barrier fluid in mechanical seal quotation

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As end users face increasingly restrictive leakage and safety regulations, a growing number are turning to multiple seal arrangements. Multiple sealing arrangements require a liquid or gas buffer or barrier fluid to operate, introducing a new factor that end users must monitor.

Below are some best practices for liquid buffer and barrier fluids. By selecting an appropriate fluid and following proper maintenance procedures, end users can promote system reliability and extend their systems’ operating lives.

In addition to process fluid, all multiple seals use an external fluid. Depending on the sealing arrangement, this external fluid is called buffer fluid or barrier fluid. American Petroleum Institute (API) Standard 682 specifies that unpressurized dual seals, also known as traditional tandem seal arrangements, use buffer fluid. Pressurized dual seals, on the other hand, use barrier fluid, which isolates the pump process liquid from the rest of the system.

When selecting a fluid, end users should weigh the pros and cons of their applications. Some common barrier and buffer fluids, which have benefits and potential risks, are:

Glycol solutions — These, which usually contain 50 percent ethylene glycol and 50 percent water, are the simplest and most common barrier or buffer fluids. Because inhibitors can come out of the solution and damage the seal faces, end users should use uninhibited glycol in these solutions instead of glycol with inhibitors, such as antifreeze. Since some areas restrict the use of ethylene glycol, end users may need to use propylene glycol instead.

Petroleum-based hydraulic, conventional gear and bearing lubricating oils — Because they are widely available, they are popular choices. However, the viscosity of these oils can cause carbon seal face blistering, particularly with oils that are Grade 32 or higher on the International Organization for Standardization (ISO) scale.

Synthetic oils specifically formulated for barrier or buffer use — These have grown increasingly popular during the last decade. These synthetics are typically polyalphaolefin-based, and they range between ISO Grade 5 and Grade 20 (approximately). Lower-viscosity synthetics are the most popular option among end users. Higher-viscosity synthetics, which are more expensive, are the best choice for applications with high temperatures or low shaft speeds.

Heat transfer fluids — Although useful in extremely high-temperature services, these fluids can pose problems because they tend to decompose and form coke, or hard carbon formations.

After choosing the correct fluid for their system, end users must maintain the fluid and the sealing environment properly to ensure peak performance. Checking the fluid each month for changes in pH, color, viscosity, consistency and the presence of solids is a good way to help promote system reliability.

While users should change their barrier and buffer fluids regularly, service life can vary dramatically. In general, fluids operating at high temperatures need changing more frequently than those at lower temperatures.

According to API 682, the allowable temperature rise is 15° F for systems with buffer or barrier fluids that are water-based, diesel or kerosene, and 30° F for systems that use mineral or synthetic oil as buffer or barrier fluids. For example, a system using oil could have an average reservoir temperature of 130° F with an outlet temperature of 115° F and an inlet temperature of 145° F.

When monitoring the decomposition of buffer or barrier fluids, end users should consider this rule of thumb for chemical reactions — the rate of reaction doubles for every 18 F rise in temperature. For example, if a barrier fluid needs changing every six months at an average reservoir temperature of 130° F, the same fluid would need to be changed every three months if the reservoir temperature is 148° F. This simple guideline can be useful for evaluating heat transfer options during system design.

In addition to temperature considerations, buffer fluids can become contaminated by the process liquid and may require more frequent changing than barrier fluids.

While selecting the proper buffer and barrier fluid is an important first step toward sealing system reliability, the following considerations also have a big effect on performance:

API 682 provides useful guidelines and default selections for standardized dual seal systems — including Piping Plans 52, 53A/B/C and 54. By combining the API guidelines with the best practices for buffer and barrier fluids described in this article, end users can keep their systems operating smoothly.

Our barrier seal reservoirs are built to ASME Section VIII standards and ASME U code stamps are available. All our barrier fluid systems, whether custom or standard designs are designed and built to the current API 682 requirements.

DuraClear Crystal 7 Seal Lubricant is a premium barrier fluid for use on equipment handling high purity, high value or highly reactive product fluids such as strong acids and bases. It has been specifically formulated for the lubrication needs of dual mechanical seals. When chemical compatibility is critical, this environmentally friendly and nonreactive barrier fluid extends the life of dual mechanical seals for increased process yield and throughput.

CTFE fluids may react violently with K, Na, amine, hydrazine, liquid fluorine, liquid chlorine trifluoride, Aluminum, Aluminum Chloride (AlCl3) and Aluminum Oxide (Al2O3)

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Chesterton 662 FG is an ISO VG Grade 22 high-performance lubricant designed specifically as a barrier fluid for double mechanical seal applications. 662 FG is suitable for all industrial and food/beverage/pharmaceutical applications.  662 FG is NSF H1 registered.

The ultra-clean 662 FG delivers premium thermal stability while minimizing the abrasive-particle wear of the seal faces and extending equipment ​life.

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As operators of pumping equipment become more focused on the safety, reliability and environmental impact resulting from shaft seal leakage, dual mechanical seals have become more prevalent in the industry. A dual mechanical seal offers a second (outer) seal to contain the pumped fluid by creating a cavity or chamber between the inner and outer seal that can be filled with a fluid. When this fluid is unpressurized, it forms a buffer between the pumped fluid and atmosphere and is commonly referred to as a buffer fluid. When pressurized, it forms a barrier between the pumped fluid and atmosphere and is known as a barrier fluid.

Although mechanical seal designs are available in configurations that use either a liquid or a gas as a barrier fluid, the following discussion focuses on liquid buffer and barrier fluids only. In addition to separating the pumped fluid from the atmosphere, liquid buffer and barrier fluids lubricate the mechanical seal and transport frictional heat and absorbed heat from the mechanical seal to a heat exchanger. This controls the fluid’s temperature and lubricating properties.

Buffer/barrier fluid can be stored, monitored and delivered using many methods. Each is identified by a piping plan number that describes the minimum requirements of each system. The most commonly referenced piping plan originates from the American Petroleum Institute’s standard API 682.

A Plan 52 system (see Figure 1) provides a reservoir that stores the buffer fluid. Supply and return lines are connected to the mechanical seal and circulation of the buffer fluid is achieved by an internal circulating device (pumping ring) within the mechanical seal. The vapor space above the buffer fluid in the reservoir is vented to atmospheric pressure typically via a flare or vapor recovery system. The reservoir can be instrumented to measure the liquid level and pressure in the reservoir. Ports are fitted to the reservoir to facilitate maintenance activities—such as inspection and cleaning or refilling and draining the buffer fluid. Cooling is accomplished using an internal heat exchanger.

Pressurized dual seal systems contain the same essential components as an unpressurized system. However, they also contain a way to pressurize the barrier fluid. The following plans may be used for pressurized dual seal systems:

Plan 53A—A pressurized gas blanket in the reservoir pressurizes the fluid. Nitrogen is normally used and the pressure is controlled via a pressure regulator (see Figure 2). The barrier fluid is in direct contact with the pressurized gas.

Plan 53B—Pressure is generated as a nitrogen-filled bladder is compressed by the addition of barrier fluid into the bladder accumulator. The bladder prevents direct contact of the pressurized gas with the barrier fluid.

Plan 53C—A pressure amplifying piston uses pressure from within the pump (typically the seal chamber) to amplify the barrier pressure by the ratio of the area on each side of the piston. The barrier fluid is not exposed to any pressurized gas.

Plan 54—An external system is used to pressurize and circulate the barrier fluid. A Plan 54 system can be broadly classified into two groups: closed- and open-loop systems. In closed-loop systems, the barrier fluid is stored in a large reservoir and pumps pressurize and circulate the fluid. In open-loop systems, a compatible process stream is used as the barrier fluid and is circulated through the mechanical seal and returned to another point downstream in the process.

Several critical properties of a buffer or barrier fluid must be considered when making a selection. An ideal buffer or barrier fluid will have the following properties:

Water offers several benefits as a buffer/barrier fluid. Its thermal conductivity is about three times greater than oils and its specific heat is about twice that of oils, so it is good at transporting heat away from a mechanical seal. Water is inexpensive, easy to handle and store, has few seal material compatibility issues and is nonflammable. It is also compatible with many aqueous pumped solutions. Its viscosity is generally around 1 centistoke at moderate temperatures which offers low resistance to flow in the barrier system.

However, the viscosity becomes low at elevated temperatures limiting its effectiveness as a lubricant for the mechanical seal faces. Water is also susceptible to freezing during the winter months. This results in a narrow window of service and environment temperatures in which water can be used.

Generally, oils can be used in a much wider range of service temperatures. Compared to water, oils offer greater fluid stability at elevated temperatures and are not susceptible to freezing. They also provide excellent lubrication of the mechanical seal faces and, therefore, have the potential to offer longer seal life. Few compatibility issues with mechanical seal materials exist.

Oils are available in a wide range of types, compositions and viscosities. Traditional oils used in the industry include turbine oils and automatic transmission fluids. However, performance as buffer and barrier fluids has not been as successful as other oils, primarily because of the complex mixture of additives in these fluids.

Good performance can be achieved from oils with viscosity below that of ISO Grade 32 oils. High viscosities can result in damage to the mechanical seal faces, particularly when carbon is used as a face material. Paraffinic-based oils also generally perform better than naphthenic oils while synthetic oils offer even better performance. Synthetic lubricants specifically developed for use as a buffer/barrier fluid are now available in the marketplace and offer excellent performance. However, this performance is achieved at the sacrifice of cost.

We invite your suggestions for article topics as well as questions on sealing issues so we can better respond to the needs of the industry. Please direct your suggestions and questions to sealingsensequestions@fluidsealing.com.

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Mechanical seals are designed to prevent leakage of fluid from centrifugal pumps that support industrial processes. Mechanical seals depend on mechanical seal support systems for reliable operations. I’ve provided information below to help explain mechanical seal support basics. I’m hopeful it’ll help you gain a better understanding of mechanical seals and the various types of mechanical seal support systems, their applications, and optional configurations to help boost reliability in your Northern California Bay Area refinery.

A mechanical seal is used to contain fluid within a centrifugal pump where the impeller shaft passes through a stationary housing. There’s a range of mechanical seal designs to cover every conceivable pumping process. Low to high pressure, low to high fluid temperatures, clean plant water to heavy hydrocarbons. To cover that wide range of pumping processes and conditions there’s an equally wide range of seal support systems and custom configurations to match the need.

At its simplest, a mechanical seal support system is designed to provide the proper seal chamber environment to maintain the integrity of the mechanical seal. The system provides cooling and lubrication to reduce mechanical seal friction and heat and prevent leakage. To accomplish this, mechanical seal support systems deliver process fluid, water, oil, or inert gas to the seal chamber at the required pressure, temperature, and flow.

Maintaining the proper seal chamber environment prevents leakage that could lead to loss of profitable products, degradation of pumps and their supporting infrastructure, or in the worst cases, conditions that pose environmental risk and subject you to Cal/OSHA and BAAQMD sanctions.

Centrifugal pumps and mechanical seal support systems are critical to the petroleum industry. As a result, the American Petroleum Institute has developed a standard to describe the different seal support systems, known as piping plans. See API Standard 682: Pumps—Shaft Sealing Systems for Centrifugal and Rotary Pumps for a listing of the various plans. The complete document is over 250 pages, but below I"ve distilled the document into a greatly simplified overview of mechanical seal support basics.

Mechanical seal support systems can be grouped into three categories—process side, dual or in-between, and atmospheric side. Let me explain the basics of these categories by describing the type of mechanical seal, the typical pumping applications, and the various API plans that provide the required environment for the mechanical seal and pumping conditions.

Process side mechanical seal support systems provide the lubrication and cooling to a single mechanical seal to keep process fluid within the pump volute. Process fluid is used for lubrication and cooling in three ways: it is circulated from the discharge to seal chamber, from the seal chamber to the suction, or from discharge to seal chamber and then to suction. Alternatively, a flush fluid that provides lubrication and cooling can be delivered from a reservoir which is part of the seal support system or an external source, such as plant water.

This single-seal solution is used when the pumped fluid poses no environmental threat in the event that the pumped fluid vaporizes as it crosses the seal faces and dissipates into the atmosphere. The table below summarizes the API Plans in the process side category, indicates the types of fluids used to provide cooling and lubrication, and the components that differentiate the plans and their capabilities.

Process side mechanical seal support systems cover a range of pumping processes, from clean, moderate-temperature, non-polymerizing fluids to high-temperature dirty or contaminated fluids. Cooling and filtering options enable these plans to remove contaminants that would damage seal faces. Pumping applications can include:

Dual or in-between mechanical seal support systems deliver a buffer (unpressurized) or barrier (pressurized) fluid to a seal chamber that contains a double mechanical seal—two seals arranged in series to maintain the buffer/barrier fluid between the two seals. The inboard (primary seal) keeps process fluid within the pump housing. The outboard (secondary seal) prevents the buffer/barrier fluid from leaking to the atmosphere. The buffer/barrier fluids that lubricate the seal faces and dissipate heat can be gas or liquid.

Pressurization of barrier fluid is provided by plant nitrogen, bladder accumulator, piston accumulator for API Plans 53A, 53B, and 53C respectively. Plan 54 is pressurized by the external pump. Plan 72 buffer fluid is plant nitrogen.

Atmospheric side mechanical seal support systems deliver an unpressurized fluid (also known as a “quench”) to the atmospheric side (exposed to air) of a mechanical seal. This method is used when a single mechanical seal cannot operate properly without the aid of the quench. In comparison to the process side and dual seal support systems, there are only two variants:

API Plan 62 - Quench From External Source delivers clean water, low-pressure steam, or nitrogen to cool the seal faces and prevent oxidation or coking of process fluid.

Our brief explanation of mechanical seal support system basics shows you the wide range of capabilities and applications. There’s a solution for every type of pumping process. You don’t need an in-depth understanding to obtain the maximum benefit from a mechanical seal support system if you work with a local vendor in the Northern California Bay Area who has deep industry experience.

In addition to knowing which mechanical seal support system is best for a specific pumping process, a local vendor who conducts an on-site evaluation is able to make specific recommendations regarding system design, instrumentation, and components to boost pump reliability. Fabricated and thoroughly tested in Swagelok’s Fremont, Santa Clara, or Concord facility, you’ll have a mechanical seal support solution custom-configured to the specific requirements of your pumping process.

Swagelok Northern Californiawill be happy to explain mechanical seal support basics and advise you on the specific plans to improve pump reliability. To arrange an on-site consultation by one of our Field Engineerscontact our teamtoday by calling

Flexaseal offers replacement seals for a full array of compressors, mixers, pumps, and other rotating equipment. Direct replacements are available in standard inch and metric sizes and materials for major brands, including

With four (4) configuration options all incorporating additional engineered features such as reverse pressure capability, non-clogging multi-springs, rugged seal drive operation, and hydraulically balanced faces, the RKCS single and RKCD dual seals successfully contend with the industry’s toughest slurry challenges.

Flexaseal provides component seals for a wide range of challenging applications where cartridge seals are impractical or incompatible with current rotating equipment. This may be due to equipment not having a seal chamber or the seal need to be installed on the wet side of a pump. We offer a sturdy single spring component seals, externally mounted mechanical seals for extremely corrosive applications, and stationary seats (mating rings).

There is no one universal seal for all mixer applications. Every mixer, agitator, and reactor model is distinctive and engineered for a specific application. Many of these applications require seals to perform in environments that would destroy common seals due to extreme drag and shear forces, abrasive materials, or other challenges. That means successful sealing requires clearly defining the type of equipment, the product, and the sealing conditions. Flexaseal’s design and engineer team are capable of providing innovative solutions for your toughest challenges.

The mechanical seal style GFR/GFL offers a number of benefits over liquid lubricated dual seal for API plans 53 and 54. These include lower maintenance costs for the seal and support system since there is no barrier fluid to fill and the ability to retain 100% product purity through the use of nitrogen as a lubricant.

The resultant gas film pressure provides an opening force slightly greater than the net closing forces, which cause the faces to separate and not contact.

Simple support system – utilizes API 682 Plan 74 instead of more complex Plans 53 or 54, lowering the cost of operation and maintenance of the seal support system

Viscous substances such as syrups, tars, thick oils, resins, and glues prove to be challenging for most mechanical seals. Lip seal designs have been the go-to option for these processes that have centipoise values well above the normal range for seal face operation. The MLC3 cartridge seal achieves optimum pumping rates at lower speeds with fewer sealing issues than products currently in the field and requires virtually no seal support system.

Machined lip seals with deflected lip geometry ensures reliable sealing while producing a smaller footprint compared to competitor designs. This smaller footprint reduces parasitic torque and heat generation.

Single Lip Seal with anti-rotation ring and integrated back up ring: Energized front lip prevents leakage when transitioning between high viscosity and high fluidity processes. Anti-rotation rings statically seal even under normal temperature cycling. The integral back up ring provides added lip support under higher pressures and potential pressure spikes.

Double Lip Seal with anti-rotation ring: The PTFE-ML compound is formulated with a lower coefficient of friction, which coupled with the enhanced heat dissipation leads to lower under-lip temperatures. Lower temps = lower seal and sleeve surface wear.

Lantern Ring: Multifunctional PTFE ring provides additional bearing support as well as even dispersion of lubricant or barrier/buffer fluid around the lip seals.

Energized O-ring front lip tolerates lower speeds and higher shaft runout. This design increases sealing viability with certain emulsifiers and fluid viscosity transitioning such as CIP applications.

Sleeve: Sintered Silicon Carbide sleeve for durable wear and sealing surface. Inboard and outboard sleeve O-rings dampen vibration and aid in easy removal and repair.

With barrier fluid pressure higher than product pressure, the AST80 prevents leakage of toxic or hazardous fluids into the environment. The barrier fluid provides lubrication to seal gases and non-lubricating fluids.

With unpressurized buffer fluid, the outboard seal of the AST80 runs "at idle" as a standby seal. If the inboard seal fails, the outboard seal provides primary protection, eliminating unscheduled shutdown of batch processes.

Cyclone separators are typically used in an API Plan 31 arrangement and incorporated in the seal flush line (API Plan 11 ) from the discharge of the pump.

53B accumulator-based seal support systems utilize a bladder to maintain system pressure to pressurized dual seals and absorb barrier fluid thermal expansion while separating the pressurizing gas and barrier fluid.

53C accumulator-based seal support systems utilize a piston to maintain system pressure to pressurized dual seals and absorb barrier fluid thermal expansion while separating the pressurizing gas and barrier fluid.

Used to detect and monitor leakage of the inboard seal, these seal support systems can detect liquid leakage (API Plans 65 and 75) or gas leakage (API Plan 76), or a mixture of gas and liquid leakage (API Plan 75).

Used to detect and monitor leakage of the inboard seal, these seal support systems can detect liquid leakage (API Plans 65 and 75) or gas leakage (API Plan 76), or a mixture of gas and liquid leakage (API Plan 75).

Used to detect and monitor leakage of the inboard seal, these seal support systems can detect liquid leakage (API Plans 65 and 75) or gas leakage (API Plan 76), or a mixture of gas and liquid leakage (API Plan 75).

A PG 72 (API Plan 72) system is used to provide a clean, regulated gas supply to a dual unpressurized seal arrangement where the containment seal is dry running.

A PG 74 (API Plan 74) system provides a clean, dry, regulated supply of pressurized barrier gas (usually nitrogen) to dual pressurized, non-contacting seals.

These reservoir-based seal support systems are designed for both API Plan 52 and 53A applications to support unpressurized and pressurized dual seals.

Plant seal water filtration system, maintaining clean water supply to improve the reliability mechanical seals and gland packing and also flow control and pressure-regulating devices.

SafeJet is an automatic seal water filter. Its operation is based on “flow-through” filter technology, which utilizes reliable laminar filtering method.

Water-cooled heat exchangers may be applied where water is readily available. Heat exchangers may be packaged together with seal support systems when additional cooling is required.

Water-cooled heat exchangers may be applied where water is readily available. Heat exchangers may be packaged together with seal support systems when additional cooling is required.

Indufil® fuel gas filtration units are individually tailored to maximize reliability regardless of the condition of the supply gas. They are fitted as original equipment by most major gas turbine suppliers and EPCs around the world.

Indufil® liquid filters can be applied to almost any liquid application, from hydraulic and bearing oil systems to lubrication and water injection systems.

Most centrifugal compressors today use dry gas seals to contain high-pressure gas, whether on a high-pressure reinjection duty or a low-pressure pipeline machine.

IIndufil® ball valves are designed in-house and manufactured for use in duplex systems to enable continuous operation while one side of a system receives maintenance.