The Hydrotech 33138 Retrofit Kit is for the 101 Series, 102 Series, 103 Series, 1010 Series, 1020 Series, and 1030 Series RO Systems. The Hydrotech 40600007 Reverse Osmosis Flow Control (orange band/45 GPD) that was previously used for these systems has been discontinued. The Hydrotech 33138 50 GPD Retrofit Kit needs to be used instead. If you have a Hydrotech 40600006 Reverse Osmosis Flow Control (purple band/35 GPD), you need to use the Hydrotech 33138 50 GPD Retrofit Kit and change from a 35 GPD membrane to a 50 GPD membrane. When replacing the flow control, you only need to install the Hydrotech 33138 Retrofit Kit the first time (unless the 33138 breaks). After installing the Retrofit Kit, it is recommended you replace the 40600041 Flow Restrictor piece every time you replace the RO membrane. This retrofit kit updates the drain line flow control to the type used with the current Hydrotech Reverse Osmosis Systems (1240 Series). This retrofit kit includes an internal plug assembly for the manifold and a capillary flow control contained within the red drain line tubing.