Regarding compressor shaft end sealing

The first thing I want to tell you is that it’s not shameful to ask questions! Secondly, I would like to ask what kind of compressor you are referring to? Some compressors, such as screw-type ones, are used to compress and transport harmful and explosive gases; therefore, shaft end seals are necessary.

When you first start to get to know him, everyone tends to ask rather naive questions. In fact, if you think about it carefully, it’s not difficult; it’s just as the person upstairs said； 1. What if we are compressing or transporting some toxic and harmful gases? 2. If you use just one end cap, can it seal off gases at such high pressure? Then our efficiency in doing work drops to that level; this results in significant losses and low efficiency ； 3. From a maintenance perspective, even though end caps and packing seals can be used, frequent maintenance is required, which is not economical ；

Put simply, the medium compressed by your compressor is different from the lubricating oil, and this seal is designed to prevent the medium from leaking into the lubricating oil or into the atmosphere.

Think about it! Centrifugal! Regarding the stress on the compressor, if the medium pressure is 1 MPaG and the outer diameter of the cover to be installed is 500 mm, then what amount of force will act on this cover? This is easy to calculate. Well, it’s fine if you say that pressure vessels can withstand higher pressures; we’ll leave that aside for now. Now, let’s talk about the forces acting on rotating components. This seems to be quite complex, and I don’t know much about compressors either, but I can say that there is a limit to the axial force that a compressor rotor can withstand. There is something called a thrust bearing, which is not capable of withstanding very large axial forces. I don’t know exactly how big it is, but surely someone knows. The medium force acts on the rotating component of the seal (dry gas seal); this component transfers the force to the rotor, and it is ultimately the thrust bearing that bears this force. A single set of seals is sufficient for cantilever centrifugal compressors operating at lower pressures. But at high pressures, the thrust bearings can’t withstand it. Another set works fine; it provides good balance. My perspective might be limited; please add to it.

I am focusing on centrifugal compressors. That’s right.

The issue essentially revolves around the differences in sealing for stationary and moving equipment; reading books on this topic systematically will be very beneficial. The key point for rotating equipment is first to ensure that the rotating parts of the equipment function properly, that is, there should be proper relative movement between these rotating parts and the shaft seals. It’s simple enough to seal the ends of the shafts; such sealing is effective. But what about the rotating parts themselves? Should the moving and stationary parts be ground dry?

You also need to consider the non-driving-end bearings; these bearings require lubricating oil. You can’t seal them in together, as that would allow high-pressure gas to get into the bearing lubricant.

There must be shaft end seals to prevent gas leakage, as well as thrust bearings. I’m talking about centrifugal compressors.

The function of the shaft end seal is divided into three levels: back isolation gas, buffer gas, and main sealing gas. The back isolation gas is used to prevent the oil used to lubricate the bearings from contaminating the dry gas seal; the buffer gas serves to further ensure that oil does not contaminate the dry gas seal; the main sealing gas is intended to prevent process gas from leaking outside

The key is to consider bearing issues in the design, as most centrifugal compressors use sliding bearings that require oil lubrication. If these bearings are sealed off directly, oil will enter the system, causing contamination, and oil consumption will become uncontrollable.