Sources of Piston Pump Case Drain Flow

See also: • Pressure Compensated P...
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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[@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.

[@jamesthornton1867]

thank you for the educational video

[@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?

[@Chogogo717]

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.

[@teis79]

You wouldn't want to lead the drain line through the return filter as you don't want any pressure build up in the drain line as this will increase the case pressure

[@Chogogo717]

@@teis79 every airplane I’ve worked on is designed this way. It helps identify a failing pump before a full on unscheduled rapid kinetic disassembly. We have inspection intervals on the filters and most of them have a differential pressure indicator on the filter housings for a visual cue. As for the restriction that’s some engineering math outside my realm, but it makes sense.

[@James-fs4rn]

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

[@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.

[@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.

[@ankitsonu2511]

Excellent!!! Thanks for information

[@faridmahomed3339]

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

[@workwillfreeyou]

Farid mahomed Yes. It is most useful if you have,a base reference. Know what the case flow is when the pump is new.

[@workwillfreeyou]

It's the entire pump leakage.

[@jcolivera881]

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!

[@lunchboxsessions]

Great to hear!

[@KarasCyborg]

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

[@Eagle2pro]

KarasCyborg there’s no flow swash plate is in netural. There’s may be a little more flow on the case to tank

[@Outdoorswithmike]

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

[@simplyhuge66]

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

[@lunchboxsessions]

Hi Jamie - We're based out of Red Deer, Alberta! Small world, hey? I'd be curious to know where you're teaching. We might be able to help your students with some of our simulations. Shoot me an email: [e-mail] - Ivan, developer of the LBS website and editor of these videos.

[@10yqc]

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

[@EarthMan-hx3xb]

Thank you for this very amazing video.

[@mechspace6855]

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

[@michaelcostello6991]

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

[@jackabubba]

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

[@workwillfreeyou]

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

[@حسنجهانمنش]

Great

[@chrismaciel355]

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

[@lunchboxsessions]

Well not quite. Any liquid that splashes onto the surface inside the tank will quickly entrain air and foam the fluid. Unrestricted in this case means usually a back pressure of no more than 10 or 15 psi. So even a 20 inch fluid level above the return port in the tank won’t amount to that. Ideally below the fluid in the tank but not too low. Thanks for the question.

[@ismaelpinzon2112]

Great

[@arslanahmad7000]

All bestest videos Not discrimination for these....

[@JosePereira-cu5mc]

poxa precisava traduzido em portugues in brazilins

[@juvyslife1010]

Sending love and support to you

[@nhattruong5665]

What software are you using?

[@SAIBALYA]

Nicely explained

[@sarahm.x2136]

well done, thank you

[@akhilskumar4195]

Sir make more videos

[@sunilgoyal7739]

Great learning ❤️

[@sahadagroseeddakache1549]

I like

[@wakeelmohammed2473]

Good job

[@BarnicleBill]

Finally a excellent video to explain how those pumps work