I am removing an existing mop sink that is plumbed into a vertical 2" vented drain. my question is may i use a 1-1/2" stand pipe that will be about 30" of the floor?

Hi Keith,
[QUOTE][my question is may I use a 1-1/2" stand pipe that will be about 30" of the floor?/QUOTE] your details are kind of sketchy.
Are you saying the sanitary tee and trap will be 30" off the floor and a short piece on top of that or are you saying the stand pipe will be 30 " long?
How far is the trap off the floor? How long will you make the stand pipe?
When we plumb for a washer station we make the sanitary tee, trap and standpipe 2 inches. We place the trap as close to the floor as we can and make our stand pipe at least 36 inches long or whatever it takes to get it a few inches over the flood rim of the washer. Good luck, Tom

The trap is about 16" off the floor and the the stand pipe will be connected it and the top of the stand pipe will be above the flood rim by about 3".

Thanks

You can plumb it in that way and it might even take the washer discharge and carry it away. You're a little shy on both the size of the trap anda standpipe plus the height of the standpipe but if there's a problem with the discharge backing up we can add a fitting to compensate. Good luck, Tom

Keith, you can actually get 2" stand pipe that tapers to 1 1/2" at the trap connection.