FACTORS AFFECTING THE SELECTION OF MECHANICAL SEALS

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“FACTORS AFFECTING THE SELECTION OF MECHANICAL SEALS” 

1. Media Handled :

Corrosiveness of media decides the material of construction.
• Density of viscosity shows the lubricating properties of the media. This decides the seal arrangement.
                   

• Abrasives in the media decides the type of flushing plan required Corrosiveness of media decides the material of construction.
• Density of viscosity shows the lubricating properties of the media. This
decides the seal arrangement.
• Abrasives in the media decides the type of flushing plan required.

2. Stuffing box pressure :

• When stuffing box pressure < 10 kg. / cm2, unbalanced seals are used.
• When stuffing box pressure . 10 Kg. / cm2 , balanced seals are used.

3. Shaft Speed :

• With increase in speed the chance of seal running dry increases. So proper
flushing plan has to be decided which can give positive flush between the
faces.

4. PV Factor :

• PV factor is defined as the product of the pressure drop across the seal and
the average rubbing velocity. As a general guide, Seal capabilities can be
classified as, Low , if the PV value is 0.7 MPa m/s ( about 20,000 psi ft/min)
Medium, if the PV value is between 0.7 and 10 MPa m/s ( about 285,000 psi
ft/min) High , if the PV value ranges from 10 to 70 MPa m/s (about 2,000,000 psi
ft/min). Balanced seals reduce the pressure acting on the seal faces, therefore they have higher PV values than unbalanced seals.

5. Temperature :

• This decides the material of construction so that the seal does not fail at operating temperature.
• This will decides the seal flushing plan.

7 CONSIDERATIONS FOR MECHANICAL SEAL SELECTION

Globe Star engineers (India) PVT. ltd.

presents

7 CONSIDERATIONS FOR MECHANICAL

SEAL SELECTION

                                                 

Mechanical seals can operate for many years without issue, as long as they've been properly selected for their application. One must identify the application data (or operating conditions) to properly select the type of seal and materials of construction to ensure maximum performance from the seal over its lifetime. Below we define the operating conditions and discuss what material characteristics to consider for preventing improper material selection.

**Please note: There are many things to evaluate when selecting a seal, so be sure to speak with an experienced engineer before your final selection is made. 

LIQUID

Identifying the exact liquid being handled is the first step in the seal selection process. Seal material must be able to withstand the fluid being processed. All seal materials must be chemically compatible with the fluid, or there is an increased risk of seal failure. 

PRESSURE

Pressure in the seal chamber and seal size determines the type of seal required, balanced or unbalanced.

TEMPERATURE

Seal materials must be selected to appropriately handle the liquid’s temperature. Temperature is important because different seal materials are rated for certain temperatures and you should not exceed the temperature limit of these materials. 

LIQUID CHARACTERISTICS

Knowing the viscosity of the liquid is important to ensure appropriate seal life. Abrasive liquids can create excessive wear and will ultimately shorten the seal's life. Double seals or use of an external flush plan give operator's the option to use mechanical seals on these difficult fluids.

RELIABILITY & EMISSION CONCERNS

every company has their own standards and operating procedures when it comes to reliability and emission concerns for an application. The seal type and arrangement selected must meet the desired reliability and emission standards for the pump application. Since environmental safety has become a hot topic among manufacturing companies, double seals are peaking as the solution of choice.

After understanding the seal's exact operating conditions, you can select the seal's overall construction material and its face and component materials. When selecting the seal's material of construction, be sure to consider the following characteristics of the material:

• Temperature constraints
• Chemical resistance properties
• Flexibility 
• Wear resistance
• Thermal expansion and conductivity properties

And, when selecting the face and other component materials for the seal, consider these material characteristics:

• Wear resistance
• Low leakage & friction properties
• Good thermal properties
• Corrosion resistant

Industrial Water Pump Seal

Globe Star Engineers(India) Pvt. Ltd.

Manufacturer of Several Types of Mechanical seal, water pump seal, Rotary joint and Chemical process pump.

Industrial Water Pump Seal

Water Pump Seal

Water Pump Seal - Globe Seal is the largest manufacturer of water pump seal in India. We offer highly engineered Industrial water pump seal.

Industrial Water Pump Seals Suppler, Metal Water Pump Seal

Industrial Water Pump Seals Suppler - get metal water pump seal from globeseal.com! We are top best water pump seals Manufacture Company in India.

We have developed OP, G301, G155, G2100, G1, SB70 series of the seals. The industrial water pump seals are made of best quality raw material with technologically advanced instruments and machines. The seal can be varied as per requirement. Industrial Water pump seal is highly reliable and has long functional life.

·          

           

•        Easy to install and easy to operate
•          Perfectly finished
•          Dimensionally accurate
•          Sturdy construction 

   

    Types of Water pump seal. 

      1. Series G301

  

Application : Water, Sewage Oil Pump, Generators, Muddy Water

Features : Internal Mounting, Single acting. Independent of Direction of Rotation

Operating Conditions : -20°c .....to 100°c

Pressure : Upto 10 Bar (kg/cm 2)

Available Size : 10 mm.........100 mm

Shaft Speed : 5 m/sec.

    

    

     2.Series G155

   

     

Application : Water, Light Chemicals Viscous Fluids

Features : Single Acting, Dependent of Direction of Rotation

Operating Conditions : Temperature -20°c ...to 150°c

Pressure : Upto 10 Bar (kg/cm 2)

Available Size : 10 mm.........100 mm

Shaft Speed : 7 m/sec.

    3.Series G2100

    

Application : Water, Steam, Light Chemicals   Solvents

Features : Single Acting. Dependent   on Direction of Rotation

Operating Conditions : Temperature -20°c ...to 150°c

Pressure : Upto 10 Bar (kg/cm 2)

Available Size : 10 mm.........100 mm

Shaft Speed : 10 m/sec.

4.Series OP

Application : Water, Sewage Oil Pump, Generators, Muddy Water

Features : Internal Mounting, Single acting. Independent of Direction of Rotation

Operating Conditions : -20°c .....to 100°c

Pressure : Upto 10 Bar (kg/cm 2)

Available Size : 10 mm.........100 mm

Shaft Speed : 5 m/sec.

5.Series G1

Application : Water, Sewage Service, Light Chemicals, Muddy Water.

Features : Internal Mounting, Single Acting, Independent of Direction of Rotation.

Operating Conditions : Temperature -20°c ...to 150°c

Pressure : Upto 10 Bar (kg/cm 2)

Available Size : 10 mm.........100 mm

Shaft Speed : 10 m/sec.

Rotary union

Rotary union

This image shows the components needed to make a rotary union; a shaft, housing, bearings, seals and retaining clip. The independent shaft and housing allow for continuous rotation of either component. This is an example of a two passage rotary union with independent channels that allow both liquids and gases to transfer simultaneously. ^[1]

A rotary union is a union that allows for rotation of the united parts. It is thus a device that provides a seal between a stationary supply passage (such as pipe or tubing) and a rotating part (such as a drum, cylinder, or spindle) to permit the flow of a fluid into and/or out of the rotating part. Fluids typically used with rotary joints and rotating unions include various heat transfer media and fluid power media such as steam, water, thermal oil, hydraulic fluid, and coolants. A rotary union is sometimes referred to as a rotating union, rotary valve, roto rseal, rotary couplings, rotary joint, rotating joints, hydraulic coupling, pneumatic rotary union, through bore rotary union, air rotary union, electrical rotary union, vacuum rotary union

Rotary Joint Function, Types and Uses.

 

Function

A rotary union will lock onto an input valve while rotating to meet an outlet. During this time the liquid and/or gas will flow into the rotary union from its source and will be held within the device during its movement. This liquid and/or gas will leave the union when the valve openings meet during rotation and more liquid and/or gas will flow into the union again for the next rotation. Often functioning under high pressure and constant movement a rotary union is designed to rotate around an axis. A rotary union’s design can be altered to change this or to increase the psi or rpm it needs to withstand as well as the number of valves required.

Types of Rotary Unions

Many rotary unions incorporate multiple ports, some of which are designed to handle different types of material simultaneously. A rotary union with a straight port transfers the substance directly through the rotary union. Other designs include an elbow port, which causes the material to flow out at an angle, and multiple ports. A multiple port rotary union looks like a perforated cylinder. At the end of the cylinder is a threaded screw with seals that locks on to the output. The material being transferred flows into the cylinder and out of the input holes. In the case of a rotary union with multiple inputs, chambers separated by seals keep the materials from inadvertently mixing. This type of rotary union is often used in the manufacture of plastics and other petroleum products, for which multiple inputs may need to be streamlined, but kept separate.

Uses

Many assembly lines incorporate multiple rotary unions, because they are highly versatile and take up less space than other devices designed for a similar purpose. Rotary unions also appear in automobiles and other machines that require constant supplies of lubrication, air, or other liquids in order for moving parts to run smoothly. Brakes, for example, use rotary unions to maintain a constant supply of pressurized brake fluid. Rotary unions are also heavily used in crude oil processing, the chemical industry, commercial food production, and pharmaceutical applications.

Why Liquid Pump Seals Fail

Why Liquid Pump Seals Fail

When operating rotating equipment, some end users do not pay enough attention to transient conditions. Startup, slow-roll and standby pump conditions must be evaluated to ensure proper sealing fluid is being supplied to the seals at all times.

Startup: The pump is charged, but at or near suction pressure. Liquid ethane at the seal faces is slowly leaking and vaporizing. When the pump starts, how long does it take to build the right pressure in the stuffing box and get the pressure above vapor pressure? Additionally, the heat generation between the faces, although not significant, could be enough to increase vapor pressure and vaporize the fluid across the faces. Damage to sealing faces could be a telling sign that this is occurring.

Slow-roll: The same situation as startup but compounded. Without the right speed, the discharge pressure is not generated. The pressure in the stuffing box is not rising quickly enough to ensure the ethane will reach a high enough pressure to overcome the vapor pressure. Also, the heat generation between the contacting faces is increasing, and damage is probably taking place.

Standby: All conditions mentioned above are the same, but the seals are sitting idle for many months without a flush to the seals. During the standby time, evidence has shown that debris has collected at or around the seal faces, which, in turn, adds more complication to the sealing environment.

Inefficient operation: Operating the pump too far outside of the best efficiency range and with the wrong operating parameters results in increased demand for drive power and reduced discharge pressure. Both of these negatively impact the vapor margin in the seal area, which can result in dry running.

4 Ways to Prevent Seal Failure

Globe Star Enigneers(India) Pvt. Ltd. Presenets

4 Ways to Prevent Seal Failure

The life expectancy of a mechanical seal is determined by a wide variety of factors, most of which are independent from the seal design. Seal selection, installation technique, equipment startup procedure, operation, seal storage conditions, product variables and seal support systems all play a part in how long a seal will last.

Even with so many variables, there are steps users can take to prevent seal failure and increase seal life. Here are four proven methods to ensure any seal operates in peak condition for as long as possible.

1.     Choose the Correct Seal

Lack of knowledge and information is an obstacle in the seal selection process. Before deciding on a seal, carefully consider the application and normal operating conditions, as well as any potential off-design usage. For example, selecting a seal to operate in hot water may seem easy because the medium is not particularly difficult. However, if the application is boiler feed water, this assumption is incorrect. Hot water at temperatures above 190 F is unable to appropriately lubricate and cool the seal faces. The sealing process is then compromised by elevated friction between the two mating faces and will culminate in premature seal failure.

To solve this issue, the user must determine if the correct operating parameters are being maintained, then talk with the seal supplier to verify the appropriate American Petroleum Institute (API) flush plan and to choose the correct seal face combination and elastomer materials. Every application has unique requirements, and the proper seals are designed specifically to overcome application challenges.

2. Properly Install the Seal

Seal installation should be performed using the steps outlined by the manufacturer and with great care to avoid damaging the delicate seal faces and/or O-rings. Common issues that may occur when installing a seal include forgetting to tighten set screws before removing setting clips, not tightening gland bolts evenly, damaging O-rings, nicking seal faces or incorrectly using the piping connections. Improper seal installation caused by a lack of knowledge is a significant factor in most seal failures.

Component seal installation is inherently more prone to installation errors when compared with cartridge seals because of the extra steps and measurements needed. This is why, if possible, users should choose a cartridge seal over a component design. There is already enough to be meticulous about when installing a mechanical seal; why add additional opportunity for mistakes?

3.     Prevent Excess Heat Generation

Excessive heat generation between seal faces will drastically reduce seal life. Dry-running is the most common example of this issue. It typically occurs when a pump is flooded and/or the seal chamber is incorrectly vented before pump startup. Other situations can also lead to excessive heat generation and dry-running.

For example, the seal chamber's pressure can exceed the seal's design parameters during upset conditions. In this situation, contact the seal manufacturer. The seal design may need to be altered if condition fluctuations are an ongoing issue.

 

The use of API 682 flush plans and seal support systems is generally recommended for all applications. Piping plans such as Plan 11 (flush line from pump discharge), Plan 13 (recirculation to pump suction) or Plan 53A (pressurized barrier fluid with a seal reservoir) can be simple or highly complex, but they all have the same goal: to keep the seal faces clean, cool and well-lubricated.

The correct seal support system (based on API 682 flush plans) will have an overwhelming impact on the overall success of production. For example, if abrasives are present in the product, the seal manufacturer may recommend changing a softer carbon face to either silicon carbide or a tungsten carbide face. This hard face combination has proven to be successful in abrasive services. However, if there are no abrasive solids or chemical issues with the process fluid, the carbon versus silicon carbide face may be the best seal face combination to achieve long seal life. In all cases, it is easy to remember: A cool-running seal is a happy seal.

4.     Maintain Proper Storage Conditions

Mechanical seals are composed of many unique parts formed from a variety of materials. Because of the diverse properties and the precise, delicate nature of these components, it is important to understand how long a seal can be stored safely without compromising function.

If the following procedures are followed and the seal is stored in a clean, temperature/humidity-controlled environment, a seal can be stored effectively for five years.

To store a new seal for less than two years, store it in a clean, cool environment. Prevent face lock and loss of face flatness by rotating the seal faces against each other (by rotating the sleeve or shaft) two turns every three months if the seal is not used in operation during that time.

To store a new seal on a shelf for more than two years or to store a seal that has been in service already and will be stored for more than one year:

·        Disassemble the seal and store all parts as individual components. Ensure that O-rings are in a relaxed state and meet the appropriate environmental conditions. For a seal that has been in service, clean and dry all components before storage.

·        Plug all openings in the seal's gland as well as the unused pump's seal chamber.

·        Do not store seal faces (silicon/carbon/tungsten) together in the same packaging. Faces are best separated into individual, protective, bubble-wrapped package

To reassemble the seal after storage:

·         Check O-rings for cracks, cuts and wear, and lubricate O-rings for easier assembly.

·         If O-rings are damaged or have experienced compression set, replace them.

·         Check mating ring/seal ring for cracks or chips, especially on the sealing faces. If they are damaged, contact the vendor for a replacement.

These are just a few of the basic recommendations for storage, maintenance and reintroduction to service for a mechanical seal. For more details, see international standards such as Detaches Institute für Normung (DIN) 7716 and International Organization for Standardization (ISO) 2230, which detail fundamental instructions on the storage and maintenance of elastomeric seal elements.