Shane,
Greg explained most of it. (Thanks for your input Greg!)
I explained in a previous post some of the things double pilot operated check valves do. Like Greg said, they hold the cylinder in the position you put it. There is no (or very little if any) leak down at all. There is no movement in the hydraulic cylinder once you set it's position. Leak down is caused by small leaks in the valve or even in the cylinder itself where fluid seeps by the seals and lets the cylinder move. I've found that most cylinders are very good but the valves let fluid pass a little, so I like using the check valves. If the cylinders themselves leak, the check valves won't help... but generally it's the valve controlling the cylinders where the problem is.
Another benefit from hard plumbing them onto the cylinder like I did is that if a hose ever ruptures, the cylinder will still stay in it's position ... it won't collapse. It's also a "safety" feature in that respect. One drawback is you can't "float" a cylinder with DPOCV's on it because it stays locked until you move it. Some guys don't like them for that reason. But that is no reason not like or dislike the check valve ... it's just another feature that may not apply to your kind of cylinder use.
For me, I do a lot of grading and road work around my place with the boxblade.
After hours of dragging the boxblade, the setting never changes. That's important to me so I don't need to constantly adjust the cylinder to get the boxblade back to where it was a perfect setting. It takes some fiddling around to get the desired levelness and tilt of the box for crowning or smoothing, so it's a benefit for me. I don't use float in the top link or side link cylinders, I use the float from the 3pt to get that. I can see where float on a top link would be desirable when mowing with a rotary cutter though. But I have a slot for my mower that provides some float so the mower can flex back and forth.
Some have flexible links.
I installed them (dpocv's) on my backhoe stabilizer legs because they were constantly leaking down when I was digging. I was constantly "bumping" the stabilizers to keep the backhoe up. It was a small annoyance but more so, not good to operate the backhoe when it was not stable on the ground. After I added them they don't leak down at all. Another thing is when I park the 3pt backhoe, it stays up in the exact position where I set the legs. It's stayed in the same position for up to six months before I used it again. Before, I would come back to the property and it was flat on the ground! I bought these DPOCV's fro Mark at CCM.
