Hi Everyone. It's Megan and Adel the LIFCO content team. Do you know what variable and regulating controls mean? Neither did we! Today were asking Fraser some questions regarding an HPV 55 pump that came in for troubleshooting. We go more into depth regarding the meanings of the controls of the pump. Read our conversation below and then click on the link and watch the youtube video we made on the HPV.
Video Link : HPV 55 Youtube Video
Megan: I just learned that the V in HPV means it's a variable pump. What exactly does that mean?
Fraser: Names are what make a lot of hydraulics more complicated than necessary. It is a variable pump but that V in HPV is referring to the variable control. There are fixed pumps and variable pumps. Fixed have a set displacement and if you want to change the flow then you need to change the rpm that it spins at. That's simple. But this V for variable in the HPV refers to the ability to control the pump. You are able to vary the flow rate based on a signal.
The alternative are the "regulating" pumps, which respond to feedback like system pressure. But this "variable vs regulating" verbiage is not common across all manufacturers. It is Linde that likes to make the distinction. In Linde's case, variables (HPV) are closed loop while the regulating pumps (HPR) are open loop. This makes sense because a closed loop can be open/flowing two ways (A or B) and so it needs a signal to be told which one to do. It is more clear in the motors: HMR motors are a regulating motor in that going uphill would increase the displacement to turn slower but more torque. The HMV motors would receive a signal saying "Slow Down" thus increasing displacement.
Adel: So when another manufacturer doesn’t use “variable vs regulating," how would they describe the same pumps?
Megan: Sorta along the same lines as Adel's question, if it's not in the name how would you know if it's regulating or variable? Is it just if it's open loop or closed loop?
Fraser: Parker's Gold Cup has a lot of features combined so they don't have such strict categories. But they will call the variable controls as "strokers". And the regulating controls as "compensators". Closed loop (meaning also a variable control) can still have regulating features, but often call it an "override" like a pressure override that de-strokes the pump if the pressure gets too high. There are a few geographical differences as well: pressure override is more common in Europe while pressure compensation is more common in the US.
Megan: I think analogies help a lot with learning, can you give us one about this?
Fraser: Gas pedal is like a variable control. Cruise control is like a regulating control.
Megan: Do you think it is necessary to know these terms to understand pumps/motors?
Fraser: No. The most important thing is to understand how it works by looking through the catalog and reading the descriptions, charts, and hydraulic schematics. The jargon you will just naturally pick up. Even this "regulating vs variable" controls is not a distinction that anyone really cares about. It is just that you asked what the letters HPV stand for. Hopefully you are not sorry you asked! But if you really want to get a headache, I attached an application that uses those external servo ports. (See attached images)
Megan: On the HPV 55, we added those 2 servo ports to the back end. From my basic understanding the servo port allows you to add an external signal to control the control. And because this is a variable control you can do that! But why, like what is an example of when someone would use this?
Fraser: Those servo ports allow you to override anything that is controlling the pump. So it allows it to override even regulating functions like pressure compensation/override (In that case it is overriding the overriding functions). The whole "regulating vs variable" controls isn't such a strict or even that useful of a distinction. It is just good to know how Linde Hydraulics separated their pumps and motors based on the control. Don't worry too much about it.
Megan: Haha, well thank you, it's definitely a lot to understand but it all makes sense how it all comes together.
Adel: Ha, so we just learned something most people don’t know, and even fewer people actually care about.