Gate Valves – what they are & when to use them
There are too many types of valves to cover them all. An earlier post covered some valve basics, you can click here to start there if you like.
Basically there are valves that start and stop flow completely, or valves that throttle and control the flow of fluid. Valves are designed with their purposes in mind, if we need to shut off fluid flow completely, we will use a stop valve.
One of these stop valves is called a gate valve. We are going to briefly discuss gate valves, their design, and classification types.
When To Use A Gate Valve
We should use or install gate valves on systems when we want a straight line flow of fluid along with minimal restriction.
Gate valves got their name because basically the disc, or the part that starts or stops the flow through the valve, behaves kind of like the opening or closing of a gate. Mind blowing right? They named this part, shockingly, the gate.
The gate can be sometimes wedge shaped, picture an inverted triangle. When the valve is fully open, the gate is completely up inside the valve. This leaves an opening for flow through the valve pretty much entirely unobstructed. Because of this, there is very little pressure drop or flow restriction through the valve.
This is why gate valves, and more broadly, stop valves, are used to start and stop fluid flow. Gate valves are not ideal candidates for throttling fluid flow. As we already discussed, the metering or control of flow would be difficult due to valve design. Unless specifically authorized, gate valves should not be used for throttling in an engineering setting or system.
Look at the gate valve pics included here. Imagine how much wear the gate will go under if we try to
throttle flow with it, i.e. not have it completely open or closed? The fluid flowing through it will constantly hit up against the gate causing it to wear unevenly and prematurely.
Gate Valve Classification Types
Gate valves are classified as either rising stem or non-rising stem valves.
You can see the stem of the gate valve in one of the other pictures with the gate removed. The gate simply slides over the notched end there. This valve would be classified as rising stem.
Starting with the non-rising stem gate valve, the stem is threaded on the lower end into the gate. As you turn the gate valve hand wheel, the gate travels up or down the stem on the threads, while
the stem remains vertically stationary.
The rising stem gate valve has the stem attached to the gate; the gate and stem rise and lower together as the valve is operated.
Pro Engineering Tip
A gate valves used in a steam system may have a flexible gate. I haven’t seen one in a long time though. The reason some gate valves are designed with a flexible gate is to prevent binding of the gate within the valve when the valve is in the closed position.
When steam lines are heated, they expand. And as we all know, different metals have different rates of
expansion. This expansion can cause some distortion of the valve bodies or components. Let’s say we had a solid gate that fit tightly in a cold steam system. When we heat the system and the pipes expand, the seats will compress against the gate. This causes the gate to wedge between them and almost pinch the valve shut.
Engineers got around this by designing and using a flexible gate. The flexible gate of a gate valve is essentially two circular plates attached to each other with a flexible hub in between. This allows the gate to flex as the valve seat compresses it, gives it some wiggle room. This prevents the pinching or clamping.
You should know everything there is to know about gate valves. This post covered when to use a gate valve as well as the why. It also described how gate valves can be classified, rising or non-rising stem types. If you’ve got any questions or comments about gate valves, or anything else, let us know by using the comment form below or by sending us a message.