How do Hydraulic Control Valves

[craigermags]

I recently registered with TractorbyNet and find this a very useful sight. I have also attempted to find what I am trying to learn from reading all of the throughtful comments of others. I am still confused with the operations of a hydraulic cylinder and valve so I come to the experts out there to help me if you would.

I recently purchased a Hercules tractor (Chinese made by Beyne). It is about 40hp and is actually a reverse steer system. It runs very well. I also purchased a Buhler Farm King Snowblower that has a hydraulic Cylinder system to operate the discharge chute. This hooks up to the 3 point hitch.

Now my issue. I want to install an after market Control Valve to run the cylinder. The cylinder is two way. On the back of the tractor there is an auxillary hydraulic outlet to run other attachments. I was told this is where I would hook up the valve.

Not knowing anything about valves, but and easier learner most I have seen have an inlet and outlet on the sides and then to other inlets and outlets. I am assuming that the one larger intake on the side of a valve is where I would tap off the tractor to. The inlet and outlet on the tops hook into the cylinder. The larger outlet on the far side of the valve must hook somewhere to reroute the fluid back into the internal system but I am undercertain what I am looking for.

Can anyone out there help me with this.

Thanks

 

[uhmgawa]

</font><font color="blue" class="small">( Can anyone out there help me with this. )</font>

Things you'll need to understand/determine is whether
your system is open or closed center (likely open), if this
outlet you mention is at the end of a loop or within the
loop, and where you can dump to a tank port.

If you search the archives you will find enough
discussion on 'tractor hydraulics' to help answer
(or possibly answer) most of the above.

 

[MMM]

As posted above, if manual is in english, check type of pump. Variable displacement piston pumps need closed center control valve. Gear pumps need open center. The inlet side of valve may be marked "P" and outlet "T". If there isn't a return quick connect already fitted, there should be a plug on tractor you can remove and fit return oil line to (with quick connect).

 

[Villengineer]

Do these aux outputs have quick disconnects already on them? If they do then chances are it already has a control valve in the circuit. I've never seen a tractor with QD's that didn't have a valve. Not saying it doesn't happen, just never seen a manufacturer go to the expense of adding the remote lines and QD's w/out having the valve.
Anyway, if it doesn't have a valve and you want to add one then you need to find out which of the two lines is supply, the other will be return. Often valves will have their ports marked with numbers, or P & T & some numbers. The only ones you really need to worry about are the tractor side ports. If it's marked with P & T then you need to hook up the supply remote to P and the return remote to T. The other 2 ports are interchangable depending on your handle vs cylinder positions. If it's opposite your preference just swap the lines. If your valve is marked with all numbers then you need to either consult the instructions or do the trial and error method. Valve manufacturers don't necessarily all configure their valve bodies the same way. If you haven't purchased your valve yet, like stated before, you need to find out what type of center spool position your system requires. Some will need a closed center and others may need a return to tank center (the P port dumps to the T port). Hope this helps.

 

[DaveNay]

Others have mentioned closed center vs open center valves which leads me to a question:

If the pump requires an open center valve, then It should be safe to assume that the manufacturer has put an open center valve into the system. How then do other secondary valves work??? /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif I would assume that there would be minimal working pressure available at other valves. If the system were plumbed in "series" then I could figure it out, but I have always been under the impression that the valves are all plumbed in "parallel" with the "P" side of the valves essentially connected to a manifold.

Dave

 

[Bird]

Dave, I don't know how many different ways different tractors are plumbed, but I think you'll find the majority use the open center and that they are plumbed in series. I don't have a problem with that myself, but it does require some getting accustomed to, in some cases. For instance, I learned pretty early with my Kubotas that the front end loader got the hydraulic flow first, if that joystick was not centered (closed), the 3-point hitch would not work (raise). I then plumbed into the rear hydraulic outlet on my B2710 (could have used the Power Beyond port on the FEL valve just as well) for the two spool valve for the top 'n tilt. So the hydraulic flow went from the FEL valve to that valve, then to the 3-point hitch last. Couldn't use more than one of those 3 valves simultaneously, but since I've only got one right hand, no problem. /forums/images/graemlins/wink.gif /forums/images/graemlins/laugh.gif

 

[MadReferee]

The typical compact tractor has an open center system with a continuous running pump. The valve blocks are connected in series with each other. The spools are sort of in parallel with the valve block which is why 2 operations can be performed simultaneously (ie. dump and raise).

The usual connection path is from the tank to the pump to the loader to any aux valves and finally to the 3pt then back to tank.

The loader and aux valves are "power beyond" meaning that fluid flows thru them to the next valve in series when (a) the levers are in the neutral position and (b) whatever fluid is not being used by the spools. These valve blocks have 3 hoses connected to them, the high pressure inlet (comes from the previous valve's PB), power beyond outlet, and a low pressure exhaust/return to tank.

Its really a very simple series circuit and when you see a diagram/picture it will become very clear. I know there have been links to circuit diagrams on TBN so if you do a search you should be able to find one.

 

[JohnS]

I am not sure about Beyne, but the Jinma aux is only one way, and is activated when 3pt is at max raise position. Mine does not have this, but it is on many newer Jinmas.

If you haven't already, contact your tractor supplier for recommendation for adding, but suspect it will be open center after the fel, if installed. Your Beyne probably has metric fittings that will take a little more effort to find/modify.

 

[uhmgawa]

</font><font color="blue" class="small">( Its really a very simple series circuit and when you see a diagram/picture it will become very clear. I know there have been links to circuit diagrams on TBN so if you do a search you should be able to find one. )</font>

Here is one from our fine friends at Prince. Note the power beyond
valve is added upstream of the existing single spool valve.

Another consideration for open center series systems is to size the
added valve to minimally impact pressure drop of the loop. This
can require using a higher GPM rated valve than currently exists
within the system. Assuming the max loop GPM flow is known
you can determine the pressure drop from the valve manufacturer's
data sheet.

 

[craigermags]

Thanks for your help on this to all . Craig