How to block Auto Approval of PurchaseRequisition created by preparer, and it should route to his manager for approval,though preparer has approval Authority
Navigation to change the setup as below
PO Super User--->Setup--->Purchasing--->Document Types (Select Purchase Requisition)
Now uncheck the Attribute (Owner Can Approve). Save the work and close the form.
Once the above setup is done, no preparer can approve the requisitions he created rather it will route to his manager, though he has Approval Authority.