Here's my plan. I want to mount the DPOCV's with hard lines to the cylinders. That means I have to make a fitting that goes into the cylinder ports. Guess what, they are 13mm x 1.5 pitch. Yup, not 12 or 14 but 13mm! The bolts measure .511" in diameter. I looked all over and found a supplier in Florida who sells 13mm x 1.5p taps and dies so I bought one of each.
The fitting I will make will have a 13mm male thread and an "O" ring groove to seal it. Then I will drill and tap it on the side for a 1/4NPT hole. I wil shave off what I need to have it facing the right way when tight... whatever it takes. That will fit the tube I am making too. Reason is because the DPOCV's have a compression fitting, not a flare end! And it is 12mm so no one has tube in stock and the minimum you have to order is a 20' length, so I'm making my own out of tubing stock I have for my plastic injection molds.
OK, now the tube will have a 12mm OD on one end that will fit into the compression fitting of the check valve and the other end will screw into the 1/4 NPT port fitting. The reason for a compression fitting is so you can assemble the whole thing with the tube inside the check valve and screw in the 1/4NPT into the port fitting. Wherever it screws to, it will leave some tube inside the check valve and you tighten the compression fitting at that point. After that, I plan on reusing the hoses, which have the banjo fittings and bolts. But they are the 13mm ones. They also have a 90° metric JIC on the other end to fit the valve spool, so I'm not going to try to chase that down too.
Now for the last fitting. The outlet and inlet on the DPOCV is 3/8NPT of all things! So I got a 3/8NPT bushing to thread into the check valve and will drill and tap the inside of it to 13mm x 1.5. Then I can bolt the old hoses on with the old 13mm banjo bolts and be done with it.
This how I'd like to have the check valve sit on the cylinder.
This adds another dimension to my "no-brainer" project.