How do you adjust a hydraulic valve?

rambler · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

( This is what Junk said in an earlier post:

 This is how the valve is plumbed into the system. I disconnect the hoses going to the loader valve and put these in between the loader hoses.... )

Which is still a little grey to me.

If he is disconnecting the regular loader disconnects, & adding in his grapple connects on _that_ side of the tractor hyd controls, then he is getting _zero_ pressure to the grapple from the tractor pump. All the pressure is supplied by the weight of the loader. The grapple would be piggy-backed onto the loader, and only works by shuffling oil from one side of the loader cylinders to the other - by the pressure of gravity on the bucket.

Now, if this 'Tee' plugs in somewhere between the tractor pump output and the loader valves - then it is real confusing that a closed center valve can work at all on an open center circut. I understand it does work - how is the mistery. An open center system would supply close to zero pressure to a closed center control - they are not compatable.

An out is that some control valves are easily convertable from one style to the other with the right parts inside a plug, and this would be the obvious answer - the grapple maker supplies a controller that will work on either OC or CC with the right plugs/parts.

--->Paul

Henro · Mar 1, 2005

If there's pressure being generated to run the Power Steering (due to there being a load there), then that same pressure flows out the non priority side of the priority valve, and has to be dissapated (as heat) somewhere on it's journey back to the tank 

Banjo,

I think this is an assumption. Might not be true. As a matter of fact I doubt it is true, but I don't know for sure. I would only ask if the output of the flow priority valve had nothing connnected to it, would there still be pressure there? If not, then the only pressure that could be there when something was piped up to it would be due to whatever backpressure was developed in the piping.(or hoses, or whatever...}

 OC hydraulic systems are like a constant current, variable voltage electrical system, something that's not too common.


That is kind of an understatement, to say the least. I doubt that in theory there is such an animal as a constant current, variable voltage source. /forums/images/graemlins/grin.gif I do think that a fixed displacement hydraulic pump running at constant RPM really is comparable to a constand current electrical source. It is just that voltage on the terminals of a CC electrical source is dependent on resistance existing between the terminals, not internal voltage which is by definition zero. Voltage felt at the terminals of the CC electrical source would be comparable to pressure developed at the output port of the hydraulic pump, both the result of resistance to flow. (Maybe you meant to write a variable, constant current source? )

(like you said, it is an engineering thing... /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif )

I too look forward to the actual readings!

Henro · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

 If he is disconnecting the regular loader disconnects, & adding in his grapple connects on _that_ side of the tractor hyd controls, then he is getting _zero_ pressure to the grapple from the tractor pump. 

rambler,

This thought went through my mind at first too, but in the real word is certainly is not the case. Without doubt there will be pressure in the loop at the point where Junkman tied in to it. This is due to flow resistance in the loop. The question is not if, but how much.

Junkman was pretty clear in how he hooked into the system, and if it is as he said, the CC valve is hooked between the incoming line to the loader valve and the return to tank. There would be some pressure there, likely enough to move a cylinder that was not pushing against much resistance.

An open center system would supply close to zero pressure to a closed center control - they are not compatable.

Without a measurement to back it up, this statement is speculation. I don't have a measurement, but as I mentioned in the thread above(I think) JerryG has reported seeing system pressure of 100~200 psi in open circuit systems with all valves centered, if I remember his post correctly. While less than 10% of max system pressure, this would be enough to work a cylinder against little resistance to movement.

Myself, I've concluded hooking a control valve/cylinder up this way is kind of neat. I might do it myself if I build a light duty grapple that I don't want to tear apart with the normal force generated by a standard hook up.

The mystery that remains is the 1,500 PSI that Junkman referred to. This seems way too high. We are waiting for some further feedback from Junk and a couple other/repeat measurements that should shed more light on the situation.

Banjo · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

I'd be surprised if the PS was running at 1500 PSI regardless, since as you say all the excess flow would also have to be at that minimum pressure and converted into heat. How that happens depends on the system (most likely to take place in the PFD as the flow is forced through a small orifice).

That's one of the problems with a priority flow divider (and/or with having more flow than you need). With a rotary flow divider, you can have high pressure on one output and zero on another if there's no load there. They're very efficient that way. However the rotary one will just split the flow, it won't give a minimum priority flow.

We'll have to wait for all the pressure readings from the system in use to know for sure.

cheers, Andrew

Steve_Miller · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

I'm not sure how the valve for the power steering controls flow, but it only loads the sytem when the wheel is moved. This is evident when your tractor is sitting there at idle, turn the wheel slightly and you'll here the tractor come under a small loading because the hydraulic pump is being loaded somewhat, turn the wheel hard one way and you'll here tractor load up quite hard, at least mine will, it sounds like it is going up to relief pressure. The priority flow valve (if this is the proper name, I'm not sure) will direct (in the case of a single pump) the hydraulic flow (this case the steering cylinders) and divert the preset amount of oil flow into the PS circuit, the remaining oil is passed to the rest of the system, the pressure will depend on how much resistance is in the steering system, since at this point (we'll assume there are no OC valves closed at this point) there are no restrictions, the oil will flow freely back to the tank virtually unobstructed. Yes, there is heat loss with the oil passing through an orifice, but it is usually for a short period of time that the steering wheel is turned. Granted the more hard steering you will do the more heat that will be generated, the same can be said if you have an implement that is connected to the hydraulic system, say a backhoe, now you are probably going to be using a lot of high pressure oil with all the functions involved. The system is designed to be able to dissipate the heat at a certain rate. There could be instances where you exceed these limitations but they are usually short lived. If not, your tractor is undersized for the task you are trying to use it for. As for Junkman's setup, let's wait til the warmer weather comes and Junkman gets some time to take some measurements and we'll get the beating sticks out again.
How that for a bag full of wind.
/forums/images/graemlins/blush.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/wink.gif
Steve

P.S. This post is not intended to imply that I know hydraulics, just my observations from years of experience, good or bad.
I mean no one any harm with my explanations or point fingers at anyone. How's that for a disclaimer?

MMM · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

Henro, I'll answer your normal hyd press post here
I have on my Case, 180psi on OC loader pump ,with 140mesh suction filter and 30u return with cold AW68. Hitch/steering/clutches OC system is about 220psi with cold AW68i (if guage is correct).

bugstruck · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

Banjo, This thread is so large my dialup won't load the entire post so I'm just using you from page 11. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif Wow! Took a couple evenings to read the better part of this in my spare time. I think many of us are struggling with the WHY on the workings of the grapple circuit. If I understand this correct the original post stated that 1,500 lbs was observed downstream of the CC valve. In my feeble understanding of fluid and pressure I at least know you can't get more out than you put in. Therefore if 1,500 PSI is present downstream of any valve it must be that or more present at the line supplying the valve (backpressure). That's where the struggle is. Many have observed or stated that the static open center loop pressure may be in the 100 to 200 PSI range. Not on this tractor. It's at least 1,500 PSI on the section of the loop where the tap is made. If I read correctly the 1,500 PSI was observed with none of the OC valves in operation. So nearly everyone is right in one sense or another. It's something in that system that makes that pressure available in a static state. Just a rather elevated one. Think about it in a water system context. You can't tap a lateral line into a water line with 40 lbs of constant pressure, install a valve and then read 400 lbs on the downstream side of the valve. The 400 lbs would have to be available on the feed side of the valve for that to occur....or we've discovered how to circumvent the laws of hydraulics, probably physics, etc.. So the real question is what in the open hydraulic loop is boosting (restricting) the static pressure to 1,500 plus PSI. I can't believe it's line or fitting resistance. That's what is creating the 100 to 200 PSI being bantered about.

I've actually learned more than a few things here. So this monster post is worthwhile to me. Sure beats the bashing of the 3130 in the Kubota forum. /forums/images/graemlins/blush.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

Now, somebody find that restriction. It's there. . Forget the heat and the electricity. Save that for later cause IMO the heat dissipation is a real question for a 1,500 lbs static system.

MMM · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

It isn't actually a friction thing as with oil through an orifice. It's more like oil molecules under compression being reintroduced to the stream colliding and exciting. It creates much more heat than flow friction and is proportional to pressure.

Junkman · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

I don't know that I have brought this fact out before, so I will try to explain this further in the likely event that I didn't do a good job originally or left out some facts. The tractor is running at maximum RPM when this 1500 PSI is registered at the end of the hose coming off the valve when the valve is operated. If I allow the tractor to just idle, I know that there is not very much pressure at the end of the hose, but I have no idea as to how much that pressure is. I do know that at an idle, the grapple will barely close or open. More like slow motion. At full throttle, it will open or close fairly quickly. The same with the hydro..... at an idle, the speed is very little no matter how far you depress the pedal. At full throttle, you can get the tractor moving quite fast. The engine speed has to be factored into this equation if we are to come to a common consensus as to how and why it works. Could it be that the pump that Kubota uses on the BX is putting out more PSI at the higher engine speed? My observation is YES. I have looked over the plumbing and I can convert this to a Open Center valve with Power Beyond, but there is no reason to do so at this point, since it works as it is presently plumbed. Could the quick disconnects be what is raising the pressure? If so, that would account for some of it because Kubota uses a multitude of quick disconnects in the system...

WhiteRock · Mar 1, 2005

Re: How do you adjust a hydraulic valve? *DELETED*

I have a few questions. I don't understand all of the acronyms used here(AW68i, AW68, maybe oil viscosity?). I have psi. /forums/images/graemlins/smile.gif

I read 220 psi at the pump (single pump system) before everything else?

I assume the 180 psi represents the drop across the steering diverter, that then feeds the OC FEL valve?

I assume the PB then proceeds to the (OC) 3pt hitch, to filter, to tank?

Clutch must be PTO?

I have been looking at a lot of connector specs. I am a little surprised at the pressure delta across the various connectors. Do you know what your flow rate is and the size or your connector's ISO body (1/4, 3/8, 1/2,etc.)?