Restriction in open and closed center systems

[AKKAMAAN]

How do we use the control valves and restrictions to control cylinder speed in an Open Center, OC, system (Constant Flow, CF) and a Closed Center, CC, system (Constant Pressure, CP)???

 

[jcims]

Yay, i need to bone up on my hydraulics knowledge.

Since you say 'or', I'm assuming it's one or the other, not both.

With that in mind, I'd say you have to put the valve at Y for the open center system, otherwise you could not build a working pressure.

For a closed center system with constant pressure, I'd guess the valve would have to be at X to (not sure what the technical term here would be) block pressure to the cylinder.

It seems that the 'real world' is more complex, because open center systems will always have some pressure just to maintain constant flow through the circuit. So i'd guess that open center does both X and Y in reality. Closed center seems like it could get by with just X...not sure.

Does one have to be plumbed in series and one in parallel if there are multiple cylinders? I would guess open center is series and closed is parallel.

 

[AKKAMAAN]

Yay, i need to bone up on my hydraulics knowledge.

Since you say 'or', I'm assuming it's one or the other, not both.

With that in mind, I'd say you have to put the valve at Y for the open center system, otherwise you could not build a working pressure.

For a closed center system with constant pressure, I'd guess the valve would have to be at X to (not sure what the technical term here would be) block pressure to the cylinder.

It seems that the 'real world' is more complex, because open center systems will always have some pressure just to maintain constant flow through the circuit. So i'd guess that open center does both X and Y in reality. Closed center seems like it could get by with just X...not sure.

Does one have to be plumbed in series and one in parallel if there are multiple cylinders? I would guess open center is series and closed is parallel.

My example just now is only about the "minumum requirement" to make cylinder move....oh yes, a real control valve (spool valve) have some more "features"...:thumbsup:

 

[wdchyd]

Can't you just smell that gray matter cooking out there

 

[AKKAMAAN]

Can't you just smell that gray matter cooking out there

gray matter=brain cells huh??!!:thumbsup::laughing:

 

[Jerry/MT]

How do we use the control valves and restrictions to control cylinder speed in an Open Center, OC, system (Constant Flow, CF) and a Closed Center, CC, system (Constant Pressure, CP)???

X for open center and X or Y for closed center.

 

[AKKAMAAN]

Thats right...we use two different parts of the control valve for controlling the output power of the pump.....for a single action actuator we basically use three different valve function on a spool valve (open center system)
A the open center "valve" function, wide open in neutral
B the flow/pressure supply "valve" function into cylinder, usually fully closed in neutral
C the return flow "valve" function, usually closed in neutral

In an Open Center system we need to restrict the center to build pressure enough to move load....we can say that the valve is a variable pressure valve, that can divert flow....

How much do we have to restrict flow through center before load starts moving??

How much do we have to move the spool before pressure starts building up?? Depends on what?? Can a control valve be over sized??

When does valve B start opening??

Whats the purpose with the check valve C??

 

[mmurphy]

Are we asking still, or pointing out??
Seems to me cylinder will start moving as soon as flow restricts enough to build pressure greater then load as soon as A is closing and B is opening.
Did you mean check valve D instead of C ???
If you did then, check valve C will hold load on cylinder untill pressure from A port closing off is more then load.

 

[AKKAMAAN]

Are we asking still, or pointing out??
Seems to me cylinder will start moving as soon as flow restricts enough to build pressure greater then load as soon as A is closing and B is opening.
Did you mean check valve D instead of C ???
If you did then, check valve C will hold load on cylinder untill pressure from A port closing off is more then load.

sorry about my little error on the check valve....D it should be...D, the "load check valve" will prevent load from dropping when Valve B starts to open.
We build pressure with valve A, and pressure will depend on current flow, viscosity and the orifice opening at A....of course A and B a "synched" to each other...the are on the same spool, but the spool design will determine which of them will open/close first, how long they will be open/closed at the same time during the spool travel.....spool design is much more than just this symbol will tell you....

Depending on pressure built flow can divert into 3 different path's in current diagram....

In a constant flow system we control work port B flow with the pressure, orifice at work port B is usually not a factor for flow control...

 

[mmurphy]

Hey no problem on the error, I make errors anytime I think!
What type of circuit is in mind with this configuration?
I am looking at this at a practical side of who in this forum would use a valve like that? Most valves that are shown here will not have that. I have an idea what got it started.
And the feature of spool opening with some ports changing position before other is a good reminder that there is a difference, depending on what type of valve is needed, or what should be happening.