The Third Hydraulic Hose: What a Case Drain Does and Why It Matters

If you've gone to hook up a winch, a high-flow drum mulcher, or another hydraulic attachment and found three hoses where your machine only has two, you're not alone. Most skid steers and track loaders have the standard pair of hydraulic hoses - one male, one female - so that third hose raises questions. Here's what it is, what happens if you leave it off, and what to do if your machine doesn't have a place to connect it.

What is the third hose on a hydraulic attachment for?

The third hose is a case drain. Hydraulic motors build up internal pressure that has to relieve somewhere, and the case drain line is where it goes. It's basically a relief drain: it sends hydraulic fluid back to the reservoir tank in case the motor starts to overpressurize.

That's the same job whether the attachment is a winch on a skid steer or a high-flow drum mulcher on a track loader. The standard two hoses run the attachment. The case drain is there to protect the motor while it runs.

Can you run an attachment without hooking up the case drain?

We don't recommend it. If the case drain isn't connected, or your machine doesn't have one, the pressure inside the motor has nowhere to go. It builds up over time, and eventually it can blow out the end seal on the motor.

Because that pressure builds over time, a missing case drain won't necessarily cause trouble the first day you run the attachment. That's what makes it easy to overlook, and it's why it's worth checking before the attachment goes to work.

Will a Raytree drum mulcher run without a case drain line?

No. Our tech confirmed the Raytree drum mulcher will not work on a track loader that doesn't have a third case drain line - running it without one will blow up the motor. If your machine doesn't have a case drain, it needs one added before you run that mulcher.

Do older skid steers have a case drain line?

Generally not. Machines didn't start including a third case drain line until around 2010-2013. An older machine, like one from around 2007-2008, likely won't have one.

If you're running an older skid steer or track loader and looking at an attachment with three hoses, check your machine first. If you only find the standard two hoses, plan on sorting out the case drain before the attachment goes on.

Can a case drain line be added to a machine that doesn't have one?

Yes, it can be added. It's essentially just a hydraulic line run back to your tank. Check with your equipment dealer to see what they recommend for adding one to your specific machine.

The short version

• The third hose on a hydraulic attachment is a case drain. It relieves pressure from the motor back to the tank.
• Running an attachment without it hooked up is not recommended and risks damaging the motor.
• The Raytree drum mulcher will not work without a case drain line.
• Machines built before around 2010-2013 generally don't have one.
• A case drain line can be added. Your equipment dealer can tell you what they recommend for your machine.

If you're not sure whether your machine has a case drain or what a particular attachment needs, ask us before you hook it up.