Depump is specialized in producing centrifugal pump and has many years’ experience. We provide good quality products and good after-sales service. I will conclude some common questions and give answers to you all next.
1. What is the normal state of mechanical seal application?
1) The only part of the mechanical seal that should be sacrificed is the carbon surface. The seal shall operate without leakage until the carbon surface is worn. If the seal leaks for any other reason, we consider it premature and can always be corrected.
2) When carbon is not accepted in the application and you have used up all the options, it is recommended to select two hardfaces. Then you are trying to get as long a life as possible.
3) The only variable for seal life should be the lubricating quality of the product being sealed. Hot water, many gases, and most solvents are typical non lubricants.
4) To sum up, the fact is that more than 85% of mechanical seals will fail prematurely. When the seal was removed from the running pump, most of the carbon surfaces were still intact. A small number of sealing surface wear is normal rather than exceptional.
2. Why do most seals fail prematurely?
1) One of the seal components is damaged.
2) The sealing surface is opened.
3. What is the most common cause of seal component damage?
1) Corrosion.
2) Physical damage, including effects of high temperature or overpressure.
4. What is the most common reason for the lapped sealing surface to open?
1) Sealing installation and matching problems.
2) The solid in the sealed product blocks the movable parts.
3) The product changes its state and interferes with the free movement of the seal. It:
-Crystallization;
-Become sticky;
-Curing;
-Forming a film on the sliding part and the sealing surface;
-The product is vaporized on the sealing surface and blown away.
5. Does the sealing surface have to be lubricated? Can it run dry?
1) The graphite in the carbon/graphite surface is a natural lubricant. In operation, graphite is separated from the mixture and transferred to the hard surface. This means that the sealing surface combination you usually run on is carbon graphite. Residual graphite is often seen on the hard surface.
2) It must be kept wet in order to separate the graphite from the carbon/graphite mixture.
3) Dry running means that the heat of the sealing surface is high. If you are using a good unfilled carbon/graphite (and should be), the sealing surface will not be a problem. Elastomers and sealed products may be very sensitive to temperature changes in the stuffing box or temperature increases on the sealing surface.
6. Must the sealing surface be kept cool?
1) Most carbon and hard sealing surfaces can withstand a lot of heat. Elastomers (rubber parts) are the parts you must pay attention to. They are most sensitive to stuffing box temperature changes, especially when they are on the sealing face.
2) Hydraulic balanced seals generate very little heat between sealing surfaces.
3) Unbalanced seals usually require cooling because they generate excessive heat.
4) Some sealing surface combinations generate more heat than other sealing surface combinations, such as two hard surface combinations.
5) Some sealing materials conduct heat better than others. Ceramics are a poor thermal conductor, and carbon is not much better. Tungsten carbide and silicon carbide are excellent thermal conductors.
7. When should I use a combination of two hardfaces?
1) Contains any oxidant.
2) When sealing any halogen.
3) If the product tends to stick the sealing surfaces together.
4) If hot oil is sealed, it must pass the unorganized emission test.
5) Some deionized water will attack carbon.
6) When no black is allowed in the system (to avoid color pollution).
7) At any time, carbon/graphite will fail for some reason.
8) The specification requires two hard faces.
8. Why not standardize the two hardfaces?
1) They generate more heat than the carbon/hardfacing combination.
2) They are not very easy to use. If the sealing surfaces are not fully fitted during installation, they can rarely be adjusted to the fully fitted state by themselves during operation.
9. Must the seal leak?
1) Any high-quality mechanical seal shall operate without visible leakage.
2) As long as the rotating part of the seal is designed to be perpendicular to the shaft, a single fixed (spring does not rotate) hydraulic balanced mechanical seal can pass the unorganized emission test.
3) Rotating seals (springs rotating with the shaft) rarely pass the fugitive emission test. They are too sensitive to various forms of misalignment.
4) Cartridge fixed seals usually cannot pass the unorganized emission test, because fixing the cartridge components to the shaft will damage the perpendicularity of the rotating seal face and the shaft. Some seal companies provide some type of self centering design to solve this problem.
10. Why do most original equipment seal designs fret under dynamic elastomer or spring-loaded Teflon and damage the shaft?
1) Corrosion resistant shafts and bushings protect themselves from corrosion by forming a protective oxide (ceramic) layer on the metal surface. Due to shaft vibration, pipe strain and misalignment, when the shaft slips over the elastomer, the dynamic elasticity in the seal will polish the layer.
2) The ceramic protective oxide removed by polishing embeds itself in the elastomer, making it act as a grinding wheel, increasing the damage of the shaft sleeve or shaft.
