Very Basic Question

[DanielVT]

I was looking at a web page that shows you how hydraulics work, and their simple logsplitter diagram got me wondering: once the ram is extended all the way, what does the pump do? Does it stop, does it keep exerting the same pressure on the cylinder, or does something inside the cylinder let the fluid go past and back into the tank? Same question on the other end, I guess - when the ram is retracted.

 

[Gale Hawkins]

Most pumps just move fluid in one direction. Control valves controls the action/direction of flow at the cylinder as I understand it.

 

[Barely Smokin']

Pump keeps spinning. Fluid does not bypass piston inside cylinder. Instead, pressure relief valve (usually one for each direction), opens up when the piston reaches its max stroke and allows the fluid to enter a bypass circuit, which returns fluid to the low-pressure side of the circuit (where the holding tank is). By switching out or adjusting the pressure relief valves, you can increase or decrease the max pressure sent to the cylinder. Relief valves are usually screwed into the valve bank (where the control lever is).

 

[AKKAMAAN]

L]If we are talking about a fixed displacement pump system, type gear pump on a log splitter, there is ONE main pump and system protecting pressure relief valve, PRV, on the line between pump and first control valve.....

Then if this pressure setting is to high for a certain actuator and it's FEL etc, there can be one or two work port relief valves to protect cylinder and the mechanical hooked up to that actuator...the pressure setting on a work port PRV can vary a lot, and can, on certain hook ups, be set higher than the main relief valve....

So at a stall on the cylinder, either the main PRV, or the work port PRV, will by pass flow, depending on which one is set on the lowest pressure....

(Tractor system often have a pump with variable displacement, and the flow is controlled by a pressure compensator (instead of a main PRV)....these pumps can shut of flow, while they are still turning.....)

Fixed displacement pump system.....here is a little animation show a work port PRV open

 

[mmurphy]

:laughing:AKKAMAAN, I wish I had your toys. Then again, I probably wouldn't know how to work them!

 

[mbohuntr]

AKKAMAAN, Can you give me a link to that animation site?? I love that stuff...:thumbsup:

 

[AKKAMAAN]

AKKAMAAN, Can you give me a link to that animation site?? I love that stuff...:thumbsup:

Sorry mbohuntr, there is no site more than mine...I made this animation, I am very happy

you like it.....
I'll look on my shelfs, to see if I have something more worth showing....

 

[DanielVT]

here is a little animation show a work port PRV open

Wow, thanks, this is great!