How does a Hydraulic pull-back Ram work?

[StevePgh]

I'm curious as to how a Hydraulic pull-back Ram works. It's easy to understand how a normal Ram works - the Hydraulic fluid pushes out a piston. But a pull-back? I dunno. Anyone happen to know?

I'm planning on picking up a cheap one (HF) to pull two parts of a deck frame back together (2"), and I've never used a pull-back before. This frame is about the shoddiest design and construction I have ever seen (fortunately it is just above ground level). On top of that they used composite decking boards (the 1st generation grey recycled plastic type) that were not gapped (contrary to the recommendation from the tags stapled on the ends of the boards). It took 15 years, but freeze-thaw and heat/expand will win over toe-nailing every time.

While I'm at it - any hints/tips in using the pull-back?

 

[iajonesy]

Could you use a come along on this project? It would be much cheaper than a hydraulic cylinder and useful for other projects, too.

Pull back cyl. has the fluid on the top side of the piston, I think. Might be wrong on that, but I would think that's the way they work. More guys on here with more knowledge than me will no doubt correct me.

Mike

 

[WhoWhatNow]

They are called double acting cylinders. Fluid can enter or leave through either side of the piston.

 

[A_Pmech]

Fluid acts on the rod side of the piston. Which is also why a double acting cylinder has more force available in the "pushing" direction. The available force is reduced in the "pulling" direction by the area of the cylinder rod.

 

[StevePgh]

Could you use a come along on this project? It would be much cheaper than a hydraulic cylinder and useful for other projects, too.

Great question! I have a 2 ton come along that I was going to try first, but I think it would be rather hard to spread the cable out over enough surface area to not cut through the 2x12's - the chain I have won't fit in the come along hook but may work for the pull-back ram. The other fear was that I may not be able to get it pulled to exactly the correct position due to the coarseness of the ratcheting mechanism. I figured I'd have the pull-back ram ($40 after the 20% off) sitting in the box in case the come along doesn't work out - or perhaps in addition to the come along. I've only removed half of the decking boards from the end where it separated, so I anticipate some resistance, but 2 tons should probably be more than sufficient.

They are called double acting cylinders. Fluid can enter or leave through either side of the piston.

After googling for double acting cylinder, I found this article with a cutaway view that allowed me to visualize what you folks are talking about. Very cool. http://hydraulicspneumatics.com/200/TechZone/Cylinders/Article/False/6423/TechZone-Cylinders

 

[turbowoodworker]

Search "bow wrench deck tool" at Rockler.com. Tool made for the job. Item #21117.

 

[MJD1]

I would use a ratcheting load binder for what your trying to do. A lot cheaper, especially when you figure you will need a pump to operate the pb ram.

 

[turbodave]

I figured I'd have the pull-back ram ($40 after the 20% off) sitting in the box in case the come along doesn't work out - or perhaps in addition to the come along.

Keep in mind that's just the ram, you'll need a hydraulic port-a-power style pump to actuate it.

I would try the come along, maybe with a turnbuckle connected to the chain if you need finer adjustment. Sometimes even a few ratchet straps will get the job done.