pressure relief question

[Henro]

<font color="blue"> Your earlier example of a PRV in parallel with the cylinder will not work unless I misunderstand you definition of parallel. </font>

I'll try to be less wordy this time... /forums/images/graemlins/grin.gif

Easy to say, hard to prove. Explain why your statement is true. I doubt you can.

Jinman's modification of your drawing (what you show in your drawing will certainly work and is traditional design) is exactly what I suggested as an alternative thought.

Rather than just say something will not work, please add a few words to explain why it will not work. Doing so is all around helpful for whoever may come upon this thread in the future. /forums/images/graemlins/smile.gif

Edit: I guess you posted a reply while I was typing this one...

 

[BigAl]

WoW!!! Thanks for all the responses . This is why I love this site .
OK , I will admit that I am "hydraulic challedged" and need to learm much more . /forums/images/graemlins/crazy.gif I called and talked with a "tech person" at the Surplus Center this morning . He told me a "pressure relief valve" would work just fine as long as I had a return line in the system . This is what he sold me : http://www.surpluscenter.com/item.asp?UID=2004120115123318&catname=hydraulic&qty=1&item=9-1034 . The part I like about being able to adjust my pressure is the ability to multi task my remote hyd. valve .
I know I could have got a smaller ram in place of the existing one ,but it might have been difficult to get it right the first time and not ended up with one that was to weak . Besides it would be hard to find a ram for $42 dollars,which is the valve cost , and I can keep adjusting to where I want my psi to be . I will keep you all informed as to how well it works .
I'll post some pictures when I get this grapple all painted and reinstalled on the loader .
I have even named my new grapple design the " Thumbmasher Chickenchaser Grapple & Ripper 3000 " . Kind of catchy ,huh? The name was actually developed during the construction stage . "Thumbmasher" is from my experience with a hammer while center punching drill holes and the "Chickenchaser" part comes from that being the only animal around when we got it installed on the tractor and wanted to try it out .That hen has not laid a egg since . I wonder if it is connected to our field testing research ? /forums/images/graemlins/grin.gif "3000" stands for the number of beers consumed during design and construction ! /forums/images/graemlins/crazy.gif
Thanks again everyone ,
Big Al

 

[MMM]

Not sure if poster has 3 spool valve or seperate valve for grapple. If it's a 3 spool, all circuits are tied to one relief. For that the afore mentioned smaller dia cyl is simplest and cheapest. Personally, I'd rather run power beyond and seperate valve with adjustable relief for the versatility (shearer).
You have to have power beyond sleeve on most loader valve returns or use a flow divider upstream of loader valve to grapple control. Open center systems can't be tee'd on press side unless you're willing to dog a downstream control handle off so all the flow doesn't pass through it. Wouldn't work so good for loader application.

 

[RickB]

Both my posts were crystal clear. I said a smaller diameter (bore) cylinder. Although the rest of this thread has clearly gone in another direction, for the MadReferee's benefit here is some info. Most any generic cylinder style found can be bought in a variety of bore sizes, usually in half inch increments. At 2000PSI, cylinders of the following bores will exert these respective amounts of force on their rods in the extend direction.
2" bore 6283.2 lb @ 2000psi
2.5" bore 9817.5 lb @ 2000psi
3" bore 14137.2lb @ 2000psi
3.5" bore 19242.3lb @ 2000psi
4" bore 25132.8lb @ 2000psi
Retractive force is reduced by the section area of the rod times pressure. The above are selected bore diameters commonly found in off the shelf cylinders used on Agricultural and some industrial equipment. As you can see, changing from a 2" bore to a 3" bore increases the force applied to the rod by 2.25 times. Somewhat more than "a very little difference".

 

[Wall]

Just turn the Hyd cylinder around,,, swap ends that would reduce the pressure about 1/2

 

[RickB]

I would like to read your explanation of that.

 

[Bluecheck546]

Here is a formula to figure the force created by different diameter cylinder piston.
CYLINDER FORCE in Pounds, Push or Pull FORCE = PRESSURE(PSIG)x NET AREA(Square Inches) (Inches2) F = PA

I'm in total agreement with RickB on that one... smaller diameter cylinder piston = less force= less damage to the FEL bucket

/forums/images/graemlins/smile.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

 

[Wall]

"Retractive force is reduced by the section area of the rod times pressure"

 

[Henro]

Wall,

Granted that most hydraulic cylinders push harder than they pull, because of the cylinder rod. It is unlikely that reversing the cylinder would make any difference in the grapple application though, since reversing it does not change the mechanics of the grapple.

Regardless of which way the cylinder is put on the existing mechanism, it will still have to either extend or retract to make the grapple move. Generally the cylinder will extend to close a grapple, and retract to open.

So there is no way reversing the cylinder would help in this situation.

This is just a guess though. Maybe you would like to explain what you were thinking when you posted your comments?

 

[Eebbee]

Just a dumb question on the topic.
Wouldn't you be able to reduce the applied force on the grapple significantly by changing the pivot position ?

Doesn't the lever principle apply here?

Eebbee