Rising Stem Gate Valve vs
Non-Rising Stem Gate Valve
There are mainly two types of gate valves on the market: the valve with rising stem and the valve without rising stem. This article explains the difference between these two types of gate valves and what are the advantages of one valve over the other.
Rising gate valves are usually made of cast or forged steel, while non-rising gate valves are usually made of brass, bronze or cast iron. Non-rising gate valves take up less space while rising gate valves need more space.
In the gate valve with rising stem, the round handle rotates a threaded shaft fixed in the centre. By turning the handle, the rod rises when it opens the valve and lowers when it closes the valve. In a gate valve with a rising stem, it is easy to tell whether the valve is open or closed by looking at the amount of stem exposed. If the handle is flush with the pipe (no visible stem), the valve is closed. If a lot of stem is visible, the valve is open.
This simple system has a few drawbacks that can be avoided compared to another type of gate valve: the non-rising stem valve.
The non-rising spindle valve is usually suitable for tight places where there is not enough space for the spindle to go up, for example places with underground pipes. The non-rising gate valve is fully open when the lever is turned as far as possible to the left and fully closed when the lever is turned as far as possible to the right. In both cases, the lever is flush with the pipe because the mechanism in the pipe opens and closes the valve without lifting the stem.
Another advantage of the non-rising stem valve is that it is easier to lock with a padlock. With the rising stem valve, two padlocks of different sizes may be needed to lock the valve open and closed. With the non-rising valve, one padlock is sufficient. But the disadvantage of a non-rising valve is the fact that the threads that lift the valve are exposed to the fluid controlled by the valve. This can cause problems if the liquid tends to contaminate the threads, so non-rising valves are usually used only for clean liquids and gases.
What is a rising stem gate valve (OS&Y gate valve)?
OS&Y is an abbreviation for “outside screw and yoke” (also, sometimes “outside stem and yoke”), which explains the parts that make this happen. The gate is attached to a threaded screw/stem fitted into a handwheel. The handwheel is held in place by the yoke. Turning the handwheel moves the stem (and the disk) up and down.
Rising Stem Gate Valve is a type of gate valve that can track the opening/closing position by moving the stem up and down movement, electronically track the movement by adding a control key, and a fully open position does not interrupt the flow. The rising stem gate valve generates low pressure loss compared to e.g. butterfly valves.
The outer screw stem rising through handwheel type gate valve has extensive applications. Rising gate valves can be used in high pressure classes up to class 2500 or up to 420 bar, while non-rising gate valves are normally used for medium pressure classes.
This way, you can visually track how far open the valve is. With a rising stem gate valve, it is easy to tell whether the valve is open or closed by looking at the amount of stem exposed. If the handle is flush with the pipe (no visible stem), the valve is closed. If a lot of stem is visible, the valve is open.
How does a Rising Stem Gate Valve (OS&Y Gate Valve) work?
Rising valve stem valves have the structure that the valve stem nut sits on the valve head or valve yoke. When the gate is opened and closed, the valve stem nut is used to rotate and raise the valve stem. This kind of structure is beneficial for valve stem lubrication and makes the opening and closing process visible.
Pros and cons of Rising Stem valves
- Easy to open and close.
- Small fluid resistance, sealing surface due to medium erosion and erosion.
- Medium flow is not restricted, with no turbulence and no pressure drop.
- Larger structure requires more space and long opening time.
- Sealing surface is easily eroded and scraped and difficult to maintain.
Large image of Rising Stem Gate Valve
What is a Non Rising Stem Gate Valve?
Non-rising spindle means outer spindle, also referred to as the rotary spindle gate valve or blind spindle gate valve.
A gate valve with a non-rising spindle requires an indicator that shows the degree of opening and closing of the valve itself. However, the non-rising spindle gate valve with inner screw has the disadvantage of being easily damaged, as the thread of the spindle cannot be lubricated and is directly corroded by media.
How does a non-rising gate valve work?
In an NRS valve, the stem rotates to open and close the valve, but the stem does not move up and down as it rotates. As the stem rotates, it moves in or out of the valve, so the valve disc also moves to open or close the valve.
Pros and cons of non-rising gate valves
- Non-rising gate valves take up less space, ideal for confined spaces. Generally, an open-close indicator should be installed to indicate the degree of open-close.
- If the rod threads are not lubricated, this can lead to erosion by the medium and damage can easily occur.
Large image of Non Rising Stem Gate Valve
Difference between RS gate valve and NRS gate valve
The difference in transmission mode: The transmission mode of the rising stem gate valve is that the handwheel drives the nut to turn in place and the valve stem moves up and down linearly. Through the threaded transmission of the valve stem and steering wheel, the valve disc moves up and down to complete the switch; the non-rising stem gate valve is a handwheel that drives the valve stem to rotate. The handwheel and valve stem are interconnected and relatively immobile. There is thread in the valve and the valve stem rotates at a fixed point to move the valve up and down.
The difference in structure: The structure of the rising stem gate valve is that the stem nut sits on the bonnet or bracket. When the gate is opened and closed, the stem nut is turned to achieve the lifting of the stem. The structure of the concealed stem gate valve is that the stem nut is in the valve body and is in direct contact with the medium; when opening and closing the gate, it is realised by rotating the stem.
The difference in installation space: The valve with rising stem requires a larger installation space because of the stem; the height of the valve with non-rising stem is small and will not take up too much space during installation.
Application difference: The structure of the rising gate valve favours the lubrication of the stem and the degree of opening and closing is obvious; the stem thread of the non-rising gate valve not only cannot be lubricated, but is also directly affected by the medium and easily damaged. Therefore, the open stem gate valve is more the non-rising stem gate valve has a wider range of applications.
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