All hydraulic post driver

Verticaltrx · Apr 10, 2014

After a couple years hiatus I'm finally getting back to finishing a post driver I've been working on. I'm a farmer and fencing contractor so I've run several different model drivers and tried to make something a little different that suits my needs. The design criteria was that it would be light enough to use with a compact tractor, powerful enough for driving 6-7" posts in most conditions, and easy to keep a post plumb. I roughly modeled it after some of the New Zealand and European designs which I like much better than the American designs.

The completed unit should weigh about 800lbs and the driving weight is ~450lbs. At max height there is a little over 10' between the weight and the ground. The weight has 8' of travel and is carried low for maximum stability on small tractors. Front to back and side to side tilt is all hydraulic. I used a 2" bore, 24" stroke and a 4:1 pulley arrangement to get maximum travel and free-fall speed on the weight. There is also a post cap that will securely hold the top of the post as it is being driven to assure it is plumb (not installed yet.)

I just assembled it for the first time yesterday and the initial tests are promising. All the hydraulics function as the should, the weight drops with a lot of force, and it seems to drive a post as well as most other drivers I've used. I've got a bunch of little things to finish up like greaseable pins for the pulleys, swapping out some bolts, adding a way to lift the post cap, paint, etc.

Here are the only two pics I have so far:

TomSeller · Apr 10, 2014

Verticaltrx said:
After a couple years hiatus I'm finally getting back to finishing a post driver I've been working on. I'm a farmer and fencing contractor so I've run several different model drivers and tried to make something a little different that suits my needs. The design criteria was that it would be light enough to use with a compact tractor, powerful enough for driving 6-7" posts in most conditions, and easy to keep a post plumb. I roughly modeled it after some of the New Zealand and European designs which I like much better than the American designs.

The completed unit should weigh about 800lbs and the driving weight is ~450lbs. At max height there is a little over 10' between the weight and the ground. The weight has 8' of travel and is carried low for maximum stability on small tractors. Front to back and side to side tilt is all hydraulic. I used a 2" bore, 24" stroke and a 4:1 pulley arrangement to get maximum travel and free-fall speed on the weight. There is also a post cap that will securely hold the top of the post as it is being driven to assure it is plumb (not installed yet.)

I just assembled it for the first time yesterday and the initial tests are promising. All the hydraulics function as the should, the weight drops with a lot of force, and it seems to drive a post as well as most other drivers I've used. I've got a bunch of little things to finish up like greaseable pins for the pulleys, swapping out some bolts, adding a way to lift the post cap, paint, etc.

Here are the only two pics I have so far:

<img src="http://www.tractorbynet.com/forums/attachment.php?attachmentid=370077"/>

<img src="http://www.tractorbynet.com/forums/attachment.php?attachmentid=370078"/>

Nice. More pictures please.

BHD · Apr 11, 2014

looks like a good simple design, let us know how you like it and how it works,

Verticaltrx · Apr 11, 2014

Sorry, no more pics yet. I took the camera with me but realized I forgot the memory card in the computer.

I've run into a bit of a snag with my design. I calculated the cylinder to be able to lift the weight, but neglected to factor in the weight of the post cap. It raises the weight just fine, but raising the 40lb post cap is too much. I might try to check some pressures, but I think the cylinder just can't do it.

Looks like I'll have to make a lighter weight post cap.

breadtrk · Apr 11, 2014

Get a bigger cylinder. Lighter cap will just crack, bend, smash, whatever. 40lbs isn't stalling the hydro brother.

BHD · Apr 11, 2014

Funny you say that I have the same problem My design is such that I can work around it easily, and all I have to do is to push it up and it is enough to allow it all to lift, and I have a telescoping mast, that I can lift it as well and set on the post and then reposition the unit to drive the post, If I would tweak the pressure on the tractor, just a few lb's I am sure it would lift it all, I am guessing that I am short less than 20 pounds on the final lift.

KubotainNH · Apr 11, 2014

Cool setup. Looking forward to seeing more. Can you crank up the PSI a bit for the extra few pounds or is it maxed for the cylinder? Seems like your valve is going into bypass.

TO_Bud · Apr 13, 2014

Great project. How do you release the weight for free fall?

franklin2 · Apr 13, 2014

breadtrk said:
Get a bigger cylinder. Lighter cap will just crack, bend, smash, whatever. 40lbs isn't stalling the hydro brother.

On the one hydraulic post driver I messed with(commercially available model) the biggest concern with it was getting rid of the oil out of the cylinder fast enough so it would free-fall. It required a huge hose and a special port had to be installed in the hydraulic tank on the skidsteer to handle the volume of oil from the cylinder. It looks to me like a bigger cylinder would compound this problem, more oil to get rid of.

Verticaltrx · Apr 13, 2014

breadtrk said:
Get a bigger cylinder. Lighter cap will just crack, bend, smash, whatever. 40lbs isn't stalling the hydro brother.

A bigger cylinder wont work. I need the smallest cylinder possible otherwise the amount of fluid that has to be displaced is too much and it can't free fall. I'm already having to use a 3/4" hydraulic line between the valve (21gpm valve) and the cylinder and a 1" return line to the tractor tank. There is only so much fluid that you can move. The only option if I went to a bigger cylinder is to step up to a 30-40gpm valve and much bigger lines which would be very expensive.

BHD said:
Funny you say that I have the same problem My design is such that I can work around it easily, and all I have to do is to push it up and it is enough to allow it all to lift, and I have a telescoping mast, that I can lift it as well and set on the post and then reposition the unit to drive the post, If I would tweak the pressure on the tractor, just a few lb's I am sure it would lift it all, I am guessing that I am short less than 20 pounds on the final lift.

I looked at your thread a while back and noticed a lot of similarities between our designs. Mine actually will lift the current post cap, but the tractor has to be at max throttle and you have to quickly pull the hydraulic lever to get a quick burst to lift it. Even then sometimes it opens the relief valve before it's all the way up. I'm thinking a lighter post cap will either a)be easy enough for the hydraulics to lift or b)be easy enough to push it up by hand using the top of the post.

KubotainNH said:
Cool setup. Looking forward to seeing more. Can you crank up the PSI a bit for the extra few pounds or is it maxed for the cylinder? Seems like your valve is going into bypass.

I'm going to hook up a pressure gauge to the tractor remotes and the valve on the post driver to see what it's actually at before I do anything else. The valve 'should' be set at 2500psi and the tractor should be a little higher than that.

TO_Bud said:
Great project. How do you release the weight for free fall?

The lever to raise the weight also drops it. Push the lever forward and the weight goes up, pull it back and it comes down. If you pull it back just a little the weight will descend as slow as you want. Pull it quickly all the way back and it free-falls, basically the same as any post driver.