Towable backhoe

[12barber12]

Thank you all for the advise these are the specs on the pump and it is run by 11hp Briggs
GPM: 11
Shaft: 1/2in.
Inlet: 3/4in.
Outlet: 1/2in. NPT
Dimensions: 5.5in.L x 3in.H x 4in.W
Minimum HP: 5
RPM Requirement: 3600
For use with open center hydraulic systems only
1st Stage: 11 GPM@650 PSI
2nd Stage: 2.9 GPM@2500 PSI
Maximum Pressure: 3000 PSI
Bolt Circle: 2.83in.
4 Bolt Holes Spaced 2in. on Center
Bolt Hole Diameter: .344in.
Rotation: Clockwise

 

[12barber12]

These are the control valves

 

[J_J]

12barber12,

I don't know if you know this, but hardly anyone uses a two stage pump on anything other than a log splitter.

Irregardless, with that HP and the pump turning at 3600 rpm, you should have the pressure when a load is placed on the cyl.

Get your self a single stage pump, and you will be glad you did.

Your 11 HP engine should turn a .4 cu in pump at 3600 rpm and produce about 5.5 GPM at 3000 psi.

Set the valve relief about 100 psi below the pumps max pressure.

Do you have PB on the one valve, and is it setup to run another valve.

Your flow should be something like this. Pump to IN port of first valve, PB out to IN port of second valve. The first valve will have priority.

Both tank ports should go a filter , then to tank.

I would also not recommend galvanized fitting.

 

[J_J]

As far as the bucket not picking up a load, it may be that the two stage pump is still in the low pressure, at 650 psi, mode and can not generate the force required to lift. If you could somehow lock out the low pressure your system might work.

For example.

The push force on a 2 in cyl 1 in shaft at 650 psi is only about 2,042 lbs

------------------------------------------------3000 psi is about 9.425 lbs

Larger cyl will have a high push force.

 

[12barber12]

I do have pb and it is piped exactly how you said this is similar to the pump I had on it but the 2 stage seemed a little better

 

[J_J]

I can't see the model number, but that pump should have provided you all the pressure you would need, and about 3 GPM.

What are some of the pressure you are reading on the different cyl's with a load?

Do you have a a 3000 psi hyd gage in the system?

 

[SSdoxie]

First you need to figure out why you have only 1100 psi max pressure.
Then look at your design. You mounted the boom cylinder on top of the boom, which means its lift force is in the retract mode. A cylinder retracting has only a fraction of the force as extending.
Many backhoes and excavators are made this way to help protect the cylinder from damage of getting in the dirt or getting hit by the bucket if you crowd to close, but those have larger diameter cylinders with smaller rods to compensate for this reduced lift force.
Other backhoes mount the cylinder under the boom to take advantage of the extra force while using a smaller diameter cylinder.

Here is an example figuring a 3" cylinder barrel with a 1.5" rod @ 2000 psi:
The extending force (base end) is 7 tons. The retracting 1.77 ton. That means in the cylinder was under the boom it would have an additional 5.3 tons of force. You would be able to lift more with less pressure but the cycle time would be reduced.

 

[Stimw]

You also need to check your cylinder to be sure it is not bypassing internally.
To check remove the down hose and see if fluid keeps coming out when trying to lift.

 

[12barber12]

I have another problem the backhoe is running descent after adjusting the pump but now after running for 25 min or so it tends to lose strength any ideas I would greatly appreciate it

 

[12barber12]

I also noticed I had a slight leak in the line from the valve to the tank could that be the problem

 

[Redneck in training]

So I made some updates to my backhoe and it still isn't working right . I installed a bigger pump (11 gpm) I also put casters in the front and the axle in the back and that solved the tipping problem. It seems as if the pump or the motor isn't strong enough although with the new pump it doesn't bog down the engine anymore but with the bucket full it won't pick it up if anyone could help me I would greatly appreciate it thank you

I think your problem is geometry of the cylinder versus the boom. It is almost parallel to the boom. In other words it acts on very short lever to lift the boom.
The cylinder has to have more obtuse angle relative to the boom.

 

[R W]

I think your problem is geometry of the cylinder versus the boom. It is almost parallel to the boom. In other words it acts on very short lever to lift the boom.
The cylinder has to have more obtuse angle relative to the boom.

I am of the same opinion.
Also lack of hydraulic pressure and/or cylinder dia being to small may be contributing factors but overall I would say what ever ram/pump is used the
ram angle needs to be addressed.

 

[12barber12]

I am going to address the problem of the lift cylinder but it doesn't make sense because the cylinder that moves the dipper arm if that's what it's called seems very weak also and that cylinder is pushing but the bucket cylinder seems to have descent strength I know it's hard to understand but I don't know the correct terminology any advise is greatly appreciated

 

[R W]

but the bucket cylinder seems to have descent strength

The bucket cylinder set up enables it to
essert more mechanical advantage than the other two cylinders.

 

[R W]

the cylinder that moves the dipper arm if that's what it's called seems very weak also and that cylinder is pushing

In my opinion the geometry on this is not to the best advantage of the cylinder, main pivot could be lower or underneath the boom.
Also feel the dipper arm could be to long.

 

[Attono]

I am going to address the problem of the lift cylinder but it doesn't make sense because the cylinder that moves the dipper arm if that's what it's called seems very weak also and that cylinder is pushing but the bucket cylinder seems to have descent strength I know it's hard to understand but I don't know the correct terminology any advise is greatly appreciated

What are the lengths of the boom arms you're using?

 

[J_J]

A 11 GPM single pump needs about 23 HP to run it at 3000 psi.


If you are trying to use a 2 stage pump, it is not a good idea.

How did you ge the 1100 psi?

Did you hold the lever to max, and if so, the gage should have peaked out at the relief setting.

What is your relief setting on both valves.

Set both reliefs the same, at 100 psi below pumps max pressure.

 

[chad22]

I agree you need a single stage pump for it to work properly. Look on ebay and you can sometimes find some new single stage pumps for real cheap. I found a hydraulic pump on ebay that was brand new but was discontinued. I purchased the pump for $40.00 including shipping.

I have it on my home made excavator now and it's working perfectly. Dug plenty of holes with it. Not a bad deal. I found out it was discontinued when I contacted the company about port sizes. It was an MTE Brand.

Don't know if you can find the same one I bought. But there are still plenty of deals out there on ebay. You just have to dig a little to find them.

Best of luck with your backhoe.

 

[tcreeley]

I have a Northern Tool trencherman mini backhoe. It came with a single stage 1.2 gpm pump which was too slow for me- swinging the bucket side to side for next scoop. I swapped the pump for a 2 stage 11 gpm/2.9 gpm pump like this one - Concentric/Haldex Hydraulic Pump — 11 GPM, 2-Stage, Model# 1001689 | Pumps| Northern Tool + Equipment . I swapped out the 5hp motor for a Tecumseh 8 hp. I've had it for close to 20 years and it works great.

 

[12barber12]

The dipper arm is 49" and boom is maybe 42" then angles around 30 degrees and is 30"