Code To Make Dynamic Dropdown Boxes

I've been farting around with trying to make some dropdown boxes populate based on the value selected from the first drop down box..

I have 3 DropDowns..

1)PumpType
2)PumpMfg
3)PumpModel

the first one takes all the pump types from a database table called pumptypes and populates it

the second dropdown gets its values from an sql query to a second database table called pumpdata that puts all the manufacturers that have that have a pump that matches the type selected in the first dropdown.

the third box does essentially the same thing but looks for all the models based on the values of the first 2 dropdowns..

whats happening is when I select the pump type it goes to the next page without allowing me to select the other 2 boxes.

heres the code I have .....