What is the purpose of the copper sleeve in a valve?

What does LZ mean by the steel sleeve of the valve? Could you explain it more clearly? Does it refer to certain special valves (such as those on samplers), namely the retaining sleeves that are fitted over the valve stem to limit the position of the valve stem? If so, it’s used to limit traffic.

Is it fitted over the valve stem? When the valve is opened and closed, the valve stem needs to move; some valves use copper sleeves as self-lubricating bearings to reduce friction

Yes, it’s the copper sleeve that fits over the valve stem. Because I often hear the maintenance technicians here say that when a valve stem gets stuck, it’s usually due to a problem with the copper sleeve, but they don’t explain exactly what the cause is

The valve stem has external threads, usually trapezoidal threads, which connect it to the valve disc. The copper sleeve mentioned by the original poster likely has internal threads; this copper sleeve with internal threads is fixed on the valve seat. The valve stem with external threads rotates, moving relative to the copper sleeve with internal threads, thereby causing the valve disc to open and close. Wear is inevitable during this relative motion, even though lubricant is applied. The valve stem is generally long and requires sufficient strength; its material is usually stainless steel, medium-carbon steel, or other special materials. It is difficult to process and costly. The copper sleeve with internal threads is generally smaller, easier to process, and convenient to replace. Its material is softer than that of the valve stem, so it wears out first during relative movement with the valve stem, thereby protecting the latter. Moreover, if the hardness of the screw and nut is similar, wear can lead to jamming, making it impossible to open or close the valve. Maintenance technicians say that when a valve stem gets stuck, it is often due to a problem with the copper sleeve – presumably because wear occurs on the copper sleeve during relative movement between the valve stem and it, which causes the sticking. I’m not sure if what I said is correct, haha

Reply to 6# Xiao Yu: There are two solutions for relative motion. One is to use rolling bearings, which require more space for installation; the load is moderate, and this approach is suitable for medium to high speeds. Second, sliding bearings are used, which can handle large loads and require a small installation space. What the original poster mentioned falls under the second category.

The copper sleeve fitted over the valve stem should serve as a guide; sticking is caused by issues with clearance or coaxiality