[Jim27]

Found a used 50 Ton press that uses a 5" bore x 7" stroke cylinder and a manual pump similar to a hydraulic jack - place is closing and selling off things. Was used for heat embossing but wondering what I could do to add some sort of pump and make it more useful. Looking to do some very low volume punching and drawing of sheet metal. Air over hydraulic is one option but would prefer smoother operation as I will be doing some sheet metal drawing. Doing some calculations I come up with 5000 PSI to reach 50 ton rating. Have done a few things with hydraulics but not a lot so looking for some input from others. Looks like the speed will be very limited at that pressure unless I have a large motor driving the pump. I could use a log splitter type pump to get higher flow at low pressure but most are for much lower pressure. Punching some numbers into the Surplus Center calculators

For 3 GPM at 5000 PSI I need a 10 Hp electric motor. Travel would be 0.6 in/sec.

I could just go for a 3000 PSI system and have a 30 ton press. I have a 20 ton HF press with air over hydraulic jack so this isn't a huge upgrade from what I have.

I looked quickly for air over hydraulic pumps and found them to be more expensive than a jack with the pump but perhaps I was not comparing the same quality. I also found most of them for 10,000 PSI system.

[Jim Dawson]

''For 3 GPM at 5000 PSI I need a 10 Hp electric motor. Travel would be 0.6 in/sec''.

That specification is both correct and incorrect. It is correct for load lifting applications but not for pressing applications. The pump performance curve charts are not calibrated for normal pressing applications. For lifting a load you need constant pressure over a long distance, think forklift.

But in pressing applications, you only need to build enough pressure to move the cylinder against the internal friction of the cylinder until the ram contacts the work. Very little pressure is required. Then in the last fraction of an inch, you need to build pressure to do the pressing work, normally at a much lower speed. The HP required for pressing applications is a fraction of what is required for load lifting applications.

The problem with the charts is that they are presented in required HP, but that is not the parameter that should be used in pressing applications. The real parameter is the required torque to drive the pump to achieve the desired pressure without regard to the RPM of the pump shaft. (We're going to ignore internal pump leakage for the moment)

So how do you get the relatively high speed ram positioning combined with low speed high pressure for the actual pressing work? You use a two stage pump.

A quick search on Amazon turns up this 750W (1 HP) unit.
https://www.amazon.com/BestEquip-Electric-Hydraulic-Single-Solenoid/dp/B06XSZ6N66/ref=sr_1_45?keywords=Hydraulic+Pump+for+Log+Splitt er&qid=1649176777&sr=8-45

According to the specs, it seems to have a two stage pump, 5 LPM for low pressure, and 0.9 LPM for the high pressure range. Given the source, I would take the specs with a grain of salt. But it says it's rated at 10,000 PSI. You should be able to adjust the pressure relief valve to max out at 5000 PSI.

EDIT: I just noticed that the motor RPM is rated at 1400, this would indicate the specs were generated at 50 Hz, running at 60Hz, the low pressure performance would be a bit better than indicated.

[Jim27]

Thanks Jim. Yes, the log splitter pumps I mentioned are two stage but don't develop as much pressure. Same idea though - higher flow at low pressure and then low flow for high pressure to keep the peak horsepower down. Still I think I will be unhappy with the unit you linked to because of flow limits but that's the basic idea. Will look that direction some more. I need high pressure for about 1/2" of travel. At 0.9 LPM with a 5" cylinder it will take about 10 seconds to move 1/2". I like the idea of turning the pressure down to half of what they claim - I see that 10,000 PSI is past the red line area on the gauge. If I go to 5000 it might last for a while.

[Jim Dawson]

Well there is more than one way to skin a cat here. The base unit is the absolute cheapest solution. That doesn't stop you from adding to the system. I recently went through all of the calculations for a hydraulic press brake, so most of this is fresh in my mind. What I came up with for the press brake is hanging a servo motor on the pump so I have an RPM range of 0-5000 RPM, I have no problem over speeding the pump intermittently. There are a few ways to control this, and that solution might be overkill for your application. The nice thing about servo motors is that they can be operated at 2 to 3x rated torque intermittently. Servo systems are so cheap today that they are price competitive with standard 3 phase/VFD systems. Much higher power density and great torque curves.

But hanging a larger, maybe 2 HP, 3 phase motor on the pump and controlling it with a VFD might be in the ballpark, or just run the pump at higher speed than the rating to get the speed you want. You could even run a 3450 RPM, single phase 2HP motor on it and double the speed and maintain the same torque as the original motor.

[Jim27]

VFDs are getting easier to do and I am in that field so even easier for me. Was looking at an old band saw that had a small 3 phase motor on it. It was ancient so I passed because of the motor. Later realized I could just use a small VFD. It was old and looked pretty rough needing new surface on the wheels but maybe I should reconsider. I think I could get it for scrap value as someone else had already passed on it due to the motor. VFD would also let me slow it down as you had mentioned.