What is "Neutral Position"

[JC-jetro]

Hi all,

I'm having a bit of confusion with a neutral position of a hydraulic control valve. please correct me if I'm wrong. I gathered in an open center system where hyd pump is on with constant flow (at given rpm) and variable pressure (depending load and restriction). In order not to dead head the pump (positive displacement) some or all flow will be diverted to oil sump by the action of spool valve and the safety relief valve as the last line of defense. Now I have the following questions;

1- Is neutral position of the control valve same as the lowest setting of position control Rod?

2- Is there full flow back to the sump in the neutral position?

3- What happens when you reached the 3 pt height ? all the while spool valve partially returning some flow to the sump? what happens to the flow going to the piston at the desired height?

4- Is there a same normal position at any given height? what I mean by that is when you achieve the height needed, the cylinder is full, check valve in the spool and drop poppet valve should maintain the height without further flow unless piston seal is leaking. In that fix you must return all oil back to the sump. Am I correct?


Please chime in if you know the answer. Appreciate it.

 

[MadReferee]

In an open center system, the pump is always pumping which means the fluid always has to have somehwere to go, either to a cylinder or back to the sump. When the spool of a control valve is in neutral, all fluid is passed completely thru the valve and no fluid will flow to the work ports.

From your questions I am assumin you are talking specifically about the 3pt. That being the case, here are the answers:

1. Yes. Once the feedback linkage of the 3pt has determined that the lift arrms have moved the required amount, the 3pt valve spool is internally pushed back into a neutral position which allows fluid to flow back thru the valve and to the sump.
2. Yes, see #1.
3. There is no flow going to the piston cylinder at full height, just like any other cylinder. The feedback linkage is what determines when to shut off the flow to the 3pt.
4. Yes. See #1 and #3.

BTW, why is this posted in the JD forum? You have a Ford 1700. Anyway it doesn't really mater since this applies to 3pt's in general.

 

[JC-jetro]

[*]Yes. See #1 and #3.[/LIST]BTW, why is this posted in the JD forum? You have a Ford 1700. Anyway it doesn't really mater since this applies to 3pt's in general.

Thank You for your reply. I posted in JD forum by mistake right befor I left work. I had a hard time finidng where my origibnal post was.

I suppose the spring on the spool releases the valve to neutral position. I had a hard time to see that from the way linkages were put to gether on the parts breakdown. I'll have to study the linkages to see it. I suppose the feed back arm has to have arelase of some kind when the height is achieved.

 

[MadReferee]

Get yourself a workshop manual (WSM) or whatever Ford calls theirs. The Kubota WSM's have about 4 pages of description and plenty of diagrams that explain how theirs work. Yours is probably similar but the principle of opertion is the same.