mrcaptainbob
Platinum Member
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?
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?
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?
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.
AKKAMAAN said,
I stay with my statement "Full flow to work port will require a fully closed 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. ]
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.
Well, that was predictable, because you did show so much off....but thats OK, thats why we have a forum to share and learn....I disagree with that statement.
I agree 100% about the pressure!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.
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...
- Which one of ABCD have an undersized OC CV??
- Which one of ABCD have an oversized OC CV??
- Which one of ABCD need most spool movement before OC restrict the flow??
- 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!