In industrial uses, gate valves are supposed to be fully open or fully closed.
Why?
Well, that’s because when a gate valve is left in a half open position, the gate edge is exposed to the flow passing by. That may not mean much for non-viscous fluids like water in the short term, but the gate can be warped or may erode over time. The wear would be concentrated on the lower section of the gate, making the valve seal less effectively.
However, when the valve is completely closed, the gate provides a solid surface to stop flow with the disc’s edges protected in the gate’s seating area.
An undamaged gate valve will provide positive shutoff under pressure.
Another advantage of gate valves is minimal pressure loss, since the gate is usually made to the diameter of the piping connection. That full port design means less restriction of flow.
Gate valves stems come in two main types, rising and non-rising.
Rising stems are useful in visually determining whether the valve is open or closed, because the stem will be higher when open. Non-rising stems are often used when there is limited space available and the rising action of the stem would make the valve more difficult to operate.