splitter control valve...

[mrcaptainbob]

Is there an issue if using a larger flow control valve but actually having lesser flow? That is, would it be okay to flow less than 20 gpm through a 20 gpm valve?

 

[Willl]

No issues that I know of.

It's like driving 35 in a Corvette.

 

[AKKAMAAN]

Is there an issue if using a larger flow control valve but actually having lesser flow? That is, would it be okay to flow less than 20 gpm through a 20 gpm valve?

Generally speaking not an issue at all, as Willl posted. It will actually benefit you, with an oversized valve, your system will not create so much heat losses. (That larger valve will let the oil thru with less restriction).

A logsplitter is preferred to be operated, with full strokes on the spoolvalve lever. That way we get most pressure and flow from the pump to the actuator, and that way minimize the heat losses.

But, in some other applications, the operator might want to, proprtionally, regulate the actuator speed, with the control valve. This proportional ability can be set on the side a little, if valve is "way" oversized.
This is something you do not have to worry about in this case, as long as the valve fits your system setup (open center or closed center), and logsplitter operation. That will show on the "maiden voyage" ....

 

[jinman]

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.

 

[J_J]

Is there an issue if using a larger flow control valve but actually having lesser flow? That is, would it be okay to flow less than 20 gpm through a 20 gpm valve?

The larger valve GPM will not affect anything except the lever movement. If a 10 GPM valve is used with a 10 GPM pump, you have full lever control, from feather to max flow. With a 25 GPM valve on a 10 GPM pump, you will have full flow when the lever is about half way, and anymore pushing on the lever will not produce more results. You have already met the 10 GPM flow.

Some of the log splitter have 3/4 in and out, with 3/4 in work ports. Others have 3/4 in/out, with 1/2 in work ports. Again, larger doesn't matter, except the larger fittings and hose will cost more.

It is best to try and match up valves, pumps , hoses, etc.

 

[AKKAMAAN]

With a 25 GPM valve on a 10 GPM pump, you will have full flow when the lever is about half way, and anymore pushing on the lever will not produce more results. You have already met the 10 GPM flow.

Sorry J_J, you are way off here!

Even with a larger valve you need to move the lever (spool) to end of the spool stroke to get FULL FLOW AND FULL PESSURE to the work port!!!

We build up pressure by restricting the center. A low pressure load might need only half spool stroke to start moving slowly, because we only need to build up a low pressure to make it move. Part of flow will then go to work port and the rest will go thru the partially open OC.

Full flow to work port will require a fully closed OC. Max pressure can only get reached when RV, is just about,or alraedy is open. And that require a fully closed OC as well.

Hope this clear the fog around this.....

Happy New Year to you all!!

Ps. I found this on on my laptop....

 

[J_J]

AKKAMAAN said,


[ Full flow to work port will require a fully closed OC. Max pressure can only get reached when RV, is just about,or alraedy is open. And that require a fully closed OC as well. ]


I disagree with that statement.

You will only have pump pressure when enough resistance is met. The volume is variable through the range of the valve. If a certain orifice will pass 10 gal of fluid, and if the orifice is double in size, do you think it will pass more fluid if available. Say the internal ports on the spool is 1/4 in, and designed for 10 gal flow. At full opening, the flow will be 10 GPM. Take the same pump and a larger valve, 25 GPM, which will have larger internal ports, which was designed to handle a larger flow. If you only have 10 GPM flowing through that orifice, I think you will satisfy the requirement at about the halfway point. Your diagram does not show valve size.

Just how is it that we control the speed on a hyd motor by allowing a certain amount of fluid to the motor. If a ten GPM flow can satisfy that motor, then a 25 or 30 GPM valve
with 10 GPM flowing, the max flow will be met at some point before full opening. The pressure will be dictated by the resistance of the motor.

What would happen if the reverse were true. Say the pump volume was 25 GPM, and you used a 10 GPM valve, and the motor required 25 GPM. Do you think a valve ported for a ten gal flow would satisfy the requirement of the 25 GPM motor. You would need full opening and then some.

Do you get more flow/GPM through a needle valve by opening the needle setting on the valve. Does it change pressure very much, No.

Convince me I am wrong. I am willing to learn. Perhaps common sense does not apply in this situation.

 

[AKKAMAAN]

AKKAMAAN said,

[ Full flow to work port will require a fully closed OC. Max pressure can only get reached when RV, is just about,or alraedy is open. And that require a fully closed OC as well. ]

I stay with my statement "Full flow to work port will require a fully closed OC"
I cant see how this is hard to understand, IF OC is not fully closed, flow will be divided, and part of flow will go to tank, and not help to move actuator.

I stay with my statement "Max pressure can only get reached when RV, is just about,or alraedy is open"
Do not read me like the devil reads the bible....I said "can only get reached" and that means that we will need an opposing force that creates that pressure.

I disagree with that statement.

Well, that was predictable, because you did show so much off....but thats OK, thats why we have a forum to share and learn....

You will only have pump pressure when enough resistance is met. The volume is variable through the range of the valve. If a certain orifice will pass 10 gal of fluid, and if the orifice is double in size, do you think it will pass more fluid if available.

I agree 100% about the pressure!
The volume thru the valve will be the same as long as RV stay closed. But the volume thru the work port might be different depending on how high pressure OC restriction creates. It sounds like you are talking about a variable pump here!! Any flow available will pass any restriction if there is no bypass opening, RV or a blown hose etc.

Say the internal ports on the spool is 1/4 in, and designed for 10 gal flow. At full opening, the flow will be 10 GPM.

It will be more than 10gpm if more is available and RV stays closed.

Take the same pump and a larger valve, 25 GPM, which will have larger internal ports, which was designed to handle a larger flow. If you only have 10 GPM flowing through that orifice, I think you will satisfy the requirement at about the halfway point.

Yes it will! But it will take more spool movement before OC have built up enough pressure to direct flow to work port.

Your diagram does not show valve size.

Purpose with my animation was not to show orifice sizes in detail!
For our topic this part of it is most important

It shows that both the Open Center and the work port is partially restricted or partially open, what ever you prefere.

On a over sized large OC valve the OC orifice in neutral is so large so it wont start to restrict the "Constant pump Flow" until it is almost closed....we need to restrict the flow thru the center to be able to over come the load pressure in the actuator.

Please look at these 4 different cases, and please do not start grind about that 200psi pressure...

1. Which one of ABCD have an undersized OC CV??
2. Which one of ABCD have an oversized OC CV??
3. Which one of ABCD need most spool movement before OC restrict the flow??
4. Which one or more of ABCD have an"correctly" sized OC CV??

What I have stated is that an oversized valve need more spool movement before flow can direct to work port!!

Just how is it that we control the speed on a hyd motor by allowing a certain amount of fluid to the motor. If a ten GPM flow can satisfy that motor, then a 25 or 30 GPM valve
with 10 GPM flowing, the max flow will be met at some point before full opening. The pressure will be dictated by the resistance of the motor.
What would happen if the reverse were true. Say the pump volume was 25 GPM, and you used a 10 GPM valve, and the motor required 25 GPM. Do you think a valve ported for a ten gal flow would satisfy the requirement of the 25 GPM motor. You would need full opening and then some.

"Satisfy" is a bad term here, you talk like dealing with a woman....hahaha..
Of course, same answer as above, the undersized valve will pass on the flow as long as RV do not open. BUT the prize is high!! Huge power drop over the valve, with excessive overheating as result!!

Do you get more flow/GPM through a needle valve by opening the needle setting on the valve. Does it change pressure very much, No.

Agree! Unless opening the needle valve will lower pressure so an open by passing RV will close!

Convince me I am wrong. I am willing to learn. Perhaps common sense does not apply in this situation.

Common sense always apply!! But if one is off on how it basically works...then common sense will be off too!!!

How spool valve works is a difficult thing to understand, because there are so many parameters in a spool valve design. Spool overlap and land design decide much of what we are talking about here.

I'll see if I can find some good illustartions of spools, overlap and lands!

I am ready to work this out, hope others join and fill in or ask q's!

 

[J_J]

Just a casual observation on my Power-Trac. With a possible flow rate of 4 GPM's, and I have a gage in the lift circuit. With an empty bucket, I apply a small lever movement, and the loader starts to rise slowly with about 300 psi showing on the gage. I know I am not passing the full 4 GPM to the loader, and I am not using the full pump pressure. If I want it to lift fast, I will pull the lever all the way back, and the full flow will go to the lift cylinders, and the loader will raise rapidly. Now if I try and lift my max load of 1200 lbs, the pressure jumps to 2750 psi, and I can raise slow or fast, using .1 GPM to 4 GPM hyd flow, until the relief cuts in. That is how I see it, and I am sticking to my story.

Please do not try to impress me with lesson guides and video, etc, and slight remarks.
I try to be factual as I can, honest and sincere in what I say, and as brief a possible. If I am wrong, so be it.

 

[Wayne County Hose]

AKKAMAAN, when will you learn that knowledge and facts mean nothing.

Ultimately, it's not the valve opening that determines flow, up until full valve opening. The load downstream of the valve determines flow. Up until full valve opening, a certain amount of fluid is ported back to tank. Basically, whatever the load couldn't handle. A valve rated for 10 gpm or a million gpm won't matter. The valve is still just an opening that fluid flows through. Whatever can't be used by the load is ported back to tank, until full valve stroke, no matter the size of the spool. This is the way I always understood it. AKKAMAAN, is my logic correct?

 

[AKKAMAAN]

AKKAMAAN, when will you learn that knowledge and facts mean nothing.

I hear ya....LOL....I think and hope I'll never learn that...

Ultimately, it's not the valve opening that determines flow, up until full valve opening. The load downstream of the valve determines flow. Up until full valve opening, a certain amount of fluid is ported back to tank.

I would like to say it is the pump pressure and the load pressure, that determines the flow thru the work port. How much flow depends on how much bigger pump pressure is than load pressure. That is what we call DELTA P, pressure differens.

Basically, whatever the load couldn't handle.

I do not like that way to express it....This is the tricky part of the thing...

Let us say we have a 10GPM CONSTANT FLOW from pump.
The load on the actuator creates a pressure. Let us say load pressure is 1000PSI!
If we move the lever (spool) we will restrict the Open Center, so pressure increases from pump. Now work port is open a bit! as long as pump pressure is 1000PSI or less, ther will be no flow through work port. All 10GPM will go thru center to tank!! We will need a pressure higher than 1000PSI, how much higher depends on the friction in the cylinder (seals).
Let us say cylinder starts to move just a little (0.1 GPM) at 1050PSI. Then 9.9 GPM will be directed to tank. To ACCELERATE the speed, we will need to increase pump pressure by restricting center more.

This is the part most have a hard time with, most think that it is enough to open work port, and forget that we need to increase pressure to accelerate,. It is basically pure mechanics and Newtons laws that rules. Both the "port valve" and the "center valve" is synchronized because the are sitting on the same spool.

A valve rated for 10 gpm or a million gpm won't matter. The valve is still just an opening that fluid flows through. Whatever can't be used by the load is ported back to tank, until full valve stroke, no matter the size of the spool.

When we use a manual control valve we usually want to be able regulate cylinder speed. We want as many "speeds" as possible. We call this PROPRTIONALITY. Let us say, that we want "20" different speeds or maybe more. Then the "ball head" on the valve lever, need 20 different positions within its movement. If it moves 2", then each "speed" is within 1/10 of an inch.
In our case here, we were discussing how an over sized valve operates on a small flow.

REMEMBER we are talking about a CONSTANT FLOW system. We need to introduce the term PROPORTIONALTY! PROPORTIONALTY means that a certain spool movement restricts center to a proprotional pump pressure.

PROPORTIONALTY in a CONSTANT PRESSURE system means that a certain spool movement allows a proportional flow thru the work port.

What happens when we use an oversized valve is, that, maybe the first 1" of lever movement, never restricts the center enough, to increase pump pressure. NOW we only have 10 "speeds" left. WE HAVE LOST 50% OF THE VALVE PROPORTIONALTY!!
If flow gets lower, or if we use an even larger (way oversized valve), there will be NO PROPORTIONALTY left! We just got an ON-OFF valve at the very end of the lever (spool) stroke! NOT AT THE BEGINNING!!!

This is the way I always understood it. AKKAMAAN, is my logic correct?

I think you have a GOOD idea about it!

 

[Leejohn]

Very understading. I miss something before, was easy to get side tracked.

 

[Wayne County Hose]

Interesting reading AKKAMAAN, thank-you for taking the time to go over not only this but the many other subjects you have covered in numerous posts. I know it takes a lot of time and is mostly a thankless effort, but I know I speak for many of us here when I tell you that we do appreciate your efforts.

Andy

 

[spruce Deere]

Is there an issue if using a larger flow control valve but actually having lesser flow? That is, would it be okay to flow less than 20 gpm through a 20 gpm valve?

NO PROBLEM. If that is what you have on hand, use the D*MN thing. It IS like going 35mph in a vette. Akkamaan, nice schematics Proof TBN is a wealth of knowledge!

 

[Redneck in training]

I have only basic knowledge of hydraulics but I agree with AKKAMAAN. The spool is a flow divider until the center is fully closed. That means that the "orifice" that lets the oil drain back to the tank is also large when the valve is half way so it is hard to built pressure. You have to move past the halfway point to restrict return (create pressure) and direct the flow to the cylinder. Restricting the return matters.

 

[AKKAMAAN]

Interesting reading AKKAMAAN, thank-you for taking the time to go over not only this but the many other subjects you have covered in numerous posts. I know it takes a lot of time and is mostly a thankless effort, but I know I speak for many of us here when I tell you that we do appreciate your efforts.

Andy

Thanks Andy!!

I have made my living, for 25+ years, on teaching basic hydraulics, and when students starts to ask questions....You just need, starighten it all out and tell the truth, or say, "I DO NOT KNOW, BUT I WILL BRING AN ANSWER TOMORROW!!!"....I my world it has been impossible to make up stories, because the students will come back next day and say...."THAT WAS NOT RIGHT!!!!".....and then you are the only one that got fooled.....

I love to learn more about this, and I love to share my part of it too!!

All You guys have taught me a lot about tractor hydraulic now....and I love to read all your posts!!

 

[mrcaptainbob]

WOW! I sure am the better for having posed THAT question!! Thank you ALL so much. Great dialogue from all.

 

[AKKAMAAN]

I have only basic knowledge of hydraulics but I agree with AKKAMAAN. The spool is a flow divider until the center is fully closed. That means that the "orifice" that lets the oil drain back to the tank is also large when the valve is half way so it is hard to built pressure. You have to move past the halfway point to restrict return (create pressure) and direct the flow to the cylinder. Restricting the return matters.

 

[dcyrilc]

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?

 

[AKKAMAAN]

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?

Excellent!!