open and closed centre hydrualics

nick...

Member
Arable Farmer
Location
south norfolk
Open centre system,oil is being continually pumped round the system and its diverted to where needed.the closed centre system the oil is trapped under pressure till needed.this basically stoppes oil getting too hot and saves pump continually pumping.expect somone will give a better description
Nick...
 

NZ Tech

Member
BASIS
Location
Sth Africa
Open centre the pressure is always at the valve spool(meaning alway pressure in the system). Closed the system will go to a standby pressure(meaning an idle, and then stroke up when needed).
 

DrDunc

Member
Livestock Farmer
Location
Dunsyre
Open centre the pressure is always at the valve spool(meaning alway pressure in the system). Closed the system will go to a standby pressure(meaning an idle, and then stroke up when needed).
Actually that's not quite correct.

Open centre hydraulics have a pump that outputs a constant flow at a given speed. The output is usually measured in terms of cc/rev.

The oil circulates around a circuit, hence any valves in the loop need to be "open" when in the neutral position.

When a valve is operated to divert oil, the pressure then rises to meet the resistance.



Closed centre hydraulics operate by supplying full pressure to all the valves in the system, but vary the flow rate. If there is no demand, the pump does not circulate oil around and back to tank. This reduces oil temperature, pump wear, and fuel consumption.

In closed centre hydraulics there is a load sensing pipe back to the pump. When the valve is opened to divert oil, the pressure in the circuit drops. The pressure drop causes the pump to increase output flow, meeting demand.
 

NZ Tech

Member
BASIS
Location
Sth Africa
Actually that's not quite correct.

Open centre hydraulics have a pump that outputs a constant flow at a given speed. The output is usually measured in terms of cc/rev.

The oil circulates around a circuit, hence any valves in the loop need to be "open" when in the neutral position.

When a valve is operated to divert oil, the pressure then rises to meet the resistance.



Closed centre hydraulics operate by supplying full pressure to all the valves in the system, but vary the flow rate. If there is no demand, the pump does not circulate oil around and back to tank. This reduces oil temperature, pump wear, and fuel consumption.

In closed centre hydraulics there is a load sensing pipe back to the pump. When the valve is opened to divert oil, the pressure in the circuit drops. The pressure drop causes the pump to increase output flow, meeting demand.


It was a very simple way of explaining the difference. To get the point across.
 

Mr Happy

Member
Location
Norwich
I think you want to know the difference between open centre and load sensing hydraulics, closed centre hydraulics is found on wheel drive applications.
 

Mursal

Member
Open centre cheap system simple pump, can be slow to react when the operator need response. Operator diverts oil from returning back to the tank, out to a ram/motor, takes a little time for max pressure to build up from zero.
Closed centre expensive system with variable output pump/pumps, but the operator will always have standby pressure in the system, so the response should be quicker. This video might help, to be honest I couldn't view it, due to slow broadband.This is an open circuit system.
......................
 
Last edited:

Cowabunga

Member
Location
Ceredigion,Wales
Open centre the pressure is always at the valve spool(meaning alway pressure in the system). Closed the system will go to a standby pressure(meaning an idle, and then stroke up when needed).

The fact is exactly the opposite of what you say there. There is no pressure at all, but always flow in an open centre circuit. The pump is always pumping a fixed volume of oil around the circuit per revolution of the engine and pump, straight back into the sump unless diverted by a valve for work. The oil might be diverted to a dead-end, like a ram, but has to be further diverted when the dead-end is full, because the pump continues to pump no matter what. Pressure only builds as a resistance to the flow of oil is met. When the oil travels through open centre valves and returns to sump without doing any work, the pressure in the system is near enough zero. Oil always flows unless it is in a non functioning section of the system, like a stationary ram.


The main difference with a closed centre system is that the pump stops pumping when the oil comes to an absolute dead end, like an idle spool valve…………think of a water main supplying a closed tap if it makes it easier to understand. In a CC system, when the pump stops due to a dead-end, like a closed centre spool valve, the rather complex pump stops supplying flow and the pressure drops to a stand-by level much lower than the maximum available pressure.
 
Last edited:

Roy Stokes

Member
Location
East Shropshire
Actually that's not quite correct.

Open centre hydraulics have a pump that outputs a constant flow at a given speed. The output is usually measured in terms of cc/rev.

The oil circulates around a circuit, hence any valves in the loop need to be "open" when in the neutral position.

When a valve is operated to divert oil, the pressure then rises to meet the resistance.



Closed centre hydraulics operate by supplying full pressure to all the valves in the system, but vary the flow rate. If there is no demand, the pump does not circulate oil around and back to tank. This reduces oil temperature, pump wear, and fuel consumption.

In closed centre hydraulics there is a load sensing pipe back to the pump. When the valve is opened to divert oil, the pressure in the circuit drops. The pressure drop causes the pump to increase output flow, meeting demand.

There is a difference in closed center ( up to 50 series John Deere's were closed center) and closed center load sensing, the original closed center works without the load sensing line and pumps on pressure drop anywhere in the system whereas the CCLS pumps on demand sensed by the load sensing line to give power beyond capabilities
 

Cowabunga

Member
Location
Ceredigion,Wales
There is a difference in closed center ( up to 50 series John Deere's were closed center) and closed center load sensing, the original closed center works without the load sensing line and pumps on pressure drop anywhere in the system whereas the CCLS pumps on demand sensed by the load sensing line to give power beyond capabilities

While there are still lots working, it should be noted that production of tractors with the JD radial piston pumps, with their very simple and limited closed centre system, ceased over 20 years ago.
 
what is the difference of these two systems thank in advance for your reply
In technical terms, it's all been very neatly explained in the posts above. In practical terms either system is pitched at different ends of the market. CC is invariably CCLS these days - it's found on the higher output systems where it can justify its cost premium and additional complexity by being (a) more fuel efficient (b) increasing the service intervals on oil/filters and other components (c) delivering better performance right across the rev range of the engine driving it.

On the other hand Open Centre generally is at the lower to middle output systems, with less demanding and complex hydraulic systems - hence a lot cheaper. Downside is pumps will wear out faster and the oil gets more punishment.

A good analogy is CCLS is the like a 'vario' transmission tractor, it only works as hard as it has to and the engine can be throttled back where necessary. An OC system is like a fixed ratio gearbox - to get the high output the engine needs to be revving.
 

DrDunc

Member
Livestock Farmer
Location
Dunsyre
No. But by what i can see is the op wants a simple explanation. Maybe not something he cant remember. Or something ripped from a 101 of hydraulics text book.


Whatever the OP wanted, it certainly wasn't information that is completely opposite to the facts!

I note once more that when the accuracy of your posts is questioned, your go to response is still an attempt to insult. In this instance to suggest every post with factually accurate information is some form of plagiarism.

I would respectfully request that you desist from posting inflammatory and insulting comments when anybody on here questions your views, or corrects the factually inaccurate nonsense you often post.
 

Cowabunga

Member
Location
Ceredigion,Wales
No. But by what i can see is the op wants a simple explanation. Maybe not something he cant remember. Or something ripped from a 101 of hydraulics text book.
Presumably he wants to know the truth, not complete bulls**t that would make him a laughing stock if repeated to people that have a modicum of knowledge. Your information is completely false and misleading, full stop.
 

John 1594

Member
Location
Cambridgeshire
The old jd system has a few limitations..I noticed when using a 2650 to tip a fully loaded trailer that it simply couldnt get it off the stops without jerking the clutch and trying to bounce the trailer a bit. Pump isnt worn out..unless they only last 5000hrs. Contrast this to the mf 3060 that tipped it with ease


Could it be that it the cc system is faced with a heavy load as a dead start it cant get the oil flow moving to allow the pump to increaae output..where as the oc system just gradually increased the pressure until the trailer moved

Plus point of the mf..at least you can steer it while the trailer is going up
 

John 1594

Member
Location
Cambridgeshire
Plenty..it just didnt have the guts to get it off the stops

Ok a gull trailer is hard to tip due to the rams being quite far back and almost horizontal when its down..but other tractora manage it ok

Quantity of oil was irrelevant..what I think happened was it just dead headed the system and sent the pump to idle..where the mf kept the pressure on till the trailer started to move
 

NZ Tech

Member
BASIS
Location
Sth Africa
Whatever the OP wanted, it certainly wasn't information that is completely opposite to the facts!

I note once more that when the accuracy of your posts is questioned, your go to response is still an attempt to insult. In this instance to suggest every post with factually accurate information is some form of plagiarism.

I would respectfully request that you desist from posting inflammatory and insulting comments when anybody on here questions your views, or corrects the factually inaccurate nonsense you often post.

Are you kidding me.
 

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