api plan for double mechanical seal for sale

Pumping processes involving toxic or hazardous fluids that can’t risk leakage because of stringent environmental regulations require a double mechanical seal. Compared to a single mechanical seal, a double seal gives you significantly greater protection against leaks. With a double mechanical seal, you have an arrangement of two mechanical seals (a primary or inboard seal and a secondary or outboard seal) in series—back-to-back, tandem, or face-to-face. Each seal has a rotating (R) surface and a stationary (S) seal surface. These seals can be arranged in one of three patterns.

In a back-to-back arrangement, the stationary seal faces are positioned back-to-back with the rotating seal faces on the outside. The back-to-back arrangement is easy to install and used for many general pumping applications.

The tandem arrangement has the two pairs of seals mounted with the same orientation. This arrangement is preferred for toxic or hazardous applications because the outboard seal provides full pressure back-up, allowing the outboard seal to back up in the event of an inboard seal failure.

In the face-to-face arrangement, the rotating seal faces share a common stationary seal face. This arrangement is useful when equipment space is too constrained to permit back-to-back or tandem seal arrangements.

The American Petroleum Institute (API) Standard 682 classifies double mechanical seals into two configurations—pressurized and unpressurized. The pressurized arrangement has a barrier fluid delivered to the double mechanical seal by a seal support system. The barrier fluid is delivered at a higher pressure than the process fluid and must be chemically compatible with the process fluid as it will lubricate the inboard seal faces and mix with the process fluid. The unpressurized arrangement has a buffer fluid delivered to the double mechanical seal by a seal support system. The buffer fluid is delivered at a lower pressure than the process fluid.

The barrier and buffer fluids you use can be liquid or gas. They provide lubrication and help maintain the required operating temperature of the seal faces. The typical choices are water and water/glycol mixtures, low-viscosity petroleum or synthetic oils, kerosene, diesel, and nitrogen.

To gain a better understanding of the differences between the uses of barrier and buffer fluids, let’s look at two common API plans for double mechanical seals—API Plan 52 Buffer Fluid Seal Pot and API Plan 53A Barrier Fluid Seal Pot Pressurized by Nitrogen.

API Plan 52 takes buffer (unpressurized) fluid from a reservoir (seal pot), delivers it to the seal chamber, circulates it between the inboard and outboard seals using a pumping ring located driven by shaft rotation, then returns the fluid to the reservoir. In the event of an inboard seal failure, process fluid leaks into the seal chamber. When that occurs an increase in buffer fluid pressure and/or level alerts operators to the problem. The outboard seal, however, contains leakage until maintenance can replace the damaged seal.

This plan can include cooling coils in the reservoir to maintain the required buffer fluid temperature, visual or mechanical fluid level indicators, pressure and level transmitters, and connection to a collection system and buffer fluid replenishment source.

The overall design of this API plan for a double mechanical seal is relatively simple in comparison to other plans. Design decisions involving tubing size, length, geometry, type (carbon vs stainless steel), buffer fluid type, and volume of the buffer fluid reservoir are critical in maintaining the proper operating environment for the double seal. If you don’t have this expertise in-house, work with an experienced, local seal support system vendor to ensure the API Plan 52 is designed to meet your specific pumping requirements.

API Plan 53A is conceptually similar to API Plan 52 with the difference that the fluid being circulated between the double mechanical seals is under pressure. A pumping ring is used to circulate the fluid. The reservoir that contains the barrier fluid is pressurized by plant nitrogen. Reservoir pressure should be set a minimum of 20 to 25 psi (1.4 to 1.73 bar) above the maximum seal chamber pressure, allowing the barrier fluid to leak (and lubricate) across the inboard seal faces into the process fluid. For this reason, the barrier fluid must be chemically compatible with the process fluid.

Because barrier fluid is depleted as it moves across the inboard seal faces, it needs to be replenished. This can be done manually or automatically by way of a system that serves multiple pumps. API Plan 53A design options include reservoir type and volume, cooling coils, fluid level and pressure indicators, and transmitters to alert to level or pressure changes that indicate seal failure.

When you choose an API plan for a double mechanical seal, your primary decision is between a buffer or barrier plan. I’ve highlighted two of the API plans for double mechanical seals above to show the basic differences. There are multiple API plans for double mechanical seals to choose from—pressurization from bladder or piston accumulators, plant nitrogen delivered directly to the seal chamber, and custom-engineered external systems. Your choice will be determined by the process fluid and pumping conditions and the type of double mechanical seal your vendor recommends.

With this information in hand, it’s best to work with an experienced local seal support system vendor. They’ll be able to meet with you on-site to review the specifications for the pumping process, the pump, and the double mechanical seal. They’ll evaluate your existing infrastructure and its influence on seal support system design. Based on this information, they’ll then design the seal support system to meet the specific pumping requirements.

If you work with a global vendor like Swagelok, based on the design, we can quickly assemble and thoroughly test the API plan at our local facilities prior to delivery. We’re also conveniently available for follow-up consultations, on-site, remotely, or by way of a quick phone call.

For well over 50 years, Swagelok has worked closely with Northern California process industries to confidently choose the right API plans for pumping needs. Our locally based Field Engineers and certified technicians provide field verification of your seal support requirements, designs based on best practices gained from global experience.

To find out more about howSwagelok Northern California can help you choose the right API plan for double mechanical seals, as well as process and atmospheric side seals,contact our team today by calling

Morgan holds a B.S. in Mechanical Engineering from the University of California at Santa Barbara. He is certified in Section IX, Grab Sample Panel Configuration, and Mechanical Efficiency Program Specification (API 682). He is also well-versed in B31.3 Process Piping Code. Before joining Swagelok Northern California, he was a Manufacturing Engineer at Sierra Instruments, primarily focused on capillary thermal meters for the semiconductor industry (ASML).

In Part 3 of our series on Double/Dual Mechanical Seals we take a look at the best piping plans/support systems to put in place to increase seal/equipment reliability and reduce energy/water costs.

More importantly, to extend the life of a double/dual seal, you want to control the fluid film that comes into contact with the primary seal faces to establish the ideal lubrication, temperature and pressure within the seal. Across all types of mechanical seal failures, inadequate/incorrect seal support systemsare the second highest cause of seal failures (Figure 1).

Standard environmental control plans (also called piping plans) have been developed for double/dual seals and choosing the right environmental control plan is critical to your seal performance and reliability.

This plan is used when working with hazardous process fluids in which no leakage into the product can be tolerated. It provides a backup seal in case of inboard seal failure.

If an inner seal leak is not detected early enough, the higher pressure process fluid will displace the buffer fluid. This can result in the process fluid completely filling the barrier fluid chamber between the inboard and outboard primary seals. Should the outer seal leak, product will be released into the atmosphere.

This plan is used in services where no product leakage into the atmosphere can be tolerated.  Plan 53’s biggest advantage over Plan 54DM, which does not use a tank, is its limited fluid volume.  The amount of fluid that can enter the product system is limited to the volume of the barrier fluid tank itself (usually 2-3 gallons or 8-12 liters).

Uses a pressurized external reservoir or barrier fluid tank to provide a clean, pressurized barrier fluid to both the inboard and outboard primary seals of a pressurized double/dual seal.

Leakage of barrier fluid into the product will always occur to some extent.  Normally this leakage will be small and can be monitored by the barrier tank fluid level.  Therefore, the chosen barrier fluid must always be compatible with the process fluid.

The tank pressure must be maintained at the proper level.  If the barrier fluid tank pressure drops, the system will begin to operate like a Plan 52, or unpressurized dual seal, which does not provide the same level of sealing integrity.  Specifically, the inner seal leakage direction will be reversed and the barrier fluid will, over time, become contaminated with the process fluid.

Directs a clean compatible fluid into and out of the dual mechanical seal barrier/buffer fluid ports. The purpose of this fluid is to prevent the pumped fluid from damaging the inboard seal faces, to remove heat from the seal, and to lubricate the outboard seal faces.

Careful consideration should be given to the reliability of the barrier fluid source. When the source is interrupted or contaminated, the resulting seal failures can be very costly.

The higher the differential pressure, the more transfer/migration into the product. The control should never be used where the barrier fluid pressure is likely to fall below seal chamber pressure. If this were to happen, the failure of one inboard seal from any mechanical seal in the system could contaminate the entire barrier fluid system with product and cause additional seal failures.

Once the inboard seal wears out or fails, the amount of barrier fluid that entered the product system is virtually unlimited unless it is shut down quickly.  Alerting instruments should be put in place to avoid this.

Using appropriate monitoring devices, alarms, switches, etc. will provide a means to monitor the health of your double/dual seal to identify potential issues in advance avoiding costly unplanned outages. A basic Plan 52 buffer system will have a sight glass to monitor the buffer fluid level, a pressure gauge and connections to and from the mechanical seal, as well as a vent and drain valve. Cooling coils and level switches are typically available as optional items.

A Plan 53 would have the same features as the Plan 52 with the addition of a pressure regulator, safety valve, and an optional pressure switch. These systems can be customized to meet customer specifications should they desire to have additional features incorporated into the system.

For assistance with using the best seal support system for your specific challenge, ask your local Chesterton office or contact our Ask the Expert service.

Please contact AESSEAL Systems Division for further details. Tel: +44 (0)28 9266 9966 Email: systems@aesseal.com For more information, and a video demonstrating the piping plan in operation, select a plan below

The API plans presented in this section are developed in accordance with the API 682, 3 revision / API 610, 10 revision standard. This is the standard scheme of the drilling pipes, which are widely used in industry. It is possible to customize these plans to meet the needs of customers.

The flushing of the seal from the outlet to the seal chamber via the aperture and flushing the seals from the seal chamber to the inlet through the diaphragm

Diagram of the system for ensuring the operation of a single seal with an impeller that creates fluid circulation through the stuffing box along an Autonomous circuit.

If the pressure in the oil seal chamber of the pump is less than the design pressure of the tank (4mpa), the installation of a safety valve on the tank pipelines is not required.

"Tandem" type mechanical seals can be used both with a refrigerator at the pump"s working medium temperature up to 400 °C, and without it at the working medium temperature up to 150 °C.

Diagram of the system for ensuring the operability of a double seal with a tank. The system operates at constant maintenance of the pressure of the shut-off fluid (pressure in the tank) within:

At pump working medium temperatures up to 150°C seals are used without a refrigerator, at the temperature of the pumped medium 150...400°C-with a refrigerator.

For servicing seals of a group of pumps that perform the same task and are located close to each other, it is possible to use the system diagram shown below.

The most commonly used scheme is a system with the supply of shut-off fluid from a separate pipeline with an overpressure m through the seal of the threads.

At pump working medium temperatures up to 150°C seals are used without a refrigerator, at the temperature of the pumped medium 150...400°C-with a refrigerator.

For condensate pumps, where dry operation of the mechanical seals is not excluded, the guaranteed supply of the shut-off fluid can be carried out according to the following scheme.

At pump working medium temperatures up to 150°C seals are used without a refrigerator, at the temperature of the pumped medium 150...400°C-with a refrigerator.

API plan 65 allows you to determine the volume of leaks through the mechanical seal. If the friction pair breaks through, the external strapping tank is equipped with an upper-level alarm that will trigger as soon as the liquid level in the tank increases.

To keep mechanical seal systems functioning as long as possible, we recommend using standardized seal piping plans. Detailed API seal piping plans ensure minimal seal face wear by maintaining the optimal seal chamber environment.

Since they were first formulated, seal piping plans have been maintained and remodeled by the American Petroleum Institute (API). Current plans are based on API 682 and are sorted numerically. In some cases, designated letters are also used to differentiate between plans.

Mechanical seal failure due to unfavorable operating conditions is an issue in every industry. Double mechanical seals especially require proper sealing accessories to create suitable operating environments which are key to increasing MTBF. Reservoir systems are one of the most common and effective options to supply cooling fluid crucial to successful seal operation.

A double -or dual – cartridge seal is defined as an arrangement of two mechanical seals in a series. These seals may be configured in various orientations within the cartridge. The seals themselves are referred to as the “primary” (or inboard) seal and the “secondary” (or outboard) seal. A double seal arrangement is the superior option to a single cartridge when it is imperative the product being pumped does not leak into the atmosphere. The API (American Petroleum Institute) Standard 682 classifies dual seals into two configurations. These configurations also apply to ASME (American Society of Engineers) B73.1 and ASME B73.2 pump designs.

Arrangement 2 (Unpressurized) Designs: the buffer fluid is the operating environment for the secondary seal and forms a “buffer” between the process fluid and the atmosphere.

Arrangement 3 (Pressurized) Designs: the barrier fluid is the operating environment for both the inboard and outboard seal, preventing process leakage to the atmosphere.

Buffer and barrier fluids may be either liquid or gas. These fluids lubricate seal faces during operation as well as regulate operating temperatures by moving heat—both generated and absorbed—away from the faces.

Seal support systems are necessary for the smooth operation of a dual mechanical seal. Here are two of the most common piping plans for these systems.

This is an unpressurized system consisting of a reservoir, supply and return lines, and an internal circulation device within the outer seal (commonly referred to as a pumping ring). The buffer fluid circulation rate is dependent on how this circulation device functions during seal operation.

Reservoirs may be fitted with a variety of measurement devices such as a liquid level indicator and pressure gauges as well as valves and switches to aid in various operation and maintenance functions. For instance, a typical support system configuration for natural gas liquids (NGL) would issue an alarm (visual, audible, or both) when the inner seal fails. In addition, the outer seal would take over the primary seal function until maintenance is performed.

This system forces gas from an external pressurized source into the reservoir to pressurize the barrier fluid. This means the reservoir pressure will be above seal chamber pressure; a guideline is a minimum of 20 to 25 psig (1.4 to 1.73 bar) above the maximum process pressure.

The Plan 53A is also used to maintain a specific operating temperature range to ensure optimum lubrication at the seal faces. The reservoir houses a cooling coil which actively cools the barrier fluid as necessary.

As with the Plan 52, a circulation device is used to move the barrier fluid. Replenishing a Plan 53A system with fresh barrier fluid can be as simple as a using a hand pump or a more complex arrangement which satisfies multiple seals.

& 5. Fuels such as diesel or kerosene, and alcohol solutions may also we used, but it is imperative that these fuels be evaluated for safety and compatibility before put into service.

Liquid-lubricated dual mechanical seals require an external source of clean, cool lubricating fluid. The following fluid reservoir systems create this enhanced sealing environment, enabling longer operational life for dual seals.

In the oil and gas industry, reliable seal operation is critical to running efficient, safe processes. In conjunction with API 682 Piping Plans 52 and 53A, seal support systems aid in smooth seal operation.

If you require an engineered seal support system or are interested in additional options to Flexaseal’s ANSI PLUS and ANSI LITE support systems, please contact our applications engineering team.

The mechanical seal is the most likely part of the pump to fail.  Approximately 70% of the pumps removed from service for maintenance are victims of mechanical seal failure.  Mechanical seal parts are highly engineered with very close tolerances and any upset in the pump or associated system can cause seal failure, including:

Mechanical seals are based on positioning two very flat and smooth discs called seal faces, one rotating on the shaft and one stationary in the pump, against each other.  The discs are flat and smooth enough to ALMOST prevent the pumped fluid from leaking out between them.  However, the faces do rely on a very thin film of fluid between the faces to lubricate that rubbing fit.  Without this film of fluid, the seals will overheat and fail.  Lack of lubrication is the PRIMARY cause of seal failure.  If the fluid is very hot, it can flash to a vapor as the fluid moves across the faces, again resulting in lack of lubrication.  Note that gas seals use a gas film between the faces to minimize face contact and heat buildup.

Seal flush plans are intended to keep the area around the seal in the most seal friendly environment practical, usually meaning clean and cool.  Dual seal plans also provide backup and leak detection for safety.

Note that seal flush plans use pressure differences at the pump to drive the flush fluids.  The pump suction is low pressure, the seal chamber is a medium pressure, and the pump discharge is at high pressure.

As the seal faces faces rub together (with their thin film of lubricating fluid), they generate heat.  The heat can build up in the seal chamber and push the fluid towards its boiling point, resulting in premature flashing, lack of lubrication, and failure.  This first set of seal plans is intended to create circulation through the seal chamber to dissipate the heat out of the seal chamber and back into the pumped fluid.

Flush fluid flows from high pressure at pump discharge to the medium pressure seal chamber and back into the main flow to remove heat from seal chamber

Can be used to increase seal chamber pressure.  Increased chamber pressure may be required to keep chamber fluid from flashing to vapor or to provide enough pressure to push the fluid between the faces for lubrication. (Seal chamber must be 5 psi minimum above external atmospheric pressure).

These seal plans are intended to provide the seal with the friendliest environment possible by cooling and/or cleaning the fluid in the seal chamber.  The throat that separates the seal chamber from the main pumped fluid can be further restricted by adding a close clearance bushing in the bottom of the seal chamber, better isolating the cool, clean seal chamber fluid from the hot, abrasive fluid in the pump.

Rather than a Plan 21 single pass system, a Plan 23 is a multi-pass system.  Fluid comes FROM THE SEAL CHAMBER instead of the pump discharge, is cooled, and directed back to the seal chamber.

Fluid is driven out of the chamber and through the cooler by “pumping ring” or other “pumping feature” built into the seal.  These features provide very little differential pressure.  Connecting tubing must have long, sweeping bends, well vented high points, and low point blowouts to ensure fluid flows.

Quench piping does NOT change conditions inside the seal chamber, at the wet side of the seal faces.  Rather, it affects or monitors the environment on the ATMOSHPERIC side of the seal faces.

Pumps that leak when they are filled, even before they are started, often have a flush line intended for a Plan 11 or 13 connected to the QUENCH port, leading to the atmospheric side of the seal.  There should be a “Q” or the work “QUENCH” stamped in the gland at this port.

For flush plans Plan 65A, 65B, 66A, and 66B, facility owners may want to know if their seals are leaking excessively without going to the expense of dual seals.  These seal plans direct excessive leakage on the outside of the seal to an alarm instrument.  Remember that seals leak a little bit.  They need to in order to lubricate the faces and function correctly.  The plans below handle the nuisance leakage in different ways.

Used in salting services like sodium hydroxide.  The leakage across the seal faces will turn to salt when it reaches atmosphere.  The salt crystals can wear the faces or build up in the seal, preventing the movement necessary to keep the seal faces in contact.  The salt on the outboard of the seal can be washed away with a water quench through the quench and drain ports.  Usually a close clearance bushing is installed at the extreme outboard end to the seal assembly to help keep the quench fluid moving from the quench to the drain port (or vice versa) and not just run out along the shaft.  Also used for slurry services.

Grease can be introduced into the quench port.  This external grease can provide temporary lubrication to the seal in case the pump sees large air or vapor pockets which would normally rob the seal faces of the required lubricating fluid film.

Quench can also be gas.  In hot hydrocarbon services, the fluid will turn to solid coke when it reaches the atmospheric side of the seal.  The fluid would remain a liquid if the area outside the seal faces is robbed of oxygen with a flood of nitrogen or steam.

An alarm does NOT necessarily mean a failed seal.  The collection vessel might be full from years of nuisance leakage.  Try emptying the vessel and observing how fast the vessel fills.

Two throttle bushings are used to ensure that the vapor (or fluid) leakage is limited along the shaft and out of the drain.  A pressure switch picks up a rise on pressure above nuisance levels on the outboard side of the seal.

Dual seals provide a backup seal in case the primary seal fails.  They prevent hazardous fluids from leaking to the surrounding area, desirable for both environmental protection and the safety of nearby personnel.  Dual seals also capture and control any leakage of pumpage across the primary seal. The backup seal is kept lubricated by introducing a buffer/barrier fluid (often a mineral or synthetic oil, a water/glycol mix, or diesel) into the space between the primary (inboard) and secondary (outboard or backup) seals.  The buffer/barrier fluid is contained in a tank (5 gallons is most common) adjacent to the pump.  Instrumentation on the tank indicates what is happening with the seals.

Remember that a lubricating fluid film will flow from high pressure to low pressure.  If the pump seal chamber pressure is higher than the pressure on the other side of the seal, the pumpage will be the lubricating film.  If the pump’s seal chamber pressure is lower than the external pressure, the external atmosphere will migrate into the pump.  Pumps under vacuum cannot use an ordinary single seal, since air from the atmosphere would be drawn between the faces, causing them to run dry and fail. Using a dual seal allows a fluid to be present at the outside of the seal.  In a pump under vacuum, the buffer fluid would be pulled into the pump between the seal faces, keeping the inboard seal well lubricated.

If the pump seal chamber pressure is higher than the BUFFER fluid between the primary and backup seal faces, then the pumped fluid will flow from the high seal chamber pressure into the low pressure buffer fluid.  This is called a DUAL UNPRESSURIZEDseal (formerly called a tandem seal), and the fluid is called a BUFFER fluid.

If the pump seal chamber pressure is lower than the BARRIER fluid between the primary and backup seal faces, then the barrier fluid will flow across the primary seal from the space between the primary and backup seals into the pump.  This is called a DUAL PRESSURIZEDseal (formerly called a double seal), and the fluid is called a BARRIER fluid.

Buffer fluid circulates from the buffer fluid reservoir, through the space between the primary and backup seal, and back to the reservoir.  Fluid is circulated by a weak pumping action built into the seal.

It the fluid flashes to vapor at low pressure, the vapor is piped to a flare or vapor recovery system, through an orifice at the top of the tank.  If the primary seal is allowing too much leakage, the vapor will build pressure in the reservoir against the orifice and a pressure instrument can alert the operator.

If the fluid remains as a liquid under low pressure, any leakage will cause the fluid level in the buffer tank to rise, where a high level alarm can be tripped.  Just because the high level alarm is tripped does not mean that the primary seal is failing; it is the rate of leakage filling the tank which matters.  The high level may have been reached after collecting years of nuisance leakage.  Often, an oil change to the original level is all that is required.  Be sure the fluid is disposed of properly.

Seal face friction or hot pumpage can add heat to the buffer fluid.  A cooling water coil is often installed in the reservoir to cool the buffer fluid.

Dual pressurized system (seal barrier fluid is at a higher pressure than the pump seal chamber).  Pressurized systems are used to ensure that very dangerous fluids remain in the pump.  The difference between 53A, 53B, and 53C is the method of pressurizing the barrier fluid.  Pressure in the barrier fluid should be at least 10 psi over the pressure in the pump seal chamber.

Barrier fluid circulates from the barrier fluid reservoir, through the space between the primary and backup seal, and back to the reservoir.  Fluid is circulated by a weak pumping action built into the seal.

A low level alarm in the reservoir alerts the operator that a seal may be failing, allowing the barrier fluid to enter the pump through the primary seal or the atmosphere through the backup seal.

Seal faces can be designed to maintain a gas film between them rather than a fluid film.  These piping plans are intended to work with theses gas film (dry running) seals.  Plan 72 and 74 bring the buffer or barrier gas into the seal; plans 75 and 76 are for the gas exiting the seal.

Secondary seal is ordinarily running with a gas film between the faces.  When the primary seal fails, the pumped fluid will fill the space between the primary and backup seal.  The backup seal is now working as a liquid seal rather than a gas seal and is designed to run for about 8 hours, allowing the operators time for an orderly pump shutdown.

Plan 72 buffer gas flow keeps the gas in the seal from becoming concentrated from nuisance leakage over time so that any leakage from the gas backup seal is mostly inert flush gas and not toxic pump vapors.

Seal Support Systems operate to control the fluid in between and around the seal faces whether cleaning, cooling or heating the seal media or providing a separate fluid to the mechanical seal.

Some applications are simply not suitable for mechanical seals e. g applications which are corrosive, abrasive, crystallizing or precipitative. In order for a mechanical seal to operate under these applications with reasonable mean time between failure (MTBF), either the seal fluid requires treatment before coming into contact with the seal faces or an external fluid is required which is compatible with the process. Also double mechanical seals will require some sort of fluid to act as a buffer or barrier fluid andthe system which provides this buffer or barrier fluid are Seal Support Systems.

A seal plan is used in conjunction with the API 682 Standard and it is a way to formalise the different seal support systems into a standard. It consists of seal flush plans, buffer & barrier fluid plans, quench plans and gas supply plans.

The API Plan 53A is a dual seal plan where a barrier fluid is supplied to a double mechanical seal between the 2 sets of faces of the mechanical seal.

Plan 62 is a quench seal plan where a fluid is supplied to the space between the atmospheric side of the mechanical seal and the throttle bushing on the shaft.

Flowserve provides Seal Support Systems for in accordance with API 682 but can also provide systems outside of this standard, if the application dictates.

Our Mechanical Seal specialists can advise you on the appropriate selection of a seal support system which will deliver years of reliable service and operating cost savings in the longer term.

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 PD 76 (API Plan 76) system diverts non-condensing inner seal leakage from a dual unpressurized seal where the outer seal is dry running, to a flare or vapor recovery system.

The SO-1 buffer / barrier fluid reservoir is designed to contain barrier fluid for a tandem or double mechanical seal, to provide its cooling and to control mechanical seal performance. The SO-1 barrier fluid reservoir can be used with flush plans API 52 or 53 as per API682. To operate under the API 53 Plan, the barrier fluid tank can be equipped with a manual fluid make up pump.

The reservoir can be fitted with instrumentation and control for automatic checking of mechanical seal performance and pump shut down in case of mechanical seal failure. The instrumentation and control version of SO-1 can additionally include a level sensor, a pressure switch, and a temperature sensor. Sensors and switches are either intrinsically safe or explosion proof depending on customers order.

The rare feature of this buffer fluid reservoir is that it can be disassembled for cleaning if the heat exchanger gets fouled. The heat exchanger has straight tubes that can be mechanically cleaned.

One of PPC Mechanical Seals competitive advantages in the marketplace is our knowledge, experience, and facilities to repair and recondition all major brands of mixer seals. In addition, we can manufacture and design completely new seals for your units. PPC utilizes a dedicated mixer seal repair cell and is experienced in handling shaft diameters up to 9”+ inches. Our dedicated cell and experience mean that PPC has the fastest turn around in the industry for these types of seals.

In LIDERING we have an extensive range of mechanical seals for all types of pumps: from seals for domestic pumps to seals for process pumps, specific in complex applications in the chemical and petrochemical industry. In addition, we offer a wide range of spare parts compatible with the originals of the main manufacturers of pumps (RMS). Our catalog also includes cartridge seals for more demanding industrial processes, and our extensive range of products is ever-growing in order to adapt to the requirements of our customers.

API Standard 682, titled "Pumps - Shaft Sealing Systems for Centrifugal and Rotary Pumps," is the American Petroleum Institute (API) standard for end-face mechanical seals.centrifugal pumps. It is based on the combined knowledge and experience of seal manufacturers, engineering companies, and end users. API 682 is primarily intended for use in the petroleum, natural gas and chemical industries, but is often referenced for other types of equipment and industries.

By the late 1980s, mechanical seals had been accepted as the preferred method for sealing rotating pumps for many years. However, mechanical seal standards were generally buried in other standards such as DIN 24960, ANSI B73, and API 610. All of these standards were primarily pump standards and any references to seals were directed at how mechanical seals would interact with pumps.

API 610 is the API standard about centrifugal pumps and is primarily intended for use in the petroleum, natural gas and chemical industries. Although the 1st through 7th Editions of API 610 included specifications for mechanical seals, beginning with the 8th Edition, API 610 defers to API 682 for seal specifications.

In the late 1980s a group of refinery equipment engineers and managers began to compare sealing solutions in refinery applications. This group, led by V. R. Dodd of Chevron, came up with a general plan and the American Petroleum Institute (API) agreed to establish a standard for mechanical seals: API 682. A Task Force was formed in 1990 and the first meeting was held in January 1991. This Task Force was composed of fourteen members from various refineries, seal and pump manufacturers. API 682, First Edition, was published in October 1994.

One interesting aspect of API 682 is that it includes a strong set of defaults. That is, unless the user indicates otherwise, API 682 makes default choices for specifics such as:

Some statements within API 682 are normative, that is, required, whereas others are informative, that is, descriptive but not required. In particular, many of the illustrations are informative. This distinction has not always been apparent to the reader.

The first edition of API 682 was entirely new although parts of it were extracted from the pump standard API 610 and existing API standard paragraphs.

Although this mission statement no longer appears in the standard, it remains the basic principle driving the work of the API 682 Task Force and its relevance remains the same for the 4th Edition as it did for the 1st.

In addition to providing requirements for mechanical seals, the 1st Edition of API 682 also provided a guide on how to select the correct seal for a number of common refinery applications. In order to provide this seal selection guide, it was necessary to categorize applications into a number of services:

Prior to API 682, 1st Edition, multiple seals were designated as being either “tandem” or “double” seals; however, advances in seal design had rendered these classic terms obsolete. As a result, there was some confusion on how multiple seals were designated. The task force decided to use a more descriptive designation and chose to define dual seal arrangements. A dual seal would be two sets of sealing faces used in the same seal chamber. The fluid between these two sets of sealing faces could be either pressurized or unpressurized. Three standard arrangements were defined:

After having defined the services, seal types, and seal arrangements, a series of flowcharts were created to help in selecting a seal type, special materials or design requirements, and supporting piping plans.

API 682 seals were to have a high probability of three years of reliable service. In order to prove this, seal performance testing on process fluids under representative pressures and temperatures was required. These performance tests are called “Qualification Tests”.

The general idea of the qualification test was to prove that the design was sound. The goal of the qualification test was to simulate a long-term steady state run followed by a process upset. The simulated process upset consisted of pressure changes, temperature changes and included loss of flush. The results of these tests were made available to the purchaser for evaluation. There was no acceptance criteria presented in API 682 1st Edition.

In addition to the qualification test of the design, every API 682 seal, whether new or repaired, is to be pressure tested with air before being shipped to the end user.

One of the major criticisms of API 682 1st Edition was that all the seals were “heavy duty” and therefore expensive with no alternatives for easy services. To some degree, this was intentional and was done in order to reduce inventory, promote familiarity with a limited number of seal types and to increase reliability. Another criticism of API 682 1st Edition was that it considered only API 610 pumps and only refinery applications. The chemical and petrochemical industries routinely use ASME pumps in addition to API 610 pumps. Broadening the scope of pumps covered by API 682 would allow standardized seals to be applied in a greater number of industries.

In 2nd Edition, the organization of API 682 was changed to conform to ISO standards: This reorganization means that there is no simple cross reference guide between 1st edition and 2nd edition paragraph numbers.

The 2nd Edition introduced the concept of seal categories. A seal category describes the type of pump into which the seal will be installed, the operating window, the design features, and the testing and documentation requirements. There are three categories designated as Category 1, 2, or 3.

Category 1 seals are intended for non-API-610 pumps. This category is applicable for temperatures between –40°F and 500°F (-40°C and 260°C) and pressures to 315 PSI (22 bar).

Category 2 seal are intended for API-610 This category is applicable for temperatures between –40°F and 750°F (-40°C and 400°C) and pressures to 615 PSI (42 bar).

Category 3 seals are essentially the original seals of 1st Edition and are also intended for API-610 pumps. Category 3 seals are intended for the most demanding applications. This category is applicable for temperatures between –40°F and 750°F (-40°C and 400°C) and pressures to 615 PSI (42 bar). Design features include a distributed flush and floating throttle bushing for single seals. Additional documentation must be also provided.

Containment seals are the outer seal of Arrangement 2. In the 2nd Edition, containment seals can be used with a liquid buffer fluid, a gas buffer fluid or without a buffer fluid. In the case of a dry running containment seal, the containment seal will be exposed primarily to buffer gas or vaporized process fluid. Such containment seals must therefore be designed for continuous dry running while meeting the reliability goals of the standard. Dry running containment seals may be either contacting or non-contacting.

Non-contacting inner seals are also introduced for Arrangement 2. One of the primary targets for non-contacting inner seals is in flashing hydrocarbon services. In some of these services, it is impossible to obtain adequate vapor margins to prevent flashing of the fluid in the seal chamber. This seal will be used with a dry running containment seal and the leakage past the inner seal will be piped to a vapor recovery system.

The other new seal type introduced in 2nd Edition was the dry running gas seal used in Arrangement 3. This seal is designed to run on a gas barrier fluid such as nitrogen.

Several new piping plans were introduced in the 2nd Edition. These included additional options for dual pressurized liquid seals as well as new piping plans to support containment seals and dual pressurized gas seals.

One of the strengths of the 1st Edition was to provide qualification tests in which seal vendors would be required to prove the suitability of their seals for a given service. The 2nd Edition expanded on these requirements by adding new tests for containment seals and dual gas seals as well as defining acceptance criteria for all tests.

For all practical purposes, API 682 3rd Edition is the same as 2nd Edition. The completed 2nd Edition was submitted to the ISO Organization for approval as their ISO 21049. At the time, API and ISO had an agreement to jointly issue standards. The ISO Organization made slight editorial changes to 2nd Edition, including correcting typographical errors and unit conversions. Therefore, API had to re-issue a corrected 2nd edition but choose to label it as 3rd edition. API 682 3rd Edition was published in September 2004.

API and ISO no longer have the agreement to jointly issue standards. The 2004 issue of ISO 21049 is the only issue and plans to update it are unknown.

Seal Configuration refers to the orientation of the seal components in an assembly. In previous editions, orientations were defined as face-to-back, back-to-back, and face-to-face and these terms are carried over into the 4th Edition. In 4th Edition, any orientation (face to back, back to back, face to face) can be used in a dual seal provided that the design features are appropriate to the functionality of that particular arrangement.

Fourth Edition added additional specifications for clearances, placed these requirements in the form of tables and noted that seal components are not to be considered as “shaft catchers” to restrict shaft movement. The minimum clearances specified apply only to equipment within the scope of the standard. Equipment outside that scope, such as non-cartridge seals, older pumps, non-API 610 pumps and certain severe services, might benefit from larger clearances.

Before API 682, API 610 (the pump standard) used a simple seal code to specify seals. API 682 attempted to use a more comprehensive seal code; however, that code changed with every edition of API 682. The 4th Edition code, described in Annex D, is probably the best to date and includes some concepts and codes from the historical API 610 seal code.

Annex G provides illustrations and a short tutorial about each piping plan. As has been the case for every edition, changes were made to the standard piping plans. In particular, the piping plans now default to using transmitters with local indicators as part of the instrumentation.

API standards are reviewed every five years and re-issued every ten years. A new Taskforce for API 682 was formed in 2017 and preparations for 5th Edition are underway.

Buck, G. S., Huebner, M. B, Thorp, J. M., and Fernandez, C. L. “Advances in Mechanical Sealing – An Introduction to API-682 Second Edition”, Texas A&M Turbomachinery Symposium, 2003.

API Standard 682, Second Edition, 2001, “Pumps – Shaft Sealing Systems for Centrifugal and Rotary Pumps,” American Petroleum Institute, Washington, D.C.

API Standard 682, Third Edition, 2004, “Pumps – Shaft Sealing Systems for Centrifugal and Rotary Pumps,” American Petroleum Institute, Washington, D.C.

API Standard 682, Fourth Edition, 2014, “Pumps – Shaft Sealing Systems for Centrifugal and Rotary Pumps,” American Petroleum Institute, Washington, D.C.

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.

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.

Single cartridge seal with double hydraulic balancing. The seal has a V-ring to contain the continous quench, ideal for pumps with fluids that tend to crystallise on the atmosphere and which require washing.

FeaturesSprings outiside the product and clean profile for enhanced reliability even with viscous products that crystallise, and also in processes which require thorough cleaning.