Hydraulic top links variants

[Indian Territory]

I’m going to show my ignorance here, but I can’t seem to find an answer to a question. (Yes, I did search the site.)

I have used hydraulic top links in the past by simply hooking them up to the rear remotes. The cylinder I owned was smooth, with only two connection points protruding from the side of the cylinder.

But I keep seeing hydraulic top links that—for lack of a better description—look to have exterior plumbing which includes some sort of piping and an external cube (well proud of the cylinder itself) into which you plug your hydraulic hoses.

What is this contraption accomplishing? How is it different from the smooth cylinders? Am I even making sense?

 

[LindenBruce]

It's a check valve that keeps the cylinder from moving via leak down past the valve spool. All spools bleed a tiny bit of fluid past them during operation. You usually don't notice it because you are working the spool back and forth operating your implement. So there is not enough time for you to recognize the bleed down. Does that make sense? B.

 

[ptsg]

The external cube, known as double pilot operated check valve, also works as a safety device.

Let's say you're driving on the road with an heavy 3 pt implement in the back, without the check valve, if you hit a bump, it could apply enough pressure to burst a hose. With the check valve, the hoses don't see any load at all, so it will hardly pop a hose. Sure, there is the hard line from the cylinder to the valve but that has a much higher burst pressure than a hose.

These check valves are also used on most cylinders of cranes, man lifts, telehandlers, etc, exactly as a safety feature.

 

[Indian Territory]

Wow. You guys are good. Thank you!

 

[LD1]

The descriptions are spot on.

Now the difference in reality....

IF you have a float valve for the remotes, or ever want your toplink to float, one with the DPCV will not allow that

 

[Vigo327]

A double pilot operated check valve (ie does the job in both directions for a double acting cylinder) or any pilot operated check valve can also sometimes be referred to as a load-holding valve or a holding valve. They are also sometimes built into control valve assemblies as a 'feature'.

That's the only thing left i could think to say that y'all didn't already..