Open center vs. close center

[jaydee325]

If you want an education in hydraulics, look up John Deere Fundamentals of Service Manuals. Their hydraulics manuals are used as text books in many schools. I still refer to mine from heavy equipment school many years ago!

 

[Dave M7040]

I am trying to increase my hydraulic knowledge in general.


I am looking for something a bit more advanced than that series, or the other comparable lecture series-es I've found on YouTube.

I am wonder how the two compare with multiple section in use, precomppensated vs. post compensated, stuff like flow usage, reaction times for the variable pumps and how they compare for reliability, maintenance, etc.
For systems needing larger flows, can you combine two variables? what if one is on a hot shift and one is a direct drive, what would happen as one drops out?

I realize all this stuff is maybe a bit advanced for a tractor forum, but I figure it is worth a shot.

Acquiring knowledge when it comes to hydraulics can be a big challenge. A big part of the challenge is misinformed people who post stuff on youtube which clearly flies in the face of any hydraulic principles.

Simple gear pumps with fixed displacement are used because they are much cheaper than the variable displacement pumps usually used in closed center systems.

For about $150 you can buy a flow combiner or a flow divider. . The first to combine the output of two pumps. The second to feed two independent circuits. .The combiner will work even if olne pump stops

The same device will do either job.

Shopping

I know this is not the answer you are looking for but there is no easy way outside a formal classroom setting and studying for a year or three.

If you have specific needs then perhaps you can be guided to a solution. The flow and pressure measuring instruments you need, to in effect become a designer of your own system, are very expensive.

As the size of the piece of equipment becomes larger, its operating costs become more significant. Further the equipment is built to run much longer than a typical farm tractor so efficiency in operation becomes important. It becomes worthwhile to incorporate variable displacement pumps and use accumulators to handle short peak flows. The last time I asked PARKER for a quote on an accumulator which would deliver 6 gpm for 30 seconds its cost was that of a new small tractor.

Dave M7040

 

[Groo]

Ok, now for the rant behind all this;

My company usually uses outside experts for this stuff, but far too often outside experts steer us down the wrong path. Now I find myself in the position where I need to know the intracacies of hydraulic valves and systems to protect my employer's interests. I feel I've failed again because I took the adivce of "experts".
Nothing like being told after the fact that a flow rated valve can easily handle all the flow we can toss at it and more, but the main relief on it can't handle close to half of rated flow without causing spikes (some of the duration's I saw make me question using the term "spike") more than 1500 psi over the main relief setting.
This is the crap that makes me want to go back to truck driving.

I'll look into the deere manuals.

 

[Dave M7040]

With a closed center, you normally have a priority valve that keeps oil flow and pressure for things like steering and or brakes. Also some systems have flow combiners and Regen valves that help in high flow situations.

It is the open center systems which need a priority flow control for power steering if the tractor only has one pump.

Here are two priority valves from Chinese tractors, certainly the simplest open center systems you can find

Dave M7040

 

[Dave M7040]

Like with today's newest vehicles, you can be an Ace on a BMW but useless on a Mercedes.

If you are using a specific brand of equipment such as CAT, then ask them to provide hydraulic system training unique to their product.

If you have CAT, Komatsu, Daewoo, John Deere, it is beyond most field people to be competent on all of them.

Dave M7040

 

[chevy791979]

Ok, now for the rant behind all this;

My company usually uses outside experts for this stuff, but far too often outside experts steer us down the wrong path. Now I find myself in the position where I need to know the intracacies of hydraulic valves and systems to protect my employer's interests. I feel I've failed again because I took the adivce of "experts".
Nothing like being told after the fact that a flow rated valve can easily handle all the flow we can toss at it and more, but the main relief on it can't handle close to half of rated flow without causing spikes (some of the duration's I saw make me question using the term "spike") more than 1500 psi over the main relief setting.
This is the crap that makes me want to go back to truck driving.

I'll look into the deere manuals.

That's where the good guy sand the "good" guys show their worth. I work for a Deere construction dealer as a feild tech and I know for fact we don't steer people in the wrong direction. As stated before there are ways to do about anything with any configuration of hydraulics, but without knowing ALL the specs needed it gets tough. And budget. Also power source. (HP)

Acquiring knowledge when it comes to hydraulics can be a big challenge. A big part of the challenge is misinformed people who post stuff on youtube which clearly flies in the face of any hydraulic principles.

Simple gear pumps with fixed displacement are used because they are much cheaper than the variable displacement pumps usually used in closed center systems.

For about $150 you can buy a flow combiner or a flow divider. . The first to combine the output of two pumps. The second to feed two independent circuits. .The combiner will work even if olne pump stops

The same device will do either job.

Shopping

I know this is not the answer you are looking for but there is no easy way outside a formal classroom setting and studying for a year or three.

If you have specific needs then perhaps you can be guided to a solution. The flow and pressure measuring instruments you need, to in effect become a designer of your own system, are very expensive.

As the size of the piece of equipment becomes larger, its operating costs become more significant. Further the equipment is built to run much longer than a typical farm tractor so efficiency in operation becomes important. It becomes worthwhile to incorporate variable displacement pumps and use accumulators to handle short peak flows. The last time I asked PARKER for a quote on an accumulator which would deliver 6 gpm for 30 seconds its cost was that of a new small tractor.

Dave M7040

 

[SilentJ]

Have you ever operated an orbit motor on a JD CC hyd system? Evidently not.

What does that mean ? Sounds like you have a narrow, anecdotal experience youæ±*e using as a blanket statement to disqualify anyone who dares to disagree with you. Please elaborate.

 

[Tx Jim]

What does that mean ? Sounds like you have a narrow, anecdotal experience youæ±*e using as a blanket statement to disqualify anyone who dares to disagree with you. Please elaborate.

Operating orbit motor on CC hyd's such as JD utilized from '60-'92 will cause hyd oil to get hot. Hot hyd oil is very detrimental to hyd system.

 

[SilentJ]

Operating orbit motor on CC hyd's such as JD utilized from '60-'92 will cause hyd oil to get hot. Hot hyd oil is very detrimental to hyd system.

I know all about heat. No one is saying hot oil is good

But I also know picking the right motor for the job is important. Putting the wrong motor on and trying to choke or throttle it attempting to make it “right” will be more of a culprit than the motor, or than the closed center system.

Can you tell me more about the example(s) you are familiar with ?

 

[Tx Jim]

I have operated a Vermeer R23 rake for hours on JD tractors with CC hyd that the operating hoses were too hot to touch for any amount of time. I've also utilized a gravity flow grain box with hyd powered auger that hoses were too hot to disconnect bare handed. That amount of heat can't be good for o-rings & seals. I also was employed by a JD dealer from '66-'87 serving as the dealer service manager for the last 13 years.