Typically, the counterface becomes scored when a contaminant particle is caught under the seal lip and abrades a track as the shaft rotates. As this continues, the seal will allow more particles to pass or get stuck, and seal efficiency deteriorates, eventually leading to malfunction of the component that the seal is meant to protect. To rectify the situation, it is necessary to repair the shaft surface or replace the shaft since a simple seal replacement will not be sufficient and machine needs to be disassembled. However, there is an easy solution to this problem that allows the shaft to be repaired in position and does not require a different seal size. The solution is the SKF SPEEDI-SLEEVE.

SKF SPEEDI-SLEEVE

The SKF SPEEDI-SLEEVE is a thin walled sleeve having a high quality finish to provide an optimal counterface for a radial shaft seal. The sleeve is simply pushed in to position over the worn area providing a sealing surface that is as good as a new shaft.

Features and Size Range

The SKF SPEEDI-SLEEVE is a thin walled (0.28.mm thick) sleeve made of high quality stainless steel. The contact surface is wear resistant and machined to a fine finish. The sleeve has a removable flange to simplify the installation. The flange can be removed after the sleeve is set in position. They are available in standard size range to covers shaft diameters from 11.91 to 203.33 mm (0.472 to 8.0 in).

SKF SPEEDI-SLEEVE Gold is an enhanced version of the standard SKF SPEEDI-SLEEVE, offering improved resistance to abrasive wear. They are designed for applications where extended sealing system life is needed. In these sleeves a thin metallic film is applied to the base stainless steel which gives a gold colour and surface hardness to approximately 80 – 85 HRC.  SKF SPEEDI-SLEEVE Gold is available from stock for selected common sizes.

A SKF SPEEDI-SLEEVE looks as shown below.

Installation Procedure

No special equipment is required since the installation tool is supplied with the sleeve. A mallet and a pair of pliers are all that is needed for the installation. Although installation is simple, it should be done carefully to achieve the best results. As the thin walled sleeve has an interference fit, any disturbances on the shaft surface may create a similar pattern on the sleeve surface and the seal will leak. In view of this sleeves should not be placed over ports, splines or keyways etc. Before installation clean the seal counter surface on the shaft. File down any burrs or rough spots and fill deep wear grooves, scratches or very rough surfaces with suitable powdered metal epoxy filler. The sleeve must be positioned on the shaft before the filler has hardened. Remove the installation flange if required.

Large Diameter Wear Sleeves

SKF recommends the use of large diameter wear sleeves (LDSLV) where no SKF SPEEDI-SLEEVE is available (for shaft sizes in the diameter range 211.15 to 1143.00 mm). There are two designs of SKF large diameter wear sleeves; type LDSLV3 with a flange and type LDSLV4 without a flange. Both types are made of high quality SAE 1008 carbon steel and chrome plated to enhance the wear and corrosion resistance. The sleeve outside diameter is specially ground to provide a precision counter surface for the seal. The wall thickness of the standard sleeves is 2.39 mm. SKF large diameter wear sleeves are designed for a heated slip-fit installation and must therefore be uniformly heated to approximately 180° C prior to their installation on the shaft

For more information on these products please visit SKF’s website – http://www.skf.com

Selection of Type of Mechanical Seal

Single Seal

The design, arrangement and material selection of a seal is basically determined by pressure, temperature, speed of rotation and characteristics of the pumped medium. Shaft diameters of 5 To 500 mm, pressures from 10 torr (vacuum) to 250 bar, temperatures from -200°C to +450°C and sliding velocities up to 150 m/s limit the operating range of mechanical seals. Type of a mechanical seal for various parameters may be selected as under.

m/s = meters per second

Double Seal

Double seal arrangement with additional seal supply systems or buffer fluid systems may be required depending on the quality of the medium (toxic, inflammable, crystallizing, corrosive, abrasives in fluid, etc).

Material of Construction

Seal components can be divided into three major categories – seal faces, secondary sealing elements and metal components.

Seal Faces

The rotating and stationary sealing faces commonly referred to as primary seal members are the most important components of a mechanical seal. They shall be selected based on their compatibility with the fluid being pumped. Following materials are widely used as seal face material.

Resin Impregnated Carbon

This is the normal rotary seal face material recommended in most general purpose application involving corrosive fluids. This carbon exhibits good resistance to thermal shock and good dimensional stability over a wide temperature range. It has also low permeability and good thermal conductivity.

Metal Impregnated Hard Carbon

This is an antimony impregnated hard carbon that is specially suited for extreme heavy duty application involving non-corrosive media. Boiler feed water and hydrocarbon service seals with hard carbon as a mating face have a much longer service life. Hard carbon exhibits better abrasive resistance and emergency dry running characteristics.

Ceramic

This is a super fine grain high Alumina ceramic material (99.5 % Al₂O₃) that exhibits excellent low wear characteristics. It is the best seal face material for highly corrosive chemical services. 95.0 % purity material may be used for light duty application.

Tungsten Carbide

This is universally accepted hard seal face material. It is available in two forms – nickel bonded and cobalt bonded. Solid seal rings are offered as a standard as against shrunk-fit faces with their inherent limitations.

Silicon Carbide

Technologically this is the best seal face material available to date. It is available in two varieties, reaction bonded and sintered. It is highly resistant to thermal stress and corrosion in high temperature oxidizing atmospheres. It has low wear properties and is an idle seal face material for most of sealing applications. Silicon carbide also exhibits better dry run capabilities making it an ideal choice for critical duties in the nuclear and thermal power industries.

Glass filled PTFE

It is offered as a standard seal face material on outside mounted PTFE bellows type seals. It is recommended for corrosive applications. Safe working temperature rang for PTFE is -200 to 260° C.

Other Materials

Alternate face materials are available for custom seals and other special applications. Seal faces of stainless steel with stelliting and Ni-resist are available. Cast iron faces are also available for certain non-critical applications.

Note:
Carbon face is made in many grades and is priced from the cheap / mass-produced grades to expensive metal-powder impregnated varieties. While ordering spare carbon ring from local supplier, specify correct grade of carbon for your application.

Properties of various face materials are as under.

Seal Pressure – Velocity Limitations

Seal faces require cooling and lubrication to function properly. The hydraulic pressure acting on the seal faces and the rotating speed of the rotary seal will generate heat. This heat limits seal design and material. The PV – (face pressure x velocity) capability of two opposing material is indicative of an ability to sustain a fluid film for long operational life. Typical PV – Limits of face material combinations in non-lubricating fluids, i.e. watery substances are as under.

Note: For lubricating fluids multiply number by 1.5.

Seal Face Surface Finish and Seal Face Flatness

To maintain a healthy lubricating fluid film between seal faces they are lapped to make them flat and smooth. If faces are not flat, waviness will generate hydrodynamic lifting force on seal faces as we try to compress non-compressible liquid trapped between the lapped faces. Seal surfaces shall be smooth also to reduce friction between them by increasing contact area.

There is often confusion between the terms "Seal face flatness" and "Seal face surface finish". Seal face surface finish addresses the subject of roughness, and is measured in terms of "rms" (root mean square) or CLA (center line average). One of the ways to measure roughness is by comparing our sample to standards that have been polished to different degrees of roughness. Flatness is a different term that describes a level surface that has no elevations or depressions. We use term waviness to describe this condition when we refer to mechanical seal faces. It is this flatness that is of the most concern. One can read the flatness by using an optical flat and a monochromatic light source as explained below.

Flatness is measured by using light characteristic – that when two lights of the same wave length interfere with each other, the light disappears and the reflecting piece goes black. A monochromatic or single wave length light source (mono means one, and chromatic means color).) is used for this. Most companies use a pink color that comes off a helium gas light source. This color has a wave length of just about 0.6 microns (0.000023 inches). To measure flatness, an optical flat (a precision ground and polished clear glass of optical quality) is placed on the piece to be measured. The monochromatic light is aimed at the piece and this light reflects off of the piece back through the optical flat causing interference light bands. If the distance between the optical flat and the piece we are measuring is one half the wave length of helium, or an even multiple of the number, the band will show black. This is referred to as a helium light band and because it is one half the wave length of helium it measures 0.3 microns or 0.0000116 inches. Flatness is checked by comparing the pattern we see with a chart supplied by the measuring equipment manufacturer.

Flatness of lapped faces should be within following light bands:

Carbon and GFT: 2 to 3 light bands.
TC, SiC and Ceramic: 1 to 2 light bands.
For high pressure application (> 40 bar), faces should be lapped within 1 light band.

Carbon graphite faces relax after lapping. Although lapped to less than one light band by the seal manufacturer, you will see readings as high as three light bands if you check the faces. These faces should return to flat once they are placed against a hard face that is flat.

Seals that are going to be used in cryogenic (cold) service should be lapped at the cryogenic temperature.

Finished faces shall have following average surface finish:

Tungsten Carbide: 0.01 µm
Silicon Carbide: 0.04 µm
Hard Carbon: 0.1 µm
Ceramic: 0.07 µm

Hydrodynamic Grooves.

Sometimes hydrodynamic grooves are provided on hard face as shown above for effective lubrication between faces.

Secondary Sealing Elements

Secondary seals perform the function of sealing between mechanical seal elements as well as sealing the mechanical seal and the equipment. They are either static or dynamic type in the form of O-rings, wedges, bellows and gaskets.

For information on gaskets used for sealing seal and the equipment, please refer an article on gaskets. Bellows and wedges are made from PTFE. Bellows are also made from elastomers and metal. O-rings are made from elastomers.

Elastomers

To be classified as a true elastomer you should be able to compress an O-ring and have it return to 90% of its original shape in less than five seconds after the compression force is removed. It is this elasticity that gives the compound its memory and eliminates the need for external loading to seal. If the compound does not return to 90% of its original shape in five seconds or less it is called a "plastic" material and becomes less desirable as a dynamic seal in mechanical seal design. Most of Perfluoroelastomers are plastics. Generally one of the following elastomer materials is used to make an O-ring.

• Butyl
• Buna N
• Neoprene
• Ethylene propylene
• Fluorocarbons: They are sold by manufacturers under their style / produce number. Dupont E60 Viton ®, 3M Fluorel 2174, Parker 747-75 and Parker V884-85 are typical examples.
• Perfluoroelastomers: Chemraz (a registered trademark of Greene, Tweed & Co.) or Kalrez ® (a registered trademark of Dupont, USA) are typical examples. They are used for high temperature and aggressive chemical applications. Their chemical resistance is often compared with PTFE. They are very expensive compounds.

The O-ring selected must be chemically compatible with fluid to be handled. It is very common to clean and flush process lines with a solvent or steam. The O-ring selected must be chemically compatible with them also. Most of the chemicals can be handled by either fluorocarbon (Viton/ Fluorel) or Ethylene Propylene. Ethylene Propylene is easily attacked by any petroleum product so be careful with the type of lubricant you use to lubricate it. For all practical purposes silicone grease is probably the safest lubricant but to be sure check for its compatibility.

Each of these elastomers has an upper and lower temperature limit. Although the elastomer may be chemically compatible with the sealing fluid it could still fail if the temperature limit is exceeded. Safe temperature range for various elastomers is as under.

Note:
Elastomers are poor conductors of heat. Cooling one side of the O-ring does not always allow the coolant to conduct to the hot side.

Most of the o-ring compounds are available in a wide range of durometer or hardness. The average mechanical seal uses a durometer of 75 to 80 (as measured on the shore A scale), but harder durometers are available for high pressure applications.

One measures o-ring sizes by the inside diameter (D) and the cross section diameter (d). O-rings are the most precision rubber part that one can purchase. They are manufactured to a tolerance of ± 0.08 mm.

The maximum volume of the o-ring should never be more than the minimum volume of the gland groove. The groove depth must be less than the o-ring cross-section and the groove width must be larger than the o-ring cross-section.

Identification of O-ring Material by Burning Test (destructive test)

To identify Viton, Burn Test may be carried out. When ignited, Neoprene and Ethylene propylene burns with a flame where as Viton does not burn with a flame.

Metal Components

Metal is used for making mechanical seal hardware. This hardware, depending on seal design can include sleeves, retaining rings, set screws, pins, springs, bellows and glands. Although mechanical seal have some unique requirements, the material selection generally does not differ much from material selection for the equipment. As seal components are thinner than equipment components, materials offering best corrosion resistance are selected for hardware. Many of the common names used for material designation are actually trade marks of the material manufacturer. Following material are widely used for making mechanical seal hardware.

Stainless Steel 316

AISI 316 (UNS S31600) is considered the base material for most seal designs. It should not be used in service with high chlorides since it is susceptible to pitting corrosion.

Alloy C-276

Alloy C-276 (UNS N10276) is one of the most widely used high alloy material used for aggressive environments. It is used for all major seal components including sleeves, glands and fasteners. C-276 is a nickel-molybedenum-chromium alloy. It is used as standard alloy for springs and is defined as the default spring material in API 682 (2004).

Alloy 20

Alloy 20 (UNS N08020) is a nickel-chromium-molybdenum alloy. It was originally developed for hot sulfuric acid application. It is used for applications that cause stress corrosion cracking.

Alloy 400

Alloy 400 (UNS N04400) is a copper-nickel alloy that exhibit good corrosion resistance against many chemicals. It is used for sea water, sulfuric acid, hydrochloric acid, hydrofluoric acid and alkalies.

Alloy K 500

Monel alloy K 500 (UNS N05500) is used for components requiring high strength like set screws and fasteners.

Alloy 350

Alloy 350 (UNS S35000) is a chromium-nickel-molybdenum alloy that exhibit high strength in high temperature applications. It is mainly used for making bellows.

Alloy 718

Alloy 718 (UNS N07718).is a nickel-chromium alloy that exhibits excellent corrosion resistance and high temperature properties. The material is mainly used for making welded metal bellows. This alloy has been adopted as the default material for Type C seals in API 682 (2004).

Note:
UNS stands for Unified numbering system.

For more information on mechanical seal material selection please refer API Standard 682, 2004 –“Pumps-Shaft Sealing Systems for Centrifugal and Rotary Pumps”.

Acknowledgment:

Information about metal components in this article is briefly reproduced from Proceedings of the Twenty Second International Pump Users Symposium 2005.

The initial cost of a mechanical seal is high as compared to compression packings. However, the power consumed, maintenance and downtime spent in renewing or tightening the compression packing overweigh the initial cost of a mechanical seal, which works unattended for a long time. Because of the absence of visible leakage, environment is clean and hazard free when mechanical seals are used. In this article, information is given on working of a mechanical seal, types of mechanical seals, methods of environment control, equipment parameters, installation instructions, start-up procedure and check list for identifying causes of seal leakage.

Working of a mechanical seal

A basic mechanical seal is a simple device. It has two flat faces running against each other. The rotating face is secured to the pump shaft while the stationary face is held in the gland. This is the first and most important of the four possible leak paths (Primary Seal). This leakage path is sealed by providing absolutely flat mating surfaces perpendicular to rotating shaft centre line where they come in contact and maintaining healthy lubrication film between the two mating faces. Since both the surfaces are continuously moving with respect to each other, there is heat generation which keeps on evaporating the liquid film and new liquid film is formed. These vapours keep on escaping to the atmosphere. Thus mechanical seal is not a zero leakage seal. There is always invisible leakage in vapour form between the faces.

The others three paths are:
Between the Rotating Face and the Shaft (Secondary Seal),
Between the Stationary Face and the Gland, and
Between the Gland and the Stuffing Box.

Leakage at secondary seal is arrested by a dynamic O-Ring, sliding wedge or a bellow (elastomeric, PTFE or metallic). Metallic bellows are used for high temperature application.

The last two are jointly referred to as the “Tertiary Seal”, and both are fairly simple seals as there is no relative motion between the two parts involved. These leakage paths are sealed by elastomers, PTFE, gasket, etc.

If shaft sleeve is used, one more static leakage path will be there between shaft and shaft sleeve. This leakage is arrested by O-Ring or gasket.

Although the main closing force on primary seal faces is normally provided by the pressure in the stuffing box, some force is required to keep them closed during startup and shutdown and to take care of the shaft movement. This force is supplied by a single large spring, a series of small springs, or a bellows arrangement.

Types of Mechanical Seal

There are many types of seals each having definite advantage as under.

Inside Seals

When a seal is mounted inside the stuffing box of the pump, it is called an inside seal. Inside seals are more difficult to install and maintain. However, main advantage is that it is possible to control the seal environment inside the stuffing box.

Outside Seals

An outside seal is located outboard of the pump stuffing box. Where stuffing boxes are shallow and it is not possible to install a seal inside the stuffing box, it is installed outside. It is also easy to install and maintain. Due to lake of heat dissipation from below the seal faces, outside seals are suitable for low temperature, low speed and low pressure (as in these seals, fluid pressure is exerted outward on seal face rather than inward) applications.

Balanced Seal

All seals are available in either unbalanced or balanced versions. A seal is unbalanced when fluid force to close the seal faces (due to the area of rotating seal face exposed to the pumped fluid in stuffing box) is greater than force acting on rotating seal face at the area of contact (pressure gradient between rotating and stationary seal faces). In simple terms, it has a seal closing force in excess of the actual pressure to be sealed. In a balance seal as seal face is subject to low force, less heat is generated and seal life is more. As a stepped shaft sleeve is required for balancing, coat of a balanced seal is higher than unbalanced seal.

To balance a seal, area of rotating seal face exposed to stuffing box pressure is reduced using a stepped shaft sleeve. In a standard 70 – 30 balanced seal design used by most mechanical seal manufacturing companies, only 70 % of rotating seal face area is exposed to stuffing box pressure as shown in above sketch.

Double Seals

Double mechanical seal arrangement is used to handle toxic, volatile, hazardous or abrasive fluids. In a double seal arrangement, there are two seals with a fluid circulating between them. The fluid that circulates between the seals is called a barrier fluid if its pressure is higher than stuffing box pressure and it is called a buffer fluid if its pressure is lower than stuffing box pressure. The two seal faces are installed in three different configurations as under.

Back to Back or facing in opposite directions

This configuration requires a higher barrier fluid pressure between the seals. In this arrangement an inner seal leak will cause a dilution of the product. In case of failure of the barrier fluid system, the inner seal can blow open dumping the pump contents to the environment.

Tandem or facing in the same direction

In this configuration two glands are required to house both seals and this adds to the cost as well as the axial space requirement. A low pressure buffer fluid is circulated between the seals, eliminating the possibility of product dilution. In this arrangement loss of buffer fluid will not cause the seal faces to open. This configuration is generally found in Oil Refinery applications.

Face to Face or facing towards each other

Face to face configuration is a compromise between the "back to back" and the tandem arrangements. Here half the seal is housed in the stuffing box and the other half outside it. In this arrangement a lower pressure buffer fluid is supplied between seal faces.

Catridge Seals

The catridge design changes none of the functional components of the basic seal. In a catridge seal, all items are containerized and preset to working dimensions. They eliminate need to scribe lines and make critical measurements during seal assembly. Such seal installation requires only tightening of the gland bolts.

Methods of Environment Control

The successful and reliable operation of a mechanical seal is dependant upon the conditions that are imposed on the seal assembly during running. The fluid being sealed fills the stuffing box in which the seal is mounted and thus the physical and chemical nature of this liquid will have direct effect on seal operation and life. Slurries and fluids carrying solid particles are especially dangerous as there is a tendency for solid particles to collect in the vicinity of the mating faces and finally even entering the fluid film gap between the mating faces. Hard particles entering this gap will cause premature seal face failure.

Improved seal operation is possible by controlling the environment surrounding the seal. The most commonly used methods for control are flushing and quenching.

Flushing

In flushing, a fluid is injected (through connection F as shown in API Gland – Plan # 62) into the stuffing box such that it impinges or jets onto the mating faces. This fluid may be the same fluid that is being sealed, tapped from a point at a higher pressure than that existing in the stuffing box, or any other fluid, preferably at a lower temperature, that may be permitted to mix with the sealed fluid.
Flushing effectively aids cooling of the seal mating face area. In addition, the introduction of a pressurized clear fluid ensures that solid particles present in the sealed media do not collect near the sealing faces.

Quenching

In quenching, a fluid is introduced (through connection Q as shown in API Gland – Plan # 62) on the atmospheric or outer side of the seal mating faces that either helps in cooling or in maintaining a require temperature at the mating faces. This also creates a barrier between the atmosphere and seal faces as the atmospheric air creates problem to seal faces in some cases. Few such applications are given below.

• When pumping cool media (say at – 40 deg. C), moisture in the atmosphere condenses and ice is formed below seal face hindering its operation.
• In case of high temperature oils when vapors keep on escaping in the atmosphere, they come in contact with oxygen and burn. These carbon particles cerate problem in seal area.
• Crystallizing media gets into crystals when solvent in it gets evaporated because of the atmospheric air present blow seal faces. These crystals create problems for seal faces.

The American Petroleum Institute (API) issues guide lines to help petroleum people select and then pipe various types of controls for mechanical sealing applications. These piping arrangements are described in API standard 610.

Equipment Parameters

For satisfactory seal performance, equipment parameters shall be as under.

Radial movement of shaft (runout / deflection) shall be less than 0.08 mm.
Axial movement of shaft (end play) shall be less than 0.26 mm.
Stuffing box face squareness (face runout) shall be less than 0.05 mm.
Stuffing box bore concentricity (with respect to shaft) shall be less than 0.13 mm.
Stuffing box shall be free of burrs and sharp edges.
Shaft / sleeve shall be free of burrs and sharp edges.

Please refer to manufacturer’s drawing /instruction for above checks.

Installation Instructions

A component seal is one where each part of the seal must be assembled on the equipment individually. This requires considerable skill and significant time as compared to installation of a catridge seal. During installation of a mechanical seal take care of following.

• Assemble seal parts in a clean environment.
• Do not use hammer for assembly as seal faces are delicate and may crack / break.
• Check that seal parts, gland and stuffing box are free from burrs, sharp edged and deep scratches / damage.
• Check surface finish at elastomer area to be as per manufacturer’s recommendation.
• Check that set screws on either the rotary unit or the drive collar of the seal assembly are free in the threads.
• Confirm hardness of shaft / sleeve to be such that after tightening set screws, rotating assembly does not get loose (if set screws are tightened against a hard surface, they will fail to hold assembly in desired position during operation). Alternatively, use hardened set screws.
• It is a good practice to check fitting of shaft sleeve, rotary assembly and gland without O-Rings to ensure that are fitting freely before assembling them with O-Rings.
• Use correct size O-Rings at all places.
• Do not use used O-Rings and gaskets.
• Never use "glued together" O-Ring for any "dynamic" application. A hard spot will be created that will interfere with the movement of the O-Ring.
• Lubricate shaft and secondary seal (O-Rings / bellows) as per manufacturer’s recommendation. If assembling is difficult, apply water as lubrication. Rubber bellow seals should be lubricated with Vaseline. Don’t apply silicon grease on them. EPR (Ethylene Propylene Rubber) elastomers should not be lubricated with petroleum based oil. For EPR material use silicon grease.
• Install seal at its correct operating length as per manufacturer’s drawing.
• Check direction of helix of coil for single spring seal. Helix should be R.H. for C.W. rotation and L.H. for C.C.W. rotation when looking at seal face.
• Gland bolts or nuts should be tightened only enough to effect a gasket seal at the stuffing box face. This can be achieved by initial finger tightening and further tightening with ½ to ¾ turns. Over tightening could result in distortion of seal faces.
• Cartridge type seal assemblies are provided with axial location plates that hold the assembly together before installation in the equipment. Make sure that the axial location plates are moved out of the grooves provided on the shaft sleeve after their fitting.
• When seal assembly is complete, connect all piping, check that all environmental controls have been connected, and all unused holes in the stuffing box / gland are plugged.

Start-up Procedure

Take care of following before starting equipment and its operation for the first time after installation of mechanical seal.

• Equipment should be aligned with the drive as per manufacturer’s recommendations.
• Check the shaft for free movement. Manually rotate the shaft several turns. If shaft binds due to any reason, investigate and correct it.
• Activate all auxiliary systems like flush, quench, barrier lines and vent the stuffing box until all trapped air has been released.
• Pump should have adequate NPSH and it should work with out cavitations and vibration.
• No noise should come from stuffing box.
• Excessive heat generation should not be there. This may be due to stationary parts contacting the rotating shaft or rotating seal parts contacting the housing of the equipment.
• Examine the seal. Slight leakage should stop when the faces “wear in”.

Causes of Seal Leakage

The operating life of a seal is complete when either face has worn entirely. If either face has completely worn, the cause of failure is evident and no further inspection is required unless this occurred in a very short time. If both faces are intact, seal parts shall be inspected. Major seal problems and possible causes are as under.

Note:
API 682 (Shaft sealing systems for centrifugal and rotary pumps) requires that the sealing system supplied, “have a high probability of meeting the objective of at least three years of uninterrupted service while complying with emission regulations”.

Acknowledgement:

In this article sketch of basic mechanical seal is reproduced from website http://www.practicalpumping.com owned by Ross Mackay Associates Ltd.