Mechanical seal assembly with improved fluid circulation

Posted by 8 February, 2011 (0) Comment

Mechanical seal assembly with improved fluid circulation

A seal assembly for a mechanical seal includes a rotatable shaft with at least one mechanical seal disposed about the shaft, the seal having a rotatable face coupled to the shaft and a stationary face, wherein the respective faces of the seal are in contact with one another, and a chamber for holding a cooling fluid, disposed about the shaft and in communication with the faces of the seal, and a closed loop fluid path disposed about the outer diameter of the shaft, preferably or in a non linear manner, in fluid communication with the chamber, for circulating fluid about the seal faces.

A variety of mechanical seals have been developed for use along a shaft, often in the context of pumps. One typical configuration is a mechanical seal with one stationary face and one rotating face. The rotating face of the seal rotates with the shaft of the pump, while the stationary face of the seal is generally coupled to the housing of the pump. In order to provide a tight seal, the two faces are typically in contact with each other. The frictional contact between the faces generates heat.

In order to dissipate heat, a fluid may be added to help transfer the heat away from the seal faces. Typically, a small fluid chamber is disposed about the shaft, so that the fluid is in communication with the seal face. As these mechanical seals are frequently used in a double or tandem configuration, the chamber may be disposed along the shaft, between and including the two mechanical seals. Often, a cooling fluid reservoir is added, with an auxiliary pump to circulate the fluid between the reservoir and the chamber. However, the addition of an auxiliary pump adds cost, requires additional space, and adds another component that is subject to failure, thereby reducing reliability.

There are many applications where a mechanical seal is subjected to fluid at the ID of the face. One of the most common is that of an unpressurized tandem seal where the barrier fluid is in contact with the ID of the primary seal and at the OD of the secondary seal. There is circulation of the barrier fluid into and out of the seal chamber by means of some type of pumping device that is usually part of the secondary seal rotating element. This circulation is adequate for cooling the secondary seal but is less than satisfactory for cooling the primary seal. This lack of cooling performance for the primary seal is due to the inability of the fluid to circulate to the ID of the seal.

Another application where cooling is needed at the seal face is in a vertical pump gear box seal oriented with the gear box oil at the ID of the seal. Gravity ensures that oil is at the ID of the face. However, during dynamic operation this fluid can not circulate with the bulk fluid in the gear box. This leads to increased seal temperature and possibly coking of the oil at one or both of the seal faces. Coking leads to increased leakage and damage to seal faces.

Rather than use an auxiliary pump, other configurations have built a “pumping rotor” into the system. See, e.g., U.S. Pat. No. 4,466,619 to Adams U.S. Pat. No. 4,560,173 to Adams et al. A slotted sleeve is fitted concentrically about the shaft, whereby the rotational movement of the shaft aids in circulating fluid along a fairly linear path, drawing the fluid from the reservoir into the chamber through an inlet, moving it radially around the shaft, and pushing it out of the chamber through an outlet and back into the reservoir. Another type of seal uses screw-type threads on the shaft to move the fluid between an inlet and an outlet. However, the fluid may only be moved in one direction in the chamber, between the inlet and the outlet, and away from the mechanical seal.

Because of the seal mechanisms themselves, it is generally not possible to position an inlet or outlet directly adjacent a seal face. Thus there is a space in the chamber between the inlet and outlet, which define the path of circulation, and the seal face, where the heat is generated and where the fluid will be heated the most. This causes a “dead end” space in the chamber between the seal faces and the respective inlet and outlet, where the cooling fluid is substantially stagnant, and does not circulate with the rest of the fluid. In the “pumping rotor” configuration discussed above, the radial circulating action occurs in a “band” that is aligned with the inlet and outlet; fluid outside this band remains substantially uncirculated. In the screw type circulator discussed above, these dead spots occur on either side of the inlet and outlet, as the fluid is substantially circulated only between the inlet and outlet. In the double or tandem configuration, there is generally a band or path of circulation between the seals, but there is inadequate circulation directly at the seal faces, where circulation is most necessary.

Thus there exists the need for a circulation device for mechanical seals which provides circulation to the seal faces, preferably without the use of auxiliary pumps, which can circulate fluid about the seal faces beyond the respective inlet and outlet locations, and which operates under rotation of the shaft in either direction.

An important feature of the present invention is the ability to circulate the fluid within the “dead end” space at the opposed faces of the seal. Although fluid cannot be pumped beyond this point, the present invention provides both radial and axial circulation, lifting the heated fluid away from the opposed seal faces and replacing it with cooler fluid.

Another important feature of the present invention is that it operates effectively upon rotation of the shaft in either direction. Thus the mechanical seal remains cooled regardless of the direction of shaft rotation.

Categories : Cartridge Seals Tags : , , , , ,

Fully split cartridge mechanical seal assembly

Posted by 30 December, 2010 (0) Comment

Fully split cartridge mechanical seal assembly

The fully split cartridge mechanical seal assembly is comprised of two unitized self contained assemblies which fit together to form a unitized cartridge design. The assembly uses set screws to position the seal assembly to the rotating shaft or sleeve and slots in the gland to receive attaching means to a fixed stationary or chamber.

The stationary components of the assembly include the following: a split stationary seal ring, a split stationary seal ring packing, springs set into apertures in the split gland, the split gland, the split gland gasket, gland bolts, a gland split gasket, and setting clips and screws. The rotating components include the following: a split rotary seal ring, split rotary seal ring packing, a split sleeve, the split sleeve packing, the sleeve bolts, cup point set screws, and sleeve split gasket. The fully split cartridge mechanical seal design eliminates the handling of a lot of loose, delicate, precise manufactured components and allows for very simple, easy and time saving installation with no measurements or guess work.

This invention pertains to mechanical sealing assemblies, and in particular to such sealing assemblies that use a fully split cartridge mechanical seal assembly, for use in overcoming inherent handling and assembly problems, due to the complexity of the multitude of delicate components and loose parts and the difficulty of fitting them together precisely and accurately to insure a proper seal.

Mechanical seals are well known in the field and the difficulties found in these systems are well known. Since mechanical seals are Subjected to wear, corrosion, abrasion vibration, thermal, pressure and other effects, they must be replaced periodically. This normally may require the removal of the coupling, bearings and motor which can be a very involved and costly procedure with a lot of resulting down time for the equipment. By splitting the mechanical seal allows for the assembly and disassembly of the seal without dismantling the equipment.

There have been a number of attempts to deal with these difficulties. Examples of these type devices include the United States Patent issued to Azibert, U.S. Pat. No. 4,576,384 on 18 Mar. 1986 and the United States Patent issued to Ballard U.S. Pat. No. 4,576,383 also issued on 18 Mar. 1986. A U.S. Pat. No. 3,025,070 issued to J. C. Copes for a Split Mechanical Seals on 13 Mar. 1962 is another example of standard mechanical seals.

The general function of these references and a number of others in the art is to have a rotating seal assembly attached to a shaft or sleeve and a non-rotating seal assembly attached to a stationary housing or chamber surrounding the shaft or sleeve. However, all of these designs and many others still have inherent problems. The primary difficulty is that these devices have a great number of loose parts that must be handled with extreme care, especially the two precision manufactured primary faces to insure good seal performance and life.

They also require measurements, or the use of various shims or special tools to set and align the seal assembly accurately. They typically use internal clamping designs with their limitations of torsional and axial holding power to locate on the rotating shaft or sleeve and cannot be moved after setting without complete disassembly of the seal if readjustment is required. Some also require a receiving unit on the outer faces of the outer flange of the stationary hounding or chamber which assists the concentricity of the seal assembly to the rotating shaft.

It is the object of this invention, then to set forth a split mechanical seal assembly which avoids the disadvantages limitations, above-recited, which obtain in prior mechanical sealing apparatus. It is also the object of this invention to teach a fully split cartridge mechanical seal assembly that can be positioned on a rotating shaft or sleeve easily and quickly and which will eliminate many of the problems found in standard mechanical sealing systems.

Particularly, it is the object of this invention to set forth a fully split cartridge mechanical seal assembly, for use in situations that use rotating equipment, such as pumps, agitators and mixers that are difficult and time consuming to disassemble, comprising two unitized self contained assemblies; said unitized self contained assemblies having means for attaching said unitized self contained assemblies over a rotating shaft or sleeve; said complete solid cylindrical assembly having setting means for aligning and retaining said complete solid cylindrical assembly in position and for removing said complete solid cylindrical assembly after permanently attached; said complete solid cylindrical assembly having fastening means for connecting said complete solid cylindrical assembly to a fixed stationary housing or chamber; and attaching means for connecting said complete solid cylindrical assembly rotating portion to said rotating shaft or sleeve.

Ningbo Yinzhou Guowei, mechanical seal Component Factory is a professional engaged in the design, development, manufacture, sale of various cartridge seal and flygt seals business. Production and testing are well-equipped with a high-quality staff.

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Categories : Cartridge Seals Tags : , , , , ,