I will explain where to use gland packing in a chemical plant .
The gland seal is the oldest technology in the sealing system, and is still in use today.
However, mechanical engineers are strongly aware of gland seals as an alternative to mechanical seals, and often do not recognize their existence.
I don’t understand the principle of the gland seal well, and I use it somehow, but I will make a mistake thinking that I don’t use it properly.
It is a ground seal that can be said to be the basis of seals, so let’s understand the basics.
The Grand is a classic, versatile seal.
What is gland packing?
Have you ever seen a grand seal?
There are even fewer opportunities to see the real thing.
A more appropriate term would be gland packing .
An object that is made into a string by knitting fibers is rolled into a ring shape.
Stack one ring four times and use it as a seal.
ground seal + lantern ring
A common type of gland seal connects four stages of gland packing in series.
Set the gland packing in the stuffing box and press the gland to apply pressure.
This will force a seal.
When the shaft rotates at high speed, the gland packing generates frictional heat.
Cooling water is drawn in from the outside for cooling, as there is a risk of ignition and explosion of hazardous materials that are process liquids.
Make a hole in the stuffing box and make a passage for the gland packing.
The part that serves as this path is called a lantern ring.
The figure above shows the configuration of 2 stages of gland packing + lantern ring + 2 stages of gland packing .
Whether the gland packing has two or three stages depends on the device.
3 stages of gland packing + lantern ring + 2 stages of gland packing (Added)
Consider a case with three stages of gland packing + lantern ring + two stages of gland packing.
It’s a common example, but it’s a well-thought-out structure.
The 3rd stage of gland packing is on the process side, and the 2nd stage of gland packing is on the atmosphere side.
This is the reason why the gland seal is said to be used while leaking water.
A gland seal is sealed somewhere in multiple stages of gland packing.
The concept of a tier itself is strange, but it’s better to think of it as being sealed at some point on one of the 3 tiers.
This part is sealed by the gland packing deformed by the pressure of the process liquid and the pressure of the seal cooling water.
When the gland packing receives sliding heat, it deforms and wears out.
Cooling water is required to prevent this.
It is desirable that the liquid flows through all stages of the gland packing, but if cooling water is poured from the lantern ring, it is not possible to see how far the cooling water is flowing.
Therefore, since water is flowing from the atmosphere side of the two stages of the gland packing, we can assume that water or process liquid is flowing through all the stages.
If there is no two-stage gland packing on the atmosphere side, there will be almost no pressure loss on the atmosphere side, and cooling water will not flow to the process side.
The process side has 3 stages and the atmosphere side has 2 stages, but if the process side has 2 stages and the atmosphere side has 3 stages, there is a high possibility that the cooling water will flow to the process side due to pressure loss.
Considering this, it is easier to understand if the process side is set to 3 stages and the atmosphere side is set to 2 stages.
Maybe there are cases like this:
- The 3-stage ground on the process side is no longer effective, and it is sealed at the 2-stage on the atmosphere side.
- The 3-stage ground on the process side is no longer working, and cooling water is mixed in on the process side.
1 may be identified by coloring the cooling water leaking into the atmosphere.
In case 2, when the water stops flowing to the gland packing on the atmosphere side, wear progresses, and all stages of the gland packing lose their effectiveness, and as a result, cooling water leaks to the atmosphere side.
No lantern ring
There are also types of gland seals that do not have a lantern ring or that do not require water injection.
For example, powder seals are basically not cooled by water injection.
There is also the aspect that the rotation speed of the powder equipment is generally slow and the frictional heat of the gland packing is not high.
Blockage prevention using lantern rings
Lantern rings are often assumed to be cooling water, but there are actually other uses.
That is powder clogging prevention.
The gland packing part tends to be a so-called “reservoir part”.
If it is powder, there is a possibility that it will accumulate in such a reservoir.
A nitrogen seal is effective to prevent this .
By flowing nitrogen through the lantern ring, a gas flow is created in the reservoir to prevent powder from entering.
Whether or not to use a nitrogen seal must consider many factors such as process safety, facility characteristics, and work safety.
Material
There are many different ground materials.
The following materials are available for glands used in chemical plants alone.
- graphite
- aramid fiber
- PTFE
If you get the hang of it here, you ‘re a gasket maniac .
that’s right. These materials are non-asbestos joint sheet gaskets themselves.
Gaskets and packings are the same in the sense of sealing, so it is natural to say that it is natural.
The ground doesn’t have a high existence value, so it’s hard to notice until you say it.
Reason for multiple stages
There is a proper reason for stacking multiple stages of grounds.
Of the multiple stages of the gland seal , only one stage is actually effective.
Let’s assume that the packing has been pumped up in four stages, and that the seal in the first stage is effective and the life of the packing has come to an end while it is being used.
At this time, any one of the 2nd to 4th stages will function as the next sticker.
If all 4 seals fail repeatedly, the end of life is reached.
This idea is the same as V-packing and oil seal .
Both the V-packing and the oil seal are the same as the gland seal , which is a seal for moving equipment , so it is natural.
Where to use gland packing
We will explain where gland packing is used in chemical plants.
pump shaft seal
A gland seal is used to seal the shaft of the pump.
Even today, some water-based pumps still use gland seals.
Please note that it is not suitable for dry floors .
Coolant is usually leaking from the gland seal.
It is abnormal that it is not leaking .
Leaking water means that the area around the pump will be flooded.
There is a risk of falling while walking, and if it becomes a cause of foreign objects, it can also cause algae.
Leaking water is rarely a good thing.
Stirring tank shaft seal
Use a gland seal on the stirring shaft of the stirring vessel.
Dry seals and mechanical seals are used for general agitation vessels, but gland seals may be used for agitation vessels where leakage is not a concern .
The ground seal is cheaper, so there may be cases where it is actively used.
Compared to pumps, agitation tanks have a lower number of revolutions, so there is less sliding heat, and in some cases they can be used without cooling water, making it easier to use gland seals.
fan shaft seal
A gland seal may be used to seal the shaft of the fan.
It is easier to use a gland seal for fans than for pumps.
Worried about dry floors?
A fan that does not use cooling water will be in an environment where it is easier to use the gland seal.
When a gland seal is used with a fan, the gland wears and loses its sealing function, but the narrow opening keeps the leakage low .
However, if the same leakage is allowed, the labyrinth seal is safer…
valve seal
You may not realize it, but glands are used to seal valves.
The stem of the valve is also a moving part, just like the shaft of the rotating machine.
The only difference is whether it is moved by a human or by a machine.
A sealing mechanism is required.
With a manual valve the seal will use the cheapest gland.
If it is a rotating device, you can think of means other than the gland, but you can think of the valve as the only choice for the gland .
Reasons to avoid gland packing
Here are some reasons why gland packing should be avoided in chemical plants.
We will compare with mechanical seals, which are alternative candidates.
need cooling water
Gland seals require cooling water .
The gland is an idea to forcibly cover the shaft and casing with knitting.
There is always friction between the shaft and gland seal.
Without seal water, the gland will heat up in an instant and deteriorate (burn, break, etc.)
Seal water is injected from the lantern ring so that the liquid flows to both the process side and the atmosphere side.
This is because only the first stage of the gland seal is effective in cooling with the process liquid.
The ground seal consists of 4 to 5 bullets, and even if you expect a multi-stage sealing effect,
Without seal water, the design concept of the gland seal collapses.
In contrast to gland seals that require cooling water, mechanical seals may eliminate cooling water.
This is because there is a possibility that it can be handled by self-flushing .
As much as you need cooling water. Variable costs (water treatment, power), etc. will be a big disadvantage.
leak from mechanism
Gland seals leak more than mechanical seals.
Contrary to the dry floor, it will deviate from the idea of TPM.
The ground is the biggest reason to avoid it as much as possible .
big loss
Gland seals have higher losses than mechanical seals .
A large power loss is nothing but a disadvantage for centrifugal pumps.
The reasons for using centrifugal pumps are as follows.
- high pump efficiency
- Liquid can be sent even at high flow rates
Of these, mechanical seals are more advantageous for optimizing pump efficiency.
Since large capacity pumps cannot be used with sealless pumps, centrifugal pumps are used.
Unlike process liquids, we often target utility liquids, and we are thinking of using them 24 hours a day, 365 days a year.
Even a small loss is a disadvantage here.
reference
Gland seals are inexpensive, so keep a spare for stable use.
lastly
I explained where to use a gland seal in a chemical plant and what it means.
After introducing the materials and functions of gland seals, he introduced examples of rotary machines and valves where they are used in chemical plants.
Cooling water, dry floor, and power loss are summarized as reasons for avoiding gland seals.
Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (Comments are at the bottom of this article.)
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