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