splitter control valve...

[J_J]

Not clear. If you have 10 GPM flowing through the neutral port, there are no restrictions, and when you activate the valve to the extend position the neutral port is blocked and all the fluid goes to the work ports. Starting from neutral again, push the lever just a little. Now some of the flow from the neutral position, is going to the work ports, and the cylinder starts to move, and continue to move as long as you hold the lever until the relief goes off. By feathering the valve, you are only using a small amount of the fluid for the cyl, and the remaining fluid goes back to tank, or beyond. You are going to build up pressure with what ever fluid is going to the cylinders. If this valve had a PB in the circuit, and being utilized, if you were to put a flow meter in the PB line, and activate the cylinder, with a ten gal pump, how much fluid would flow through all circuits if you were feathering. and how much would flow at half lever, and how much would flow at full lever? It doesn't take much pressure or volume to operate a hyd cyl, with no load. Why does the cyl move slow when feathering? Because you are only using a small amount of fluid out of the ten gal available. That is just the way I see it.

Now, don't get all happy and saturate me with copies out of book, etc.

 

[spruce Deere]

JJ,
Maybe I can explain it in a simpler way. Take a 3/4" garden hose connected to a faucet and nothing on the other end (simulates return to tank). Use a nail to put a hole in the hose (simulates work port). Turn on the faucet at a trickle (simulates large valve with small flow). Now begin pinching the hose near the end (simulates actuating the OC valve. How much will you have to pinch off the hose before you begin spraying water from the nail hole in the hose? Try this with the faucet all the way on (simulates mached flow and valve). The water will begin spraying through the nail hole much sooner (less valve actuation to generate power to the work port).

Clear as mud?

Amazingly simple description ....

 

[dcyrilc]

Not clear. If you have 10 GPM flowing through the neutral port, there are no restrictions, and when you activate the valve to the extend position the neutral port is blocked and all the fluid goes to the work ports.

Agreed.

Starting from neutral again, push the lever just a little. Now some of the flow from the neutral position, is going to the work ports, and the cylinder starts to move, and continue to move as long as you hold the lever until the relief goes off. By feathering the valve, you are only using a small amount of the fluid for the cyl, and the remaining fluid goes back to tank, or beyond. You are going to build up pressure with what ever fluid is going to the cylinders.

Only if the port back to the tank or PB creates restriction to the flow. Fluid will take the path of least resistance. Even though the work port is opening, the OC port must create resistance to build pressure to the work port. In our hypithetical 10GPM system, until the OC port is closed enough to restrict the flow below 10GPM no fluid will be diverted.

If this valve had a PB in the circuit, and being utilized, if you were to put a flow meter in the PB line, and activate the cylinder, with a ten gal pump, how much fluid would flow through all circuits if you were feathering. and how much would flow at half lever, and how much would flow at full lever? It doesn't take much pressure or volume to operate a hyd cyl, with no load. Why does the cyl move slow when feathering?

Place a pressure gage before the valve. You will see that pressure is inversely proportional to valve movement. I agree that it doesn't take much pressure to operate with no load, but it does take some. Until the OC port is restricted, there is no pressure beyond restrictions created by the hoses and valves.

Because you are only using a small amount of fluid out of the ten gal available. That is just the way I see it.

Back to my analogy of the garden hose...
The work port (nail hole) is fully open and unrestricted. With the faucet turned on to a trickle (no restriction created by the hose), you will be lucky to get drips out of the hole. As you begin to pinch off the hose and create restriction to the water flowing out the end, water will begin to be divirted out the nail hole. The greater the restriction, the greater the flow and greater the pressure. This is a simulation of an oversized valve.

On a properly designed system, I agree with your thoughts. With a 10GPM pump and valve, if you begin feathering the valve, the flow is immeadiately restricted and fluid begins to be divirted.

Find an old garden hose and play with different flows and watch the result. Bring the grandkids over and you might even find a way to make it fun as well.

 

[J_J]

Understand all that, but if you block off half of the neutral port, say 5 gal flow, where is the other five gal going? Now you have a restriction, and some pressure will start to build up, and the work port is open somewhat. Now, say you block off 7 GPM, and 3 GPM flowing on down stream, then the cyl will operate faster. As you finally block off the flow downstream, all the pump volume is going to the work ports, until the pressure is relieved.

How else can a feather situation work?

 

[dcyrilc]

Understand all that, but if you block off half of the neutral port, say 5 gal flow, where is the other five gal going? Now you have a restriction, and some pressure will start to build up, and the work port is open somewhat. Now, say you block off 7 GPM, and 3 GPM flowing on down stream, then the cyl will operate faster. As you finally block off the flow downstream, all the pump volume is going to the work ports, until the pressure is relieved.

How else can a feather situation work?

You are absolutely correct. I think it was the discussion of a 25GPM valve on the 10GPM flow where we were having confusion. I was trying to help explain why there would be no feather control (or control period) until he got past half way on the valve. Once the valve restricted flow to less than 10GPM through the OC (neutral) port, function is exactly as you describe.

 

[mrcaptainbob]

So, as I understand it so far, I'm holding the (20gpm valve with only 10gpm total available) at a halfway point, the cylinder starts to move. As I would expect it to. Now it comes to bear on the log to be split. Still holding the lever at the halfway point, I would expect it to cease movement at a point convenient for the control valve to prefer returning fluid to the tank. It seems to me it's not able to build much pressure because of the 'leak', if you will, to the tank. The closer I move the valve to shut the flow to the tank (consequently making more pressure/volume available to the cylinder side) the more the cylinder will be able to move. Sounds almost like a balancing act of controlling the pressure (and volume) between the tank and the cylinder. Am I on the right track in understanding?

 

[dcyrilc]

So, as I understand it so far, I'm holding the (20gpm valve with only 10gpm total available) at a halfway point, the cylinder starts to move. As I would expect it to. Now it comes to bear on the log to be split. Still holding the lever at the halfway point, I would expect it to cease movement at a point convenient for the control valve to prefer returning fluid to the tank. It seems to me it's not able to build much pressure because of the 'leak', if you will, to the tank. The closer I move the valve to shut the flow to the tank (consequently making more pressure/volume available to the cylinder side) the more the cylinder will be able to move. Sounds almost like a balancing act of controlling the pressure (and volume) between the tank and the cylinder. Am I on the right track in understanding?

You seem understand to the general idea. On an OC/CF system, is the restriction of flow through the neutral port which creates pressure. The neutral and work ports open and close opposite of each other. As the neutral port is closed, the work port is opened and vice-verse.

To move any cylinder, sufficient pressure must be created to overcome the resistance on the cylinder.

Added:
On our hypothetical 10GPM log splitter system, it the output on the neutral port is restricted to , say 9GPM, pressure will build until something changes. That could be the log splitting, RV opening, change in valve position, etc...

 

[J_J]

My logsplitter valve is rated for 25 gpm, but my tractor can't produce much more than 7 or 8 gpm to the remote valves. If you had a hydraulic motor rated at 25 gpm, much lower flow would not produce satisfactory results. On a log splitter, it doesn't matter about the valve. The size of the cyliinder will determine your cycle times for a given flow rate.

Your log splitter valve is about 3 times the volume from your tractor. Do you notice any difference as to lever movement, say from your tractor. Do you have feather control from the git go?

I think that is what [ mrcaptainbob ] wants to know. My view, is that you will not have the fine control as with a matched up valve/pump. It should work if the pressure and port requirements are met.

Sorry for any confusion.

 

[AKKAMAAN]

You guys are really discussing this in a great way now.....But I want to add something that still sounds to be little diffuse.

A fixed displacement pump at a given rpm, will always deliver its rated flow thru a control valve or any other orifice, restricted or not, all the way to tank or the cylinder(s).
There is a few exceptions:

• 
  Internal leak in pump, RV, control valve, etc.

• 
  External leak

• 
  Any by-pass in RV or flow split in other valves

Edit:

• 
  And of course, not to forget, if suction line restricts

So saying a 10 GPM flow will be reduced to 9 GPM because of a restriction, will allways mean that one or more of the listed points above is the reason for the loss of 1 GPM.

What happens in a restriction is that flow in and out will be the same, but the fluid velocity at a certain cross section will be different if the cross section area is different. Velocity will be proportional to the cross area.
See Bernoulli

Fluid velocity is proportional to created pressure by a restriction. If you look at a Nomogram for hoze size recommendations, fluid velocity and flow is the inut parameters.

 

[dcyrilc]

You guys are really discussing this in a great way now.....But I want to add something that still sounds to be little diffuse.

A fixed displacement pump at a given rpm, will always deliver its rated flow thru a control valve or any other orifice, restricted or not, all the way to tank or the cylinder(s).
There is a few exceptions:

• 
  Internal leak in pump, RV, control valve, etc.

• 
  External leak

• 
  Any by-pass in RV or flow split in other valves

So saying a 10 GPM flow will be reduced to 9 GPM because of a restriction, will allways mean that one or more of the listed points above is the reason for the loss of 1 GPM.

What happens in a restriction is that flow in and out will be the same, but the fluid velocity at a certain cross section will be different if the cross section area is different. Velocity will be proportional to the cross area.
See Bernoulli

Fluid velocity is proportional to created pressure by a restriction. If you look at a Nomogram for hoze size recommendations, fluid velocity and flow is the inut parameters.

Thank you.
I don't think I stated it, and probably should have, but my statement for the neutral position being restricted to 9GPM was intended to indicate that 1GPM was diverted to the work port, or another path, for the total of 10GPM. This was a good point to bring up though, as the pump will continously deliver it's proper volume assuming there is no failure/leakage and if the work port cannot accept the fluid, the velocity of flow through the restriction will increase to maintain the 10GPM flow until relief is found. Now I'm starting to get deeper into it than I really wanted to for basic theory of valve function though.