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case drain through second aux circuit?

tomv

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May 12, 2017
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2
Location
Minneapolis MN
Many small excavators are equipped with a second (medium pressure) aux circuit which has its own pump. Can this serve as a case drain? I think it depends whether the medium pressure system has its own filter. Can anyone say? I'd be curious to know this for a Cat 312, Doosan DX140, and a Komatsu PC138. (Assume recent versions of each.)

For the curious, here is the backstory: A while ago I floated the idea of leasing an excavator to use with an attachment that required a case drain. All the rental agencies around here were receptive and figured adding the case drain would be in the hundreds of dollars. On closer inspection, that number has gone up to a couple thousand. Seems high, but that's something else.
 

hvy 1ton

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Jul 24, 2006
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Lawrence, KS
Case drains need to be near zero back pressure. Ideally they go directly into the tank. I haven't heard of any excavators with 3 pumps.
 

hvy 1ton

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Admittedly I've only ever messed with case drains on tractors. I don't know the ones i have been around have a filter on the case drain, but they definitely skip the oil cooler. Considering the function of a case drain the filter is definitely a good idea. Had a planter tractor running high hydraulic temps. Someone smarter than me figured out it was bypassing tons off oil which was never making it to the cooler. As a bonus i got to play with a FLIR gun.

Edit: hydraulic motor for the vacuum planter was bypassing
 

f311fr1

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May 11, 2016
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698
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Middle TN
See the case drain running along the boom that I fabricated from schedule 80 seamless 3/4 inch pipe and CAT clamps. ran the hose to an unused return port in the return filter portion of thr hydraulic tank. Bent the pipe with a $80.00 Harbor Freight pipe bender. I fabed this so i can run brush mulchers that require a case drain.
 

lantraxco

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Elsewhen
It depends on the attachment, some things will live with *some* back pressure, some will live with a lot of back pressure, some motors and hammers won't like any form of cooler or filter, they want as hvy 1ton said, near zero back pressure direct return to tank and woe betide you and your wallet over the years if you don't provide it. Case drain filters may be a fine thing in some instances, but with some motors they're more likely to cause a failure due to the piston slipper feet lifting off the swash plate than any good they do catching the odd bit of metal.
 

Tones

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Ubique
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Ex land clearing contractor, part-time retired
If anything lunches that requires a case drain the debries goes through there rather than the return line. I helped plumb a 320 Cat many years ago. The bloke doing the job was going take the return directly to the tank.I insisted the return went to the cooler first. That machine ran cooler hydraulic temps than any others in the fleet with no back pressure problems
 

lantraxco

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If anything lunches that requires a case drain the debries goes through there rather than the return line. I helped plumb a 320 Cat many years ago. The bloke doing the job was going take the return directly to the tank.I insisted the return went to the cooler first. That machine ran cooler hydraulic temps than any others in the fleet with no back pressure problems
I agree, given that the attachment will handle the back pressure, both the cooler and a filter are best, but you can't make a blanket statement it depends on the actual attachments intended to be used on the machine.
 

Tones

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Ex land clearing contractor, part-time retired
The 320 I mentioned was plumbed for a breaker. The only attachments I have come across the requires a case drain are hydraulic motors, ie plate compactors, mulchers and mowers, bucket crushers etc.
 

lantraxco

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The 320 I mentioned was plumbed for a breaker. The only attachments I have come across the requires a case drain are hydraulic motors, ie plate compactors, mulchers and mowers, bucket crushers etc.
Splitting hairs really, while not technically a case drain, many hammers require a large low pressure direct return to tank or they won't function properly due to back pressure on the low side accumulator. YMMV
 

tomv

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May 12, 2017
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Location
Minneapolis MN
Cat machines (and possibly others---idk) have filter for the case drain returns for traction and swing motors, and I assume they had good reason to do this. Still hoping for an answer to the original question. If a secondary aux circuit is truly independent (separate pump, filter, and cooler), then I don't see why this couldn't be used as a case drain, if the spool can made to play. If it uses the same filter and cooler, that's a problem.
 

lantraxco

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My response without knowing the exact details would be a blanket NO, any double acting auxiliary circuit with a spool valve for return oil to flow through would most likely return through the same cooler and return filter as all the other pumps, they share a common tank, even IF there is a separate third or fourth pump there's no reason to design in a separate return to tank circuit. The only way to give a qualified answer would be to know the exact attachment and the exact make model, serial number of machine with exact options installed or not.

On the flip side a roll of hose a bag of zip ties and an unused tank port where you can remove a plug to tap your line in makes it all moot.
 
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