Posthole Driver Confusion and questions

[Bigeclipse]

My wife and I want to put in a pasture for her horse. This pasture will consist of 160 posts. Our soil is right in the middle between sandy and clay but contains rocks (we live on the side of a mountain/hill). We got a quote from a local person for just 80 posts and they will want 3500$ to drive them so my guess is 160 would be close to $6000!!! For that amount we are now considering buying our own post driver but it would appear our tractor may not have the right hydraulics to run them. specs are as follows:
Hydraulics:
Type: open center
Valves: up to 3
Pump flow: 9.5 gpm [36.0 lpm]
Steering flow: 4.9 gpm [18.5 lpm]


The two models we were looking at were the Kencove PD80 and PD100. The PD80 is like the Shaver HD8 and the PD100 is like the HD10. Specs are virtually identical and so are requirements for hydraulics. From the forum threads I have read, it sounds like if we tried to use the PD100, it would take the hammer longer to lift up but the driving force would be the same BUT when we called Kencove they said 9.5gpm would not be enough to lift it...so im confused. We would prefer to get the harder hitting one because of our soil conditions but we don't want to buy something our tractor couldn't run. Please, any thoughts would be greatly appreciated. thanks!

 

[boomer1025]

Get a post hole digger for the 3pt on your tractor.

 

[CobyRupert]

Yeah, I'm confused too.
The specs do say: 12gpm at 1500psi requirement.
The product page says maximum hydraulic pressure limit is 2500psi.

My understanding of how these operate is the hydraulic pressure extends/cocks the springs and then releases, with the energy stored in the extended spring doing the pounding. I also don't understand why you need "gpm" to cock it, when it's pressure that is required to oppose the springs. One would think that a lower GPM just makes it lift/cycle slower.

If anything, it seems there would be a danger from some tractors supplying too much pressure. Tractordata says my tractor has 2828 psi. So although the pounder would fit a Cat II hitch tractor, it's not rugged enough to handle the psi that comes with one?

But at the same time my tractor only has 11.4 gpm, which wouldn't meet the 12gpm required?! Weird.

Nowhere, that I found, do they mention this 2500psi MAXIMUM limit in the manual!! THAT'S IMPORTANT!!
They have plenty of other warnings.

I don't think they know what they're talking about.

 

[BHD]

The only way I can see a possible problem is if the tractor hydraulic system is such small passages, that it would restrict the flow of the oil returning to the reservoir when the driver is dropped,

If the pump system is small most of the time all that is the problem is the speed of the extension of the cylinder,

and if you are going to buy a driver, get the tilt option,
(my ground is considered flat, but I use the tilt on mine a lot, I would say 90% of the time),

 

[Fuddy1952]

I got a good deal on a Danuser auger. 38 go tractor (I'm not sure about PTO hp...30 maybe), but I put in a bunch of 5"-6" posts using the 9" auger. Tamping is the hard part but wasn't bad...good exercise!

 

[Fuddy1952]

Stupid spellchecker...38 horsepower tractor.

 

[Diggin It]

OK, so obviously some people are confused. My take is we're talking about driving metal T-Posts and NOT drilling holes for wooden posts? Or .....



..... shoulda' looked first. Driving wooden posts? Into ground with rock? How would the wood not split when driven into a rock? I'd think you'd end up with toothpicks.

 

[LouNY]

Most of the wooden fence post set in this area are sharpened and driven in.
Locust post split or rounds tend to last the longest.
They are extremely hard to put a staple into also, a cordless drill and a pair of pilot holes work very good,
especially if you are going with High tensile electric or barbed wire.
The sharpened wood post will actually work the smaller rocks in the ground as it goes down.
I don't know of any farmers in this area that use a post hole auger for fencing there are way too many stones.
As to the original question I have no idea why they would have a minimum flow spec.
I don't know off the top of my head what brand the driver over at the farm is.
It is being used this week to drive a lot of post probably over 100.
One thing to consider ours is mounted to a ssqa plate so we can use it on the loader arms, we find it much easier
to reach were the post needs to be with the loader and it allows easy leveling in one direction. Also you can get into tight spots
and corners this way. All split locust on rough stony ground.

Almost forgot this point in regards to flow ours is usually on a 40 hp tractor and we just run it a bit over idle when driving posts,
maybe 900-1000 rpm so it is not pushing even half the flow it would be rated for.

 

[aczlan]

The only reason I could see for the flow requirement is to have enough flow on the exhaust side that the hydraulic fluid can flow freely back into the hydraulic sump.

Aaron Z

 

[LouNY]

The only reason I could see for the flow requirement is to have enough flow on the exhaust side that the hydraulic fluid can flow freely back into the hydraulic sump.

Aaron Z

All the post drivers I have seen and also the ones mentioned require a line directly to the sump not back thru the system. This one calls for an unrestricted 3/4" return line.