Erratic Hydraulics

[Gary Sweat]

Ok, that makes sense. The steering valve is an open center that passes the oil straight through when not needed.

But, if the loader works until the bucket is dumped, why did it work then and not after? Seems if it was a low rpm issue, it would not have raised or curled at all

 

[Jbrink64]

I think TRH needs to input some at this point. We're chatting among ourselves with limited info.

 

[AKKAMAAN]

Ok, that makes sense. The steering valve is an open center that passes the oil straight through when not needed.

But, if the loader works until the bucket is dumped, why did it work then and not after? Seems if it was a low rpm issue, it would not have raised or curled at all

Since your CV is over 10 gpm sized, you will need to give your CV lever a full push/pull to be able to build enough pressure. A over or under sized CV will limit the proportionality in the CV. With an under sized CV, pressure will build early of the lever movement, and with an over sized CV, pressure will only build enough at the end of the lever movement.

In an open center system, the pump flow is considered "constant", and the pump flow goes through the open center in the CV while in neutral. To build pressure, we need to restrict the "orifice" defined by the open center, and at the same time open the connection between pump and work port to cylinder. When pump pressure is higher than load pressure in cylinder, cylinder will start moving. If CV is way oversized related to the pump flow, it will take almost some where close to 100% CV spool movement to create enough pressure to lift FEL. It will of course depend on load pressure in cylinders. It will also depend on the pump flow, which can be increased by throttling engine.

There are still some question marks to be answered....

Your 4gpm pump is rated at a certain pump speed or rpm, probably around 1800rpm......if you idle at 600rpm, your pump flow is only 1.33gpm, and that will make your CV even more oversized.

So when you say FEL is not working after dumping, are you 100% sure you pull CV lever to the end??

 

[RickB]

I think TRH needs to input some at this point. We're chatting among ourselves with limited info.

Often that's what we do best here!

 

[Gary Sweat]

Since your CV is over 10 gpm sized, you will need to give your CV lever a full push/pull to be able to build enough pressure. A over or under sized CV will limit the proportionality in the CV. With an under sized CV, pressure will build early of the lever movement, and with an over sized CV, pressure will only build enough at the end of the lever movement.

In an open center system, the pump flow is considered "constant", and the pump flow goes through the open center in the CV while in neutral. To build pressure, we need to restrict the "orifice" defined by the open center, and at the same time open the connection between pump and work port to cylinder. When pump pressure is higher than load pressure in cylinder, cylinder will start moving. If CV is way oversized related to the pump flow, it will take almost some where close to 100% CV spool movement to create enough pressure to lift FEL. It will of course depend on load pressure in cylinders. It will also depend on the pump flow, which can be increased by throttling engine.

There are still some question marks to be answered....

Your 4gpm pump is rated at a certain pump speed or rpm, probably around 1800rpm......if you idle at 600rpm, your pump flow is only 1.33gpm, and that will make your CV even more oversized.

So when you say FEL is not working after dumping, are you 100% sure you pull CV lever to the end??

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.

 

[Jbrink64]

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.

I don't really know your system, but a quick guess. Without any flow control devices, and a properly functioning CV, if you double your engine speed, you will double your flow minus a little due to leakage. A common pump test is check the flow at 1000 rpm, then 2000 rpm with no pressure on the pump. If the flow doesn't double, chances are there is a suction side restriction (filter, crushed line, screen, or under sized suction line). So, hypothetically speaking, if you double your engine speed, the loader should move at twice the speed, or at least noticeably faster. I don't think the 3/8" lines would be a restriction, unless there is a 3/8" suction line. If the pump was worn, or internal leakage in the CV or cylinders, the loader would be weak/slow at idle.

 

[Gary Sweat]

I don't really know your system, but a quick guess. Without any flow control devices, and a properly functioning CV, if you double your engine speed, you will double your flow minus a little due to leakage. A common pump test is check the flow at 1000 rpm, then 2000 rpm with no pressure on the pump. If the flow doesn't double, chances are there is a suction side restriction (filter, crushed line, screen, or under sized suction line). So, hypothetically speaking, if you double your engine speed, the loader should move at twice the speed, or at least noticeably faster. I don't think the 3/8" lines would be a restriction, unless there is a 3/8" suction line. If the pump was worn, or internal leakage in the CV or cylinders, the loader would be weak/slow at idle.

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.

 

[SPYDERLK]

Since your CV is over 10 gpm sized, you will need to give your CV lever a full push/pull to be able to build enough pressure. A over or under sized CV will limit the proportionality in the CV. With an under sized CV, pressure will build early of the lever movement, and with an over sized CV, pressure will only build enough at the end of the lever movement.

In an open center system, the pump flow is considered "constant", and the pump flow goes through the open center in the CV while in neutral. To build pressure, we need to restrict the "orifice" defined by the open center, and at the same time open the connection between pump and work port to cylinder. When pump pressure is higher than load pressure in cylinder, cylinder will start moving. If CV is way oversized related to the pump flow, it will take almost some where close to 100% CV spool movement to create enough pressure to lift FEL. It will of course depend on load pressure in cylinders. It will also depend on the pump flow, which can be increased by throttling engine.

The term here should probably be tandem center. Open center connects all ports together when centered. That doesnt seem right for cylinder control.
larry

 

[Gary Sweat]

The term here should probably be tandem center. Open center connects all ports together when centered. That doesnt seem right for cylinder control.
larry

I understood it to mean it was open form in port to out port (be it tank or PB) when the levers are centered.

 

[RickB]

The term here should probably be tandem center. Open center connects all ports together when centered. That doesnt seem right for cylinder control.
larry

The rest of the world describes this system and valving as open center. Suggesting otherwise adds nothing but the potential for confusion and misunderstanding.