Backhoes, Simultaneous Action Possible?

[andyfletcher]

I have been looking at homemade plans for backhoes, but by the schematics and spools they recommend, it doesn't seem possible to extend the bucket arm and raise the boom at the same time, or for that matter activate more than one member at a time.

I'm pretty sure the commercial jobs can do more than one action at once. Is there another spool configuration do they use? Is that what demand connectors are for?

With open center spools the first one activated and downhill from the pump would get all the pressure, and the ones behind that(next in line) would need to wait. That would be a hassle wouldn't it, or does it just need getting used to.?

Other questions. What is the amount in sweep in degrees does the boom make right to left and vise versa. I thing I read somewhere 240- 270deg, but i could be wrong.

How many minimum GPM@PSI do I need for a medium sized setup with quick response, but not a commercial rig?

Thanks

Fletch /forums/images/graemlins/confused.gif

 

[bobodu]

You would want to get a "valve stack".This is a series of valves with a common manifold.Seperate valves would require "power beyond', a port that would let flow go elsewhere.

 

[MadReferee]

It really depends on the design of the valve. On most valves with multiple spools when any spool is opened the closest one to the inlet gets priority and the others get what is left over. Your loader valve works that way. Other valve designs have only the opened spool getting fluid.

Ganging multiple valves together is quite different from having a single valve with multiple spools. You have got to look at the manufacturer's specs to make sure you get a valve that has multiple spools all sharing the same flow. Also check to see which one gets priority if multiple spools are opened at once. Selecting which function goes on which spool will also effect operation.

 

[andyfletcher]

Thanks Bobodu and Madref,

I was just looking at a hydraulic sales manual. They have what's called a Priority Flow Divider, which allows 2 cylinders to work at once.

Now the way I see it, the 3 sections I need to work independantly are the boom, forward arm, and bucket. The swing cylinder can wait for the pressure.

If I can find a 3 section Priority Flow Divider, then maybe that would settle the problem.

I'm going to try to find the valve stack you mention Bobodu, it sounds like what I want. I'll check my options and see what's best.

Thanks

Fletch

 

[MadReferee]

Check out Surplus Center. They always have multiple spool backhoe valves in the catalog.

 

[3RRL]

Fletch,
Just to let you know, my hoe has joystick controls that lets it move the bucket, dipperstick, boom and swing at the same time. Just not the stabilizer legs at the same time, those are on different valves. Also, swing is 180°. Some are less than this.

 

[john_bud]

Andy,

On the pump and flow. You want to match the pump to the spool valves you use. Probably 15 gpm would be good. Pressure will impact the force the cylinders give. 1800 - 2000 psi is a pretty good target. Higher pressures tend to have the side impact of heating the fluid faster.

the target rpm of 1800-2000 is my guess at mid way between peak Torque and peak Hp.

jb

 

[1948berg]

Listen to bobodu, A common manifold is what you need. When you use the digger you steal and borrow oil to fill the cylinder that needs oil, you dont use them one at the time. To get floating movements on the digger it is necessary to use more than one cylinder at the time. And you need 4 valves, you must include the swing. (actually you need 6 but the supporting legs can have other solutions.

 

[MMM]

I believe you need to search for sectional with paralell flow. With PFD you will have to add an oil cooler and you would never have 100% flow through one valve bank. I have an adjustable one to slow down my 6gpm hoe on a 23gpm circuit.

 

[dfkrug]

What you need is an open-center stack valve. Prince is the common after-mkt valve system. Surplus Center has a complete menu for building the Prince stack valve you need. This is the system specified in the CADDigger plans. The simplest setup will have 4 control levers for your home-made hoe. Two joysticks for the 4 valves are another option. All your 4 cylinders can be operated simultaneously with this setup. The cylinder with the least back pressure will get priority. With practice, you will see how you can be operating multiple handles at the same time to get your hoe to do amazing things.

Now as to flow rate. You only need about 8-10 hp to get 4-5 GPM at 1500psi. 4-5 GPM is enough flow to get an acceptable speed for 2 3/4-3" cylinders. I limited my CADDigger 728's pressure to 1500 psi, but I currently allow 2400psi in my factory-built Prairie Dog 7.5.