Above is the 155 Valve Body Diagram
Below is the newer 255 Valve Body Diagram
Click on to ENLARGE VIEW
1. The Series 155 was replaced by the Series 255 late 1995 ( early 1996 ). An easy way to tell the difference is, the brine control ( salt dial ) is located on the front ( just beneath the timer housing ) on the 155 and it has been relocated to the right side ( looking from the front ) on the 255.
Another noticeable difference is the Injector Cap, and Injector Screen/Cap are the size of a quarter on the newer 255. They are about the size of a dime on the older model 155.
Note: The Brine Control and the Backwash Flow Control plugs are identical in size on both the 155 and the 255. However, another difference is the location of the Backwash Flow Control Plug ( 25F )is on the right hand side ( looking from the front ) on the 155 and has been moved to the left side on the 255.