A rising stem is a type of valve mechanism in which the stem of the valve rises along with the gate, disk, or globe when opened. This gives a good visual indication of whether the valve is open or not because the raised stem is clearly visible. Rising stem valves may feature static handles or wheels in which the stem rises out of the center of the handle or handles when opened or which rise with the stem.
Vertical action valves typically feature a gate or disk which obstructs the liquid flow path when closed. These gates are lifted vertically by a valve stem when the operating handle or wheel is turned. This opens a valve's flow channel and allows unimpeded passage of liquid through the valve. There are two basic internal gate and stem designs used on this type of valve: non-rising and rising stem. Non-rising stem designs raise the gate around the stem and rising stem types feature a stem and gate which move up and down together.
The rising stem valve types are also divided into two different types. The first is a valve with a handle which has a threaded stem nut attached to it. The valve stem is threaded with a similar thread and passes through the stem nut and on down to the valve gate. When the valve wheel is turned, the stem is drawn up through the center of the handle, thereby pulling the gate up with it and opening the valve in the process. With this variant of valve, the handle revolves but does not rise with the stem.
The second type of rising stem valve also features a threaded stem that passes through a matching thread in the bonnet of the valve. In this design, the handle is fixed to the stem and when turned rises with the stem as it rotates through the bonnet thread. Other than this difference, the operation of the two types is similar. One of the positive features of both is that they give a good, at-a-glance visual indication of whether they are open or not.
Valves with non-rising stems valves operate in a similar fashion but feature a gate with a threaded hole through which the similarly threaded stem passes. As the handle is turned, the gate rises up the stem opening the flow path. This type of valve gives no outward physical clue of its status and relies on a pointer or dial to indicate whether it is open or not.