I've designed a drive system for a project and I've just shelled one of the motors.....

I'll sum it in a nutshell
I'm using a tandem 54 series eaton pump with an "A" pad pump
One pump feeds on single 46 series motor(this circuit is fine)
the other pump feeds into a remote loop flush valve then into a series parallel valve (feroy) the into 2 54 series motors connected via a common shaft. i was running in series mode when the failure occurred,
my question is when in series how does the second motor in line keep filled with oil assumming that the first motor losse some oil... because they run at the same speed assuming a 95% effieciency motor 2 should be starving of a little oil?? yes no maybe I dont think I lost charge pressure because I never lost control via the manual lever....Please help if someone has designed a circuit like this...

My buddy tore it apart in hs hydro shop and found that one of the motors tore the cylinder sleeves out of the piston bore so we a have what we think is a solution...... using check valve and secondary system flow "injection" Looks like no one here wanted to tackle the tough question....hmmmm ????

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Originally posted by tinkster:
My buddy tore it apart in hs hydro shop and found that one of the motors tore the cylinder sleeves out of the piston bore so we a have what we think is a solution...... using check valve and secondary system flow "injection" Looks like no one here wanted to tackle the tough question....hmmmm ????

I suppose everone is a little lazy after tho holidays, and do not want to struggle, with trying to gather more and better info from you....lol....the more complete info about a project.....the faster an answer will be posted....

Can you, please, provide a complete drawing over your system? That can wake up some of the "gurus" here....

Hey Thanks AKKAMAAN for responding I wondered if anyone used this site. I don have a good way to draw the diagram.. other than MSpaint or on paper by hand.. my writing or drawing skills are rudimentary at best...(best described as 6 year old level) I will try this evening to draw something up...

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Looks like no one here wanted to tackle the tough question....hmmmm ????

For those of us that do this for a living, money making jobs take priority over free advice.
More info does get quicker responses.

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"one of the motors tore the cylinder sleeves out of the piston bore

Cavitation won't pull sleeves out. There are two common causes for this, one is over pressure, it will usually happen to more than one sleeve though, the second reason is contaminiation trapped between the piston and sleeve. Look at the faces of the piston shoes to determine which one it was, If the piston shoes face has smeared against the swash plate and left a burr around the edges of the shoe, it was pressure, if there are scratches in the piston shoe faces then it was contamination, also should show up on the face of the valve plate.

Two motors hooked in series and linked by their shafts will have the load distributed inversely proportional to each motors internal leakage.

When motors with the same displacement that have case drains are used in series with their shafts connected together directly or through the load, the downstream motor will cavitate.

Post a picture that will help things greatly.

May not be able to change now, but why are the motors in series? If the shaft provides mechanical parallelling, the motors could be teed together in parallel. You would need motors half size of course to maintain speed.

Or, just remove one motor. The total torque is pressure across displacement of one motor. With two in series, there is twice the displacement, but (ideally) only half the pressure drop across each motor. So there is not a gain in torque with two in series.

As doug said, the load each motor carries in series is proportional to pressure drop across that motor, which is related to motor leakages. If motor 1 has appreciable leakage to case drain, motor 1 provides torque, motor 2 provides no torque and may cavitate.

You are correct my local hydro stat builder and I came to the same conclusion. I am using this combination as a drive train in a large truck for an agricultural use. we have these 2 motors feeding a reduction box which in turn drives the rear axles... the purpose of the the 2 motors is when in parallel mode I have full power necessary to propel the truck, but when in series mode i will also get my speed I need. that's why I am doing it this way. I know that I could probably go expensive and use all new larger displacement components, in addition to one variable displacement motor. but I am trying to do this on somewhat of a budget, to make this affordable but yet effective. and relatively easy to repair.

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As doug said, the load each motor carries in series is proportional to pressure drop across that motor, which is related to motor leakages

Not quite what I said, but I overlooked the case drain anomily in my statement. Two motor hooked in series, with output shafts locked together, that have no external drains will see loads inversely proportional to their internal leakage. Meaning if the first motor had more internal leakage than the second, the second motor would see more load. (This is a common problem on Vertical Double Arbor Edgers in sawmills, where to extend motor life, new motors are swapped in threes. One motor into each series circuits. There are usually three motor groups in series, each group having two motors in parallel, or a similar number depending on edger size. This is a great example of how much simpler VDF motor drives are. Self destructing motor problem gone.)

The above problem would also be true with motors that have case drains if not for the fact that the first motor would be 'over running' the second motor because the flow through the second motor is less.

The series/parallel selctor valve is a common arrangement, especially on sileage truck decks. The difference is they usually have Charlynn 2000, or 4000 series motors with no case drains.

So one solution would be to change motors out to a LSHT design that did not require a case drain.

Another solution would be to have the motors arranged in parallel, with the addition of an isolation/float valve on one motor which would remove the motor from the parrallel connection, but which would also provide boost pressure and allow the motor to freewheel.

This still doesnt explain why one or more piston sleeves pushed or pulled out. Are there cross port reliefs installed. How is that drawing coming along?

Just thought you guys may want to see what my end product was soo here is the raw video file on youtube..
I will give more description of what we did when i get time

http://www.youtube.com/user/Ma...#p/a/u/0/o8zLKzz4RwY