Fast Approach Speed in Hydraulic Presses

You might want to look at air over hydraulic. The approach is speeded up by pressurizing the oil tank with air and then switching over to hydraulic. It is an old trick.

The best trick!

No changes needed to Pump/piston/press.Just add a coiuple of valves to Air line.And add a simple DCS .

Skelley--thanks!

Hi,

There are regenerative circuits by which you can achive faster speeds but in that case your cylinder may rquired to change. or you can have a hydralic accumulater which can help to improove the speed.

regards,

vap.

Two or three stage pump would help obtain faster no load speed to minor working pressure until the press makes contact to the work. Pump Manufacturer could develop the pump for necessary flow requirements needed to produce the cycle times you require. No cylinder modifications would be necessary.

Ladies & Gentlemen; this is an issue which needs more discussion, because it is a problem in numerous applications. One that concerns me is a mechanical wrench to make up drill string on a drilling rig. The repondents have all submittd partial solutions, but the solution must be economical and I believe it has to do with pressure compensated flow control valving. BudT, you're teaching this stuff, surely there's a cleaner solution than motor type flow dividers?

A regenerative circuit is the most cost effective way of achieving the faster approach speed you require in my experience. Your maximum approach speed would be 2.53 times greater than the normal cycle speed. The requirement for 12 fold increase in speed would require a more costly and complex solution provided this is not a typo. Cylinder changes would probably involve larger cylinder ports to avoid pressure losses. You might consider a smaller cylinder working at higher pressure to generate the required tonnage and use less oil for the fast approach.

2.53 times? I think it would be a variable depending on rod size, relatve to piston diameter. Furthermore, a regenerative circuit is limiting the speed increase available.

Yes the ratio of the cylinder area and rod area governs the maximum regenerative speed for a given input flow. The speed is governable below this maximum but greater speed is only possible with greater input flow.

Accumulator circuits give such flows but the volume needed for a reasonable stroke is large and would require many accumulators to say nothing of the regulatory valving (as in meeting safety requirements) required.

External jack cylinders would work but this would require a large prefill valve, probably an external overhead tank and considerable control systems.

Most things are possible but as in cars, speed = money, how much money do you want spend.

SilverGhost wrote;

"BudT, you're teaching this stuff, surely there's a cleaner solution than motor type flow dividers?"

If there is one I have not come across it. However, I have used Motor type Flow Dividers numerous times to speed up applications while using the original pumps and valves.

Modified a 10" Bore Cylinder circuit that had a 2.5" Rod and was run by a 10 GPM valve that was over 75' from the cylinder that took over 6.5 minutes to raise and almost 8 minutes to lower.

With the Motor type Flow Dvider circuit it now raises empty in 2.5 minutes and lowers empty or loaded in 2.7 minutes. Fortuanately it is feeding material that weighs up to 30,000# on a line that only requires a load every 2-4 hours.

BTW, could you explain how a Pressure Compensated Flow Control would speed up the cylinder stroke?????? I'm alays interested in new ways to operate Fluid Power applications.

BudT, I'm thinking of a spool that would allow full pump flow at no load. As load is applied, pressure would shift the spool choking off the flow, slowing down the apparatus.

Maybe I ms-understood the original request. I thought the poster wanted the press to go 12 times faster not slow at the tonnge stroke????