Gallery, Projects and General => How do I?? => Topic started by: PK on August 05, 2016, 12:20:02 AM

Title: Hydraulic help
Post by: PK on August 05, 2016, 12:20:02 AM
A question for the slippery handed pro's

So we have a hydraulic press (actually it's a tension test rig). It consists of a single acting 'enerpac' style ram and a two pump (low/hi pressure), 1HP power pack.

What we want to do is to have some finer control over the force we apply. By finer control I mean, the 10000 PSI system can generate about 20T. We would like to be able to ramp this up a couple of percent or so at a time.

It doesn't need to be calibrated or repeatable, we have a load cell in the system for that, we just want a knob we can twiddle to adjust the force..

Is the best way to do this with some kind of PRV, a regulator, or just a fine adjusted pressure switch for the motor?

Many thanks in advance.

Title: Re: Hydraulic help
Post by: Lew_Merrick_PE on August 05, 2016, 10:38:42 AM
How about an adjustable needle valve to control the volumetric "inrush" rate?
Title: Re: Hydraulic help
Post by: Noitoen on August 05, 2016, 04:31:19 PM
They have these from Schneider Electric with digital (On/Off) output up to 600 Bar 8700Psi. Other brands may have a little higher. I use 400 bar types and they work well.

Title: Re: Hydraulic help
Post by: mexican jon on August 05, 2016, 09:12:01 PM
Do you have the details of the pump / schematic drawing ?  Basically the 10000psi system will normally have a pilot operated pressure relief valve, which would normally be set to open at the maximum pressure that you want to see on the system, these are quite often adjustable (you could then use this to bring up your pressure in increments) so you may already have all you need hence the need to see a schematic.
Title: Re: Hydraulic help
Post by: PK on August 06, 2016, 08:52:51 AM
Good point. No schematic but it's a small unit. We'll pull it apart next week...
Title: Re: Hydraulic help
Post by: PekkaNF on August 06, 2016, 02:15:30 PM
Flow restrictor would be most simple method, but if elastic modulus of the material is high, very little volume=time will be on the measurement window....hmmm....what time resolution do you have on the force measurement loop?

I would use proportional pressure regulatin or restricting valve, you don't need great sophistication or accuracy, because you have load cell. Smallest possible valve for the flow (minimal) but you might need additional circuiry to set the rig - or patience and software to trigger from meaningfull load.

Title: Re: Hydraulic help
Post by: David Jupp on August 06, 2016, 03:02:00 PM
Many small hydraulic pumps are (fixed) positive displacement devices, so a flow restrictor won't actually achieve much unless there is somewhere else for the fluid to go.  If the pump is a variable displacement type, some fancier options may well be possible via the built in compensator - but it will depend how the pump is configured.

Operating the pump motor via a VFD may be an option, though performance might well be poor at very low speed.

Will be interesting to see what you end up doing.