Terms and definitions....(from Erratic hydraulics thread)

[AKKAMAAN]

Originally Posted by AKKAMAAN
Since your CV is over 10 gpm sized, you will need to give your CV lever a full push/pull to be able to build enough pressure. A over or under sized CV will limit the proportionality in the CV. With an under sized CV, pressure will build early of the lever movement, and with an over sized CV, pressure will only build enough at the end of the lever movement.

In an open center system, the pump flow is considered "constant", and the pump flow goes through the open center in the CV while in neutral. To build pressure, we need to restrict the "orifice" defined by the open center, and at the same time open the connection between pump and work port to cylinder. When pump pressure is higher than load pressure in cylinder, cylinder will start moving. If CV is way oversized related to the pump flow, it will take almost some where close to 100% CV spool movement to create enough pressure to lift FEL. It will of course depend on load pressure in cylinders. It will also depend on the pump flow, which can be increased by throttling engine.

The term here should probably be tandem center. Open center connects all ports together when centered. That doesnt seem right for cylinder control.
larry

I do not want to "high jack" that other thread with this, so I start a new one...

You are right Larry, that all ports connected is not what we want here, and that was not my intention either.
There is a lot of different terms and definitions, and many times they are used different ways.....I have tried to find a "bible" for hydraulic terms, but I am still looking....

My "term" open center system is perfectly fine here....open center valve I never mentioned. The valve that have ports connected to center in neutral, have a motor spool and makes the cylinder or motor float in neutral. These valves, are for sure, sometimes named open center valves. And a tandem valve is the one with ports isolated to hold load in neutral....

This site have some definitions, and they are mixing apples and oranges a little...this closed center valve, all suddenly refers to the closed center system which is a discrepancy here...

tandem valve

open center valve

closed center valve

On a forum like this it is very important that we use the same "language or lingo", so we can understand and get understood. I have seen other technical forums that have a forum dictionary that the members build by posting their terms, and everybody helps out to phrase the proper definitions.

I do not think there yet is a 100% accurate standard of definitions and terms.....I hope someone can give some more input to this. I would appreciate that!!!

 

[AKKAMAAN]

Hydraulic Glossary

This link to Scribd is the most comprehensive hydraulic dictionary I have found so far...
Scribd is a great site for sharing documents, and you get one free down load for for within 24 hrs if you upload a useful file or document

 

[Jbrink64]

A great publication is the Vickers Mobile Hydraulics Manual. It's available at Amazon. Mine is pretty well worn and dog eared.

 

[AKKAMAAN]

A great publication is the Vickers Mobile Hydraulics Manual. It's available at Amazon. Mine is pretty well worn and dog eared.

Oh yea...I know there are hundreds to buy in real paper, that's not a lot of help online, unless you want to scan that Vickers book and upload it as a pdf.....:laughing:

Well I'll keep look'n...

 

[AKKAMAAN]

http://www.hydraulicspneumatics.com/200/eBooks/

This is a very good source for hydraulic explanations, it is just not indexed for quick search...

 

[Jbrink64]

Oh yea...I know there are hundreds to buy in real paper, that's not a lot of help online, unless you want to scan that Vickers book and upload it as a pdf.....:laughing:

Well I'll keep look'n...

Yeah, I never thought of that.

 

[Gary Sweat]

Yeah, I never thought of that.

For future, I should say I have an "open center system" with a tandem valve so as not to confuse anyone. Got it, thanks.

Question, why do they put check valves in a tandem valve? Seems like they should not need them since the ports are closed off

 

[AKKAMAAN]

Question, why do they put check valves in a tandem valve? Seems like they should not need them since the ports are closed off

They are called load check valves, and are there to prevent the load from dropping down (flowing backwards towards the pump flow), when CV opens. Depending on load pressure, pump pressure need to be built higher before pump can move cylinder. CV build pressure by restricting center opening.

 

[Gary Sweat]

They are called load check valves, and are there to prevent the load from dropping down (flowing backwards towards the pump flow), when CV opens. Depending on load pressure, pump pressure need to be built higher before pump can move cylinder. CV build pressure by restricting center opening.

Thanks. I was always curious why they were in there. Keeps the load from dipping when you move the handle.