I am not the brightest crayon in the box

[Wagtail]

G'day Wags jump on the bare co site and look under the hyd banner you will find a good explanation of basic hyd

Jon

Ta Mate.

 

[CJONE]

Can someone name one modern CUT or SCUT tractor that uses closed center? I can't think of a one.

None to my knowledge, and a guess that the cost is the reason. But John Deere has put out a bunch of the older farm tractors with closed center systems. CJ

 

[MHarryE]

SCUTs and CUTs are price sensitive. Gear pumps are cheap. Gear pumps have a fixed output. If it is a 20 gpm pump, it is pumping 20 gpm continuously. Most of the time it is circulating through valves, oil cooler, and back to tank. Move a valve to a cylinder that requires 1 gpm at 2,000 psi to extend, and all 20 gpm produced by the pump will be at 2,000 gpm. When you shift that valve the hydraulic system suddenly uses 23 horsepower.

In a closed center system there will generally be an expensive piston pump that will be pumping almost no oil at standby (using no power). Shift the valve to give 1 gpm flow at 2,000 psi and the pump will stroke to supply that flow at that pressure. The hydraulic system will use 1.2 horsepower.

Ironic that the small tractors that have low power use an inefficient hydraulic system that wastes power while the large ag tractors with high power capability use the much more efficient closed center systems, but its a matter of what the consumer will pay.

SCUTs and CUTs - consideration in comparing specs - a larger hydraulic pump will absorb more power when a hydraulic function is used leaving less available for the tractor itself. Its a balancing act.

There are other considerations. Gear pumps tend to be less sensitive to contamination so filtration does not need to be as stringent. In the case of a hydrostatic tractor (I am familiar with JD and Kubota) there is generally a hydraulic filter for the gear pump and a finer hydrostatic filter. The hydro transmission like a Kubota Grand L is a closed center system. The oil going into the piston pump has much finer filtration and consequently, the filter costs much more than the similar sized hydraulic system filter.

 

[CJONE]

The hydro transmission is actually a closed loop system with most of the oil remaining in the loop until it goes over a charge relief on the low side or past the pistons and port plates on the high side. The last few ag tractors I have worked on for my customers are now using a closed center system with 500psi stand by pressure for the remotes. Saves even more on horsepower and heat. The forestry industry and county road trucks have been doing this for awhile now, the ag industry is catching up. CJ

 

[hawkeye08]

So.. if I am reading and understanding correctly, at the risk of over simplifying, I can take the power beyond from my loader valve and plumb that to some rear remotes and from there the tank line from the rear remotes can come back and T into the loader valve tank line?

 

[Fallon]

So.. if I am reading and understanding correctly, at the risk of over simplifying, I can take the power beyond from my loader valve and plumb that to some rear remotes and from there the tank line from the rear remotes can come back and T into the loader valve tank line?

Yes, the power beyond loop must be a loop. Generally with the 3pt being the end & dumping to tank. You can't tee the PB loop. You can tee the tank circuit or have multiple separate lines dumping to tank as long as its not restricted.

The 3pt generally doesn't have any tank plumbing as its part of the transmission & tank assembly. It just has a hole directly attached to the sump. The loader & other stuff has a tank line you can tee into.

 

[IceStationZebra]

SCUTs and CUTs - consideration in comparing specs - a larger hydraulic pump will absorb more power when a hydraulic function is used leaving less available for the tractor itself. Its a balancing act.

There are other considerations. Gear pumps tend to be less sensitive to contamination so filtration does not need to be as stringent. In the case of a hydrostatic tractor (I am familiar with JD and Kubota) there is generally a hydraulic filter for the gear pump and a finer hydrostatic filter. The hydro transmission like a Kubota Grand L is a closed center system. The oil going into the piston pump has much finer filtration and consequently, the filter costs much more than the similar sized hydraulic system filter.

Piston pumps are physically larger for a given displacement, can not tolerate cavitation (due to filter restriction or excessively cold oil), generate more heat, have greater internal leakage, has higher lubrication requirements and are more difficult to diagnose when things go wrong. And the higher cost of the filter is only partially due to the finer filtration, it's also because it has much more filter media to keep the restriction low with cold oil. ISZ