As per the explanation given by you , as u r providing crushing work , u shall be charging service tax to ur customers . And in this case , if the vat purchases made by you directly relate to ur business , you can claim input .
For this , the entry at the time of paying service tax on purchases:-
Purchases A/c Dr. (excluding Service Tax Amount)
Service Tax Input A/c Dr. (can be grouped under Current Assets)
To Creditor/cash/bank
Regarding VAT , if you charge vat on ur bill to customer , then while filing VAT return monthly , u can claim input and the entry shall be same as above .
Purchases A/c Dr. (Exclusive of S.T. and VAT)
Service Tax Input A/c Dr.
VAT Input A/c Dr/
To Creditor/Cash/Bank A/c
Both Service Tax and VAT Input accounts may be classified under Assets.