I have created new field "Facility_Type" to the existing feature class and applied coded value domain. but during editing domain value is not populating.
You can refer the attached screen shot.
you have set the domain of the field at table level. You are using subtype with your table and you must set domain at subtype level.
Follow this path:
Right click your FeatureClass (PW_Facilities) in ArcCatalog > Subtypes Tab > Select Pump Station subtype > set facility_type field domain to FacilityType.