With the stem difference,it can be:
1. Rising stem gate valve :Stem-nut in the bonnet or yoke,when you open or close the disc,the stem can be up and down through the rotation of the stem-nut.It’s good for the lubrication of the stem ,easy to see epen and close,widely used now.
2. Non-rising stem gate valve :Stem-nut in the body ,contact with the media directly.Disc is is open and close through the rotation of the stem.The advantage is :the height of the valve keep same which can save the installation space.Its widely used for the application of big size or limited installation space.There is switch indicator to show the level of open and close. Disadvantage is :The stem thread can not do self-lubricate but also touch the corrosion which is easily broken.
The main difference:
1. Can see the stem outside,nut with worm gear tightly and fixed ,it rise the stem through the rotation of the nut,just make the relative rotation but not relative displacement.There is door type yoke from outside.
2. Thread stem outside
3. Rise and down the disc through the transmission of the stem and thread of the wheel.Wheel keep fixed.
1. Stem move through rotation but not up-down ,just show a stem from outside,nut is fixed on the disc,disc raise through the rotation of the stem,no visible yoke.
2. Stem hidded
3. When open and close,the wheel and stem not have a relative move,it open and close through the rotation in a fixed position which can drive the disc’s move.