Question
I have seven stations on my system. station 4 recently has lost water pressure. it still comes on but the flow is greatly reduced.

Answer
If it happened suddenly I feel you may have a break or a blockage. Walk the entire zone area inspecting all of the heads. If there is not a break where water is flowing out from where it shouldn't, then next check the valve. If it has a flow control handle check if it is open all the way and while the water is on open it all the way and shut it all the way by turning counterclockwise and then clockwise several times. if these do not work then you may need to turn the water supply off and disassemble the valve by removing the bonnet and checking for debris in the line/valve that may be affecting its performance. try that and let me know what happens.