Center vs Power Beyond

[tshep]

I've read and read and read....

What I don't see is a definitive description of why and when a good engineer selects one or the other.

I get the impression that if the port is the LAST port then power beyond really doesn't matter - no beyond exists.
What if that changes?
In my case, BX23 backhoe hose port sure seems easy to 'tag' onto, but should my new port be last or next to last if I chose the simplicity of the open center type - now two open center types in a row.

Or, why not all open center types?
Why did Kubota chose Power Beyond for loader? Right decision?

THX!

 

[/pine]

I've read and read and read....

What I don't see is a definitive description of why and when a good engineer selects one or the other.

I get the impression that if the port is the LAST port then power beyond really doesn't matter - no beyond exists.
What if that changes?
In my case, BX23 backhoe hose port sure seems easy to 'tag' onto, but should my new port be last or next to last if I chose the simplicity of the center type - now two center types in a row.

Or, why not all center types?
Why did Kubota chose Power Beyond for loader? Right decision?

THX!

The Power Beyond on many K_ubota loader valves is used to power the 3 point hitch...

Not sure what you mean by "center" a valve either has PB capability or it does not...most can be adapted for either open or closed center operation...

If a valve is the last in a series there is no need for PB (until you want to add something else)...

IMO buy a valve with PB whether you plan on using the PB or not...just keep the insert sleeve handy...!

 

[RickB]

I've read and read and read....

What I don't see is a definitive description of why and when a good engineer selects one or the other.

I get the impression that if the port is the LAST port then power beyond really doesn't matter - no beyond exists.
What if that changes?
In my case, BX23 backhoe hose port sure seems easy to 'tag' onto, but should my new port be last or next to last if I chose the simplicity of the open center type - now two open center types in a row.

Or, why not all open center types?
Why did Kubota chose Power Beyond for loader? Right decision?

THX!

Because the last valve in the system is almost always the three point hitch valve. CUT systems are all open center. CUT loader valves are open center and power beyond capable because the hitch valve and any backhoe valve are downstream from the loader valve. CUT backhoe valves are typically not power beyond valves because a backhoe installation usually disables the hitch valve by sending return oil directly to tank rather than to the hitch valve.

 

[oldnslo]

Closed center systems use variable volume pressure compensated pumps which are far more expensive than gear pumps. These are typically used on higher horsepower tractors and construction equipment vs lower cost CUTs. These do not require power beyond since the pump destrokes and only produces flow on demand. The valves are connected in parallel on these systems also much easier to run multiple functions simultaneously.

Open center: used fixed displacement pumps typically gear. These produce flow whenever the pump is turning. These require power beyond so that flow goes from one valve, to the next in series. Usually more difficult to operate multiple functions simultaneously

Guesstimate on prices: 10 GPM Gear pumps for CUTs are maybe $500 while similar sized variable volume could be $1500 - $2000

Ultimately decision to use closed center vs open depends on system requirements, cost, etc.

 

[Tx Jim]

What year was open center power beyond valve introduced? I remember back in the '60-'80's attaching OC hyd valve on tractors such as JD 420 or 430 & Farmall M or H ""without utilizing power beyond"" & the hyd control valve operated a hyd cylinder just fine. Does hyd pump GPM affect need for PBY?

 

[oldnslo]

TxJim
I do not know when power beyond was developed.

Today I believe that system requirements are the biggest factor in decision of open center Vs closed center. Closed center is usually considered to offer lower operating costs for higher flow higher pressure systems that frequently do not require full flow. The variable volume pump only produces flow required saving energy.

 

[rScotty]

The original title for this thread was confusing because it mixes a couple of terms.

There are basically two different ways that tractors generate and use hydraulic pressure and flow. They are commonly referred to as "open center" and "closed center". Oldnslo in reply #4 did a good job of explaining why the more inexpensive "open center" type with an inexpensive fixed gear pump is commonly used in CUT tractors. I can't think of an exception offhand.

So when using this common open center type of hydraulic system, the way to get hydraulic power to multiple control valves is to put them all in series by connecting them in such a way that every downstream control valve is fed from the power beyond port of the control valve just upstream of it. The last valve in the series returns any unused flow to the sump, as does each valve in the series when it is actuated.

To say it another way, to get power to work multiple control valves with this an open center type of hydraulic system the fluid simply goes from one valve to the next with the PB of one feeding the input port of the next one in the chain of valves.

Now the downside to this open center hydraulic system begins to be more obvious. One downside is that the more downstream in the hydraulic system you get, the more hydraulic pressure and flow has been lost to resistance. This loss is inevitable even when no upstream control valve is being actuated. And of course WHEN any upstream control valve is being used & actuated, all the ones downstream will suffer from loss of pressure and flow. How many valves you can work simultaneously in an open center hydraulic system is simply a function of how much extra flow & pressure that the basic gear type hydraulic pump is creating. The bigger the pump the more valves it will work at the same time, the more it will cost, and the more HP it will demand at all times.... whether using the hydraulics or not.

The alternative "closed center" hydraulic system uses and "on demand" type of hydraulic pump and stores unused flow in a pressure tank. It is more efficient and way more expensive. Top of the line stuff.
rScotty

 

[BukitCase]

This is the info sheet on the Prince SV valve I bought to add extra remotes to one of my tractors -

http://www.princehyd.com/Portals/0/valves/ValvesSV.pdf

On the first page, notice that the max pressure is 3000 psi - but just below that, they list the TANK pressure at max 500 psi. As I understand it, that's because the TANK gallery seals won't handle full pressure (probably a cost-cutting measure, never DID get an answer to that) -

What I DID get an answer to was exactly what that PB "adapter" does - it is stepped down in size to allow for separate O rings that, when fully installed, SEAL OFF the TANK gallery from the full pressure OUT port. THAT is where the PB for the next valve (or 3PH) goes.

I looked at a couple other mfg's at the time, don't recall which ones - but they ALL had the REDUCED pressure on tank and offered the PB adapter if that valve was NOT the last one in the (open center) loop... Steve

 

[Tx Jim]

TxJim
I do not know when power beyond was developed.

Today I believe that system requirements are the biggest factor in decision of open center Vs closed center. Closed center is usually considered to offer lower operating costs for higher flow higher pressure systems that frequently do not require full flow. The variable volume pump only produces flow required saving energy.

I still remember the JD sales meetings I attended back in the 60's-80's with JD rep's explaining how "great closed center hyd's" were compared to open center! Now a lot of new JD tractors have open center hyd's.

 

[RickB]

What year was open center power beyond valve introduced? I remember back in the '60-'80's attaching OC hyd valve on tractors such as JD 420 or 430 & Farmall M or H ""without utilizing power beyond"" & the hyd control valve operated a hyd cylinder just fine. Does hyd pump GPM affect need for PBY?

Ford compacts (Shibaura) started using PB capable loader valves in the late 1980s. What can happen in the absence of a PB circuit is pressure caused by a load on the work ports of a downstream valve builds in the return circuit of a simple pressure/return valve. This can and does overstress the spool seals in the upstream valve and can cause seal failure, possibly catastrophic. I suppose this is dependent on how much pressure can be built in the work side of the downstream valve and the design and construction of the spool seals in the upstream valve. A power beyond circuit segregates power beyond flow from return flow and protects the return circuit from extreme pressures.