Pneumatic gate valve family creation

[BapiUdhaya]

I am trying to create pneumatic gate valve family. It was easy for me to model the valve. but when it comes to defining parameter, I find it hard and getting few errors. 

The following are the error that I get when I try to change the Diameter DN. I couldnt align the arc properly. If you have any ideas to do it easy, please let me know. share some ideas.

thank you in advance.

[iainsavage]

Difficult to tell from your screenshots but one thing that I can see is that your geometry does not appear to be locked to the origin by aligning and locking to the principal planes.

The centrepoint on the bottom image appears to have drifted away from the crosshairs: