1.0 The Difference Between OS&Y Gate Valves and NRS Gate Valves

Commonly seen in gate valves are the rising stem gate valve and the non-rising stem gate valve, which share some similarities, that is:

(1) Gate valves seal through the contact between the valve seat and the valve disc.

(2) Both types of gate valves have a disc as the opening and closing element, and the movement of the disc is perpendicular to the direction of the fluid.

(3) Gate valves can only be fully opened or fully closed, and cannot be used for regulation or throttling.

So, what are the differences between them? TWS will explain the distinctions between the rising stem gate valves and non-rising stem gate valves.

OS&Y Gate Valve

Rotating the handwheel drives the threaded valve stem up or down, moving the gate to open or close the valve.

NRS Gate Valve

The Non-Rising Stem (NRS) gate valve, also known as a rotating stem gate valve or a non-rising stem wedge gate valve, features a stem nut mounted on the disc. Rotating the handwheel turns the valve stem, which raises or lowers the disc. Typically, a trapezoidal thread is machined at the lower end of the stem. This thread, engaging with a guide channel on the disc, converts the rotational motion into linear motion, thereby transforming the operating torque into thrust force.

A Comparison of NRS and OS&Y Gate Valves in Application:

1. Stem Visibility: The stem of an OS&Y gate valve is externally exposed and visible, whereas that of a NRS gate valve is enclosed within the valve body and not visible.
2. Operating Mechanism: An OS&Y gate valve operates via the threaded engagement between the stem and the handwheel, which raises or lowers the stem and disc assembly. In an NRS valve, the handwheel turns the stem, which rotates in disc, and its threads engage with a nut on the disc to move it up or down.
3. Position Indication: The drive threads of an NRS gate valve are internal. During operation, the stem only rotates, making visual confirmation of the valve’s status impossible. Conversely, the threads of an OS&Y gate valve are external, allowing the disc’s position to be clearly and directly observed.
4. Space Requirement: NRS gate valves have a more compact design with a constant height, requiring less installation space. OS&Y gate valves have a greater overall height when fully open, necessitating more vertical space.
5. Maintenance & Application: The external stem of an OS&Y gate valve facilitates easier maintenance and lubrication. The internal threads of an NRS gate valve are harder to service and are more susceptible to direct media erosion, making the valve more prone to damage. Consequently, OS&Y gate valves have a wider range of application.

The structural designs of OS&Y gate valve and NRS gate valves are categorized as follows:

1. OS&Y Gate Valve: The valve stem nut is located on the valve cover or bracket. When opening or closing the valve disc, the lifting or lowering of the valve stem is achieved by rotating the valve stem nut. This structure is beneficial for lubricating the valve stem and makes the opening and closing position clearly visible, which is why it is widely used.
2. NRS Gate Valve: The valve stem nut is located inside the valve body and is in direct contact with the medium. When opening or closing the valve disc, the valve stem is rotated to achieve this. The advantage of this structure is that the overall height of the gate valve remains unchanged, so it requires less installation space, making it suitable for large-diameter valves or valves with limited installation space. This type of valve should be equipped with an open/close indicator to show the position of the valve. The disadvantage of this structure is that the valve stem threads cannot be lubricated and are directly exposed to the medium, making them prone to damage.

Conclusion

Simply put, the advantages of rising stem gate valves lie in their ease of observation, convenient maintenance, and reliable operation, making them more common in regular applications. On the other hand, the advantages of non-rising stem gate valves are their compact structure and space-saving design, but this comes at the cost of intuitiveness and ease of maintenance, so they are often used in situations with specific space constraints. When choosing, you should decide which type of gate valve to use based on the specific installation space, maintenance conditions, and operating environment. In addition to its leading position in the field of gate valves, TWS has also demonstrated strong technical capabilities in many areas such as butterfly valves, check valves, and balancing valves. We can help you select the optimal type for your application and welcome the opportunity to tailor it to your exact requirements. We will provide a more detailed explanation of the differences between rising stem and non-rising stem gate valves in our next section. Stay tuned.