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A dry gas seal is a revolutionary way of sealing machines and protecting them from dust, moisture and other contaminants. A dry gas seal is a sealing device that uses pressurized gas to keep two surfaces from touching. The most common type of dry gas seal is the O-ring, which is used in many applications, including mechanical seals, piston rings, and gaskets. Dry gas seals are also used in many other industries, such as the food and beverage industry, where they are used to seal containers and prevent contamination. This type of seal not only helps to keep the machine running with maximum efficiency but also significantly reduce downtime, making it cost-effective in the long run. In this article, we"ll explore what a dry gas seal is, how it works and why you should consider using it for your machinery. By understanding the benefits of a dry gas seal and its uses, you can make an informed decision about the best sealing system for your needs. How does a dry gas seal work?Dry gas seals work by using a series of labyrinths to separate the high pressure seal gas from the atmosphere. The labyrinths are formed by a series of grooves and ridges on the surface of the seal ring. The seal ring is rotated at high speed, causing the gas to flow through the labyrinths. The gas is then forced through an aperture in the center of the seal ring, where it escapes into the atmosphere. What is a dry gas seal used for?Dry gas seals are used on rotating equipment to help minimize the leakage of high pressure gases from the inside of the machinery. This helps to reduce maintenance costs and improve safety. Dry gas seals are commonly used in applications such as pumps, compressors, turbines, and blowers. Advantages of a dry gas sealThere are many advantages of a dry gas mechanical seal. One advantage is that they are much simpler in design than other types of seals, making them more reliable and easier to maintain. Additionally, dry gas seals do not require the use of any lubricating fluids, which can leak or evaporate over time. This makes them more environmentally friendly and cost-effective in the long run. Finally, dry gas seals have a much longer lifespan than other types of seals, meaning that they need to be replaced less often.Disadvantages of a dry gas sealThere are several disadvantages of dry gas seals, including: - they can be expensive to purchase and install- they require careful maintenance and regular inspection- they can be susceptible to wear and tear- they can leak if not maintained properlyHow to choose the right dry gas seal for your applicationThere are a few key factors to consider when choosing the right dry gas mechanical seal for your application. The most important factor is the type of fluid being sealed. Gas seals are designed to seal either liquids or gases, but not both. Make sure to choose a gas seal that is compatible with the fluid you are sealing.Another important factor to consider is the pressure of the fluid being sealed. Gas seals are rated for different maximum pressures, so make sure to choose one that can handle the pressure of your application.Finally, take into account the size and shape of the sealing surfaces. Gas seals come in a variety of sizes and shapes to fit different applications, so make sure to choose one that will fit your needs.ConclusionDry gas seals are an extremely important component for many industrial operations, and their ability to prevent leaks has made them invaluable in a variety of applications. Understanding the basics of how dry gas mechanical seal work and how they can be used effectively is helpful when considering the various options available for any specific application. With the right choice, dry gas seals can provide reliable, leak-free performance which will save time, money and resources while ensuring safety and reliability. Lepu dry gas seal manufacturer provides best quality flowserve dry gas seal and dry gas seal. Welcome to contact us!

This cartridge grundfos mechanical seal is a smart design pump seal for grundfos vertical pump, this seal suit for grundfos CR CRI and CRN series vertical water pumps. As a special cartridge mechanical seal, we follow the original grundfos design 100% for this seal, this help to avoid any installation mistake when you install the seal for the grundfos pump, and make installation easy. Our grundfos mechanical seal frame and spring are made by strong quality stainless steel SS304( SS316 available too) material, help to against rusty problem. We use SSIC (Pressureless Sintered Silicon Carbide) as stationary and rotary seal face, it is much better than normal material RSIC(Reaction sintered Silicon Carbide), offer more wear resistance for the grundfos mechanical seal. For Rubber part, normally people choose EPDM or VITON for secondary seal. Our grunfos mechanical seal will make your pump as good as new and reduce downtime, and last longer time when pump running.

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Mechanical seals operating under the correct conditions can provide years of trouble-free service. Most mechanical seals are designed to be surrounded by liquid to provide cooling and to avoid running dry. In pumps used for liquids, it is a common requirement that they must not run dry.

It is often assumed that if the pump is pumping liquid, then the seal must be surrounded by liquid. In a horizontal pump, this is almost always the case. In a vertical shaft pump, it should not be taken for granted. A simple way to illustrate this is to push an empty cup with the open end down into a container filled with water. Air is trapped in the cup because it has nowhere to go, and if a sealed shaft passed through the cup the air would remain trapped.

If we turn the cup horizontally, the air escapes from the cup’s open end like it would in a horizontal pump. In a vertical pump with a mechanical seal, this principle must be considered: If air is trapped in the seal chamber, the seal is running dry.

A wastewater plant in Amherst, New York, uses several vertical shaft end suction pumps to return activated sludge and raw sewage. These pumps were originally braided packing sealed pumps. They had a history of requiring frequent gland adjustments and shaft sleeve wear that required rebuilding the pumps.

The plant decided that the energy savings and reduced downtime of split mechanical seals were worth the investment. The seals were installed with a restrictor bushing in the stuffing box to reduce flush water usage and limit solids entering the seal. The seals were flushed with process water and vented at startup. Pressure in the seal housing is maintained as recommended by manufacturers and industrial practice. The seals were vented by releasing the air through a vent before startup.

One day a plant manager noticed the air release valves on the plant’s hot water heating system were called “high vents”—they release air from the heating lines, and they are located at the high points in the system. Even though the seals were vented before starting the pump, the flush water carries entrained air that is probably collecting in the seals. Because the seal is the highest point and is working properly, over time enough air collects to create a dry pocket around the seal faces. The flush water is going through the air pocket but not displacing it. (The faces were getting splashed but not surrounded with water.)

In order for this valve to work, the seal chamber or housing pressure must be high enough to push water up into the valve. The manager looked into the specifications of the air release valve used on the heating system, a float and needle valve type similar to a carburetor float—only air passes through the needle valve, so it is unlikely to clog.

Plant personnel attached the valve to the pump frame above the seal and placed a shutoff valve below it so it could be closed in the event the valve requires repair. Plastic tubing connected it to the vent port on the seal housing (opposite the flush port). The seal is now constantly vented, and the seals operate as they should. The plant modified all similar pumps.

In a pump with double mechanical seals (horizontal or vertical), the flush water is deadheaded between the seals. Venting at start-up should be adequate. In any case the vent should be the higher port and the flush the lower; this removes the most air possible from the seal.

In the situation described in this article, a pump designed to be operated horizontally was installed vertically. The seal chambers may or may not have flush and vent ports installed. Even though it is equipped with two single seals, they are naturally vented and flushed by the pumped liquid when used horizontally.

Once the pump is installed vertically, the upper seal chamber acts like the cup with the open end down. The upper seal runs dry. In this case, the pump is pumping clear cooling water. The suction pressure is probably lower than in the seal chamber. If no port is provided, the plant operator recommends drilling and tapping a hole in the seal chamber as high as possible.

If this is the case, connect the seal chamber vent that was just made with a similarly drilled and tapped hole in the suction line. Connecting them creates flow from seal to suction line, commonly called a suction recirculation system. The clear cooling water is unlikely to plug the line. The higher the pressure differential, the greater the flow. By doing so, it is drawing air and water from the seal chamber continuously

If the pump were in a flooded suction condition with the suction line pressure higher than the seal chamber, the air release valve may be an option. This does not address every possible cause of seal failure, but it eliminates an environmental problem created by operating a pump designed for horizontal use in a vertical orientation. Proper venting of the seal chamber is critical, particularly in a vertical shaft pump.

Vertical, multistage centrifugal pumps from the IN-VB range are non-self-priming high pressure pumps characterized by a high rate of efficiency as well as durability. Wetted parts are made from AISI 304 or AISI 316 L stainless steel. The ≥ 0.75 kW three-phase motors correspond to the energy efficiency classification IE3.

Equipped with ceramic, wear resistant, liquid lubricated bearings. Shaft seal in the form of a mechanical seal. The pump has the CE sign of approval and corresponds to the newest safety regulations.

A mechanical seal is simply a method of containing fluid within a vessel (typically pumps, mixers, etc.) where a rotating shaft passes through a stationary housing or occasionally, where the housing rotates around the shaft.

When sealing a centrifugal pump, the challenge is to allow a rotating shaft to enter the ‘wet’ area of the pump, without allowing large volumes of pressurized fluid to escape.

To address this challenge there needs to be a seal between the shaft and the pump housing that can contain the pressure of the process being pumped and withstand the friction caused by the shaft rotating.

Before examining how mechanical seals function it is important to understand other methods of forming this seal. One such method still widely used is Gland Packing.

Packing needs to press against the shaft in order to reduce leakage – this means that the pump needs more drive power to turn the shaft, wasting energy.

The stationary part of the seal is fitted to the pump housing with a static seal –this may be sealed with an o-ring or gasket clamped between the stationary part and the pump housing.

The rotary portion of the seal is sealed onto the shaft usually with an O ring. This sealing point can also be regarded as static as this part of the seal rotates with the shaft.

One part of the seal, either to static or rotary portion, is always resiliently mounted and spring loaded to accommodate any small shaft deflections, shaft movement due to bearing tolerances and out-of-perpendicular alignment due to manufacturing tolerances.

The primary seal is essentially a spring loaded vertical bearing - consisting of two extremely flat faces, one fixed, one rotating, running against each other.  The seal faces are pushed together using a combination of hydraulic force from the sealed fluid and spring force from the seal design. In this way a seal is formed to prevent process leaking between the rotating (shaft) and stationary areas of the pump.

If the seal faces rotated against each other without some form of lubrication they would wear and quickly fail due to face friction and heat generation. For this reason some form of lubrication is required between the rotary and stationary seal face; this is known as the fluid film

In most mechanical seals the faces are kept lubricated by maintaining a thin film of fluid between the seal faces. This film can either come from the process fluid being pumped or from an external source.

The need for a fluid film between the faces presents a design challenge – allowing sufficient lubricant to flow between the seal faces without the seal leaking an unacceptable amount of process fluid, or allowing contaminants in between the faces that could damage the seal itself.

This is achieved by maintaining a precise gap between the faces that is large enough to allow in a small amounts of clean lubricating liquid but small enough to prevent contaminants from entering the gap between the seal faces.

The gap between the faces on a typical  seal is as little as 1 micron – 75 times narrower than a human hair.  Because the gap is so tiny, particles that would otherwise damage the seal faces are unable to enter, and the amount of liquid that leaks through this space is so small that it appears as vapor – around ½ a teaspoon a day on a typical application.

This micro-gap is maintained using springs and hydraulic force to push the seal faces together, while the pressure of the liquid between the faces (the fluid film) acts to push them apart.

Without the pressure pushing them apart the two seal faces would be in full contact, this is known as dry running and would lead to rapid seal failure.

Without the process pressure (and the force of the springs) pushing the faces together the seal faces would separate too far, and allow fluid to leak out.

Mechanical seal engineering focuses on increasing the longevity of the primary seal faces by ensuring a high quality of lubricating fluid, and by selecting appropriate seal face materials for the process being pumped.

When we talk about leakage we are referring to visible leakage of the seal. This is because as detailed above, a very thin fluid film holds the two seal faces apart from each other. By maintaining a micro-gap a leak path is created making it impossible for a mechanical seal to be totally leak free. What we can say, however, is that unlike gland packing, the amount of leakage on a mechanical seal should be so low as to be visually undetectable.

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Pumping of low-temperature and cryogenic fluids requires specific and unique engineering technologies for the shaft sealing system. When correctly applied, these technologies provide the containment and reliability to meet pumping equipment operators’ requirements.

Due to their extreme sub-zero temperatures, low-temperature hydrocarbons and liquefied atmospheric gases pose significant challenges to pumping, and particularly to the specification of their shaft sealing systems. To provide long-term reliability while ensuring that these pumped fluids are safely contained, the designs of the shaft seals used in cold-fluids pumps are often highly specialized.

For example, low temperatures have significant implications for the choice of materials used in the seal construction. Metals become increasingly brittle as the temperature is reduced; therefore, thermal constriction and expansion must be factored. The volatility and flammability of low-temperature hydrocarbons pose special challenges for the design of pump shaft seals, as well as for the release of hazardous emissions to the atmosphere. Liquefied oxygen, with temperatures much colder than these hydrocarbons, is a strong oxidizer and can cause certain materials to spontaneously combust.

Low-temperature hydrocarbons are typically pumped at sub-cryogenic temperatures, between –20°C and –140°C (–5°F to –220°F), although lower temperatures are occasionally encountered. They have high vapor pressures at ambient temperatures and are pumped at low temperatures to reduce the pumping pressures. These hydrocarbon fluids include ethylene, LNG, LPG, methane, butane and propylene.

Liquefied atmospheric gases include oxygen, nitrogen, argon and the noble gases. They are typically pumped at cryogenic temperatures ranging from –175°C to –198°C (–285°F to –325°F). Impeller inducers are often used, as they are frequently pumped with a low vapor pressure margin at the pump suction.

Low-temperature hydrocarbons are commonly pumped with API 610 (VS6) vertical multistage double-casing pumps that feature a warming chamber, known as a cofferdam (Fig. 1), which thermally isolates the shaft seal from the cold pumped fluid. Cofferdams enable a greater range of shaft sealing solutions to be used on these pumps, utilizing traditional sealing technology.

A cofferdam is a chamber between the pump discharge and the mechanical seal that is connected to the pump suction, or the vessel from which the pump is drawing suction. Ambient heat surrounding the pump, together with energy from the shaft and bearings, causes the liquid in this chamber to vaporize into a gas, which forms an insulating barrier between the seal and the process fluid. Cofferdams can be incorporated only into vertical pump designs.

Although vertical arrangements are common, various horizontal pumps can also be used. In these types of pumps, the shaft seal is in direct contact with the cold-pumped fluid; therefore, selection of the seal materials for low-temperature operation becomes more critical.

Similar to pumping equipment for low-temperature hydrocarbons, pumps used for liquefied atmospheric gases have a combination of vertical multistage pumps, together with horizontal single-stage pumps. These systems generally do not follow API pump design standards.

However, as the temperatures of liquefied atmospheric gases are much colder than those at which hydrocarbons are pumped, cofferdams cannot be used on these pumps. Although a mixture of vertical and horizontal pumps is commonly used at air liquefaction plants, mobile trailer truck unloading pumps are almost exclusively overhung single-stage pumps, either with direct-drive or speed-increasing gearboxes.

For pump designs where the mechanical seal is immersed in the pumped fluid, the vapor pressure margin in the seal chamber becomes critical. Where the vapor pressure margin is low, the heat energy from the mechanical seal faces can vaporize the fluid around the seal and in the seal interface, resulting in dry running of the seal. In this situation, a dual-pressurized seal is required. A dual-pressurized seal provides a stable barrier fluid to lubricate the seal faces, thereby negating the effect of vaporization of the pumped liquid at the seal faces.

API Plan 53B and 53C barrier systems are commonly selected for dual-pressurized seals to provide a source of warm, clean and stable barrier fluid to the mechanical seal. When an API Plan 53C system is selected, extra care should be taken to ensure that the pressure-amplifying piston and rod seals are insulated from exposure to cold temperatures.

The availability of suitable barrier fluids becomes limited at low temperatures, as the viscosity of many fluids becomes too high at the seal chamber operating temperatures. Mono- and di-ethylene glycol mixtures with water can be used down to temperatures of –29°C (–20°F). Alcohols, such as propanol (propyl alcohol), are suitable for even colder temperatures reaching –70°C (–95°F). Synthetic oils can also be used; however, careful consideration to their pour point is required, and a heating system may be needed to warm the barrier fluid to maintain a suitable viscosity.

When sufficient vapor pressure margin exists within the seal chamber, a dual-unpressurized seal can be selected. Typically, these designs feature a dry-sliding containment seal fitted with API Plan 76, or a combination Plan 72 and 76. These seal arrangements have the advantage of removing the low-temperature limitation of barrier fluid selection.

Pump designs utilizing a cofferdam require a dual-pressurized mechanical seal, as the seal chamber contains no liquid to lubricate the mechanical seal faces.

Icing, due to condensation of atmospheric humidity, can create a problem for sealing systems handling cold hydrocarbons. Since condensing water expands as it freezes, it can interfere with the operation of the mechanical seal if it reaches the seal’s operating mechanism. Extra protection should be applied to equipment exposed to atmospheric elements, such as rain. An API Plan 62 using a dry nitrogen quench can displace atmospheric humidity, thereby protecting the mechanical seal from these effects.

In applications handling liquefied atmospheric gases, pump seal reliability takes precedence when selecting a shaft sealing system. Unlike hydrocarbons, emissions of gases to the environment by liquefied atmospheric gases pose relatively minor hazards and, therefore, are not as critical a factor as seal reliability.

Two commonly employed shaft sealing technologies are used in pumps handling liquefied atmospheric gases: single mechanical seals and segmented bushings.

Single mechanical seals.The most common solution for pumps used in air liquefaction plants and mobile-transportation unloading pumps is the single mechanical seal. The major difference between the two is that the mobile unloading pumps tend to be smaller and often use non-cartridge seals. Cartridge seals are commonly found in larger machinery at air liquefaction plants. Single mechanical seals fall into two sub-categories: contacting wet seals and vaporizing liquid gas seals.

Contacting wet seals utilize a metal bellows to provide elastomer free-axial flexibility. Seal face materials typically include filled tetrafluoroethylene running against a tungsten carbide or hard-coated, stainless steel mating ring.

Vaporizing liquid gas seals (Fig. 2 and Fig. 3), similar in construction to contacting wet seals, feature engineered seal-face topography that allows the controlled vaporization of the pumped atmospheric gas to produce a highly reliable seal that exhibits controlled, low-level leakage rates.

Segmented bushings.A segmented bushings sealing configuration is often found in vertical multi-stage pumps at air liquefaction plants. The design provides a controlled leakage by breaking down the sealed pressure over a series of tightly controlled bushing clearances. Leakage rates are higher than those of mechanical seals; however, these leakage rates are often considered acceptable by this industry.

As mentioned, low temperatures have significant implications for the choice of materials used in the seal construction. This is especially true for elastomers applied in seals for pumps handling low-temperature hydrocarbons. Depending on the material grade used, elastomers have a variety of minimum temperature limits, but none can survive dynamic operation at true cryogenic temperatures.

Engineered polymer seals are an option at temperatures below the limits of elastomers; however, many of these designs will not function with pressure reversals applied to the sealing ring, which may be required in the mechanical seal design when support system failures occur.

Elastomers can survive at significantly lower temperatures below their operational limits when the seals are not in operation (i.e., static); however, they must be warmed up prior to operation. Commissioning of shaft seals containing elastomers must be completed carefully to ensure that equipment is at the correct temperatures before startup. Blowdown—the rapid depressurization of a vessel/pipeline—is one situation that can create excessively low temperatures for mechanical seal elastomers.

Thermal expansion and contraction are also considerations. The cavities in which elastomers or engineered polymer seals are installed will change with decreasing temperatures, as well as the dimensions of sealing elements installed in these cavities. Additionally, clearances between dissimilar materials, such as bushings, will require review. Mechanical seal manufacturers take these factors into consideration during the design of the mechanical seal for these cold services.

Since pumping equipment is often used interchangeably between different atmospheric gases, sealing of liquefied atmospheric gases presents some unique challenges to the selection of materials.

Liquefied oxygen is a strong oxidizer and can cause certain materials to spontaneously combust. Additionally, any organic contaminates on the seal can lead to spontaneous combustion, including metal cutting fluids, fibers from cleaning rags, and even oils from human fingerprints. To meet oxygen service requirements on seals, stringent cleaning specifications must be employed to ensure that the seal is free of any contaminates that may create a fire hazard while in service. Additionally, the materials of construction must include materials that are compatible for use in oxygen service.

Aluminum alloys should be avoided, as they can become hazardous when their protective oxide film is stripped from the material, such as when abrasion occurs. Lubricants used in the assembly and operation of the mechanical seal must be free of hydrocarbons and compatible for use in oxygen service. Packaging of the seal should also be suitable to preserve the cleanliness of the seal prior to installation into the pumping equipment, which must be performed in a suitably clean environment.

Of the many pump mechanical seal applications in use throughout various industries, those that deal with low-temperature and cryogenic processes rank among the more challenging.

It is critical to keep these seals, which handle low-temperature hydrocarbons and liquefied atmospheric gases, in optimal operating condition to ensure that the pumped fluids are safely contained, while providing long-term reliability. HP

Mark Savage is a Product Group Manager at John Crane, responsible for the application, design and development of metal bellows seals for pumps, compressors and rotating machinery. He has worked in the sealing industry for 25 yr and has been involved with the development of best practices for shaft seals and their support systems. Mr. Savage holds a BE degree in mechanical engineering from the University of Sydney, Australia. He is a member of the Fluid Sealing Association and Vice Chair of the Association’s Mechanical Seal Division, Chair of the Mechanical Seal Technical Committee and Vice Chair of the Government Relations Committee. He is also a member of NACE International and the Society of Tribologists and Lubrication Engineers (STLE). Mr. Savage has authored several publications on mechanical seals and support systems and their application to minimize environmental impact.