we have 400t hydraaulic press SMG make , return is through prefill valve . There is no prefill tank above cylinder nor main tank is above cylinder . TANK OIL level is approximately one metre below cylinder cap . It is sucking oil from it . My question is that after return stroke completion , whether the oil remains fully filled in prefill drain pipe till the next cycle completion or not ? If yes why does not it falls due to its weight .Above press is very fast . Cycle time is 4 sec for 600 mm stroke

Not the most common setup for a Pre-Fill system but is used by some manufacturers and (see Below) shown in at least one manufacturers catalog as a viable mounting condition.

From your post it appears the press actually runs satisfactorily so you need to figure our why it does.

What is the Pressure Drop available on the Suction Line as the press is decending and the cylinder is being filled from the tank/

What is the flow velocity through the Pre-Fill valve and its supply line from the Tank to the cylinder?

No fluid fall if no way for atmosperic air to enter the valves, plumbing or actuator.

You can see one companies Installation Instructions on mounting of Pre-Fill valves here.
http://www.oilgear.com/documen...p?cid=2&gid=7&mid=23

They show a Tank Below mounting configuration in their "Type VPE" literature.

quote:

You can see one companies Installation Instructions on mounting of Pre-Fill valves here.
http://www.oilgear.com/documen...p?cid=2&gid=7&mid=23

IT IS INERESTING TO SEE THIS TYPE MOUNTING . COST CAN BE REDUCED TO AVOID PREFILL TANK . THE INSTRUCTION IS ABOUT MAXIMUM ALLOWABLE DISTANCE IN HORIZONTAL DIRECTION AND MINIMUM ALLOWABLE DISTANCE IN VERTICAL DIRECTION . I AM INTERESTED IN HOW THEY CALULATED FOR A PARTICULAR SIZE VALVE , FLOW VELOCITY ? CAN ANYBODY HELP ?

maglub wrote:

quote:

I just guesss again....

Best Disclaimer I've ever heard maglub, Wow.

quote:

I AM INTERESTED IN HOW THEY CALULATED FOR A PARTICULAR SIZE VALVE , FLOW VELOCITY ? CAN ANYBODY HELP ?

You might find this spreadsheet made by Peter Natchwey helpful.

http://www.patchn.com/downloads/cylcalc.xls

and this article.

http://www.hydraulicspneumatic...Zone-HydraulicValves

and these formula's and calculators.

http://www.hydra-dyne.com/Tech...ces.php?_a=cylinders

This message has been edited. Last edited by: Woodygb,

Pre-Fill circuits follow almost the same parameters as a Suction Line (Pump Inlet Line).

Velocity of 2-4 FPS would be great, however, I've seen 4-8 FPS recommended in some training and catalog material.

The main idea is to keep the chance of cavitation out of the picture so the cylinder is full of oil when the work is met and the pump/s do their work. Any voids have to be filled and will slow cycle time unless pump flow is increased.

The basic Ebook covers Pre-Fill Valves in Ch. 10.

quote :What is the Pressure Drop available on the Suction Line as the press is decending and the cylinder is being filled from the tank/

quote :What is the flow velocity through the Pre-Fill valve and its supply line from the Tank to the cylinder?
Recently I came across simillar press . PRESS FREE FALL SPEED IS 600 MM /SEC . CYLINDER PISTON DIAMETER IS 400 MM . TOTAL FREE FALL DISTANCE IS 600 MM .PRESS STARTS PRESSING IMMEDIATELY WITH A SPEED OF 80 MM / SEC .THERE IS NO DATA ( FLOW VELOCITY AND PRESSUREDROP AT PREFILL VALVE ) FROM MANUFACTURE SIDE . I AM INTERESTED IN CALCULATING VACUUM PRESSURE AT THE PISTON SIDE DURING FREE FALL . COULD WE CALCULATE IT FROM PISTON FREE FALL VELOCITY ? I THINK WE CAN CALCULATE USING ORIFICE EQUATION BY USING TOTAL OIL VOLUME FILLED IN CYLINDER IN ONE SECOND AND EQUATING IT TO K*deltaP^1/2 . IS THERE ANY OTHER METHOD FOR CALCULATING FROM KNOWN PISTON VELOCITY .