Texas Tech of Engineering wrote a 17 page report going through the various details of the Searco© post puller, such as maximum psi. Here are a few pages from the report, which can be fully viewed and read by clicking the button below!
INTRODUCTION AND BACKGROUND:
The hydraulic fence post puller is a device that can pull fence posts, street signs,
concrete plugs, and many more objects. It possesses the strength to pull temporary telephone
poles weighing approximately 700 pounds out of the ground and has the structural integrity to
lift even more weight. The post puller uses a 3-ton double pump ram to pull beams out of the
ground. The hydraulic force uses approximately 4600 lbs of force on a vertical beam or post.
From personal experience pulling a t-post with the machine is very easy and virtually labor-free.
Although the weight of the unit is 119lbs, it is easily maneuverable because the device is on
wheels. The fence post puller is also efficient and self contained. Unlike other designs, it
requires no expensive fluid pumps or electricity. The unit can be easily loaded into the back of a
pickup by two men and operated under the power of only one man. Our sponsor, Mike Sears of
Searco, sells these fence post pullers. His target market consists of individuals with interests in
ranching, farming, or landscaping projects. Our design’s team goals was to test the hydraulic
fence post puller under an 8 ton loading using our own methodology and recommend design
improvements. Using the software, integral points of stress under heavy loading were located.
Several computer software programs were used to test and improve the fence post puller.
Through theoretical modeling our design team was able to discern the behavior of the fence post
puller while operating under an 8 ton loading and also to recommend design modifications.
DESCRIPTION OF NEED:
Mike Sears manufactures hydraulic fence post pullers. He desired to know if the
prototype furnished to our design group could undergo an 8 ton loading successfully. Mr. Sears
would like to include the lifting capability of the puller in promotional literature, and to define
the limits of safe operation for the puller. Mr. Sears also challenged our design group to suggest
alternate designs or materials to improve the overall strength of the machine. While we
formulated these suggestions we had to take into consideration what possible changes might be
most feasibly implemented by Mr. Sears. The scope of our project also included interviewing
potential and existing customers for opinions on the functionality of the hydraulic fence post
puller. In formulating recommendations, the group considered ease of manufacturability, cost,
market needs, weight, and strength of the unit.
ORIGINAL FENCE POST PULLER INVENTOR MODEL
Once the model was completed, the group tried several times to import it into ANSYS
CFX Workbench 12, a finite element analysis solver that could determine maximum principal
stresses. First attempts were unsuccessful because of licensing conflicts between ANSYS and
Inventor Pro 2009 . In the preliminary setup, all contact points on the bottom of the fence post
puller were constrained. While using the fence post puller to remove posts, the group intuitively
realized that it would most likely not be possible to pull up a cylindrical object that required 8
tons of force. Even if such an object requiring this force were available, assuming the chain and
claw attached to the lever bar, would contain enough contact friction to lift the object out or off
the ground, the front of the fence post puller would likely start to rise off of the ground if it were
not physically constrained. While performing the 8 ton load tests we assumed 100% jack
efficiency and reliability. Based on customer reviews from ME 4370 it was discovered that most
all problems occurred with the functionality of the jack. No problems were reported with the
actual steel structure.