure should be for your equipment. 

Conclusion

If you've got a final drive that is weak or no longer turning, the problem may be with the charge pump instead of your drive motor. In such cases, you can replace the final drive and still have the same issues. If you suspect the charge pump may be the issue and aren't sure how to check, give us a call at 281-968-4773 or send us an email at sales@texasfinaldrive.com and one of our experts will be happy to talk with you.

Additional Resources:
Fundamentals of Mobile Heavy Equipment (2019) by Owen C. Duffy, Gus Wright, and Scott A. Heard