Our dish washer is hooked up to drain into our disposal. My wife does not always turn the disposal on when she is washing dishes. I was wondering if the disposal is getting plugged and draining backward into the dish washer. Is there a 1 way valve which could prevent this.

Yes, it is called an air gap, shown below. Also there is the "high loop" also shown below. Some plumbers prefer the high loop. The air gap is required by some municipalities.

Could that go bad. Is it possible for that to leak. THat is the valve that we have.

Yes, the air gap and its hose can get clogged. If the air gap gets clogged the dishwasher won't drain. Remove the hose between the air gap and the disposal, make sure it is clear. Check the port of the disposal also. Pull the chrome off the air gap. Unscrew the domed top cap of the air gap. Use a wire coat hanger down the center pipe to make sure it is also clear.

Thanks for your help.