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Converting an inverted hydraulic press into a light-duty forging press


JHCC

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3 hours ago, JHCC said:

What the Dickens is going on here?!?

I can't keep details straight when you've made so many changes and such.

If it's traveling at the same speed then your pump isn't delivering more gpm. Did you change pump? If increasing RPM doesn't increase gpm then you have a pump that limits output over bypass. Some are metered for flow though I don't know what they're called.

It's supposed to escape over bypass when the piston tops or bottoms out, even with a self returning valve it'll give a little squeek. That's normal.

Tank looks good, a little red pin striping would really snazz it up. 

Frosty The Lucky.

 

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A quick recap:

1) Before July 6, I had a 5 hp motor running at 3450 rpm turning a single stage pump that gave me 3.14 gpm. I was getting about 17 tons at around 0.8"/sec. This was an upgrade from the 3 hp motor installed previously, although with the same rpm and therefore the same ram speed.

2) On July 6, I installed a two-stage pump that was supposed to give me 11 gpm in the first stage and 2.9 gpm in the second. With the 5 hp motor running 3450 rpm, that should have produced about 4 tons at 2.85"/sec in the first stage and about 18.5 tons at 0.75 gpm in the second. As noted in this comment, it didn't. Instead, (as shown in the video in that comment), I got about 0.56"/sec in ram speed and the pump cutting out when I reached the limits of ram travel.

3) I called Northern Tool and had them send a replacement pump, and I sent the other one back. While I was waiting, I acted on the advice of the members here and added a 5 gallon reservoir tank and a filter. When I installed the replacement (again, using the same motor at the same speed), I got a slightly faster unloaded ram speed (0.66"/sec) and the same cutting out at the limits of the ram's travel, as in the video posted earlier today.

I just went and checked what happens to the motor when the ram reaches its limits, and it looks like the motor is starting to stall out, or at very least slowing down. Does that mean that the motor is underpowered? I don't understand how that would affect the ram speed, and I was never getting that kind of stalling back when I was running a single-stage pump.

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First stage in the current setup goes to 650 psi, at which point it's supposed to kick over to about 2950 psi.

Another thought that occurs to me is that the tubing that carries the fluid from the pump to the valve might be too small? It wasn't carrying as much volume with the previous setup (3.14 gpm, as opposed to about 11), so maybe it's just not big enough to allow enough fluid through? Could the back-pressure be causing the problem?

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I don't have a gauge, no.

54 minutes ago, Randy Griffin said:

Your tubing should be ok as long as it is at least the same size as the outlet of the pump

The tubing is actually a bit smaller than the opening: I switched in some metal tubing (from a hydraulic setup I got for cheap at the industrial surplus center) for the original hoses when I was still running high pressure/low volume. One of the pieces is a larger diameter; I'll see if I can fit that in.

 

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That still shouldn't cause it to do what it's doing. You really need a pressure gauge in the system. You can get a 3000 psi liquid filled gauge at tractor supply. Need to know what the pressures are during stroke and at end of stroke.

Does the new pump have a built in relief? I think it is called an unloading valve. I bet the control valve has a relief also. You could be getting conflict between the two.

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On a side note, I'd noticed while looking at hydraulic reservoirs that some of them have magnetic drain plugs to trap any metal particles in the system that somehow make it through the filter. My propane tank's drain is just a 3/4" plug, but I decided to put a magnet on the bottom of the tank just for giggles. No idea if it will do anything or not, but figured it can't hurt.

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Seriously thinking of ditching the two-stage idea and going with a higher volume single-stage pump for a lower pressure and a higher speed.

One option is a 5.5 gpm pump, which (with the existing 5 hp motor and 85% pump efficiency) will give me 9.94 tons at 1.44"/sec.

Another option is a 7.32 gpm pump; that would give me 7.36 tons at 1.91"/ sec.

Thoughts?

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John, if your circuits are so constricted it's kicking your pump to 2nd. stage you have other problems.

It won't take but 10psi to move that piston at the pump's full gpm rate unless something else is wrong. No, I'm not saying 10psi is enough to do work but it's plenty to make the piston and draw works move at the pump's flow rate/speed. 

How many sq" is the piston again? 

Frosty The Lucky.

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231 cu" to a gallon. so 1 GPM moves it 18.38" so 11gpm should move it 202"/min. or 3.4"/sec.  3gpm should move it 55.7"/min or 0.93"/sec.

I know I'm going to tick a bunch of folks off (again) but forget about PSI, you have a GPM problem. And yes the tubing is probably a contributing if not causitive factor. You might be better off buying some hose, I NEVER undersize hydraulic circuits. You want the pressure working for you not forcing it's way to the job.

Frosty The Lucky.

 

 

 

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There is the possibility that the cylinder ports are to small for the desired flow rate also. It not uncommon for us to drill out cylinders port to improve machine cycle times at work. (Usually pneumatic cylinders thought.) 

Anyone ever consider putting an accumulator in the system. You could size the accumulator to the same size as the cylinder and pump GPM would be almost meaningless. Just need enough time to recharge the accumulator between cycles.

David

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Hmm. The current hard pipes from the reservoir to the pump and from the pump to the valve have an OD of 3/8”. I have some 1/2” OD pieces that I think I can replace them with, although I’ll need to get the proper fittings. That would increase the cross section by about 78%. Worth a shot. 

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Sorry, I wasn’t referring to the pressure the cylinder can withstand, but what flow it was ported for. The chart I referred to recommends 0.425” diameter minimum for 11GPM, so I would assume the ports and fittings on the cylinder should be about the same. 
 

Just something to consider,

David

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