different fluid effect on hydraulic motor

[J_J]

I am thinking the only true answer will be with a flow and pressure test, and if it checks out correct, then a good 24 cu in hyd motor, and 3400 psi should generate about 12,994 in lbs or 1,082 ft lbs, and that should dig a hole in just about any ground.

Put the hyd gage in the auger motor IN hose in a tee and you will see the pressure developed by the hyd motor.

In neutral, the motor spool work ports are tied to tank, and I can see that if the aux valve OUT port is tied into a common return line, that return/tank flow from other hyd flow could make fluid come out the motor spool using back pressure.

In order to get the max flow through the hyd motor, you could bypass the QD on the return path and run a hose directly to tank.

Can you make a video of both skid steers using the same auger, showing the pressure gage.

Are you using an aggressive starter bit like these?

 

[bdog]

I hooked the auger to the new skid steer today. This skid steer flows 24 GPM and the original one 19 GPM. With the higher flow as suspected the auger spins faster but still has the same torque due to the fact the pressure is the same. I made a video of it drilling. Auger drillng - YouTube

The ground here is pretty easy and it goes good for about 5' then starts getting tough. The soil I am digging through doesn't really change at that depth it is just the resistance of the auger flighting in the hole I think. In other places where I am drilling it will sometimes stop the rotation at 2-3 feet and I have to baby it the whole way going up and down.

On this skid steer the pressure goes to 3000 PSI under heavy load and the return pressure stays around 200 PSI. I still have not found a good way to go to tank. The hydraulic reservoir on the skid steer is plastic and is buried in the engine compartment. It does not have any unused ports to connect to. There is a big line leaving the bottom of it (suction I assume) and a 1" or so line coming in the top. I guess I could tee into this line? The hydraulics on the skid steer look so complicated with lies running everywhere I hate to jack with it and screw something up.

 

[bdog]

Are you using an aggressive starter bit like these?

My bit looks a lot like the center bit in your photo. My auger is not big enough to have the outer teeth like that one though.

 

[J_J]

That ground looks hard, but if not, I believe you are adding more resistance to the load by leaving the dirt in the hole.

I would suggest driving the bit in the ground at full speed and when it slows, then pull the auger out fast still spinning, and repeat the process until you are at the depth you want.

Drilling in wood and cement for example, you have to keep the hole clean.

This video is similar to how I dig holes.

Fast Bobcat Auger - YouTube

http://youtu.be/8llPg8xeuos

Keep the speed and pressure high.

Here is the HP the pump is using to produce the 24 GPM's in order to turn the motor at

PUMP DISPLACEMENT HORSEPOWER TO DRIVE PUMP

Desired Flow 24 GPM Desired Flow 24 GPM
Operating Speed RPM System Pressure 3400 PSI

Displacement Required cubic inches Horsepower 56 HP
calculated for electric motors
double HP for gas powered motors

Motor speed should be around 241, if flowing 24 GPM's in to it, and developing about 12,994 in lbs of torque.

I observed the motor running very slow.

So by running the hyd motor slow, you are not using the GPM's necessary to put that available HP/torque into the ground.

Were you running the engine full rpm, and giving the motor all the flow available?

Those are my thoughts anyway.

 

[Leejohn]

If the cutting bit is the same or smaller then the auger it well not bore at all. Might want to double check that.

 

[bdog]

I observed the motor running very slow.

So by running the hyd motor slow, you are not using the GPM's necessary to put that available HP/torque into the ground.

Were you running the engine full rpm, and giving the motor all the flow available?

Those are my thoughts anyway.

The engine is at full throttle and I am running the auger as fast as it will go. It is slowing down due to the load. Once it starts doing that even if I just barely put down pressure it goes slow or stops.

This essentially is the core of my problem. When the digging gets tough the rotation slows to a crawl and even stops. I have to feather the auger up and down to do any drilling and while I am able to dig the holes it takes a long time. If I was just digging a few here and there it would be no problem but I want to be able to dig 100 or so per day. In my video for example I dig the first 6' in about 20 seconds which is great but the last 4' takes a minute and a half. While this is not all that bad in other ground conditions it might take me 5-10 minutes to dig one hole constantly going up and down. Not only does this take time but it seems to be hard on the machine as it gets hot.

I am wondering what my solution might be? I am guessing a bigger displacement motor would have more torque and would do better I am just wanting to make sure there is nothing wrong with my setup before I go to buying a new $1000 motor.

 

[bdog]

If the cutting bit is the same or smaller then the auger it well not bore at all. Might want to double check that.

They are the correct size as recommended by the manufacturer. 3.25" diameter auger and 3.5" diameter bit. I have wondered if a bigger bit would help but they say no because it won't be able to lift the cuttings out if the hole is too much bigger than the auger.

 

[Leejohn]

If you have it on the 3pt that case well pull it out.

 

[bdog]

If you have it on the 3pt that case well pull it out.

I am not talking about the auger. I can lift it out of the hole no problem. I am talking about the cuttings, the dirt.

If the bit is too big for the auger the hole becomes too big and the dirt is not carried up and out of the hole by the auger as it just falls back down the sides of the hole.

 

[Leejohn]

When I dig holes I don't spin the auger fast and when deep enough I pull the auger without it spinning. Realy gets big if spinning fast while pulling out. When the auger bottom gets to the top it goes all over the place. I just keep going back in the hole spin long enough for auger to fill up, stop then pull. It's not easy my yourself, need someone to the push the auger away from the hole and get the dirt off. On mine I can push it real hard to the tractor and it hits a stop and dirt well fly off if dry.
Don't get in a hurry with a post hole digger, a man can get hurt real bad.