Erratic Hydraulics

[AKKAMAAN]

Doesn't matter if the bucket is full of dirt or empty. Runs the same speed and will lift a full bucket with the valve barely opened.

As long as the PRV stay closed and open center in valve is fully CLOSED, (lever fully pulled), load do not matter to speed.

 

[J_J]

While we're waiting for TRH to get back in with better info I'd like to ask both of you a question about my loader. We can stop talking about it when TRH gets back in.

My loader seems to run (loader and bucket) the same speed at 1000 rpm as it does at 2000 rpm. I can't see any difference in speed. Shouldn't it operate faster with rpm? I can control speed only by barely moving the loader valve from just open to full open and then it's not much of a difference.

pump - 3.9gpm
valve - 10 gpm
loader cylinders - 1.75"
bucket cylinders - 1.5"
all lines - 3/8" ID

Is it because of the valve being over twice the pump gpm or could I have a problem with the pump? Doesn't matter if the bucket is full of dirt or empty. Runs the same speed and will lift a full bucket with the valve barely opened.

A logical conclusion would be that if you increase rpm, with a good pump, then the volume will increase. If you say the speed of the cyl is the same at any rpm, then some of the fluid is going somewhere else, be it through a relief, or leakage in the pump, or diverted. If some of your fluid is diverted by a priority valve for power steering, and it does this 100 %, then the fluid going through the steering valve is either being used to steer, or it is passing through to the tank. If the priority valve is using 2 GPM, and your pump is pumping 4 GPM, then you only have 2 GPM for the lift.

On my Power-Trac, my lift can use the fluid that is bypassed by the steering circuit. If my steering takes all the flow, then the lift gets none.

If your valve is a 10 GPM valve, then at 1/3 lever action, you have given all the flow to the cyl that is available, and any further push on the lever will not do any good. In order to get good feather action, a smaller valve is required.

 

[Jbrink64]

The loader cylinders and valve are all new. The pump is not new. I have not been into the pump to see if there is any signs of wear. I'm sure there must be as it appears to be the original pump that came on the tractor (YM1900). I have cleaned the filter screen and changed the oil a couple of times to make sure it's clean and the oil is not foaming or changing color. It does not have any problems lifting nor have I ran into any issues with the 3pt raising anything I attach to it.

All the comments about speed and flow increasing with rpm has got me wondering why mine doesn't seem to show any signs of change. Can gear pump keep pressure and not increase flow with rpm if it is worn inside? I would rather not invest in a new pump just to find out it didn't make any difference. Maybe it is moving a little faster with rpm but if it is I just can't see it.

Indications of a worn gear pump would be a lack of pressure/power at low speeds.

 

[Gary Sweat]

A logical conclusion would be that if you increase rpm, with a good pump, then the volume will increase. If you say the speed of the cyl is the same at any rpm, then some of the fluid is going somewhere else, be it through a relief, or leakage in the pump, or diverted. If some of your fluid is diverted by a priority valve for power steering, and it does this 100 %, then the fluid going through the steering valve is either being used to steer, or it is passing through to the tank. If the priority valve is using 2 GPM, and your pump is pumping 4 GPM, then you only have 2 GPM for the lift.

On my Power-Trac, my lift can use the fluid that is bypassed by the steering circuit. If my steering takes all the flow, then the lift gets none.

If your valve is a 10 GPM valve, then at 1/3 lever action, you have given all the flow to the cyl that is available, and any further push on the lever will not do any good. In order to get good feather action, a smaller valve is required.

Your last paragraph seems to sum it up pretty good. After less than half of the joystick movement, there doesn't seem to be any change in speed. I looked for a lower gpm (about 6-7 gpm) valve with regen but have not found one yet. They seem to all be in the 10gpm range. Still, I can't figure out why it wouldn't go faster with rpm.

I don't hear the PRV kick in until it hits the 1500psi I have it set to and it does that in less than a second once the cylinders are extended. Maybe I'm looking for a problem that doesn't exist.

 

[Gary Sweat]

Indications of a worn gear pump would be a lack of pressure/power at low speeds.

I don't seem to have that problem. It will lift a full load at 1000rpm or lower just fine. It even lifts the rear of the tractor off the ground if I hang on something stubborn. Engine bogs down a little at that lower speed but it will still lift. It just always moves at the same speed regardless of the rpm.

As soon as I get the box blade reworked to mate up with the quick attach, I'll time it with a stop watch and see if there is actually any difference in speed vs rpm.

 

[J_J]

Your statement indicates that there is a good possibility that there is a restricted fitting in the circuit, and therefore will only allow a certain amount of fluid to pass within a given time. If you have the chance, uncouple the hoses and fittings and look to see if any fitting is smaller than the inside diameter of the hose. If your system is going into relief, that indicates that the system had good pressure, although 1500 psi seems low for the modern hyd system. Someone not to long ago, purchased a fitting off the self and installed it and found out that things slowed down. The restricted fittings will have a different number, but will connect just fine. You might also find a washer with a small hole in it just for that purpose, to restrict flow and slow down the speed of operation.

What is your max pump pressure?

 

[AKKAMAAN]

Still, I can't figure out why it wouldn't go faster with rpm.

Make 100% sure you CV spool make full movement to the END....it should be about 1/2" spool movement....if there is something interfering, so you cant get that last 1/32" of spool movement, oil will still divert to tank. This can be tested with a pressure gauge while stalling a cylinder

Once again, with these constant flow systems (open center), you must "think" building pressure when using CV spool, and flow will be diverted to port when pressure is high enough to over come load pressure. Pressure build up by restricting the open center of the CV. Plumb a pressure gauge into your system to monitor PUMP pressure when operating an constant flow, open center system.

 

[Jbrink64]

Your statement indicates that there is a good possibility that there is a restricted fitting in the circuit, and therefore will only allow a certain amount of fluid to pass within a given time. If you have the chance, uncouple the hoses and fittings and look to see if any fitting is smaller than the inside diameter of the hose. If your system is going into relief, that indicates that the system had good pressure, although 1500 psi seems low for the modern hyd system. Someone not to long ago, purchased a fitting off the self and installed it and found out that things slowed down. The restricted fittings will have a different number, but will connect just fine. You might also find a washer with a small hole in it just for that purpose, to restrict flow and slow down the speed of operation.

What is your max pump pressure?

Thats got to be it. Either oil can't get into the pump fast enough, or there is a restrictor fitting. Like JJ said, look for a standard fitting with a 1/8" or smaller passage. A restrictor plate could be installed between what looks like 2 fittings. Ford use to put one way restrictor plates between 2 fittings on the hoses. The idea was a fast raise, slow drop, or fast curl, slow dump. A lot of times, these plates were installed backwards, that would cause a slow lift, fast drop, etc.

Restrictor fittings would slow the functions in both directions. A little piece of debris in the fitting would make them restrict even more.

Also, never rule out a QC as a restrictor. If they are mismatched, say a Parker w/a ball check plugged into an Aeroquip w/a poppet check, the QC's wont open all the way. And, damaged or worn QC's wont open all the way, either.

 

[Gary Sweat]

Your statement indicates that there is a good possibility that there is a restricted fitting in the circuit, and therefore will only allow a certain amount of fluid to pass within a given time. If you have the chance, uncouple the hoses and fittings and look to see if any fitting is smaller than the inside diameter of the hose. If your system is going into relief, that indicates that the system had good pressure, although 1500 psi seems low for the modern hyd system. Someone not to long ago, purchased a fitting off the self and installed it and found out that things slowed down. The restricted fittings will have a different number, but will connect just fine. You might also find a washer with a small hole in it just for that purpose, to restrict flow and slow down the speed of operation.

What is your max pump pressure?

I built the loader and all of the hydraulics are new. There are no restrictions in any of the lines or fittings. I did notice when I bought the cylinders that the fittings on both the loader cylinders (1.75" loader and the bucket 1.5") are SAE 6 which seemed kind of small to me. The holes in the cylinder fitting is smaller than the hole in the hose fittings. The work ports on the loader valve are SAE 8 and the in/out ports are SAE 10. So, if there is anything that could be called a restriction it would have to be on the cylinders. The cylinder hole looks to be about 1/4" in diameter.

When I got the loader valve it was set at 2,200 psi. The pressure gauge would hit the 2,200 real fast when the cylinders reached max travel. Since a full load in the bucket only went to around 750 psi and the bush hog only put around 850 psi, I lowered the relief valve down to 1500 psi to put less strain on the seals. I didn't see any point in it reaching 2200 psi if it didn't have to.

 

[Gary Sweat]

Make 100% sure you CV spool make full movement to the END....it should be about 1/2" spool movement....if there is something interfering, so you cant get that last 1/32" of spool movement, oil will still divert to tank. This can be tested with a pressure gauge while stalling a cylinder

Once again, with these constant flow systems (open center), you must "think" building pressure when using CV spool, and flow will be diverted to port when pressure is high enough to over come load pressure. Pressure build up by restricting the open center of the CV. Plumb a pressure gauge into your system to monitor PUMP pressure when operating an constant flow, open center system.

There doesn't appear to be any problem with the CV movement. It will move smoothly all the way through the stroke range. By the time I hit the half way point on the joystick it doesn't make any difference in the speed. I can make the loader/bucket barely creep by just a small movement in the joystick.

If I feather the CV I can get it to read varying pressures depending on how far I move the joystick while raising the loader or curling/dumping the bucket. I can tell when the relief opens as it makes a low pitched whining noise and the gauge hits 1500psi quickly.

The thing I'm trying to figure out is it doesn't make any difference in speed when I open the CV all the way at 1000rpm or 2000rpm. The loader just moves the same speed or seems that way. I'm not disappointed with the speed, just that it is puzzling as to why it is always the same speed regardless of rpm.