We are going to replace a Howden MK5/WCV255 with Howden MK6/WRVi. New compressor is supplied by a package supplier saying that the WRVi is direct replacement of WCV. WRVi model consists of a manual Vi setting in the range of 2.2 to 5.0 turning a square headed knob located below shaft on drive side end cover. For 2.2 Vi, the knob has to be rotated clockwise and for 5.0 Vi, it has to be rotated anticlockwise. WCV model don't have such a knob.

My question is what should be the initial setting of Vi when making the test run? What will be final and permanent setting for continuous operation. I am new to this field and don't have much experience for Howden.