Modular valve tree

A modular valve tree, comprising:

• two or more blocks, including:
• a first block having a flow passage therethrough, including an inlet and an outlet;
• a second block having a flow passage therethrough, including an inlet and an outlet;
• an insert comprising sealing elements, wherein:
• the insert is partially disposed within each of the first block and the second block,
• the insert has a throughbore fluidly connecting the first block outlet to the second block inlet;
• and
• the sealing elements are configured to seal external surfaces of the insert against an internal surface of the respective flow passages;
• a retention system configured to retain the blocks in position and compress and engage one or more of the sealing elements;
• wherein the insert comprises:
• a first seat pocket insert part configured to be disposed within a respective threaded seat pocket of the first block outlet, the first seat pocket insert part further including a seat pocket;
• and
• a second seat pocket insert part configured to be disposed within a respective threaded seat pocket of the second block inlet, the second seat pocket insert part further including a seat pocket;
• and
• a sealing element disposed within and sealing against each of the seat pockets of the first and second seat pocket insert parts.