VFD on hydraulic pump

[CONTROL FREQ]

CF, you obviously have extensive experience here, and there is very little you say with which I disagree. What I'll add is that there is an active movement to maximize energy efficiency at almost any cost. If I'm going to do a system design, there are numerous options which depend on the system requirements.

But, in general ... for a multiple "axis" system ...

fixed speed fixed displacement ... simplest, least efficient
fixed speed, variable (pressure compensated) displacement, next efficient, sometimes simpler system
fixed speed, controlled displacement, more efficient
variable speed, fixed displacement, most efficient

The HVAC guys, with SEERs of 14 and up, usually have gone the variable speed, fixed displacement route. When we do a centralized system, we often will have some energy storage (accumulators) with pressure feedback to a PLC to multiple HPUs (different pressures to minimize reducing valve use)

In industrial hydraulic pumps commonly available, I have a hard time beating an internal gear pump for efficiency. A fixed piston unit is darn good too, but there are fewer available. If I need over (ballpark) 200 bar or 3000 psi, the piston units come into significant consideration. Your recommendation of Vickers (Eaton) and Rexroth (Bosch) is good. While my own experience is heaviest in those, I'd add Parker to the list; they are a major line as well.

I regret that some who profess great (electro) hydraulic understanding do not show it. But that is not unique to any field ...

You know? That actually makes a lot of sense. I worked a long time with Desma punch presses (although we used them for injection molding) at any rate, they were fitted with dual output motors with a VERY dependable Bosch rotary piston pump on each shaft (one left---one right)... I never really saw any need for a VFD in that situation we ran a modest 1500-2000 psi. But last year, I was tasked with installing a pressure transducer, analog I/O's a VFD and programming a water transfer system to deliver more during times of high demand and less at other times. The system keeps a pretty steady 60 psi at all times with good ramping and no drops or spikes EVER. Thinking about it that way---I can see where in some applications a VFD for hydraulics would make perfect sense, and would be an excellent idea. I try to never be resistant to change and always be open-minded, sometimes 'tunnel vision' screws that up. Until someone opens my eyes a little with facts and real examples. Then I start to see oppotunities to use technologies I've already used, in a WHOLE new way. The efficiency never even occured to me, in the old presses I worked on, a VFD probably would've reduced oil temperature since during times of curing rubber in "high clamp mode" the pumps would not have been shooting oil through the manifold stacks at full bore back to the reservoir the whole time... Makes all the sense in the world. Not even my thread but I just now got a heck of a lot from it.

Thanks for the push my Friend,
Mike

 

[weressl]

And some grumpy 'ol fart rides in on a hov-a-round with a powerflex 700!:grin:
Just expressing my opinion about the VFD, all funning aside, I LOVE technological advances... I just think some engineers are a bit overzealous and tend to "OVER engineer", for crying out loud--- its a REALLY big door. Not a scissor lift. I'm just saying... wasn't trying to step on anyone's toes. Sorry if I did. Been a LONG time since I was the FNG!:roll:

The point is that the best efficiency is always accomplished when the enrgy is controlled closest to its source. In this case the ft/sec movement is directly proportionate to the amount of hydraulic displacement that is directly controlled by the speed of the positive displacement pump. So if the objective is to slowly accelerate a large mass to a certain speed, hold it at this speed until it is close to the final position and then slowly deccelerate it to until it is closed, I can't think of a more efficient transfer of the required energy than a constant torque drive for the hydraulic mechanism.

The comparison of hydraulic to the HVAC system is only aplicable with some great caviats since air is compressible and liquids aren't.

 

[weressl]

Frankly speaking, I think his thought is absolutely wrong.

I don't know the exact application at the moment. But I think there may be some problem of the wrong installation of VFD on the motors.

Absolutley. If variable torque control is attempted instead of constant torque and the equipment is sized so the failure would occur.

 

[CONTROL FREQ]

The point is that the best efficiency is always accomplished when the enrgy is controlled closest to its source. In this case the ft/sec movement is directly proportionate to the amount of hydraulic displacement that is directly controlled by the speed of the positive displacement pump. So if the objective is to slowly accelerate a large mass to a certain speed, hold it at this speed until it is close to the final position and then slowly deccelerate it to until it is closed, I can't think of a more efficient transfer of the required energy than a constant torque drive for the hydraulic mechanism.

The comparison of hydraulic to the HVAC system is only aplicable with some great caviats since air is compressible and liquids aren't.

You sir, are correct (as usual). and before some new college grad throws out some "compressible liquid" to try and "prove you wrong"... I'd like to say---thanks for your input. It IS OBVIOUS to me, that you know exactly what you are talking about---About a lot of things. Sometimes I don't get what someone is saying until I see it "in crayon". My boss got tired of being 'lost' when I tried to explain things to him, so he just started saying "just make it happen". As of the past few years, I've been dealing with mostly retro, mixed with some newer technologies. for example we move large loads across a horizontal plane using stepper motors to signal hydraulic valves to fire, then on the same machine, limit switches fire the "slow down" valves on the hydraulic elevator, as well as cam eccentrics that make and break proximity switches for timing. I never mean to be "thick" but as I said, sometimes I get tunnel vision. I hope I never come off as disrespectful. I owe EVERYTHING I have to guys a lot smarter than me, who were patient and willing to share their EXTENSIVE knowledge. Thanks for the patience, when I stop learning it'll be over.

 

[weressl]

You sir, are correct (as usual). and before some new college grad throws out some "compressible liquid" to try and "prove you wrong"... I'd like to say---thanks for your input. It IS OBVIOUS to me, that you know exactly what you are talking about---About a lot of things. Sometimes I don't get what someone is saying until I see it "in crayon". My boss got tired of being 'lost' when I tried to explain things to him, so he just started saying "just make it happen". As of the past few years, I've been dealing with mostly retro, mixed with some newer technologies. for example we move large loads across a horizontal plane using stepper motors to signal hydraulic valves to fire, then on the same machine, limit switches fire the "slow down" valves on the hydraulic elevator, as well as cam eccentrics that make and break proximity switches for timing. I never mean to be "thick" but as I said, sometimes I get tunnel vision. I hope I never come off as disrespectful. I owe EVERYTHING I have to guys a lot smarter than me, who were patient and willing to share their EXTENSIVE knowledge. Thanks for the patience, when I stop learning it'll be over.

Appreciate the sentiment, but you sir, would be doing a disservice to yourself if you think that being correct is what you can expect from me with any consistency. We are all human being, continously learning, advancing and growing in knowledge and experience.

I often put my foot in my mouth, but found that crow eaten warm is best tolerated by my digestive system.

I also hope that I am not being viewed as disrespectful, but I hard-suffer fools and after the initial encounter measure my respect as it is earned. "Respecting" somebody undeserved does more harm and disservice to them than to the other party.