On Wed, 26 Jun 2013 17:31:55 +0000 (UTC), "Danny D."
wrote:

Do you think I can just pull out the green water restrictor
with pliers and shove the slip-fit shutoff valve onto the existing
white pipe coming out of the elbow?

I highly doubt that you can. Remember how hard you pulled to remove
the poly from the insert? The insert is already a reduced size so not
likely you will find a ball valve in that size.

I'd cut off the elbow (save as much pipe as possible).

Then you will need:

- new 3/4 elbow

- PVC ball valve (like on your pool pump)

- a new insert for the poly

- small section of pipe (elbow to ball valve)

Repeat on the other line in the other garden section.

Unless I missed something...