Slide Valve partially broken

[TSH Tech]

Ouch That means those rubber seals inside swelled up, jamming it in there pretty good.

Ok, when it comes time to cut the backwash valve out, if you are comfortable, you're going to end up doing some PVC pipe plumbing work. Use Red Hot PVC glue. Probably the one tricky part when making PVC pipe repairs in the filter/pump area is having enough "play" to glue the final pipe, so you can glue the pieces, move the pipe back slightly, then press them into place to the glue will make a tight seal. It's easier to add a piece of flex PVC pipe, so it will bend for the repair. Occasionally, I'll have to cut pipe back further so that I can create a pipe piece with enough play so I can glue it into the valve successfully. Under that scenario I have to replace any 90 degree PVC parts I cut out to make the layout resemble everything I removed. Heres a rough diagram how it would be cut, removed and replaced.
http://i46.tinypic.com/vyr3bt.jpg

If for some reason you feel uncomfortable and rather let a "pro" do it, call a pool tech for an estimate on the repair. Skip a regular plumber, 1) plumbers don't think swimming pool and 2) they all charge sky high Union rates.

[cpo2go]

If you have to replace the whole assembly, it's not that big of a deal if you've got room in your piping to do it.
Like THS Tech said, unscrew the 2 bulkheads from the filter side and cut the plumbing (influent, effluent and backwash) leaving yourself enough piping to glue the new pipes to.
Buy 3 couplings and some good PVC glue (I use Christy's Red Hot Blue but that dries very quickly so you may want to use something that allows for a longer cure time in case you need to set and re-set your new pipe job). Measure the couplings' length (should be 3") and measure the inside depth, per side (1 1/2"). Cut 3 pieces of pipe 3" long and glue them into the 3 ports on the valve; glue the couplings on the opposite ends; glue the 3 pipes (influent, effluent, b/w) onto the couplings then move the filter into position and tighten the bulkheadsd onto their respective fittings on the filter tank.