When I think about gate valves, I think about castle warfare.
Stop giving me that blank stare and let me explain.
You’ve probably seen it in medieval war movies. Some great horde is bearing down on the castle. Archers man the walls. The villagers scurry in fear.
The call goes out. “Close the gates!!!!”
An iron barrier with wedge-shaped points slams down into holes designed to receive them, keeping the barbarians at bay.
That’s kind of what happens when you turn the handle on a gate valve … you know, on a MUCH less dramatic scale.
Gate valves, which are also known as sluice valves, function by lifting or lowering a moveable “gate” to fully allow or stop the flow of liquids or gasses. Gate valves are some of the most commonly used valves in the petroleum industry.
They are best used in systems where full shutoff is the norm and long service life is required.
HOW DO GATE VALVES FUNCTION?
Although there are other designs, most gate valves are operated via hand wheel.
That hand wheel drives a spiral grooved stem, moving the rectangular or disc shaped gate.
The wheel may take several turns to fully close the valve, making the action relatively slow compared to a ball valve or another shutoff valve.
But that can be an advantage. Since flow is introduced gradually, the damaging effects of fluid hammer are greatly reduced.
Because of the hand wheel, the gate valve’s exterior may resemble the water spigot you connect your garden hose to.
Do not confuse the two, though. Spigots are a kind of control valves, which you can use to increase or decrease flow.*
Gate valves are designed as shutoff valves and should not be used as control valves, although they often are in non-industrial settings.
TIPS FOR USING GATE VALVES
In industrial uses, gate valves are supposed to be fully open or fully closed.
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.
* Tune in next time for a discussion of globe valves, a type of control valve similar to the water spigot.