Youli MB3 valve question.

[rScotty]

Yes, you can see how it would make sense if the spool was not milled correctly for the body. It wouldn't take very much of an error to make all kinds of odd things happen with the fluid flow. But the same could be said of the position of the ports in the body...or even about which internal ports are selected to be active as the spool is moved. Or for that matter a leaking relief valve that leaked more than the spool position was trying to flow might do be able to deadhead the flow.

Selecting an alternate flow path is what those open-vs-closed system PB plugs do in other brands of valves. In those directional control valves, using the wrong plug in the wrong system will deadhead the flow because then the valve can't simulaneously open a working port and a return port. But unlike your situation, when that mistake is made it tends to deadhead the pump regardless of valve position. It sounds to me like yours is only at certain positons.....and that might be the key.

I'm still not completely sure how Youli's valve design does it's job, but in an attempt to educate myself a little more I went to the Youli site yesterday Products | Youli-America and read up on their valves. Very impressive site. Absolutely great illustrated pictures and in color, too. I haven't seen color illustrations that nice in the tractor world since the old Yanmar Technical Publications Powershift Booklets from the 1980s.
From there I went over to the Allied Valve site & others to read more on set point and back pressure. This is fun stuff.

The result of all this study isn't that I know much more than before, but my confusion is in nice colors and I'm likely to spout hydraulic fluid if pressed.
rScotty

 

[bigdeano]

Very interesting bigdeano, I have been around tractors and other equipment with hydraulics my whole life and this is the first time I have ever seen this issue. Just curious, does the press have a float position? The spool I am having an issue with has float position and my hydraulic guy thinks that might be the issue. I tend to think the spool is just not milled correct. I think it can get into a position that stops flow to the power beyond port and has not opened to the cylinder creating a dead head in the valve. I am strictly guessing as I have a very limited knowledge of how the valve works. We always had someone else on the farm rebuild our valves, pumps and cylinders. I would remove and replace but that was about all I ever had to do. I kinda wish now Dad would have taught me more about that stuff.

No float position, just a simple 1 spool 4 way valve. The valve bodies are sand cast and the internal passages are just made by sand cores in the mold. It's not a real accurate process. On a more expensive valve they probably do some machining in there to true up where the passages meet the spool.

Your valve is probably just a defective one. Another valve of the same model may work properly, or not.

 

[rScotty]

No float position, just a simple 1 spool 4 way valve. The valve bodies are sand cast and the internal passages are just made by sand cores in the mold. It's not a real accurate process. On a more expensive valve they probably do some machining in there to true up where the passages meet the spool.

Your valve is probably just a defective one. Another valve of the same model may work properly, or not.

It's been a good mystery, and looks like we'll know whether it is a defective valve body in a day or so.

I didn't know that about the casting process. You might want to check your source. It seems strange that anyone today would cast blind internal passages with sand molds. There are lots of inexpensive and accurate alternative molding techniques. Seems as though truing up the edges of those internal passages would be very difficult.
rScotty

 

[oldnslo]

rscotty,
The power beyond plug should have no influence on how the spool operates. All the power beyond plug does is isolate the tank port from the power beyond function.

What K5l is experiencing does sound like a timing problem with the valve spool vs the lands in the body. On most "open center" valves the spool meters oil from the pressure port to a work port. During this metering the work port is opening to pressure while the pressure port is being closed off. Sounds like this valve has a position where it is blocking pressure in all directions.

 

[K5lwq]

Update. Today we tested the new valve he had on the shelf and it had the same issue, on the same spool and in the same position. We then took the valve apart and compared the float spool to the standard spools and there is a slight difference in the milling at the main flow port. It was also interesting that the spool was a little shorter causing the joystick not to be completely centered in neutral position. I never noticed this because of the boot cover. So the journey begins! My guy happens to be friends with the owner of Youli USA and gave him a call. He is going to test one at his location to see if he understands the issue as well. He also is going to reach out to Youli in Taiwan or wherever they are built. My guy has quite a few different spools for the Youli valves and is going to machine one of those to be a float spool but give just a little more channel opening like the standard spools that are working have. He thinks it will work. He told me that his buddy was very interested in finding a solution and apparently they have worked on designing other valves in the past together. It will be next week before we know anymore info but it is encouraging to see the interest to find a solution. Who knows, if they are successful we might have a real nice option for people wanting to add a mechanical third function to their tractors. Other than this one issue and the falling thing which could be related, I really like the valve. All the other functions are really smooth and the handles are very comfortable to operate from where it mounts on the tractor. Thanks again for all the help!

 

[rScotty]

rscotty,
The power beyond plug should have no influence on how the spool operates. All the power beyond plug does is isolate the tank port from the power beyond function.

What K5l is experiencing does sound like a timing problem with the valve spool vs the lands in the body. On most "open center" valves the spool meters oil from the pressure port to a work port. During this metering the work port is opening to pressure while the pressure port is being closed off. Sounds like this valve has a position where it is blocking pressure in all directions.

Yes, I agree with you on the function of the PB port, and also that his problem is sounding more and more like a question of spool-to-port timing.

What I was referring to in a pevious post is that there are some valve bodies made that use the same PB port to also fit a conversion plug that allows the same valve body to be used in open versus closed loop hydraulic systems simply by changing what is knows as a "conversion plug".

One of the Cross B? valve bodies is still built that way, and I think the old AICO was as well. I don't know about the Youli, but it seemed worth checking.
B Series Directional Control Valve Plug | Cross Mfg.

A problem can happen because if a person doesn't have a use for the PB function that PB port still needs to be blocked. And sometimes a conversion plug is used just because it is handy and it will simultaniously block the PB port. Grabbing the wrong conversion plug leads to problems. I know it can happen; I've seen it happen. If the wrong closed loop conversion plug is fitted into the PB port of an open loop system, it will obviously deadhead and cause a leak & then anything is possible. Might be an internal leak between any two ports or channels, relief valve constant actuation, or external. The deadhead pressure forces an alternate return path.

But I agree that after reading the testing it doesn't sound like this is the problem.
rScotty

 

[K5lwq]

The Youli MB3 is shipped closed center and comes with a conversion plug that is installed into port "c". This port becomes your PB port. In my mind, I can see what you are saying rScotty could cause an issue. In this case, the spool is just not cut properly to allow flow on to the PB as it is opening to the work port then closing to PB. Because it closes PB and has not opened to the work port, the fluid has no where to go but over the relief valve. What we are unsure of is the spool really the problem or the lands in the body. Although we want to, cutting the valve in half to see inside is not an option. Therefore the thoughts of trying to machine a different spool to see if we can correct the issue. I did not take a picture of the two spools but it was definitely less of a channel cut between the lands on the spool that is giving us the issues.

On another note, his test station is pretty cool. He can set flow to match any size pump and has an electric motor almost as big as my tractor turning that pump. They do more oil field type work and don't get many calls for help with tractors. They hardly ever sell a valve with a joystick to the point he was confused on how to open just the first spool. He will be an expert by the time this project is finished though.

 

[bigdeano]

Sounds like an interesting and educational project. I've thought about machining the spool on my press, but I don't use it often enough to make it worthwhile.

 

[K5lwq]

Sounds like an interesting and educational project. I've thought about machining the spool on my press, but I don't use it often enough to make it worthwhile.

It is that for sure! The guys at Tejas Hydraulics are really great to work with. John, the owner, is very knowledgable and takes time to explain as much as possible every time I go into their shop. I don't think I have been in yet we did not visit at least an hour.

 

[K5lwq]

Today I got the valve back form the shop. Unfortunately there was not a fix for the problem I am having. Turns out that once they were able to communicate with the Youli factory, Youli was aware of the issue. They have had a few other complaints about the float spool blowing over the relief valve when opening port B. They tried machining different spools but they could not overcome the issue. The problem is in the valve body and there is no plans to redesign the valve body at this time. John at Tejas offered to refund my money on the valve. I chose to keep this valve because we could not find one that was in the footprint I wanted. I would have had to step up to a much larger valve to get a similar set up in one body. This would have put the valve sticking out past the loader frame and that is something I don't want. My biggest concern was with the inability to feather lowering a load in order to set it down gently.

The solution John came up with was to put a adjustable flow valve on port A that would allow me to slow down lowering to what ever speed I want. He provided the adjustable valve and all the fittings I needed at no charge. I tried my best to pay him but he refused to let me. I installed the valve this afternoon and the results are positive. By slowing the flow, I have a lot more control lowering the boom. I still am not happy that it has to blow over the relief every time I want to lower the boom, but I can live with it. I am very happy with the way Tejas Hydraulics handled this situation and would highly recommend them for any hydraulic needs. They are an outstanding company that care about customer satisfaction.

Anyway, thanks again to everyone that tried to help me understand what was happening with my valve. Great people on TBN and I am glad to be a part this community!