Sources of Piston Pump Case Drain Flow

The case drain line — it's a critical feature of piston pumps, allowing for lubrication of pistons and slipper pads, absorbing exhaust flow from the pump controller, and preventing the swash plate from moving over center. In this video, we take you through the different flow sources that end up in the case drain line, why they happen, and what you should do to maintain your case drain flow and prevent catastrophic failure.

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[jcolivera]

I have been a service tech for about 5 yrs. these videos have been very helpful through out my years to better understand hydraulics to diagnose failures! Thank you!

[Chogogo]

Thanks for putting this together. I’ve got some schematics I have to teach from but they aren’t as detailed and didn’t show how the compensator provided the case flow along with other clearances. I’d like to add in my experience in aircraft maintenance we almost always have filters on the case drain lines. We do scheduled inspections on the filters to find impending pump failures, and the filters also prevent any debris contaminating the rest of the system. Some smaller aircraft may route the case fluid through the return filter, but the larger aircraft will have a separate one. It makes it a lot easier to find the failure point without having to do a metallurgy test to see what other hydraulic components is failing.

[eduardodpoletti]

Nice content! Thank you so much for sharing it. Tip: to check if your piston pump like A4VSO is bad, close your relief valve and measure drain liters, it should be less than 10% of your pump. Example: A4VSO125 piston pump is around 196 liters per minute, drain on pressure should be up to 19 liters.

[BarnicleBill]

Finally a excellent video to explain how those pumps work

[James-fsrn]

very nicely done and informative!
it's clear now why a pump would overheat with a high case drain flow. thank you!

[workwillfreeyou]

Awesome job. I've seen some pumps with pointers on them that would indicate pump plate stroke in degrees. That would fit nicely with your software. I worked at a place that tested pumps by hooking up flow meters to the case drain port.

[jackabubba]

Best explanation ive seen yet. Now to figure out why my system case drain is at 70 deg C...

[simplyhuge]

Excellent series of vids. I teach mobile hydraulics in the apprenticeship system in BC, Canada. What a great resource!

[michaelcostello]

Excellent training. Sincere thanks. Trying to learn that from a poor handout in class impossible.

[EarthMan-hxxb]

Thank you for this very amazing video.

[workwillfreeyou]

In your Video : Closed Loop ( Hydrostatic) Charge pressure. The pump case was seeing up to 300 psi. Was that pump built especially to take that much pressure? Thank you, Jim.

[masperso]

Would you care to explain why the pressure regulator in the pump works in a different way than an external pressure relief valve. Or where do I find it explained on your internet site?

[workwillfreeyou]

Thanks . I believe case flushing will become more common. Maybe a brief video?

[mechspace]

Thank you for uploading very informative data. Can u please upload same videos for radial piston pumps...

[Outdoorswithmike]

How do you fix it if you introduce air into the system by draining the tank

[arslanahmad]

All bestest videos
Not discrimination for these....

[faridmahomed]

is possible to test the condition from the load sense pump. seeng the leakage on case drain line??

[yqc]

In a hydraulic system such as an excavator where is the heat generated? Is it the pump, valves or rams?

[KarasCyborg]

For the Flow in B, how does it return to the tank Reservoir? Or does it just empty the Tank.

[chrismaciel]

I have a question about where the case drain connects to the tank. I assume as you said " unrestricted flow" it should connect to the top of tank. I have just noticed all are hydraulic power packs at the place I work at have the case drains connected to the bottom on the tank. Is this not wrong, or is there a reason for routing it this way? Thank you