Loader Woes

[RonMar]

Assuming it's an open center valve there's always fluid going through the valve to the return line to the sump.

This is not necessarilly true, only if it was the last valve in the system would you see the high pressure side(power beyond) plumbed to the return, but this is usually accomplished inside the valve with the use of an open center plug.

Unless the power beyond is plumbed to the 3 pt hitch, or something else, then the fluid only goes through the return line when you use a spool in the valve. If you didn't have the power beyond hooked up and the return line was plugging up it would do it whether you were using the valve or not.

But he does have a power beyond outlet. A return line restriction also matches his description of heavy load only when a valve lever is operated(requiring a clear return path).

If the power beyond is plumbed (tee'd) into the return line then the plug (if it's the return line) is between the valve and the power beyond tee connection.
Monte

That would still be a return line problem as I described earlier. Again the connection of the supply line to the return in the last valve in the system is usually accomplished with the appropriate configuration plug (OC plug)in the valve so you only have one line leaving the last valve back to the sump(from the return port). Since he describes the power beyond port being used, I am guessing it feeds another device.

I have seen many times where people get confused about what "Power Beyond" is. "Power Beyond" is nothing more than a high pressure outlet from a valve to feed the high pressure inlet of another valve or device. You could plumb a hundred valves onto a pump in this fashion, pump to first valves inlet port, and the PB outlet to the next valves high pressure inlet. If I place a heavy load on a valve, that high pressure is felt all the way back to the pump. The high pressure passage thru a valve is able to handle the system pressure applied to it by any work being performed by a valve farther downstream. Using power beyond requires another line leaving each valve(return) back to the resovoir so the safety and the fluid returning from a moveing cylinder via the working ports has someplace to go. The return port is supposed to be an outlet to a low restriction path back to the sump. As such it is usually limited in the ammount of pressure it can deal with. Most of my experience is with Prince valves. Many of their valves that I have seen have a 500 PSI pressure limit on the return port. Exceeding this pressure can cause the "O" rings that seal the spools to leak fluid.

 

[montejw]

Quote:
Originally Posted by montejw
Assuming it's an open center valve there's always fluid going through the valve to the return line to the sump.


This is not necessarilly true, only if it was the last valve in the system would you see the high pressure side(power beyond) plumbed to the return, but this is usually accomplished inside the valve with the use of an open center plug.

Not knowing how the OP's system is plumbed, there is the possibility that the PB could be plumbed into the return line IF there isn't anything else downstream. The PB would need to be tee'd into the return line in that case.

Quote:
Originally Posted by montejw
Unless the power beyond is plumbed to the 3 pt hitch, or something else, then the fluid only goes through the return line when you use a spool in the valve. If you didn't have the power beyond hooked up and the return line was plugging up it would do it whether you were using the valve or not.


But he does have a power beyond outlet. A return line restriction also matches his description of heavy load only when a valve lever is operated(requiring a clear return path).

True, but I don't know what's downstream on his PB line. He states "Cub Cadet 7275, FEL, MMM, Box Blade, Scaper Blade, wish I had a backhoe for it.", so the PB might be plumbed into the 3 pt hitch, or the return line.

Quote:
Originally Posted by montejw
If the power beyond is plumbed (tee'd) into the return line then the plug (if it's the return line) is between the valve and the power beyond tee connection.
Monte


That would still be a return line problem as I described earlier.

True. At the same time I think it could be narrowed down to being between the valve and the tee because the only time that section would see pressure is when a spool gets used, IF the PB is tee'd into the return line.

Again the connection of the supply line to the return in the last valve in the system is usually accomplished with the appropriate configuration plug (OC plug)in the valve so you only have one line leaving the last valve back to the sump(from the return port). Since he describes the power beyond port being used, I am guessing it feeds another device.

I have seen many times where people get confused about what "Power Beyond" is. "Power Beyond" is nothing more than a high pressure outlet from a valve to feed the high pressure inlet of another valve or device. You could plumb a hundred valves onto a pump in this fashion, pump to first valves inlet port, and the PB outlet to the next valves high pressure inlet. If I place a heavy load on a valve, that high pressure is felt all the way back to the pump. The high pressure passage thru a valve is able to handle the system pressure applied to it by any work being performed by a valve farther downstream. Using power beyond requires another line leaving each valve(return) back to the resovoir so the safety and the fluid returning from a moveing cylinder via the working ports has someplace to go. The return port is supposed to be an outlet to a low restriction path back to the sump. As such it is usually limited in the ammount of pressure it can deal with. Most of my experience is with Prince valves. Many of their valves that I have seen have a 500 PSI pressure limit on the return port. Exceeding this pressure can cause the "O" rings that seal the spools to leak fluid.

We're on the same page here. I was just bringing up the possibility of the PB being plumbed into the return line with a tee because I've seen reference to this in the operating manuals for at least one valve. I guess it's incase the PB is installed but not plumbed into another device.

Your comment about the pressure limit on the return line is timely too. I remember another thread where someone plumbed the return line from the FEL to a backhoe and split the valve, or something like that. He was having a hard time finding a valve with PB that fit his older tractor. The FEL control valve was in a confined space with some hard lines to it.

Monte

 

[SCDolphin]

If I pull the 3 point lever all the way back to raise postition it will make a whine and my fel works very slowly if any. Apparently there is a stop adjustment on the fell that when adjusted properly will fix this.

 

[JimR]

If I pull the 3 point lever all the way back to raise postition it will make a whine and my fel works very slowly if any. Apparently there is a stop adjustment on the fell that when adjusted properly will fix this.

My FEL valve does have a PB port and I do believe it goes to the 3 point hitch. I do know that it goes to the hydraulic block on the motor where three hoses connect from the FEL valve. Yesterday I was messing around with the FEL trying to pinpoint some kind of sequence as to when this screws up. I started up the tractor and the loader worked fine for 2 ups and downs and bucket cycles. Then it started the same old routine of sometimes working and sometimes slow motion. The PB hose is not the one going stiff. I found that the PB line comes out of the top of the FEL valve and goes to the hydraulic block with a letter "N". The line going stiff goes from the bottom inside of the FEL valve to the letter "P" on the block. The other line goes from the lower outside of the FEL valve to the letter "T" on the block. According to my service manual these lines are all in the proper place. I believe the "P" line is the pressure line going to the FEL valve. One other thing I noticed is that the hydraulics only scream in the bucket curl up position once the bucket is all the way curled. It makes a high pitched squeal. Holding the lever in the other three position creates no squealing sound. It looks like I will have to pull the FEL valve off again to try and find out what the heck is going on in it. Or as mentioned earlier that I have a line that has seperated inside and the rubber is flapping over causing a blockage. The relief valve is a seperate valve mounted on the loader frame with two seperate hoses running from T fittings off of the loader lines to the pistons for the boom up and boom down. The more I think about this. I don't feel that it is a eperated line as the PB is working fine. If it were a line seperation the PB would be affected also when the loader is in neutral position. Can the spools overtravel in the valve? I did take all the slop out of the control lever.

 

[MJPetersen]

i think youve got a bad hose. It is closing up internally when you ask for fast flow. A failure of the hose inner liner.
larry

This is what I was thinking too. At low volume it retains its shape and allows flow, but when you put more volume to it it may work and then suddenly and decisively will close off and severely restrict flow. What happens is that the internal liner on the inlet side of a hose tears (usually at a connection) and acts like a one way valve at times. If you can reverse the hose you will solve the problem at least temporarily. This is what I was thinking the other day, but wanted the additional information. I would be suspicious of the return hose from the valve. Check it and if you do not see anything and can try reversing it and see if that cures it.

Mike in Warsaw

 

[SPYDERLK]

This is what I was thinking too. At low volume it retains its shape and allows flow, but when you put more volume to it it may work and then suddenly and decisively will close off and severely restrict flow. What happens is that the internal liner on the inlet side of a hose tears (usually at a connection) and acts like a one way valve at times. If you can reverse the hose you will solve the problem at least temporarily. This is what I was thinking the other day, but wanted the additional information. I would be suspicious of the return hose from the valve. Check it and if you do not see anything and can try reversing it and see if that cures it.

Mike in Warsaw

Yeah, agreed. There was a lot of missing info atthat time, but the superficial symptoms seemed to fit that as a cause. Now, with all considered, it must be the return hose if its a hose problem.
larry

 

[JimR]

This is what I was thinking too. At low volume it retains its shape and allows flow, but when you put more volume to it it may work and then suddenly and decisively will close off and severely restrict flow. What happens is that the internal liner on the inlet side of a hose tears (usually at a connection) and acts like a one way valve at times. If you can reverse the hose you will solve the problem at least temporarily. This is what I was thinking the other day, but wanted the additional information. I would be suspicious of the return hose from the valve. Check it and if you do not see anything and can try reversing it and see if that cures it.

Mike in Warsaw

I understand your thinking on this. But why doesn't it do it when the loader lever is just sitting in neutral? The oil is still flowing through the lines and valve. I can't see any of the other lines getting stiff. Although they are very short before they attach to the loader steel lines. Twice today the loader worked fine for the first time when I started the motor up and used the bucket. The next time I tried to operate it. It was back to the slow mode again. A half hour later the same thing happened. If I restrict the flow to a trickle by only moving the lever a little bit, the loader will go up faster. There is definitely something fishy going on here. If I get a chance I will pull the lines off and try to take a look through them all. Or better yet, reverse all of them. Most of the lines appear to be original. They are 12 years old with 2760 hours on them. I replaced one a few years ago that blew a hole in it.

 

[RonMar]

I understand your thinking on this. But why doesn't it do it when the loader lever is just sitting in neutral?

Fluid is not flowing thru the return line when the loader is in neutral. With the valve in neutral, the flow thru the valve is into the input port and out the power beyond port and on to the next device in line(probably the 3PH control valve).

When you operate the lever, you divert fluid that would normally exit thru the power beyond port to one of the working ports for the spool you are operating, and on to one end of a cylinder to make it move. The fluid returning from the other end of that moving cylinder returns thru the other working port for the spool valve you are operating and goes to the RETURN gallery in the valve and exits the valve thru the RETURN PORT. A restriction on the return line leaving the valve return port will cause pressure to build back up the line against the fluid comming from the cylinder you are moveing. This pressure is felt as hydraulic load on the piston face and slows the loader movement, just as lifting a very heavy load would. This also causes the pressure to build on the line supplying the cylinder and all the way back thru the valve inlet port to the pump. When this pressure exceeds the safety pressure, such as when trying to lift too much weight with the loader or when a cylinder reaches it's end point, the safety valve wants to open and dump this excess pressure. Unfortunatly, the safety valve also dumps to the return gallery in the valve and since the return gallery is backing up already, the excess pressure dosn't have any easy place to go. This is a recipe for killing the pump, damaging the valve seals or blowing a line or cylinder body/seal.

You say it moves faster when you use less valve movement. That is because you are only trying to move the load as fast as the fluid returning from the cylinder can exit the return port into the return line from the valve. As soon as you exceed the ammount of fluid that the return port can handle, the back pressure starts to build and the cylinder slows down because of the return line restriction.

Here is a test for you. Remove the return line from the loader valve. Connect up a temporary line running from that return port into a bucket. Start up the tractor, you shouldn't have any flow from that temp return line tillyou start working the loader valve. See how the loader works returning the fluid to the bucket(temp resovoir). You will have to dump this fluid that builds up in the bucket back into the resovoir from time to time to keep from running the resovoir dry. If the loader works without issue, then the blockage is downstream from the valve along your normal return line. SInce the problem appears to be intermittent, a collapsing/decaying rubber hose liner sounds like an excellent suspect.

 

[montejw]

I understand your thinking on this. But why doesn't it do it when the loader lever is just sitting in neutral? The oil is still flowing through the lines and valve. I can't see any of the other lines getting stiff. Although they are very short before they attach to the loader steel lines. Twice today the loader worked fine for the first time when I started the motor up and used the bucket. The next time I tried to operate it. It was back to the slow mode again. A half hour later the same thing happened. If I restrict the flow to a trickle by only moving the lever a little bit, the loader will go up faster. There is definitely something fishy going on here. If I get a chance I will pull the lines off and try to take a look through them all. Or better yet, reverse all of them. Most of the lines appear to be original. They are 12 years old with 2760 hours on them. I replaced one a few years ago that blew a hole in it.

I think the thought here is that when the loader is sitting in neutral the flow through the valve is going out the power beyond line. When you use the loader only then does flow go through the return line. The flow is the output from whatever cylinders are being used, it's neutral pressure as long as there aren't any restrictions.

If you didn't have power beyond the fluid would always be flowing through the valve and out the return line. As someone else said you might be able to reverse the return line end for end and see what happens. Might be a temp fix. Or at least you'll know if that's the problem.

Monte

 

[3RRL]

My money is still on a restriction in the valve itself.
Your first post told us that after you took the valve apart to look for anything floating around in it, ... it was clean, except the float detent area. Then it worked good for two days and started acting up again makes me think there is still something in there.

I don't know enough about how the valve is constructed, but it is possible that the spools that control the fluid direction are screwed up or some debris in there. They might work just fine when cracked (feathered) when there is not enough flow to disturb the debris or put a worn area inside the valve into play. But under full stroke some debris is disturbed or the wear pattern comes into play and causes this abnormal behavior. In other words, when you move the valve lever slightly, it is not enough to allow the phantom piece of debris to alter the valve characteristics. But when you move the levers fully, it does.