1. The power beyond valve will have a line to tank, and a line to the second valve. The second valve will have one line to tank.
2. What do you mean by check in return? No checks needed, unless you mean to prevent back drain of filters when changing elements. I would not put any checks in. More parts to fail. And they do...
3. Sae and JIC and ORFS only for me. NPT sucks. Have to be taped or doped, and then they leak. Never point the right direction, too loose, then one more turn can crack housings and ports. NPSM with swivels are not so bad, but the port still has to have NPT. Of you start right out with oring ports, you can avoid all the NPT as much as possible. Filters, cylinders, pumps etc in the consumer world are usually NPT. Industrial world, very few NPT left.
2. What do you mean by check in return? No checks needed, unless you mean to prevent back drain of filters when changing elements. I would not put any checks in. More parts to fail. And they do...
3. Sae and JIC and ORFS only for me. NPT sucks. Have to be taped or doped, and then they leak. Never point the right direction, too loose, then one more turn can crack housings and ports. NPSM with swivels are not so bad, but the port still has to have NPT. Of you start right out with oring ports, you can avoid all the NPT as much as possible. Filters, cylinders, pumps etc in the consumer world are usually NPT. Industrial world, very few NPT left.