Regarding 3rd function valve sticking

[J_J]

The relief only operate when you exceed the force on the grapple, so most times, it is not relieving.

 

[brocas]

The relief only operate when you exceed the force on the grapple, so most times, it is not relieving.

With no restrictors I agree, but intuiyively I would think that with restrictors restricting the flow, the pressure builds up and the releif valve starts dumping fluid (I guess it would be a function of much restriction is needed, but I know that in my case, there is a whole lot of restriction going on when restricted enough to get the speed I want, and the releif valve is definetely dumping fluid). This is why I think restrictors are not an ideal method even if the 3rd function valve worked correctely, flow diverting would be best.

 

[brocas]

Do you have a picture of your grapple set up?

If the geometry is not correct, you will have fast speed. Do you need high volume of fluid for normal FEL operations? You could run the engine at 1/4 speed, decreasing the volume by 4 . If you had 12 GPM, you now have 3 GPM.

This is a priority flow divider valve, the priority circuit uses 3 GPM, and the rest can go to tank, or to another valve.

Surplus Center - 3/30 GPM PRINCE PRIORITY FLOW DIVIDER W/RELIEF

What appears to have happen here is a flaw in the design of the grapple geometry, the cyl used and the valve used. This is where the engineers are supposed to figure all this out before it gets installed. If it doesn't work, the technician then comes in and fixes it.

I will try to get a photo. I dont blame the grapple design at all. The grapple was not designed specifically for my tractor, no matter how its built, if you use too much flow then it will move too fast. It seems 10GPM is too much flow for this grapple, plain and simple. The 3rd function is ON/OFF only so that means the grapple always gets full flow. So this flow needs to be reduced somehow. The flow restrictors work fine for this but the 3rd funtion vave sticks. What I would like to know is why, or if this is to be expected from a solenoid valve.

Even at low RPM speed is too fast, and even if it wasnt, it would be enough of a pain to keep adjusting RPM to make me want to solve this problem.

You sugest a flow divider valve, which sounds OK, but why not a so called flow control valve like this one?

Brand Hydraulics Side-Ported Adjustable Flow Control Valve 1/2in. NPT ports, 0?6 GPM, Relief Valve, Model# PFCR51-1/2 | Adjustable Flow Valves | Northern Tool + Equipment

My understanding is this valve is just an adjustable divider valve, am I wrong?

What I really want to try is a proportional valve like this one:

Brand Hydraulics Electronic Flow Control Valve 15 GPM, 3000 PSI | Adjustable Flow Valves | Northern Tool + Equipment

I would add another switch on the FEL stick to select between two current levels that would go to the proportional valve to select two flows.

If this valve is installed after the pump before the FEL block, is there any reason it would not work to control the flow to all the hydraulics?

Of course reducing the flow before the 3rd function solenoid valve may still cause the valve to stick if the valve needs some minimum flow to operate (which is what I am speculating).

 

[Rockgod]

I will try to get a photo. I dont blame the grapple design at all. The grapple was not designed specifically for my tractor, no matter how its built, if you use too much flow then it will move too fast. It seems 10GPM is too much flow for this grapple, plain and simple. The 3rd function is ON/OFF only so that means the grapple always gets full flow. So this flow needs to be reduced somehow. The flow restrictors work fine for this but the 3rd funtion vave sticks. What I would like to know is why, or if this is to be expected from a solenoid valve.

Even at low RPM speed is too fast, and even if it wasnt, it would be enough of a pain to keep adjusting RPM to make me want to solve this problem.

You sugest a flow divider valve, which sounds OK, but why not a so called flow control valve like this one?

Brand Hydraulics Side-Ported Adjustable Flow Control Valve 1/2in. NPT ports, 0?6 GPM, Relief Valve, Model# PFCR51-1/2 | Adjustable Flow Valves | Northern Tool + Equipment

My understanding is this valve is just an adjustable divider valve, am I wrong?

What I really want to try is a proportional valve like this one:

Brand Hydraulics Electronic Flow Control Valve 15 GPM, 3000 PSI | Adjustable Flow Valves | Northern Tool + Equipment

I would add another switch on the FEL stick to select between two current levels that would go to the proportional valve to select two flows.

If this valve is installed after the pump before the FEL block, is there any reason it would not work to control the flow to all the hydraulics?

Of course reducing the flow before the 3rd function solenoid valve may still cause the valve to stick if the valve needs some minimum flow to operate (which is what I am speculating).

Sounds to me like you're going to great lengths trying to sort this thing out. Kubota should put you on the payroll

Has your dealer offered any help? Does he know your valve is sticking?

 

[mmorisoli]

Gang I just bumped into this post and wish I had found it sooner.

I two have a Kubota L3940 that was purchased new almost 2 years ago with the dealer installed factory 3rd function for a grapple. It has been sticking since day one and has been an absolute nightmare to get fixed but is the best investment I have ever made. The ability to use the grapple is a huge force multiplier.

That aside, I took the tractor back to the dealer I purchased it from three times with no improvement at all. They were completely incompetent at resolve the problem. Finally I switched to a dealer that was a bit closer who I didn稚 purchase the tractor from. These guys promised me they knew exactly how to fix the problem. Well they tried three times without any success. They actually were worse than the first because each time I took it too them, it came back worse. Leaking lines, debris in the relieve valve causing the loader to not work at all and at one point they forgot to tighten an allen screw in the 3rd function that managed to puke 3 gallons of brand new Mobil 1 SUDT fluid in moments.

The second dealer first blamed everything on the first dealer, pressures were set too high etc. The last trip they said they replaced the 3rd function with a new unit. I feel like an idiot for not writing down the S/N of the first unit because I have serious doubts anything was replaced. Anyway now instead of sticking 60% of the time it is down to about 10% of the time.

Very annoying.

If I had to do over again, I would still get a third function, but I would never get a Kubota one, I would find a 3rd party 3rd function.

FYI, the rubber boot at the bottom of the loader control will not stay installed ever since they added the 3rd function to the control arm. They have tried everything including purchasing new boots to 3M cement. It won稚 stay in place longer than 1 minute

 

[brocas]

Gang I just bumped into this post and wish I had found it sooner.

I two have a Kubota L3940 that was purchased new almost 2 years ago with the dealer installed factory 3rd function for a grapple. It has been sticking since day one and has been an absolute nightmare to get fixed but is the best investment I have ever made. The ability to use the grapple is a huge force multiplier.

That aside, I took the tractor back to the dealer I purchased it from three times with no improvement at all. They were completely incompetent at resolve the problem. Finally I switched to a dealer that was a bit closer who I didn稚 purchase the tractor from. These guys promised me they knew exactly how to fix the problem. Well they tried three times without any success. They actually were worse than the first because each time I took it too them, it came back worse. Leaking lines, debris in the relieve valve causing the loader to not work at all and at one point they forgot to tighten an allen screw in the 3rd function that managed to puke 3 gallons of brand new Mobil 1 SUDT fluid in moments.

The second dealer first blamed everything on the first dealer, pressures were set too high etc. The last trip they said they replaced the 3rd function with a new unit. I feel like an idiot for not writing down the S/N of the first unit because I have serious doubts anything was replaced. Anyway now instead of sticking 60% of the time it is down to about 10% of the time.

Very annoying.

If I had to do over again, I would still get a third function, but I would never get a Kubota one, I would find a 3rd party 3rd function.

FYI, the rubber boot at the bottom of the loader control will not stay installed ever since they added the 3rd function to the control arm. They have tried everything including purchasing new boots to 3M cement. It won稚 stay in place longer than 1 minute

Are you also using flow restrictors to slow down your grapple?

I did no bother with my dealer precisely for the reasons you mention. For now I'm just learning to live with it. But when I have the time, I will solve this problem one way or another.

 

[mmorisoli]

No, just a standard installation. My grapple does not have the problem of being too fast, it is very articulate in both opening and closing. In fact to make everything function a bit crisper I operate the tractor at about 1,300 to 1,400 RPM with Auto Throttle turned on when I use the grapple.

My only problem is that quite often the value sticks in the open or close position which you can easily hear and feel due to the loss of hydraulic pressure and the oil pump whine.

 

[nybirdman]

I have the same problem with mine.Been to the dealer's three times...still does it.The only"CURE" is to leave the three point hitch slightly down,just off of full up.I know not a cure but it does work.Kubota definitely has a problem here. I use mine for a grapple and snow-plow.

 

[slowzuki]

Listening to the descriptions, the areas on the spool in the valve must cause side loading and friction or a centering force between two ports that can't be overcome by the centering springs. This is either a problem in the porting or in the spool itself. If its just the porting, you could probably fix with a little touch up of the spool.

Sticking with restrictors or when full open or close means when there is high pressure in the system that is acting on some part of the spool to pin it even when then solenoids are inactive. This is done on purpose in some spool valves like a latching relay. The reason messing with the three point helps is it momentarily stalls out flow in the hydraulic circuit letting the pressure equalize on both sides of the spool.

Kubota likely either spec'ed the wrong service to their supplier or the supplier has a bad batch of valve spools or bodies.

BTW the spool is the cylinder with holes/channels to direct hydraulic flow that slides back and forth in a valve body that has ports in it.

 

[mmorisoli]

Slowzuki I love your explanation, I can picture the problem in my head When I release the open or close button, you can actually hear and feel how the electric current to the solenoid has stopped, yet the valve just sits there stuck in the body. The tractor is heavily loaded at that point and I have played around with raising and lowering the RPM to see if that makes a difference. In some cases dropping back to idle in this state causes it to release but most of the time you have to twitch the solenoid a few times and then it releases.

When this first started happening I read a lot about the importance of the dealer installing the unit to flush out the new lines, cleanliness, etc After all of the attempts to fix it, the numerous adjustments to pressures by the two dealers I am convinced that there is just a design flaw as you mentioned in your post.

I truly wish there was a better way for a customer to connect with Kubota. I asked both dealers if there wasn稚 some way for me to speak to their Kubota rep and both claimed they were my mouth to Kubota so to speak.

Recently Kubota sent me a evaluation form that I filled out saying that I loved the tractor, but was very disappointed with the services and the 3rd function. Was hoping that would cause someone at Kubota to reach out to me, but so far nothing.