wyzard10 Posted August 24, 2016 Share Posted August 24, 2016 Im working on a press for gerbs and have an engineering question i cant find an answer to. I found the formula to convert the cylinder psi to output psi on the ram. When you use a smaller diameter rod for pressing the comp than the ram what effect does it have on the actual pressure on the comp. I know that if the surface are is larger than the ram area the overall pressure is reduced. I just dont know what it does if you reverse that. Link to comment Share on other sites More sharing options...
OldMarine Posted August 24, 2016 Share Posted August 24, 2016 (edited) I think Dan (ddewees) has a spreadsheet that figures all that as long as you know your piston diameter. Edited August 24, 2016 by OldMarine Link to comment Share on other sites More sharing options...
NeighborJ Posted August 24, 2016 Share Posted August 24, 2016 (edited) [quote name="Ne This question can get far more complicated then it is if you think about it too much. Psi is pounds per square inch so if you had 2000 psi pushing a 1square inch rammer it would make 2000lbs of force. If you take that same ram and push on a rammer with 1/2sqin of surface area it will make 4000lbs of force. The key is finding the exact surface area of each rammer. The formula to find area is (pie x R squared). This can get slightly more complicated with cored rammers because you will need to account for the missing surface area of the core but I don't think most guys get that technical. Edited August 24, 2016 by NeighborJ Link to comment Share on other sites More sharing options...
OldMarine Posted August 24, 2016 Share Posted August 24, 2016 I don't bother compensating for the hollow rammers usually but I haven't moved past BP rockets yet. I haven't found it to be crucial thus far. I have the chart and templates for my gauge for each but my rockets fly well so... Link to comment Share on other sites More sharing options...
dagabu Posted August 24, 2016 Share Posted August 24, 2016 (edited) Here is an example of a ram (hydraulic) on the top, a section of rod in the middle and a rammer on the bottom. Lets say you are using the standard 6500 LPI for your gerbs using a 3" hydraulic ram and making 1/2" ID gerbs, you will only need 181 PGIG on the 1/2" ram to reach 6500 LPI on 0.2 square inches of area and 702 PSIG on the 1" rammer making a 1" ID gerb. "When you use a smaller diameter rod for pressing the comp than the ram what effect does it have on the actual pressure on the comp."There is more pressure on the comp. Again, looking at the 3" ram and you crank it up too 1000 PSIG, you would have 9000 LPI on the comp with 1" tooling! 1/2" tooling? 36,000 LPI!!!!!!!!!!!!!!!!!!!!! The forum Passfire has an incredible tool, it's a Rocket Loading Pressure Calculator, type in the pressure you want on the comp and the rammer/ram sizes and it gives you the gauge pressure you need. (PSIG, Pounds per Square Inch Gauge) Edited August 24, 2016 by dagabu Link to comment Share on other sites More sharing options...
calebkessinger Posted August 24, 2016 Share Posted August 24, 2016 (edited) yeah.. it's real awesome when people use single 1/4in star pumps and wonder why they get fusion welded together.. " I only put 1000 lbs on it. " I did the same thing to my first star pump i made myself.. just gave it a little bump. bam.. the rammer bent over. what the heck just happened? Once a guy goes through the math a couple times it's no big thing figuring the stuff out. Edited August 24, 2016 by calebkessinger 1 Link to comment Share on other sites More sharing options...
dagabu Posted August 24, 2016 Share Posted August 24, 2016 yeah.. it's real awesome when people use single 1/4in star pumps and wonder why they get fusion welded together.. " I only put 1000 lbs on it. " Sounds just like my first pump! Link to comment Share on other sites More sharing options...
ddewees Posted August 24, 2016 Share Posted August 24, 2016 https://www.dropbox.com/s/sw4tiytiq2yzj5n/Pressing_Comps_V2.xls?dl=0 Link to comment Share on other sites More sharing options...
dagabu Posted August 24, 2016 Share Posted August 24, 2016 Beautious! Link to comment Share on other sites More sharing options...
OldMarine Posted August 24, 2016 Share Posted August 24, 2016 https://www.dropbox.com/s/sw4tiytiq2yzj5n/Pressing_Comps_V2.xls?dl=0 Yup, that's the one! Thanks again for that Dan. Link to comment Share on other sites More sharing options...
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