Hydraulic Motor questions

Very feasable. I've been contemplating the same thing for quite some time. The relief setting may be a little higher than the motor is rated for. Consider adding another valve with a relief built in. Then you could add a thumb for the bucket when not using the PHD, or vicey versa.

What is the flow from your hydraulic system? That motor turns at 250 rpm with 14 gpm flow. At say, 7 gpm from your system, it will turn at 125 rpm. Plenty fast enough, although the manufactured units turn a little faster I think.

Your list of specs is a little messed up.

Mounting Type 4 bolt
Shaft Dimensions Diameter x L (in.) 1 x 1 3/4
Port Size (in.) 1/2 NPTF
Displacement (cu. in.) 17.9
Max. RPM 250
Max. PSI 1,600
Max. Torque (in.-lbs.) 2,890
Max. Flow (GPM) 14
Manufacturer Warranty 1 year Limited Warranty
Ship Weight 16.0 lbs
Item# 1007
PRICE $309.99

Here's a Char-Lynn motor in Canada.

http://www.princessauto.com/pal/product/8179616/Gerotor/17.9-Cu.-In.-4-Bolt-Hydraulic-Geroter-Motor

And another similar one at Baileynet. Although it is a replacement for Char-Lynn

http://baileynet.com/index.php?dnfwd=1&page=ProductDetails&line=HMFH&baileyno=272-206

Looking at the Hyd. specs for the 2520 I don't think you'll be very happy with the performance. At 5gpm attachment pump flow thats just over 1/3rd the rated flow for that motor making it turn pretty slow.

Another option is to put a PTO aux. pump but I think thats probably kinda defeating the simplicity you were going for.


Brad

The specs for the Worksave hydraulic post hole digger are on page 21 of this PDF. Basically the same as what you want to do.

http://www.worksaver.com/Manuals/924.pdf

TooManyGT, I'm not too sure about the wisdom of turning a PHD at high speed at the end of a small back hoe. Think 1/2" drill with a spade bit hitting a nail when drilling horizontally over you head then apply that to hitting a rock or big root with the hoe fully extended. Probably not a problem, but .......

A regular 3PH digger turns the auger at about 175 rpm with approximately a 3.1:1 gear box. What the OP is considering will turn the auger at approximately 25 rpm. Changing the motor for one that nominally turns at 1000 rpm will net about 100 rpm with a net reduction in torque commensurate with the output rpm at a flow of 5 gpm.

My thoughts have run to direct driving the auger from the motor without the intervening gear box, making the drive unit small enough to go down an 8" hole for a little more depth without using an extension.

Tudor, I never suggested that he turn the auger at a high speed. I was under the impression that he wanted to adapt a motor to an existing PHD to gain the advantage of the gear box for torque multiplication and allow the gearbox to take the majority of the axial loads and side loads encountered by the auger itself.
Depending on the size of the auger you might want the ability to run the auger at a higher speed for clean out.

I don't see a problem with the auger being out on the BH, seems like it should have enough leverage to keep the auger in place without too much trouble.

I just wanted the OP to be aware of the reduced available speed of the motor due to the lower rated GPM of the tractor.

Brad

Gotcha! Many of my comments are along the same line of looking for problems and benefits that don't necessarily jump out at you. They're just something to be aware of.

I agree that the hoe should handle it without a problem, just be aware of the torque involved. In this situation, hydraulic flow and motor size can do all the reduction needed. The big advantage of using an existing gear box is having a ready made attachment point for the auger, rather than having to buy or make one to couple with the motor directly.

It's just a matter of sizing the motor to existing circumstances. The smaller manufactured hydraulic PHDs flow about 6 gpm.

Torque is a concern. the stated motor torque is 1600 in lbs.

That is 133 ft lbs.

Get a torque wrench and try to turn the auger with 133 ft lbs.

Some cars have the lug nuts tightened that tight.

I think the auger needs a LOT more than 133 ft lbs.

CADplans said:

Torque is a concern. the stated motor torque is 1600 in lbs.

That is 133 ft lbs.

Get a torque wrench and try to turn the auger with 133 ft lbs.

Some cars have the lug nuts tightened that tight.

I think the auger needs a LOT more than 133 ft lbs.

Click to expand...

The first post has messed up specs. The correct specs are in post #2 and the torque is actually 2890 in lb or 240 ft lb. It's also going through at least a 3:1 reduction box which will result in over 720 ft lb available on the auger.

I've tightened nuts to almost that torque level, but it was a struggle involving the use of a 4' long, 3/4" drive torque wrench and 2 millwrights.

cdhd2001 said:

Thanks for all the comments.

I was aiming for an input shaft speed of about 300 rpms. I never run a phd at full pto speed. Usually only about half speed.

Let me look at the motors again and post another possible choice.

Click to expand...

If you reduce the engine speed, pump flow will also be reduced.

Pick an engine speed and calculate the pump flow in cu. in./min., divide by 300 and that answer is the motor displacement that you want.

Lets see if I can do this.

At PTO speed = 5.0 gpm (implement)

5.0 g/min = 1155 cu.in/min

1155/300 = 3.85

closest motor on NT is Prince model #adm50-4rp

3.0 cu. in.
1,000 rpm
2,200 psi
787 in. lbs.

So, would this motor be able to do the job?

TUDOR said:

If you reduce the engine speed, pump flow will also be reduced.

Pick an engine speed and calculate the pump flow in cu. in./min., divide by 300 and that answer is the motor displacement that you want.

Click to expand...

cdhd2001 said:

Lets see if I can do this.

At PTO speed = 5.0 gpm (implement)

5.0 g/min = 1155 cu.in/min

1155/300 = 3.85

closest motor on NT is Prince model #adm50-4rp

3.0 cu. in.
1,000 rpm
2,200 psi
787 in. lbs.

So, would this motor be able to do the job?

Click to expand...

This question should be looked at a different way.

How much torque do you need, pick a motor that will deliver that torque.

THEN-Pump enough oil to do the job at the speed you want to get the job done.

You can't turn a 72" mowing deck with 3HP just because it turns 3600 rpm.

Yup. Torque's a little light.

I like this one better.

https://www.surpluscenter.com/item.asp?item=983-1570&catname=hydraulic

SPECIFICATIONS Disp. 3.6 cu. in. / rev.
Motor Type Geroler
Pressure:
2000 PSI cont.
2500 PSI int.
Torque:
943 in-lbs. cont.
1174 in-lbs. int

$311.95

Torque of 235 ft lb instead of 196 ft lb, after going through the gear box.

Rpm input to the gearbox of 320 vs. 385.

Assuming gearbox reduction of 3:1, auger rpm will be 107 vs. 127.

The torque is still light. Refer back to post #4. The answer is there.

You were close to a good setup for most soil conditions when you started. These last 2 motors would work well in my back yard, but that is easy digging compared to just about anywhere else. I think that I could dig a 6" hole with a descent 1/2" drill.

Seems to be a balancing act between torque and speed in relation to the lower than spec gpm's?

How about this one:

6.07 cu. in.
750 rpm
2,000 psi.
1,437 in. lbs.

Would turn at 190 rpms
reduction would be 63 rpms
torque would 359 ft. lbs.

The slower speed could be offset with down pressure from the hoe. I don't mind turning slow if I dig well.

I know with the pto drive that my best digging was with the tractor running just above idle (slow auger speed).

Thoughts?:trink39:

I used by 12" auger in dry clay/rock, you do have to go slow but I found I needed to speed the auger up for cleanout or else I would end up with a hole part full of dirt.

What size augers are you planning on using with it? Small the auger the more speed your going to want, larger less speed with more torque. Think of drilling holes in steel, drop the speed down for larger bits to reduce outisde tip speed.

I just wouldn't want to limit myself by having a low speed only. If I can find a HP vs. RPM graph for you tractor I can figure up the PTO torque at the speed you run to give you an idea how it would compare to the motors output.

Brad