Mechanical Seals

the initial symptoms indicates the seal problem

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Typically, the first symptom will be some level of leakage. This could range from a small tight spray on the outside of the seal that can be felt on the hand to a full spray out of the back of the seal to a continual drip. Another common symptom is a squealing sound that results when the seal cannot maintain a barrier/buffer fluid. Depending on the type of seal and the American Petroleum Institute (API) piping plan, symptoms could also include leaking of process water into the product or material being pumped. This may dilute the process, or it must be treated further down into the system separate contaminants.

What can cause a mechanical seal to leak or fail?

The loss of the liquid film, or lubricant, between the faces of a mechanical seal is the largest cause of seal failure. This usually results due to a lack of maintenance on the seal’s lubricating parts. Sometimes a seal fails because it wasn’t the right type of mechanical seal for the application. Other causes include improper assembly or installation, cavitation, and improper operation of the pump itself.

What can cause the seal to lose lubrication?

Losing lubrication to the mechanical seal faces can result from a number of factors. Some of these include dry start up, suction loss, plugged flush orifice, increased temperature, the wrong balance, or contamination in the cooler, water jacket, or flush lines.⁴

life cycle cost benefit to mechanical seals over regular packing

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Initially, a mechanical seal will cost significantly more than packing. However, when all of the maintenance and operation costs are taken into consideration, mechanical seals are the most cost-effective way to efficiently control and seal fluids in a manufacturing process. With packing, there are costs involved in repacking the pump at least twice a year and downtime for repacking. Because packing wears and cuts into the sleeve of the pump, there are potential costs in replacing any worn sleeves. There are also costs from the loss of product that comes from increased leakage with packing. If the product being pumped is hazardous, it must have piping to run to a drain and be treated. What’s more, because of the higher rate of friction, packing consumes more electricity than mechanical seals. If maintained properly, the life cycle of a mechanical seal can be two to three times that of packing.

Let’s look at the energy savings alone. Presume that 10 percent of a 30 HP motor’s horsepower is used in friction against the packing, and one HP equals one kW of energy. The packing then uses three kW per hour of electricity, and at a rate of 8 cents per kW, times the number of hours in a year (8760), the cost of energy using packing is $2,102.40. A mechanical seal uses only 1/6 of the electricity, which would result in a cost of $350.40. The cost savings in terms of energy alone then is $1,752.00.³

mechanical seals differ from regular packing

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Like day and night. Conventional packing requires a lubricant so as not to burn up while the shaft is turning on the equipment. Often the material being pumped serves as the lubricant. However, as a result, packing needs to leak a little to function properly. Mechanical seals, on the other hand, can achieve practically a leak-free environment. With tighter environmental emission regulations placed on manufacturers, this becomes even more important.

Packing requires a higher level of attention and maintenance than mechanical seals. Packing must be adjusted and repacked periodically. What’s more, packing tends to wear on pump parts, cutting the shaft or sleeve. With a static “O”-ring mounted to the shaft, mechanical seals will not damage the shaft or sleeve.

How to determine the right seal for my application?

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Here are some questions that will help identify the proper mechanical seal for a given application and process:

What is the temperature range for the process?
What is the pressure? Suction? Discharge? Stuffing box?
Is the product viscous? Does it crystallize, solidify, freeze or build up film?
the product corrosive?
kind of pump is used in the process?
size is the pump? What is the pump’s speed?
What are the shaft and sleeve sizes?
the pump cavitate or run dry?
Which mechanical seals are best for a given application?

The best method of specifying the right mechanical seal is to work in cooperation with a knowledgeable representative from your mechanical seal supplier. Take some of the information you’ve developed from the list above, and work with your sales representative to identify the right product and design features.

Generally speaking, a basic, single-cartridge balanced mechanical seal is adequate for applications where stuffing box pressure is less than 300 pounds per square inch (psi), the temperature is less than 400°F, and the shaft size is from 1 inch to 4 inches. Conditions in excess of these parameters, along with other requirements, might necessitate a special seal design. Double cartridge seals are best in processes where temperature and emission control are critical factors. This is typically the case when working with material that is toxic, radioactive, explosive, or is categorized as a pollutant.²

different types of mechanical seals

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There are many options, designs, and materials when it comes to mechanical seals. The configuration and features right for you will depend on your application. Perhaps the simplest, yet most traditional type of mechanical seal is the component seal, which is often mounted on the inside of the pump housing, or stuffing box.

Single cartridge mechanical seals are used in processes using non-hazardous, non-corrosive materials. A single cartridge seal is usually located outside the pump housing, and is not exposed to the material or product being pumped.

Double cartridge mechanical seals are mounted separately on the same shaft, outside of the housing, or stuffing box, and provide maximum sealing for potentially hazardous materials, such as slurries, acids, and volatile organic liquids.

The single and double cartridge seals can be designed with a number of features. They come with either single or multiple springs, or bellows. In addition, both the single and double cartridge seals are available in a split design, where the seal comes in two parts that are assembled to surround the shaft. These are mostly seen on large split case pumps.

What are mechanical seals made of?

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What are mechanical seals made of?

The materials used in the design of a mechanical seal are determined by the conditions under which it will be operating. The body of a mechanical seal is typically made from stainless steel. The wearing, or contact face of the seal, can be made from a variety of corrosion-resistant materials, such as carbon, glass-filled Teflon, tungsten carbide, and silicon carbide. The other face, the hard face, can be made from ceramic, niresist, tungsten carbide, or silicon carbide. One face rotates, while the other remains stationary. Typically, the nature of the process, the pressure and velocity of the pump, and the temperature the seal is operating in will determine the seal face material.

There is also usually a shaft or sleeve packing. The material used in this element of the seal could be “O”- rings, Teflon wedges, metal bellows, rubber bellows or elastomers such as Viton‚ EPR, Neoprene, or Grafoil packing.

Vertical Turbine Pumps

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Pump Application Data

1. DATUM OR GRADE - The elevation of the surface from which the pump is supported.

2. STATIC LIQUID LEVEL - The vertical distance from grade to the liquid level when no liquid is being drawn from the well or source.

3. DRAWDOWN - The distance between the static liquid level and the liquid level when pumping at required capacity.

4. PUMPING LIQUID LEVEL - The vertical distance from grade to liquid level when pumping at rated cap-acity. Pumping liquid level equals static water level plus drawdown.

5. SETTING - The distance from grade to the top of the pump bowl assembly.

6. TPL (TOTAL PUMP LENGTH) - The distance from grade to lowest point of pump.

7. RATED PUMP HEAD - Lift below discharge plus head above discharge plus friction losses in discharge line. This is the head for which the customer is responsible and does not include any losses within the pump.

8. COLUMN AND DISCHARGE HEAD FRICTION LOSS - Head loss in the pump due to friction in the column assembly and discharge head. Friction loss is measured in feet and is dependent upon column size, shaft size, setting, and discharge head size. Values given in appropriate charts in Data Section.

9. BOWL HEAD - Total head which the pump bowl assembly will deliver at the rated capacity. This is curve performance.

10. BOWL EFFICIENCY- The efficiency of the bowl unit only. This value is read directly from the performance curve.

11. BOWL HORSEPOWER- The horsepower - required by the bowls only to deliver a specified capacity against bowl head.

12. TOTAL PUMP HEAD - Rated pump head plus column and discharge head loss. Note: This is new or final bowl head.

13. SHAFT FRICTION LOSS - The horsepower required to turn the lineshaft in the bearings. These values are given in appropriate table in Data Section.

14. PUMP BRAKE HORSEPOWER - Sum of 'bowl horsepower plus shaft loss (and the driver thrust bearing loss under certain conditions).

15. TOTAL PUMP EFFICIENCY (WATER TO WATER) -The efficiency of the complete pump less.the driver, with all pump losses taken into account.

16. OVERALL EFFICIENCY (WIRE TO WATER)-The efficiency of the pump and motor complete. Overall efficiency = total pump efficiency X motor efficiency.

17. SUBMERGENCE-Distance from liquid level to suction bell.

Vibration Analysis

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Vibration analysis equipment enables you to tell when "normal" vibration becomes "problem" vibration or exceeds acceptable levels. It may also allow you to determine the source and cause of the vibration, thus becoming an effective preventive maintenance and troubleshooting aid.

A vibration analyser measures the amplitude, frequency and phase of vibration. Also when vibration occurs at several frequencies, it separates one frequency from another so that each individual vibra-tion characteristic can be measured.

The vibration pickup senses the velocity of the vibration and converts it into an electrical signal. The analyzer receives this signal, converting it to the corresponding amplitude and frequency.

The amplitude is measured in terms of peak-to-peak displacement in mils (1 mil = .001") and is indicated on the amplitude meter.

Some instruments are equipped with a frequency meter which gives a direct readout of the predominant frequency of the vibration. Other instruments have tunable filters which allow scanning the frequency scale and reading amplitude at any particular frequency, all others being filtered out.

A strob light is used to determine the phase of vibration. It can be made to flash at the frequency of the vibration present or at any arbitrary frequency set on an internal oscillator.

A reference mark on a rotating part viewed under the strob light flashing at the vibration frequency may appear as a single frozen (or rotat-ing) mark, or as several frozen (or rotating) marks. The number of marks viewed is useful in determining the source of the vibration. The location of the mark or marks is used in balancing rotating parts.

The first step in vibration analysis is to determine the severity of the vibration, then, if the vibration is serious, a complete set of vibration readings should be taken before attempting to analyze the cause. Fig. 1 is the typical guide for end suction stock pumps as published by the Hydraulic Institute. The amplitudes shown are the overall RMS obtained without filtering to specific frequencies. Amplitudes at specific frequencies, such as vane pass frequency with multi-vane impellers, should be less than 75% of the unfiltered amplitudes allowed in Fig. 1 at the operating RPM. For other pumps, refer to Hydraulic Institute standards or pump manufacturer.

Fig. 1 Acceptable Field Vibration Limits for Horizontal Pumps - Clear Liquid (Rigid Structures)

Severity of vibration is a function of amplitude and pump speed; however, it should be noted that a change in severity over a period of time is usually a warning of impending failure. This change is often more important than vibration in the "slightly rough" or "rough" ranges which does not change with time.

Complete pump vibration analysis requires taking vibration readings at each bearing in three planes (horizontal, vertical and axial). Readings at the pump suction and discharge flanges may also be useful in some cases.

Field Testing Methods 2

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e.)OrificeAn orifice is a thin plate containing an opening of specific shape and dimensions. The plate is installed in a pipe and the flow is a function of the pressure upstream of the orifice. There are numerous types of orifices available and their descriptions and applications are covered in the Hydraulic Institute Standards and the ASME Fluid Meters Report. Orifices are not recommended for permanent installations due to the inherent high head loss across the plate.

Fig. 6 Weirs

f.) Weir

A weir is particularly well suited to measuring flows in open conduits and can be adapted to extremely large capacity systems. For best accuracy, a weir should be calibrated in place. However, when this is impractical, there are formulas which can be used for the various weir configurations. The most common types are the rectangular contracted weir and the 90 V-notch weir. These are shown in Fig. 6 with the applicable flow formulas.

g.) Pitot tube

A pilot tube measures fluid velocity. A small tube placed in the flow stream gives two pressure readings: one receiving the full impact of the flowing stream reads static head + velocity head, and the other reads the static head only (Fig. 7). The difference between the two readings is the velocity head. The velocity and the flow are then determined from the following well known formulas.

Capacity = Area x Average Velocity

Since the velocity varies across the pipe, it is necessary to obtain a velocity profile to determine the average velocity. This involves some error, but when properly applied a calibrated pilot tube is within plus or minus 2% accuracy.

Fig. 7 Pitot Tube

Measurement of capacity

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Measurement of capacity

a.) Magnetic Flow Meter

A calibrated magnetic flow meter is an accurate means of measuring flow in a pumping system. However, due to the ex-pense involved, magnetic flow meters are only practical in small factory test loops and in certain process pumping systems where flow is critical.

b.) Volumetric measurement

Pump capacity can be determined by weighing the liquid pumped or measuring its volume in a calibrated vessel. This is often practical when pumping into an accurately measured reservoir or tank, or when it is possible to use small containers which can be accurately weighed. These methods, however, are normally suited only to relatively small capacity systems.

c.) Venturi meter

A venturi meter consists of a converging section, a short con-stricting throat section and then a diverging section. The object is to accelerate the fluid and temporarily lower its static pressure. The flow is then a function of the pressure differential between the full diameter line and the throat. Fig. 4 shows the general shape and flow equation. The meter coefficient is determined by actual calibration by the manufacturer and when properly installed the Venturi meter is accurate to within plus or minus 1%.

Fig. 4 Venturi Meter

d.) Nozzle

A nozzle is simply the converging portion of a venturi tube with the liquid exiting to the atmosphere. Therefore, the same formula can be used with the differential head equal to the gauge read-ing ahead of the nozzle. Fig. 5 lists theoretical nozzle discharge flows.

Field Testing Methods

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A. Determination of total head
The total head of a pump can be determined by gauge readings as illustrated in Fig. 1.

Fig 1 Determination of Total Head from Guage Readings

Negative Suction Pressure:
TDH = Discharge gauge reading converted to feet of liquid + vacuum gauge reading converted to feet of liquid + distance between point of attachment of vacuum gauge and the centerline of the discharge

Positive Suction Pressure:
or TDH=Discharge gauge reading converted to feet of liquid-pressure gauge reading in suction line converted to ft. of liquid + distance between center of discharge and suction gauges, h, in feet

In using gauges when the pressure is positive or above atmos-pheric pressure, any air in the gauge line should be vented off by loosening the gauge until liquid appears. This assures that the entire gauge line is filled with liquid and thus the gauge will read the pressure at the elevation of the centerline of the gauge. However, the gauge line will be empty of liquid when measuring vacuum and the gauge will read the vacuum at the elevation of the point of attachment of the gauge line to the pipe line. These assumptions are reflected in the above definitions.

The final term in the above definitions accounts for a difference in size between the suction and discharge lines. The discharge line is normally smaller than the suction line and thus the dis-charge velocity is higher. A higher velocity results in a lower pressure since the sum of the pressure head and velocity head in any flowing liquid remains constant. Thus, when the suction and discharge line sizes at the gauge attachment points are different, the resulting difference in velocity head must be in-cluded in the total head calculation.

Manometers can also be used to measure pressure. The liquid used in a manometer is normally water or mercury, but any liquid of known specific gravity can be used. Manometers are extremely accurate for determining low pressures or vacuums and no calibration is needed. They are also easily fabricated in the field to suit any particular application. Figs. 2 & 3 illustrate typical manometer set ups.

Fig. 2 Manometer Indicating Vacuum

Fig. 3 Manometer Indicating Pressure

Magnetic Drive Pumps: Recirculation Circuit

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Recirculation Circuit

All magnetic drive pumps circulate some of the process fluid to lubricate and cool the bearings supporting the inner rotor.

Magnetic drive pumps with metal containment shells, also require a circulation of some process fluid through the containment shell to remove heat generated by eddy currents. For pumps with metal containment shells, the fluid recirculation path must be carefully engineered to prevent vaporization of the process liquid necessary to lubricate the bearings. A pressurized circuit as shown in Fig. 4 offers excellent reliability for pumps with metal containment shells.

Magnetic drive pumps with electrically non-conductive containment shells, such as plastic or ceramic have no heat generated by eddy currents. Since no heat is required to be removed from the containment shell, a much simpler recirculation circuit can be used.

For liquids near vaporization, a calculation must be made to ensure the process fluid does not vaporize at the bearings. This calculation includes the effects of process fluid specific heat, vapor pressure, drive losses, recirculation flow, etc. This calculation procedure can be found in the GOULDS PUMPS HANDBOOK FOR MAGNETIC DRIVE PUMPS. An external cooling system can be added to the recirculation circuit to prevent vaporization.

Fail Safe Devices

DESCRIPTION

Condition monitoring of the pump is a "key objective" and provides the user with an assurance of safety and reliability.

System and pump malfunctions can result from the following:

No-flow condition through the pump
Dry running as a result of plugged liquid circulation paths in the pump bearing and magnets assembly section
Cavitation due to insufficient NPSHA
Uncoupling of the magnetic drive due to overload
Temperature and pressure transients in the system
"Flashing" in the pump liquid circulation paths due to pressure and temperature transients.

These malfunctions can contribute to:

Overheating of the drive and driven magnet assemblies
Overload of drive motor and drive magnetic assembly
Extreme pump bearing load conditions
Damage to pump due to extremes in temperatures and pressures due to transients that exceed normal design.

Various fail safe devices are available with the pump to control malfunctions and provide safety and reliability including:

thermocouple / controller
low amp relay
liquid leak detector
power monitor

Magnetic Drive Pumps: Stationary Shaft

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Stationary Shaft

This type of design typically uses non-metallic components such as ceramics and plastics. It is best suited for light to medium duty applications. The stationary shaft design significantly reduces the number of parts required, simplifying maintenance and reducing cost. Corrosion resistant materials such as silicon carbide ceramics and fluoropolymer plastics (Teflon, Tefzel, etc.) provide excellent range of application. The use of plastics materials does, however, limit the temperature range of these designs to 200^oF to 250^o F. (Refer to Model 3298, Section CHEM-3C).

Containment Shell Designs

The containment shell is the pressure containing barrier which is fitted between the drive and the driven magnet assembly. It must contain full working pressure of the pump, since it isolates the pumped liquid from the atmosphere. One-piece formed shells offer the best reliability, eliminating welds used for two-piece shells. Since the torque coupling magnetic force field must pass through the shell, it must be made of a non-magnetic material. Non-magnetic metals such as Hastelloy and 316SS are typical choices for the containment shell. The motion of the magnets past an electrically conductive containment shell produces eddy currents, which generate heat and must be removed by a process fluid recirculation circuit. The eddy currents also create a horsepower loss, which reduces the efficiency of the pump. Metals with low electrical conductivity have lower eddy current losses, providing superior pump efficiency. Hastelloy has a relatively low electrical conductivity and good corrosion resistance, thus is an excellent choice for metal containment shells. Electrically non-conductive materials such as plastic and ceramics are also good choices for containment shells, since the eddy current losses are totally eliminated. This results in pump efficiencies equal to conventionally sealed pumps. Plastic containment shells are generally limited to lower pressures and temperatures due to the limited strength of plastics.

Sleeve and Thrust Bearings

Magnetic drive pumps utilize process lubricated bearings to support the inner drive rotor. These bearings are subject to the corrosive nature of the liquids being pumped, thus need to be made from corrosion resistant materials. Two commonly used materials are hard carbon and silicon carbide (SIC). Pure sintered SIC is superior to reaction bonded SIC, since reaction bonded SIC has free silicon left in the matrix, resulting in lower chemical resistance and lower strength.

Hard carbon against silicon carbide offers excellent service life for many chemical applications and also offers the advantage of short term operation in marginal lubrication conditions.

Silicon carbide against silicon carbide offers excellent service life for nearly all chemical applications. Its hardness, high thermal conductivity, and strength make it an excellent bearing material. Silicon carbide must be handled carefully to prevent chipping. Silicon carbide against silicon carbide has very limited capability in marginal lubrication conditions.

Magnetic Drive Pumps

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Environmental concerns and recurring mechanical seal problems have created a need for sealless pumps in the chemical and petrochemical industries. In some cases, more stringent regulations by the EPA, OSHA and local agencies are mandating the use of sealless pumps. One type of sealless pump is the magnetic drive pump which uses a permanent magnetic coupling to transmit torque to the impeller without the need for a mechanical seal for packing.

PRINCIPLES OF OPERATION

Magnetic drive pumps use a standard electric motor to drive a set of permanent magnets that are mounted on a carrier or drive assembly located outside of the containment shell. The drive magnet assembly is mounted on a second shaft which is driven by a standard motor. The external rotating magnetic field drives the inner rotor.

The coaxial synchronous torque coupling consists of two rings of permanent magnets as shown in Fig. 1. A magnetic force field is established between the north and south pole magnets in the drive and driven assemblies. This provides the no slip or synchronous capability of the torque coupling. The magnetic field is shown as dashed lines and shaded areas in Fig. 3.

Two Types of Magnetic Drive Pump

A. Rotating Driven Shaft

This type of design typically uses metal components and is best suited for heavy duty applications. The metallic construction offers the best strength, temperature and pressure capability required for heavy duty applications. Corrosion resistant high alloy materials such as 316SS, Hastelloy, and Alloy 20 are offered. The rotating shaft does, however, increase the number of parts required and thus increases the complexity and cost of the pump. This type of design typically uses a pressurized recirculation circuit, which helps prevent vaporization of liquid required for process lubricated bearings. (Refer to Model 3296, Section CHEM-3A).

Dynamic Seal

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Dynamic Seal

On some tough pumping services like paper stock and slurries, mechanical seals require outside flush and constant, costly attention. Even then, seal failures are common, resulting in downtime. Goulds offers a Dynamic Seal which, simply by fitting a repeller between the stuffing box and impeller, eliminates the need for a mechanical seal.

BENEFITS OF GOULDS DYNAMIC SEAL:

External seal water not required.
Elimination of pumpage contamination and product dilution
Reduces utility cost
No need to treat seal water
Eliminates problems associated with piping from a remote source

HOW IT WORKS

At start-up, the repeller functions like an impeller, and pumps liquid and solids from the stuffing box. When pump is shut down, packing (illustrated) or other type of secondary seal prevents pumpage from leaking.

API and CPI Plans

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API and CPI mechanical seal flush plans are commonly used with API and CPI process pumps. The general arrangement of the plans are similar regardless of the designation whether API or CPI. The difference between the flush plans is the construction which provides applicable pressure-temperature capability for each type of pump. API plans have higher pressure and temperature capability than CPI plans. Each plan helps provide critical lubrication and cooling of seal faces to maximize seal reliability.

Environmental Controls

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Environmental Controls

Environmental controls are necessary for reliable performance of a mechanical seal on many applications. Goulds Pumps and the seal vendors offer a variety of arrangements to combat these problems.

1. Corrosion

2. Temperature Control

3. Dirty or incompatible environments

CORROSION

Corrosion can be controlled by selecting seal materials that are not attacked by the pumpage. When this is difficult, external fluid injection of a non-corrosive chemical to lubricate the seal is possible. Single or double seals could be used, depending on if the customer can stand delusion of his product.

TEMPERATURE CONTROL

As the seal rotates, the faces are in contact. This generates heat and if this heat is not removed, the temperature in the stuffing box or seal chamber can increase and cause sealing problems. A simple by-pass of product over the seal faces will remove the heat generated by the seal (Fig. 25). For higher temperature services, by-pass of product through a cooler may be required to cool the seal sufficiently (Fig. 26). External cooling fluid injection can also be used.

DIRTY or INCOMPATIBLE ENVIRONMENTS

Mechanical seals do not normally function well on liquids which contain solids or can solidify on contact with the atmosphere. Here, by-pass flush through a filter, a cyclone separator or a strainer are methods of providing a clean fluid to lubricate seal faces. Strainers are effective for particles larger than the openings on a 40 mesh screen. Cyclone separators are effective on solids 10 micron or more in diameter, if they have a specific gravity of 2.7 and the pump develops a differential pressure of 30-40 psi. Filters are available to remove solids 2 microns and larger.

If external flush with clean liquid is available, this is the most fail proof system. Lip seal or restricting bushings are available to control flow of injected fluid to flows as low as 1/8 GPM. Quench type glands are used on fluids which tend to crystallize on exposure to air. Water or steam is put through this gland to wash away any build up. Other systems are available as required by the service.

Stuffing Box Cover and Seal Chamber Guide

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The selection guide on this page and the Seal Chamber Guide are designed to assist selection of the proper seal housing for a pump application.

JACKETED STUFFING BOX COVER

Designed to maintain proper temperature control (heating or cooling) of seal environment. (Jacketed covers do not help lower seal face temperatures to any significant degree). Good for high temperature services that require use of a conventional double seal or single seal with a flush and API or CPI plan 21.

JACKETED LARGE BORE SEAL CHAMBER

Maintains proper temperature control (heating or cooling) of sea environment with improved lubrication of seal faces. Ideal for controlling temperature for services such as molten sulfur and polymerizing liquids. Excellent for high temperature services that require use of conventional or cartridge single mechanical seals with flush and throat bushing in bottom of seal chamber. Also, great for conventional or cartridge double or tandem seals.

Stuffing Box and Seal Chamber Application Guide

Stuffing Box Cover/Seal Chamber	Application
Standard Bore Stuffing Box Cover	Use for soft packing. Outside mechanical seals. Double seals. Also, accommodates other mechanical seals.
Jacketed Stuffing Box Cover	Same as above but also need to control temperatures of liquid in seal area.
Conventional Large Bore	Use for all mechanical seal applications where the seal environment requires use of CPI or API seal flush pans. Cannot be used with outside type mechanical seals.
Jacketed Large Bore	Same as Large Bore but also need to control temperature of liquid in seal area.
Tapered Large Bore with Axial Ribs	Clean services that require use of single mechanical seals. Can also be used with cartridge double seals. Also, effective on services with light solids up to 1% by weight. Paper stock to 1% by weight.
Tapered Large Bore with Patented Vane Particle Ejector (Alloy Construction)	Services with light to moderate solids up to 10% by weight. Paper stock to 5% by weight. Ideal for single mechanical seals. No flush required. Also, accommodates double seals. Cannot be used with outside mechanical seals.

Goulds Taper BoreTM Plus: How It Works

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Goulds TaperBore^TM Plus: How It Works
The unique flow path created by the Vane Particle Elector directs solids away from the mechanical seal, not at the seal as with other tapered bore designs. And the amount of solids entering the bore is minimized. Air and vapors are also efficiently removed. On services with or without solids, air or vapors, Goulds TaperBore^TM PLUS is the effective solution for extended seal and pump life and lower maintenance costs.

Solids/liquid mixture flows toward mechanical seal/seal chamber.
Turbulent zone. Some solids continue to flow toward shaft. Other solids are forced back out by centrifugal force (generated by back pump-out vanes).
Clean liquid continues to move toward mechanical seal faces. Solids, air, vapors flow away from seal.
Low pressure zone create by Vane Particle Ejector. Solids, air, vapor liquid mixture exit seal chamber bore.
Flow in TaperBore^TMPLUS seal chamber assures efficient heat removal (cooling) and lubrication. Seal face heat is dissipated. Seal faces are continuously flushed with clean liquid.

Large Tapered Bore Seal Chambers

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Large Tapered Bore Seal Chambers

Provide increased circulation of liquid at seal faces without use of external flush. Offers advantages of lower maintenance costs, elimination of tubing/piping, lower utility costs (associated with seal flushing) and extended seal reliability. The tapered bore seal chamber is commonly available with ANSI chemical pumps. API process pumps use conventional large bore seal chambers. Paper stock pumps use both conventional large bore and large tapered bore seal chambers. Only tapered bore seal chambers with flow modifiers provide expected reliability on services with or without solids, air or vapors.

Conventional Tapered Bore Seal Chamber:

Mechanical Seals Fall When Solids or Vapors Am Present in Liquid

Many users have applied the conventional tapered bore seal chamber to improve seal life on services containing solids or vapors. Seals in this environment failed prematurely due to entrapped solids and vapors. Severe erosion of seal and pump parts, damaged seal faces and dry running were the result.

Modified Tapered Bore Seal Chamber with Axial Ribs:

Good for Services Containing Air, Minimum Solids

This type of seal chamber will provide better seal life when air or vapors are present in the liquid. The axial ribs prevent entrapment of vapors through.improved flow in the chamber. Dry running failures are eliminated. In addition, solids less than 1% are not a problem.

The new flow pattern, however, still places the seal in the path of solids/liquid flow. The consequence on services with significant solids (greater than 1%) is solids packing the seal spring or bellows, solids impingement on seal faces and ultimate seal failure.

Goulds Standard TaperBoreTM PLUS Seal Chamber: The Best Solution for Services Containing Solids and Air or Vapors

To eliminate seal failures on services containing vapors as well as solids, the flow pattern must direct solids away from the mechanical seal, and purge air and vapors. Goulds Standard TaperBoreTM PLUS completely reconfigures the flow in the seal chamber with the result that seal failures due to solids are eliminated. Air and vapors are efficiently removed eliminating dry run failures. Extended seal and pump life with lower maintenance costs are the results.

Mechanical Seal Selection

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Mechanical Seal Selection

The proper selection of a mechanical seal can be made only if the full operating conditions are known:

Liquid
Pressure
Temperature
Characteristics of Liquid
Reliability and Emission Concerns

Liquid: Identification of the exact liquid to be handled is the first step in seal selection. The metal parts must be corrosion resistant, usually steel, bronze, stainless steel, or Hastelloy. The mating faces must also resist corrosion and wear. Carbon, ceramic, silicon carbide or tungsten carbide may be considered. Stationary sealing members of Buna, EPR, Viton and Teflon are common.
Pressure: The proper type of seal, balanced or unbalanced, is based on the pressure on the seal and on the seal size.
Temperature: In part, determines the use of the sealing members. Materials must be selected to handle liquid temperature.
Characteristics of Liquid: Abrasive liquids create excessive wear and short seal life. Double seals or clear liquid flushing from an external source allow the use of mechanical seals on these difficult liquids. On light hydrocarbons balanced seals are often used for longer seal life even though pressures are low.
Reliability and Emission Concerns: The seal type and arrangement selected must meet the desired reliability and emission standards for the pump application. Double seals and double gas barrier seals are becoming the seals of choice.

Seal Environment

The number one cause of pump downtime is failure of the shaft seal. These failures are normally the result of an unfavorable seal environment such as improper heat dissipation (cooling), poor lubrication of seal faces, or seals operating in liquids containing solids, air or vapors. To achieve maximum reliability of a seal application, proper choices of seal housings (standard bore stuffing box, large bore, or large tapered bore seal chamber) and seal environmental controls (CPI and API seal flush plans) must be made.

STANDARD BORE STUFFING BOX COVER

Designed thirty years ago specifically for packing. Also accommodates mechanical seals (clamped seat outside seals and conventional double seals.)

CONVENTIONAL LARGE BORE SEAL CHAMBER

Designed specifically for mechanical seals. Large bore provides Increased life of seals through improved lubrication and cooling of faces. Seal environment should be controlled through use of CPI or API flush plans. Often available with internal bypass to provide circulation of liquid to faces without using external flush. Ideal for conventional or cartridge single mechanical seals in conjunction with a flush and throat bushing in bottom of chamber. Also excellent for conventional or cartridge double or tandem seals.

LARGE BORE SEAL CHAMBERS

Introduced in the mid-8o's, enlarged bore seal chambers with increased radial clearance between the mechanical seal and seal chamber wall, provide better circulation of liquid to and from seal faces. Improved lubrication and heat removal (cooling) of seal faces extend seal life and lower maintenance costs.

BigBore^{TM Seal Chamber}

TaperBore^{TM Seal Chamber}

Mechanical Seal Arrangements

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Mechanical Seal Arrangements

SINGLE INSIDE:

This is the most common type of mechanical seal. These seals are easily modified to accommodate seal flush plans and can be balanced to withstand high seal environment pressures. Recommended for relatively clear non-corrosive and corrosive liquids with satisfactory' lubricating properties where cost of operation does not exceed that of a double seal. Examples are Dura RO and CBR and Crane 9T and 215. Reference Conventional Seal.

SINGLE OUTSIDE:

If an extremely corrosive liquid has good lubricating properties, an outside seal offers an economical alternative to the expensive metal required for an inside seal to resist corrosion. The disadvantage is that it is exposed outside of the pump which makes it vulnerable to damage from impact and hydraulic pressure works to open the seal faces so they have low pressure limits (balanced or unbalanced).

DOUBLE (DUAL PRESSURIZED):

This arrangement is recommended for liquids that are not compatible with a single mechanical seal (i.e. liquids that are toxic, hazardous [regulated by the EPA], have suspended abrasives, or corrosives which require costly materials). The advantages of the double seal are that it can have five times the life of a single seal in severe environments. Also, the metal inner seal parts are never exposed to the liquid product being pumped, so viscous, abrasive, or thermosetting liquids are easily sealed without a need for expensive metallurgy. In addition, recent testing has shown that double seal life is virtually unaffected by process upset conditions during pump operation. A significant advantage of using a double seal over a single seal.

The final decision between choosing a double or single seal comes down to the initial cost to purchase the seal, cost of operation of the seal, and environmental and user plant emission standards for leakage from seals. Examples are Dura double RO and X-200 and Crane double 811T.

DOUBLE GAS BARRIER (PRESSURIZED DUAL GAS):

Very similar to cartridge double seals ... sealing involves an inert gas, like nitrogen, to act as a surface lubricant and coolant in place of a liquid barrier system or external flush required with conventional or cartridge double seals. This concept was developed because many barrier fluids commonly used with double seals can no longer be used due to new emission regulations. The gas barrier seal uses nitrogen or air as a harmless and inexpensive barrier fluid that helps prevent product emissions to the atmosphere and fully complies with emission regulations. The double gas barrier seal should be considered for use on toxic or hazardous liquids that are regulated or in situations where increased reliability is the required on an application. Examples are Dura GB2OO, GF2OO, and Crane 2800.

TANDEM (DUAL UNPRESSURIZED): Due to health, safety, and environmental considerations, tandem seals have been used for products such as vinyl chloride, carbon monoxide, light hydrocarbons, and a wide range of other volatile, toxic, carcinogenic, or hazardous liquids.

Mechanical Seal Types

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Mechanical Seal Types

Mechanical seals can be classified into several tvpes and arrangements:

PUSHER:

Incorporate secondary seals that move axially along a shaft or sleeve to maintain contact at the seal faces. This feature compensates for seal face wear and wobble due to misalignment. The pusher seals' advantage is that it's inexpensive and commercially available in a wide range of sizes and configurations. Its disadvantage is that ft's prone to secondary seal hang-up and fretting of the shaft or sleeve. Examples are Dura RO and Crane Type 9T.

UNBALANCED:

They are inexpensive, leak less, and are more stable when subjected to vibration, misalignment, and cavitation. The disadvantage is their relative low pressure limit. If the closing force exerted on the seal faces exceeds the pressure limit, the lubricating film between the faces is squeezed out and the highly loaded dry running seal fails. Examples are the Dura RO and Crane 9T.

CONVENTIONAL:

Examples are the Dura RO and Crane Type 1 which require setting and alignment of the seal (single, double, tandem) on the shaft or sleeve of the pump. Although setting a mechanical seal is relatively simple, today's emphasis on reducing maintenance costs has increased preference for cartridge seals.

NON-PUSHER:

The non-pusher or bellows seal does not have to move along the shaft or sleeve to maintain seal face contact, The main advantages are its ability to handle high and low temperature applications, and does not require a secondary seal (not prone to secondary seal hang-up). A disadvantage of this style seal is that its thin bellows cross sections must be upgraded for use in corrosive environments Examples are Dura CBR and Crane 215, and Sealol 680.

BALANCED:

Balancing a mechanical seal involves a simple design change, which reduces the hydraulic forces acting to close the seal faces. Balanced seals have higher-pressure limits, lower seal face loading, and generate less heat. This makes them well suited to handle liquids with poor lubricity and high vapor pressures such as light hydrocarbons. Examples are Dura CBR and PBR and Crane 98T and 215.

CARTRIDGE:

Examples are Dura P-SO and Crane 1100 which have the mechanical seal premounted on a sleeve including the gland and fit directly over the Model 3196 shaft or shaft sleeve (available single, double, tandem). The major benefit, of course is no requirement for the usual seal setting measurements for their installation. Cartridge seals lower maintenance costs and reduce seal setting errors

Induction sealing

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Induction sealing, otherwise known as cap sealing, is a non-contact method of heating a metallic disk to hermetically seal the top of plastic and glass containers. This sealing process takes place after the container has been filled and capped

The closure is supplied to the bottler with foil liner already inserted. Although there are various liners to choose from, a typical induction liner is multi-layered. The top layer is a paper pulp that is generally spot-glued to the cap. The next layer is wax that is used to bond a layer of aluminum foil to the pulp. The bottom layer is a polymer film laminated to the foil. After the cap or closure is applied, the container passes under an induction coil, which emits an oscillating electromagnetic field. As the container passes under the induction coil (sealing head) the conductive aluminum foil liner begins to heat. The heat melts the wax, which is absorbed into the pulp backing and releases the foil from the cap. The polymer film also heats and flows onto the lip of the container. When cooled, the polymer creates a bond with the container resulting in a hermetically sealed product. Neither the container nor its contents are affected, and this all happens in a matter of seconds.

It is possible to overheat the foil causing damage to the seal layer and to any protective barriers. This could result in faulty seals, even weeks after the initial sealing process, so proper sizing of the induction sealing is vital to determine the exact system necessary to run a particular product.

Sealing can be done with either a hand held unit or on a conveyor system.

A more recent development (which suits a small number of applications better) allows for induction sealing to be used to apply a foil seal to a container without the need for a closure. In this case, foil is supplied pre-cut or in a reel. Where supplied in a reel, it is die cut and transferred onto the container neck. When the foil is in place, it is pressed down by the seal head, the induction cycle is activated and the seal is bonded to the container. This process is known as direct application or sometimes “capless” induction sealing.

Leak prevention/protection

Some shipping companies require liquid chemical products to be sealed prior to shipping to prevent hazardous chemicals from spilling on other shipments.

Freshness

Induction sealing keeps unwanted pollutants from seeping into food products, and may assist in extending shelf life of certain products.

Pilferage protection

Induction-sealed containers help prevent the product from being broken into by leaving a noticeable residue from the liner itself. Pharmaceutical companies purchase liners that will purposely leave liner film/foil residue on bottles. Food companies that use induction seals do not want the liner residue as it could potentially interfere with the product itself upon dispensing. They, in turn, put a notice on the product that it has been induction-sealed for their protection; letting the consumer know there was a liner on the plastic bottle prior to purchase.

Sustainability

In some applications, induction sealing can be considered to contribute towards sustainability goals by allowing lower bottle weights as the pack relies on the presence of an induction foil seal for its security, rather than a mechanically strong bottle neck and closure.

Induction heating analysis

Some manufacturers have produced devices which can monitor the magnetic field strength present at the induction head (either directly or indirectly via such mechanisms as pick up coils), dynamically predicting the heating effect in the foil. Such devices provide quantifiable data post-weld in a production environment where uniformity – particularly in parameters such as foil peel-off strength, is important. Analysers may be portable or designed to work in conjunction with conveyor belt systems, for example Edge Electronics Ltd (UK) and Relco (UK) ltd. offer a device which will pass and reject individual seal operations automatically in a high speed volume production setting.
High speed power analysis techniques (Voltage and Current measurement in near real time) can be used to intercept power delivery from mains to generator or generator to head in order to calculate energy delivered to the foil and the statistical profile of that process. As the thermal capacity of the foil is typically static, such information as true power, apparent power and power factor may be used to predict foil heating with good relevance to final weld parameters and in a dynamic manner.
Induction sealing without a cap may be achieved through the use of a sealing head that picks and places the foil on the container prior to sealing.
Many other derivative parameters may be calculated for each weld, yielding confidence in a production environment that is notably more difficult to achieve in conduction transfer systems, where analysis, if present is generally post-weld as relatively large thermal mass of heating and conduction elements combined impair rapid temperature change. Inductive heating with quantitative feedback such as that provided by power analysis techniques further allows for the possibility of dynamic adjustments in energy delivery profile to the target. This opens the possibility of feed-forward systems where the induction generator properties are adjusted in near real-time as the heating process proceeds, allowing for a specific heating profile track and subsequent compliance feedback – something that is not generally practical for conduction heating processes.

Benefits of induction vs. conduction sealing

Conduction sealing requires a hard metal plate to make perfect contact with the container being sealed. Conduction sealing systems delay production time because of required system warm-up time. They also have complex temperature sensors and heaters.
Unlike conduction sealing systems, induction sealing systems require very little power resources, delivers instant startup time, and its sealing head can conform to “out of specification” containers when sealing.
Induction sealing also offers advantages when sealing to glass: Using a conduction sealer to seal a simple foil structure to glass gives no tolerance or compressibility to allow for any irregularity in the glass surface finish. With an induction sealer, the contact face can be of a compressible material, ensuring a perfect bond each time

what is a Mechanical Seals?

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A mechanical seals is a device which helps join systems or mechanisms together by preventing leakage (e.g., in a plumbing system), containing pressure, or excluding contamination. A seal may also be referred to as “packing.”

A mechanical face seal is an important component of variety of pumps used in chemical, petrochemical and process industry. The primary function of a mechanical seal is to prevent leakage of the process fluid from the pump housing and shaft to the environment. The factors that affect the performance of a mechanical seal to leak are friction, wear and its thermal characteristics. Improving upon the thermal characteristics of a mating ring in a mechanical seal would enhance its performance. Implanting a heat exchanger in the mating ring hold great promise for improving the performance of mechanical seals from the viewpoint of reducing heat at the interface and hence enhance the performance of the mechanical seal. To reveal what affect the implanted heat exchangers can have on the thermal characteristics of different seals, in this thesis, three different designs of mating rings were tested in a test rig and the results were compared to a conventional seal in this thesis.