poleframer Posted January 13, 2011 Share Posted January 13, 2011 Got a question for the hydraulic gurus here. I'm only running 1500-2000 psi on my system (gear motor on a 12hp diesel) have pretty good flow. I have been looking for a 6" cylinder to replace the 4" in my H press. Well, I came up with another 4" cylinder, that has a bigger diameter ram, and is a fair bit longer. The 4" in the press has a 4" throw, this one has like 14". I could get the specs on them, the one in the press is pretty thick walled welded, should take higher pressure. SO, if I ran the fluid out of the ram side of the longed cyl, into the pressure side of the shorter one, I would increase the pressure there, right? Could also have a "double acton" press, with a lower pressure,faster, and longer throw side, and a shorter, slower high pressure side. Dont know if this is done much, just the idea I have looking at the pile of stuff I have. Thanks Quote Link to comment Share on other sites More sharing options...
arftist Posted January 13, 2011 Share Posted January 13, 2011 Got a question for the hydraulic gurus here. I'm only running 1500-2000 psi on my system (gear motor on a 12hp diesel) have pretty good flow. I have been looking for a 6" cylinder to replace the 4" in my H press. Well, I came up with another 4" cylinder, that has a bigger diameter ram, and is a fair bit longer. The 4" in the press has a 4" throw, this one has like 14". I could get the specs on them, the one in the press is pretty thick walled welded, should take higher pressure. SO, if I ran the fluid out of the ram side of the longed cyl, into the pressure side of the shorter one, I would increase the pressure there, right? Could also have a "double acton" press, with a lower pressure,faster, and longer throw side, and a shorter, slower high pressure side. Dont know if this is done much, just the idea I have looking at the pile of stuff I have. Thanks No. The pressure of the system is controlled by the pressure regulator. The larger diameter ram means that it will require less g.p.m. to retract, and also have less force when retracting, nothing more. With a gear pump however, you should be able to adjust your pressure regulator to 3000 p.s.i., giving a substantial increase in force. Or I completely misunderstood your idea. Quote Link to comment Share on other sites More sharing options...
poleframer Posted January 13, 2011 Author Share Posted January 13, 2011 Yea, I dont think I explained well enough. The pressure control valve is in the spool to the cylinder, it dumps at whatever pressure I set max on that spool. I do have high pressure lines from the pump, to the valve bank, and to the cyl, I'm just more geared with the flow from the pump, and the gear ratio to the diesel for more GPM, it bogs when the pressure comes up over 2000. It's not a two stage pump. I like the higher flow, since I'm running mostly motors on it, like for the bandsaw, the lathe, and the power hammer which typically run fine, and torquey at around 500-800 psi I was thinking if the small cylinder took say half a gallon to extend, and that half gallon came from the rod end of the larger cylinder, and it takes over a gallon to fill the big end of the longer cylinder, I'd be multiplying the pressure by doing that, the difference being the volume taken up by the longer cylinders rod. The increase ratio would be how much fluid goes in the top port, to what comes out the rod end port on the longer cylinder. The circuit would go something like this. Pressure to the long cyl, then a line from it's rod end to the push side of the smaller cyl, and from it back to the other spool port. Everything should just go in reverse when the spool lever is reversed. If they are both 4" diameter, and the longer cyl pushes 8" to push 4" worth of travel in the short cyl, I'd be doubling the pressure, ie; 2000psi to the longer cyl would have 4000 psi at the smaller one. I think the trick part will be in the retraction of the rods. hmmm I'm a pretty good scrounger, I might be as well off hunting down a 6" or 7" cylinder. Just wonder if anyone has done anything of the like. Quote Link to comment Share on other sites More sharing options...
arftist Posted January 14, 2011 Share Posted January 14, 2011 I think you are on the right track looking for a larger diameter cylinder. Quote Link to comment Share on other sites More sharing options...
ptree Posted January 30, 2011 Share Posted January 30, 2011 What you are describing is an intensifier. If you put a set pressure on the piston, and you have a big rod the pressure on the rod side is higher by the ratio or area. An example. If you have a 4" cylinder, then the area on the blind side is 2" times2" times 3.14 times the pressure. Since the piston area is 12.56 square inches, if you have 2000 pounds on every square inch you have a force exerted of 25,120 pounds. Now lets look at the rod side. Lets say a real big rod of 2" diameter, which has an area of 3.14inch squared. At 2000 psi that would mean that your force of 25120 in now spread over 9.42 inches squared. O a pressure of 2666 psi or a ratio of pressure intensification of 1.33. The flow will however be about 3/4s of the pump output. Think of piston intenseifiers as a transformer in electric theory. Voltage is the pressure, and flow is the amps. I used recipracating intensifiers to make as much as 33,000 psi for hydrostatic testing using only 100 psi as the prime energy source. Very small flows, very high pressure. Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted January 30, 2011 Share Posted January 30, 2011 I like the transformer analogy Ptree, very good! One thing to mention is that it's differential piston area that matters not stroke as you seemed to be asking in your question. The stroke makes no difference at all in the equation. Quote Link to comment Share on other sites More sharing options...
ptree Posted January 30, 2011 Share Posted January 30, 2011 Grant does make a good point the volume moved, only affect the speeds, not the pressure. LAST, PAY CLOSE ATTENTION!!!! THE CYLINDER BEING USED MUST BE RATED FOR THE HIGHER PRESSURE MADE. At minimum you will blow the rod seals, at worst burst the cylinder. I had a system some years ago that had a regen valve, that would use the extra pressure from the rod side, and put it back in the blind side to move the very large press cylinder in the no load fast advance mode, and would then close up once load was achieved. Very finicky adjustment, seemed to never stay in the sweet spot and I ended up removing same. That was on a little 50 ton swaging press with a 4 to 1 rod. Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted January 31, 2011 Share Posted January 31, 2011 Am I getting this right? Your using one cylinder to drive the other? Interesting idea.... Quote Link to comment Share on other sites More sharing options...
Nakedanvil - Grant Sarver Posted January 31, 2011 Share Posted January 31, 2011 Hee, Hee! Had a similar problem with a regenerative circuit once. I was using an 8" cylinder with a 5" rod (very close to 2:1). In regen mode fluid from the bottom helped to fill the top during rapid advance. Now this was a 5000 psi system too. Well, it turns out that if the valve sequence isn't exactly right full pressure can go to the top while the bottom is blocked (even for a moment at 25 gallons per minute). Well if this happens you can generate 10,000 psi in the bottom and blow the seal out and spray fluid everywhere (don't ask me how I know)! Quote Link to comment Share on other sites More sharing options...
poleframer Posted January 31, 2011 Author Share Posted January 31, 2011 Thanks for picking this thread up again. I'm already plumbing in another cylinder for the press/hammer, and soon bender contraption. Part of my situation is that I have a lot of flow, but not pressure. My pump displaces 1.69 cu (looked up the cessna number), with a 6" pulley, to a 3" pulley on my diesel. I usually run the diesel at around 12-1500 rpms for the lathe, or light hammering, if I run it at 2500 rpm the hammer really gets aggressive, and only run it wide open running 8-10 inch oak through the bandsaw. For motors, I rarely see the pressure over 500 lbs. I have a gauge at the valves, and if I bring the pressure up to around 2000lbs, that's about stall for the engine, but it works great for the hydraulic motors on my shop equipment. I'm thinking of getting the foot pedal bar out of the way (lower it, the hammer wants to be about 4" higher anyway) and attach a cross bar perpendicular and on top of the lower I-beam with a longer cyl against one of the posts, kinda like Doc's bender in macbruce's bender thread. I tried the cyl I picked up the other day, it extends 5-1/2" to push 3-1/2" on the upper cyl. Both are about 4" cyls, the longer one has about a 2" rod, the shorter one is about 1-1/2". I suppose I'll put a gauge on the line between them, and set my pressure relief at the spool accordingly. So, I'm looking for more like a short 6" cyl for the press. As it is, I'm getting good speed out of both cylinders. Thanks for the input, I'm still working on getting the regen concept straight in my head, groking one concept often leads to other solutions to problems I didnt even know I had! Like not having a bender, could have used one in there many times. Oh, and yea, Fe-Wood, one spool now runs two cyls, the lower one that will be the bender moves faster than the one for the press. NOW, is when, if I was really getting into it, I'd attach a lever from the bottom of the press ram through one of the posts, with a pin and a bushing, and have a small shear too. A blacksmiths ironworker, courtesy of ford mortor corp. Two excuses for fitting all this into one frame is to get as much action in one footprint in my ever crowding shop, and using all this cr*p I'm accumulating. Seems good to have these actions a step or two from the forge. Quote Link to comment Share on other sites More sharing options...
ptree Posted February 1, 2011 Share Posted February 1, 2011 One thing to remember is that every hydraulic spool valve has some internal leakage, and if you add enough spool valves, you will see volume loss. Second, the ratio of cylinder rods is not enough to gain a lot. A simple rule of thumb: every 2" increase in diameter of the cylinder almost doubles the piston area. so a 4" cylinder is 12.56" square a 6" cylinder is 28.26" square a 8" cylinder is 50.24" square a 10" cylinder is 78.5" square So, want more tonnage? add diameter or pressure, or both. so a 4" bore at 1000 psi=12560#(6.28 tons) Go to 5000psi and 62,800# (31.4 ton) But a 6" at 1000=28260 (14.13) and to see the 62,800# would only take 2222 psi. Since the hosing and valves and pumps last much longer at 2000 than at 5000psi, and are much less expensive, go for a bigger cylinder, and a higher volume but lower pressure pump. The motor size needed will be almost exactly the same. Quote Link to comment Share on other sites More sharing options...
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