 |
Stuffing Box
Before we get into operational practices, let’s learn about an important component of an industrial valve in more detail:
The main moveable part of a valve is its stem. The stem is designed to connect the valve plug to the actuator. An “actuator” is the controlling device designed to move the valve stem up or down – as required by the process.
One of the key requirements is that the stem should be able to move in or out without allowing any fluid to leak by. For this purpose we install a seal through which the stem moves. The seal allows the stem to move in or out, but does not allow the fluid to escape. Such seals are referred to as “stuffing boxes.” A good seal is required to do the following:
a. Minimize leakage
b. Provide low resistance to stem movement
You will notice that the above two requirements work against each other. A seal works by pressing against the stem, and while it does that, it increases the friction and may cause the valve to "bind" (difficult to move.) On the other hand, if a seal is loosely packed than it offers low resistance to stem movement, but provides a leaky seal.