Series, Parallel, and Power Beyond?

[Iplayfarmer]

Here's a general question without any immediate relevance to me, but hopefully someday I'll need to know.

Someday I'm going to try to build a backhoe. I don't need one, I just think it's a great project for a CUT owner with a welder.

My question is about the difference in valves. I'll need either a single 4 valve bank or two sets of two banks that will all operate at the same time if needed. I'll go with whatever is cheapest that will still fit.

I think I've figured out power beyond. It's a feature that allows another valve bank downstream in the hydraulic circuit to have pressure and operate at the same time as the first. But, what about Series vs. Parallel?

Does the power beyond feature have any affect on the bank of valves that it is on? Will a parallel valve bank with power beyond still only work one valve at a time?

So much to know

 

[RonMar]

Well unless you go to a closed center system, then parallel opertion is out of the picture. Hydraulic fluid, like electricity will ALWAYS take the path of least resistance. You need to build pressure to perform work. In a parallel circuit, if you operate a valve on one leg, the fluid will just flow down the other leg and no pressure will be built.

Since the spools on the valves have to operate in series, the first spool will interrupt the flow and send it to a cylinder, depriving the PB outlet and any downstream valve of fluid untill you are done working the spool on the first valve. There is not normally any restriction downstream at the next open center valve. If the first valve allowed this when a spool was activated, it would be splitting the flow and all the fluid would go there(path of least resistance) and no pressure would build or work be performed at the first valve.

Many valves have a parallel gallery internal to the valve. When you operate a spool, you send fluid to the cylinder and to this parallel gallery. If you operate any other spool on that valve, it will not be able to get any fluid from the main gallery as this flow was interrupted by the first spool, but it will get fluid from the parallel gallery and both cylinders will share the flow(both work at half speed) as long as both spools are held.

Since it is desireable to have simultaneous movement on a BH such as boom up and swing or dipper out and dump, you will probably want a single valve with an internal parallel gallery for your four main functions. A two spool on PB would work for your outriggers as they are not typically used along with the main functions.

 

[Iplayfarmer]

So I want to avoid parallel valves on my open center circuit. Right?

Also, How do I know when buying a valve if all four spools will be able to operate at the same time? Does Powerbeyond affect that?

And, If I just have a regular open center bank of two valves for the outriggers without power beyond, won't I still be able to use everthing else, just not at the same time as the outriggers?

This is one of those scenarios where the more I learn, the less I know.

 

[dfkrug]

So I want to avoid parallel valves on my open center circuit. Right?

Also, How do I know when buying a valve if all four spools will be able to operate at the same time? Does Powerbeyond affect that?

And, If I just have a regular open center bank of two valves for the outriggers without power beyond, won't I still be able to use everthing else, just not at the same time as the outriggers?

This is one of those scenarios where the more I learn, the less I know.

Think of it this way: you will have one pump supplying pressure, so you
will have one circuit of open center spool valves. Each valve, except the
last will provide "power beyond" pressure to the next valve in the series.
The last does not need pwr byd unless there is another valve downstream
that might need to be operated when the b/h is connected (unlikely).
The easiest way to build the 6-valve bank you need is to buy a "stack"
of 6 valves, where pwr byd is provided internally to each valve. Prince
makes a build-your-own stack valve to meet your needs, or you can
buy one of many 6-spool valves listed on Ebay or at Surplus Center.
I bought the Prince for my CADDigger hoe.

 

[RonMar]

So I want to avoid parallel valves on my open center circuit. Right?.

You want to avoid plumbing multiple valves in parallel. You DO want a single valve(with at least 4 spools) with an internal parallel gallery to allow simultaneous operation of those 4 spools.

Also, How do I know when buying a valve if all four spools will be able to operate at the same time? Does Powerbeyond affect that? .

The valve description/specifications should mention "parallel gallery" or "parallel operation" somewhere. Power beyond should not effect that. Power beyond is just an extension of the main high pressure gallery in the valve to the input of another valve bodys main gallery.

And, If I just have a regular open center bank of two valves for the outriggers without power beyond, won't I still be able to use everthing else, just not at the same time as the outriggers? .

Correct, provided, as Dfkrug mentioned, that non PB valve is the last in the circuit. I would imagine the flow would go something like this:
1. Pump
2. 4spool PB valve
3. 2spool non PB valve
4. Return filter
5. Reservoir.
The return line out of the PB valve gets "T"d back into the line right before the return line filter so that fluid also gets filtered.

This is one of those scenarios where the more I learn, the less I know.

Keep at it, you will soon reach a point where all the divergent paths in this subject start to tie back together. The Prince hydraulics website princehyd.com has some intresting drawings that may help close up the loose ends. The second page of this one shows a basic 2 valve circuit with power beyond. This is also for a stackable type valve so either of those valves could be built with more than the 1 or 2 spools shown in the drawing.
http://www.princehyd.com/Portals/0/products/valves/Series20InstS.pdf

 

[Iplayfarmer]

Okay then...

--A parallel valve will allow all spools to operate simultaneously.

--A series valve will only send pressure to the first open valve.

Neither series nor parallel within a valve really affects any other component of the circuit.

Now see if I understand power beyond.

My current setup for my loader has two spools in one valve and the TPH down stream in the circuit from that. I can operate a single function of the loader at a time. I can't lift and curl at the same time. And, the TPH only works when neither of the spools on the loader control are activated. That tells me that I have a series valve with the two spools that is not a power beyond valve. Is that right?

Is power beyond needed for every multiple valve system or just those systems that require more than one valve to be operated at the same time?

 

[RonMar]

I would guess that your loader valve does have a Power Beyond output. That is the high pressure line that feeds your 3PH. How many hoses does it have, 6 or 7? I would guess 7, 3 large and 4 small to the cylinders. The 3 large would be HP inlet from pump, HP PB outlet and LP return. You see when you raise a heavy impliment on the 3PH, all the lines and fittings between the pump HP output and 3PH cylinder must be able to endure full system pressure. PB is this high pressure passage thru the valve. So I would guess that your system goes like this.
1. Pump
2. Loader control Valve with PB line out to 3PH and LP return line to reservoir.
3. 3PH control valve

If it only has 6 hoses, do you have a picture of it?

 

[Iplayfarmer]

I'm pretty sure that it has just 6. At least it just has one line in and one line out.

I'll get some pictures tonight after work and post.

 

[dfkrug]

My current setup for my loader has two spools in one valve and the TPH down stream in the circuit from that. I can operate a single function of the loader at a time. I can't lift and curl at the same time. And, the TPH only works when neither of the spools on the loader control are activated. That tells me that I have a series valve with the two spools that is not a power beyond valve. Is that right?

Is power beyond needed for every multiple valve system or just those systems that require more than one valve to be operated at the same time?

Your loader has 2 spool valves in one "monoblock", operated by 2 separate
handles or a joystick to operate both. You CAN lift and curl at the same
time, though pressurized oil will take the easiest path back to the
reservoir. Since lift and curl will most likely require different pressures, you
have to feather the 2 valves to achieve simultaneous movement. A
joystick makes this process fairly easy, but requiring practice. Feathering
a valve means partially opening it, which causes a certain amount of
back-pressure. When that pressure equalizes with the back-pressure
required by the other partially open valve, both circuits operate.

In a single-pump fixed-displacement system, open-center spool valves
are placed in series. "Power beyond" is one way to provide pressurized
oil from one valve to the next (internal to a multivalve monoblock, or
externally from one multivalve monoblock to the next). Another way
to provide pressurized oil form one pump to multiple valves is using a
flow divider. This is how one pump can supply pressure to open center
spool valves at the same time as to a power steering valve.

 

[RonMar]

I'm pretty sure that it has just 6. At least it just has one line in and one line out.

I'll get some pictures tonight after work and post.

I would be interested in seeing a picture. There are some valves configured with return and HP outflow together and rated for full system pressure. But most valve designs have the return galleries from the cylinders out near the ends of the spools and contain this low return pressure with "O" rings. As such, the return pressure is usually limited to a certain level. For instance Prince on their monoblock valves limits the backpressure on the return port to 500PSI. Now if this return port feeds on to another valve, loading up that valve could force oil past the "O" rings of the first valve and cause leaks at the ends of the spools.