Why isn't my buffer working?

I'm sorting items into barrels. Since items are coming from BC pipes, sometimes two barrels would be allocated the same thing, so I put in a buffer, however the whole thing has stopped flowing. Before there was just pneumatic pipe where the buffer was. What have I done wrong?

Inputs are the BC pipes. They feed into a relay, which outputs to pneumatic. This then feeds through a buffer (to collect up stacks) and then out the pneumatic and to my barrels.