PR not generating for MRP type VB
i have bill of material wich contain some raw material. for this raw material i have maintained MRP type VB , along with reorder point and safety stock in material master
but after MRP run, i am not gettting requirenemnt of raw material, if i changed the MRP type to PD , then requirenment (PR) coming for raw material. MRP control parameter are NETCH,1,3,1,1,1
so why i m not geting requirenment with MRP type VB.