Hydraulic 3pt question

[FL_Jerry]

Does anybody have any idea how much pressure is seen with a fairly large load raised on the 3pt? I'm not looking for a specific value, just trying to determine if the pressure should go down after the load is raised to the set level or if there is pressure on it the entire time.

Jerry

 

[rdbrumfield]

the pressure is the same as the pressure that it takes to lift the 3pt. the heavier the load the more pressure until it tops out the set bypass pressure.

 

[FL_Jerry]

Thanks, I've been trying to fix something that isn't broke as usual, but I did have a bad pump.

Wouldn't know about what temperature the fluid should be on a Yanmar lifting a bush hog around?

Jerry

 

[todda323]

just out of curiosity, about what pressure is the bypass set at? in other words how much will it lift before it kicks out

 

[FL_Jerry]

I don't have any shims in to increase it from the spring tension. I'm pretty sure it's around 2000-2200. I don't leave it doing that for long to get an accurate reading out of fear of blowing a seal.

Jerry

 

[JC-jetro]

Does anybody have any idea how much pressure is seen with a fairly large load raised on the 3pt? I'm not looking for a specific value, just trying to determine if the pressure should go down after the load is raised to the set level or if there is pressure on it the entire time.

Jerry

Jerry,

Most control valve on 3 point lifts are open center. As you raise the lift, you allow more flow and max pressure developed is regulated by the spring pressure of your pressure relief system to avoid dead heading the pump. Most pump have some means of internal by pass to keep pump from self-destructing. when You achieve the intended height of 3 point lift then the feed back arm moves the spool to neutal position diverting the flow to reservoir and in most cases to differential housing. At that point the pressure is only caused by the weight of the 3 point arms and any implement attached to it, at that point pump does not contribute to pressure between the lift piston and control valve. We had a recent discussion about it in the blue forum. you might find it interesting.

JC,


http://www.tractorbynet.com/forums/new-holland-owning-operating/130597-adjust-not-adjust.html

Any flat washer preferably stainless steel can be use as a shim provided you use the right thickness needed.

 

[FL_Jerry]

I read that thread and it is very interesting considering what I'm looking at.

I replaced the 3pt control valve today and pretty much the same result... There is a constant load on the pump. It's hard to tell where if the neutral position is on these valves. I was thinking the linkage must be misadjusted, but I havn't found a procedure yet in the manual.

Of course, there is a possibilty still that this is normal... I ran the tractor today and you wouldn't know there is an issue without the guage in. Only thing that concerns me is the temperature of the hyd. fluid. I have to get one of those IR thermometers and check.


Jerry

 

[JC-jetro]

I read that thread and it is very interesting considering what I'm looking at.

I replaced the 3pt control valve today and pretty much the same result... There is a constant load on the pump. It's hard to tell where if the neutral position is on these valves. I was thinking the linkage must be misadjusted, but I havn't found a procedure yet in the manual.

Of course, there is a possibilty still that this is normal... I ran the tractor today and you wouldn't know there is an issue without the guage in. Only thing that concerns me is the temperature of the hyd. fluid. I have to get one of those IR thermometers and check.


Jerry

Jerry,

It is absolutely normal to pump have a load on it hence " live Hydraulic". Anytime the engine is running the pump is running. Neutral position is at the control valve. Once you achieve the 3 point height then the flow is returned to rear diffy. that's why the 3 point does not go any higher. The pump always pumping against a pressure relief device (adjustable spring loaded check valve). if the pump can make pressure to the setting of a relief in other word no restriction and you can not maintain head pressure or much of it. You build temp if pump is dead headed and pump internal relief port circulating the flow inside which at that point temp can rise before the pump destroys it self. I can provide more info to check the feed back arm in you 3 point arm to check the neutral position. Let me know.

JC,

 

[FL_Jerry]

Just to clarify, and thank you for the help BTW

I have a guage T'd in right after the pump. When I raise the arms with load, I have a load on the pump, usually around 1k psi. This pressure seems to be from the valve, as I have shut the lock valve eliminating the hyd lift cyl and the pressure on the pump stays the same.

The check valve in the 3ph control valve seems to be good on the new control, as the load stays up after the engine is killed.

Without the 3ph in the hydraulic circut, loader valve output to tranny directly, there is 0 psi.

I can see how the ports attached after the check valve in the 3ph control will show the load, but I'm seeing it at the pump all the time. This could be normal, but I haven't found anybody with a guage T'd in on a Yanny yet to know for sure.

The control linkage seems simple, a feedback arm is attached to the main lift arms which rotates to pull back the block pushing the 3ph control shaft in.

I was thinking that after the load is at the desired height, that the 3ph valve would shut off flow to the main lift cyl. and pass the pump flow to the resevoir, thereby having no load on the pump. However, if the nuetral positon of the valve still involves the use of the internal check valve of the 3ph control, I see why I would see the relief pressure all the time.

The Yanmar pumps have no internal relief valve, but there are Orings and pressure bypass ports to relieve pressure from spots internal. I worry about the temp getting too high and damaging those o rings. The pressure relief valve is in the hydraulic cyl. head of the lift and is the standard spring/steel ball deal.

If I'm rambling, its because this has been a long fight started by a weak pump. I then plumped the infernal pressure guage in which is like giving a stethoscope to a hypochondriac.


Jerry