Hydraulics Q

Awl --
My buddy had a custom hydraulic press built, for a job he runs, pressing grills together. Imagine an "A" frame press, except the "bed" consists of a cast iron drill
press table. iow, the ram was hung above the dp table, via 1.25" threaded rod, with the motor/reservoir (the hydraulic "unit") under the table -- all off-the-shelf Grainger parts or standard steel-house products. The unit is button-actuated, with limit switches in both up and down strokes.
Without the dp table (about 6 ft, nice), and without labor, this cost $6K. The labor was paid for with a Kent surface grinder.
Inyway, here's the Q: The ram measures 1.75" dia. The pressure gage reads 1500 psi upon application, for this job. Is it correct to assume that area x gauge psi = the actual force applied? In this case, about 3,600 lb?
If so, that would mean that for "15 ton", which was sposed to be the capacity of this unit, the pressure would have to reach 12,500 psi on a 1.75 dia ram?
I don't think the gauge reads anywhere near 12500 psi, more like 6,000, and the gauge came with the hydraulic unit. If the gauge is indeed matched to the hydraulic unit, this would make it closer to a 7.5 ton unit. Hmmmm......
--

Mr. PV'd

Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Jul 1, 5:28pm, "Proctologically Violated"

You need to know the diameter of the piston, not the ram. Use that surface area X pressure to calc. the force.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

You need to know the diameter of the piston, not the ram. Use that surface area X pressure to calc. the force.
==========================================I'm calling the "ram" the shiny protruding cylinder. Is that correct?
If so, is the piston generally bigger or smaller than this tube? Will it say somewhere on a label on the cylinder unit?
--

Mr. PV'd

Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Jul 1, 5:50pm, "Proctologically Violated"

===================>
Take a look at the many pictures avaialble on the internet....
http://www.hycocanada.com/cylinderintro.html
I don't know if your cylinder is marked or not. The ones at the local Farm and Fleet are usually marked...
In this example the Bore and Stroke are listed, along with the rod diameter. https://www.surpluscenter.com/item.asp?UID=2009070118002688&item=9-4410-04&catnameNotice that the bore is always larger than the rod diameter. Well, almost always..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Take a look at the many pictures avaialble on the internet....
http://www.hycocanada.com/cylinderintro.html
====================================OK, I see. So the "bore" dia is what I would use in the area x psi calc, right? Which in this picture is the red ditty with what looks like an o-ring seal?
Which has quite a bigger diameter than the rod!
So, now, is the gauge psi the right psi to be using? Assuming the gauge is in the right place....
--

Mr. PV'd

Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ram or rod? Is there a piston? I know the difference between ram and rod, I used to work on St Lawence forming presses.
Wes
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I was measuring the dia of the shiny protruding cylinder. The unit is that traditional black housing, w/ square plates on either end for mounting, w/ long bolts, iirc. Don't know the terminology for all the parts. I'm up for enlightenment.... :)
--

Mr. PV'd

Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 1 Jul 2009 18:28:27 -0400, "Proctologically Violated"

F = P x A, where F = lbs force, P = pressure in PSI, and A = effective ram area in in.
db
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Proctologically Violated wrote:

If, as others have said, you know the diameter of the piston (which has little to do with the diameter of the ram), then your calculations are correct. A typical motorized press will usually have a multi-stage pump system to deliver seriously big pressures, and be combined with a very large piston.
The cheaper and more common way to get lots of muscle, however, is with a hand-pumped unit. I have a 15 ton hand-operated hydraulic press that only cost a few hundred dollars. The key is leverage. When I put, say, 15 lbs of pull on a 24" long lever/handle with my arm, I've got maybe 50:1 leverage at the pump piston. If the pump piston is small, like say a quarter of a square inch, then I end up with maybe 3,000 PSI. The driven piston on my press is probably 4" in diameter, which is 12.56 sq. inches. At 3,000 PSI, that makes the ram force almost 38,000 lbs., not counting leakage, loses, and such. So I probably use less than 15 lbs to start with; but I still get lots of crunch.
What I don't get with my press is speed. That little bitty input cylinder has to do a lot of strokes to get much motion out of the much bigger ram piston. Or, to put it another way, my arm moves a lot of feet and yards for every inch that the ram decends.
Slightly better presses than mine (my log splitter has this, actually) will have one pump with a bigger input piston, to get more speed while approaching the work, and another pump with a smaller piston for actually crunching things. Works nice. Motorized presses will use valve-controls or variable ratio pumps to accomplish this. That's expensive, though.
KG
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Kirk Gordon" wrote in message Proctologically Violated wrote:

runs, pressing

cast iron drill

via 1.25" threaded

the table -- all

products. The unit is

strokes.
labor, this cost $6K.

1500 psi upon

force applied?

to be the

12,500 psi on a 1.75

more like 6,000, and

would make it

If, as others have said, you know the diameter of the piston (which has little to do with the diameter of the ram), then your calculations are correct. A typical motorized press will usually have a multi-stage pump system to deliver seriously big pressures, and be combined with a very large piston.
The cheaper and more common way to get lots of muscle, however, is with a hand-pumped unit. I have a 15 ton hand-operated hydraulic press that only cost a few hundred dollars. The key is leverage. When I put, say, 15 lbs of pull on a 24" long lever/handle with my arm, I've got maybe 50:1 leverage at the pump piston. If the pump piston is small, like say a quarter of a square inch, then I end up with maybe 3,000 PSI. The driven piston on my press is probably 4" in diameter, which is 12.56 sq. inches. At 3,000 PSI, that makes the ram force almost 38,000 lbs., not counting leakage, loses, and such. So I probably use less than 15 lbs to start with; but I still get lots of crunch.
What I don't get with my press is speed. That little bitty input cylinder has to do a lot of strokes to get much motion out of the much bigger ram piston. Or, to put it another way, my arm moves a lot of feet and yards for every inch that the ram decends.
Slightly better presses than mine (my log splitter has this, actually) will have one pump with a bigger input piston, to get more speed while approaching the work, and another pump with a smaller piston for actually crunching things. Works nice. Motorized presses will use valve-controls or variable ratio pumps to accomplish this. That's expensive, though.
KG
I've gone one step further on my press that'll put out 24 tons with a five inch bore cylinder at 3000 lbs. The primary mover is an electric motor driven pump and flow is controlled with the power angle valve section of an old Meyers snowplow providing up and down movement. I can also use a hand operated pump from the base of a one and a half ton hydraulic jack to pressurize the cylinder because the port on the blind end contains a pilot operated check valve of my own making. When applying pressure with the hand pump a method was needed to trap oil in the blind end otherwise the oil would just pass up the feed hose. A check ball stops this flow but in order to raise the ram the ball must be released and this is done by a small cylinder ported to the return circuit and pressurized to push on a small shaft which pushes on the check ball raising it off its seat allowing trapped oil in the blind end to escape. Whew, I need some air........ Only problem with my setup is that the only way to return stroke is with the electric driven pump and also all ram travel requires operating the main up/down control. That little hand pump off that cheap little jack easily puts out 3000 lbs! I've also mounted a good liquid filled gauge to measure pressure and sometimes I'll even use a dial indicator to help measure movement on the work, useful when straightening things. Another hint to remember: when pressing something straight you must look for the yield point pressure needed to effect movement. Big log harvestor saw bars can be done nicely if you pay attention to this yield point. You have to watch the gauge needle really close as it'll drop only a needle or two width quite suddenly. As soon as you see this drop in pressure check the item for improvement and for more you can pump up directly to the last pressure that gave results saving time. If you can't 'catch on' to that pressure drop you won't get anywhere, just guesswork.On a bar using 5bc chain I'll use pressures up to 1700 lbs or so. (12 - 13 tons)! Bars end up straight though.....;>)) Hope someone out there can use this little story to help make a living. I'm now officially retired..........a home shop hobbyist! phil kangas
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Phil Kangas" I've gone one step further on my press that'll put out 24 tons with a five inch bore cylinder at 3000 lbs. phil kangas
Correction: system pressure is 2500 lbs giving 24 tons with the motor driven pump. The little hand pump puts out 3000 lbs giving 29 tons. The hand pump bypasses the system relief valve. There that makes sense...... phil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 2 Jul 2009 21:31:51 -0400, "Phil Kangas"

Some pics of some press conversions I did last year.
Here a few pictures of standard presses I retofitted to fully automatic.
One is 700 ton and the other 200 ton
200 ton hydraulic system
http://s32.photobucket.com/albums/d1/debco99/Machines/?action=view&current 0ton3.jpg
200 Ton Micro Control:
http://s32.photobucket.com/albums/d1/debco99/Machines/?action=view&current 0_Micro.jpg
700 Ton:
http://s32.photobucket.com/albums/d1/debco99/Machines/?action=view&current=Press_Retro.jpg
Regards
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

http://s32.photobucket.com/albums/d1/debco99/Machines/?action=view&current 0ton3.jpg

http://s32.photobucket.com/albums/d1/debco99/Machines/?action=view&current 0_Micro.jpg

http://s32.photobucket.com/albums/d1/debco99/Machines/?action=view&current=Press_Retro.jpg
Neat stuff, all photos, videos. Need more description/text, tho, so people know what they're looking at.
--

Mr. PV'd

Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It is common but not universal for press cylinders to have the ram and piston diameter the same. You could tell the effective piston area by measuring how much fluid is expelled from the ram for a known distance of retraction, provided there is no air expelled. You could also rig a proportional lever and measure the force with a bathroom or other suitable low force scale. If you have a cylinder of known bore size, you could use it and a suitable pressure guage as a force gauge.
Don Young
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Don Young" It is common but not universal for press cylinders to have the ram and piston diameter the same. You could tell the effective piston area by measuring how much fluid is expelled from the ram for a known distance of retraction, provided there is no air expelled. You could also rig a proportional lever and measure the force with a bathroom or other suitable low force scale. If you have a cylinder of known bore size, you could use it and a suitable pressure guage as a force gauge. Don Young
If the ram and the piston have the same diameter the cylinder cannot be double acting! If the ram and the piston were of the same diameter and you wanted to know the effective area then just measure the ram and figure it out........what's with this measuring expelled fluid? A waste of time........ phil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I have not owned a lot of presses but none of mine had double acting cylinders. They were retracted by springs when the relief valve was opened. I did not say that all press cylinders have the ram and piston the same size so measuring the ram may or may not be a valid way of measuring the piston. Measuring the fluid displacement is a perfectly simple and valid method of determining the effective piston area.
Don Young
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

And while we are at it, consider regeneration where you cross connect the A and B side of cylinder and eliminate the piston.
Wes
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<Wes> wrote in message "Phil Kangas" <> wrote:

And while we are at it, consider regeneration where you cross connect the A and B side of cylinder and eliminate the piston.
Wes
Yah, that'll give you faster travel of the ram as the oil expelled from the ram side is added to the blind end side of the piston resulting in reduced force of the ram, the effective area becomes the ram itself. Can be useful in many ways. phil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.