1020 hyd jdemaris

[JCD]

jdemaris,or anyone, I was wondering if you could provide any additional insight regarding closed center hyds. I belive in an open center sys. fluid flows thru valve constantly until directed by a spool.... what is the advantage of closed center. I think my 1020 has the 8 piston pump. the loader is fed off a quick coupler connection under right floor board/axle area. No remotes however... what is the best way to tap this sys. to run a hoe , hyd. top link etc. Thanks.

 

[Tx Jim]

Closed-center hyd's are similar to a shallow well pump & pressure tank. Pressure build up in tank(lines on tractor) pressure switch cuts off pump(stroke control valve) when one opens faucet(move cylinder or steering wheel) then PSI drops then pump comes back on to build psi.

Real difference is on closed center pump keeps turning but stroke control valve directs pressure oil inside pump crankcase which pushes pistons away from pump shaft stopping oil from being pumped.

Way back when I attended JD sales meetings(brain washings) JD reps stated closed center hyd's saved HP & fuel when hyd pump went out of stroke.

IMHO they left out the inherent hyd problems both from heat and diagnostic that go along with low/high pressure closed center internal leaks

 

[JDemaris]

Well, in theory - companies that use closed-center systems claim they are better because repsonse is faster. That because the main oil line is constantly under pressure. Deere used to hype it up a lot.

I've got many manys with both systems and I've never noticed any difference in performance.

There are certainly some disadvantages to close-center systems.
On Deere tractors, they can make the engine crank over very hard and burn up starter motors. That because the starter motor has to turn a hydraulic pump trying to reach 2200 PSI. That is also why most such setups really need manual pump destrokers for good starting.
Also, closed-center piston-pumps can not draw oil to themselves like gear pumps do. So, they require a second pump somewhere to keep them fed. Deere uses a gear pump in the transmission to send oil to the piston pump in front.

"Closed-center" refers to the main hydraulic valve being closed-off in the center. I.e., all oil flow from the pump is blocked and under full pressure, all the time.

"Open-center" refers to the main hydraulic control valve being wide-open in the center. I.e., all oil flow from the pump runs through it and back to sump and flows all the time. No pressure, just flow.

So, if you hook up a closed-center valve to an open-center system, you will usually blow the hydraulic pump to pieces since it gets dead-headed. I've got a box of brand new Cessan gear pumps back from when I was a Deere mechanic. All brand new and all blown to pieces from being hooked to closed-center backhoes.

On your 1020 - it's going to have one of two little German hydraulic pumps and both are pretty small. The smallest is .68 cubic inches per revolution, and the other is 1.3 cubic inches per rev. On many industrial versions (called 300s) the USA built larger pump is used. It is 2.4 cubic inches per rev. Both my 300s have the big USA pump.

I can hop on my Deere 300B backhoe (closed-center), or any of my open-center hoes and all seem to work with the same repsonse speed. I've got a Ford 4000, an IH 3414, a Pettibone MDA, Oliver OC4, and a Deere 1010 - with open center gear-pumps.

 

[Machinery-Man]

which of the pumps does the German 2040 have?

 

[JCD]

Thanks for the explaination. I"m not sure which pump I have, but it looks quite large to me, maybe 6-8 inches in diameter, and appears to have 8 protrusions in the pump body for the pistons. I not sure what valve by backhoe has, but how do remote valves work in a closed system. I.e. could you run an open center valve body with a hold open detent remote or a selector valve off loader. Or does it not matter going from closed center to open center, just the other way around as you mentioned.

 

[JDemaris]

There are only two German pumps that I know of and they both are same size on the outside. The small .68 pump only has four pistons and bigger 1.3 pump has eight pistons. The pressure adjustment is usually a straight screwdrive slot. The USA pumps have an allen-hex adjuster.

Also the German pumps connect to the pump driveshaft with round shaft and a key. The USA pumps use only splined shafts.

You cannot use closed-center valves in open-center systems. The block the oil flow and blow the pumps up.

You also cannot use open-center valves in closed-center systems because this creates a huge "leak" and has the pump pumping oil all the time and trying to build up pressure which won't happpen.

Some newer control valves are "convertable" and can be used on both systems. They come with a big plug you change, so they can work with either system just by swapping one plug/cartridge. Deere was using them OEM for awhile, but we had a few problems. If the packing blow off that conversion plug, they sort of turn into open-center valves and overheat the pumps with high pressure leaks.

 

[buickanddeere]

Use a closed center backhoe valve or the hydraulic system will become scalding hot and the power steering/rockshaft will quit working. There will also be nasty moaning sounds as the front pump starves for oil.
Supplying oil/returning from the scv will starve the front pump unless you are a slow backhoe operator.