Cartridge Seal

the mechanical seal of hot water

by:Lepu     2019-11-02
Water is generally considered a good lubricant that can provide sufficient lubrication between the overlapping surfaces of the mechanical seal, but there are several problems: at high temperatures, the water-moistened membranes are not thick enough, the sliding surface of the sealing surface cannot be separated.
The thin film thickness of cold water is about 1 Micron, which will keep the overlapping sealing surface separated for most of the time.
Depending on the temperature, the film thickness of hot water is only 1 to half of 3 parts.
Under some combination of temperature and pressure, the water evaporates, expands and opens the overlapping sealing surface.
When this happens: 1.
With constant evaporation and subsequent cooling vibration sealing surfaces, the outer diameter of the carbon may be cut and damaged, causing them to explode together.
The driving lugs will wear, the metal bellows will break, the lugs will be hard or soft driven, and the surface will crack. 2.
When the water evaporates, the solids dissolved or suspended in the water will remain between the sealing surfaces.
They are embedded in a soft face, causing serious wear and damage to a hard face. 3.
If the size of a large particle, or any foreign matter is blown through both sides, the phonograph finish can be formed on carbon.
The seal will leak from this damaged surface.
\"Slide sticks\" can happen because the face tries to stick together due to lack of lubrication between them.
Alternating pasting and sliding creates vibration, and unless some form of vibration damping is installed, vibration causes carbon debris, broken bellows, and cracked lugs to drive the surface.
In many pipe systems, magnets (Fe304 )
Formed as a corrosion resistant covering on the internal surface.
This magnet falls off the wall of the pipe and is often gathered on sealed parts.
It can be identified by black or red as well as the attraction to the magnet.
The magnet will affect the seal in the following ways: 1.
As a grinding material, it will mechanically attack the sealing sliding elastic material by penetrating into the sealing sliding elastic material.
This will result in \"Hanging Up\" and eventually leaking. 2.
It will wear the surface of the sliding elastic seal.
Loose magnets are common in new water systems.
After the system has been used for about a year and iron oxide has formed a stable layer, the problem will eventually be solved by itself.
Hot water is dangerous.
The leak will be invisible as the steam flashes.
If hot water is part of the condensation system, it may have to be sealed under vacuum conditions.
In order to effectively seal the hot water, you have to solve all five problems at the same time.
We will start by learning how to choose the right material for the sealing part, then we will choose the sealing design and finally apply the correct environmental control to ensure that the above problems are resolved.
The right sealing material for picking: 1.
The sealing surface combination should be unfilled carbon graphite, operating with solid sic or wc.
Plating or coating surfaces should not be used in this application.
In recent years, a new type of surface material made of graphite-immersed sic is popular for its better thermal conductivity. 2. The elastomer.
Use ethylene propylene to 275 degrees Fahrenheit (135 C. )
If you seal at a higher temperature, Kalrez or equivalent products from DuPont are necessary.
In most cases, you should try to cool down the water to increase your facial life.
High temperature elastic material is not required if the water is cooled.
Please make sure not to apply oil grease on ethylene propylene.
Any oil product will attack B-C rubber (epr)3.
Metal parts.
Grade 316 stainless steel is preferred.
Do not make metal bellows or Springs with stainless steel to avoid chlorine stress corrosion problems.
Harth alloy \"C\" is the best choice for springs or metal bellows.
Choose the correct mechanical seal: balanced o-
Ring mechanical seal should be used.
Although still is preferred, both rotating and still versions are acceptable. The o-
If the application alternate between vacuum and pressure, the ring will allow two-way sealing.
For ease of installation, cartridge seals should be used, in the case of an open vane pump, the impeller should be allowed to adjust as the pump cycles between operation and ambient temperature.
Unless some type of self-alignment function is installed, do not use the fixed seal installed by the cartridge.
If the pump is equipped with a sleeve or Babbit bearing, a movement seal shall be specified.
This is a very common arrangement with a multi-stage boiler feed pump.
The pressure of the sealing cavity to be used for high-pressure sealing (
Not pump discharge pressure)
Over 350 psi. (24 bar).
The high pressure seal is a more robust structure that prevents deformation of the surface and elastic extrusion.
Split seals can be used in some of these applications, but when the pressure is alternating between positive pressure and vacuum, some designs have problems.
The sleeve mounting split seal helps the impeller to adjust, or in the case of a vacuum application, the seal can be installed backwards, or the discharge recycling line is installed to keep the positive pressure in the stuffing box.
Note: many hot water applications are dangerous, so double sealing is recommended.
If the design is sealed using a fixed metal bellows, care must be taken.
The flow through normal flushing or recycling connections may result in a large temperature difference on the surface of the mechanical seal, resulting in deformation of the surface of the overlapping seal.
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