Seal Side
Seal Side
License for phpBay Pro is invalid.
US Navy SEALs Combat Swim
Mechanical seal with cylindrical balance sleeve
A mechanical seal assembly comprising rotatable and stationary seal rings with faces opposing one another. Means are provided to insure a pressure balance on the outside surface and on the inside surface of the softer seal ring, so that this seal ring does not deflect and distort, and wear in an undesirable manner.
Mechanical seal assemblies usually comprise the combination of a rotatable seal ring connected to a rotatable shaft for rotation therewith, and a non-rotatable or stationary seal ring connected to the flange of a housing. Each seal ring has aradial seal face and the seal faces oppose one another. Whether or not the seal faces engage one another is debatable because there is usually a film of fluid therebetween providing lubrication and cooling for the relative rotation between the faces. In some mechanical seals leakage across the seal face is controlled. In many seal assemblies, one or more coil springs urge one of the rings toward the other, so that in reality, one or both of the seal rings are capable of limited axial movement, eventhough they are commonly referred to as "rotatable" or "stationary". Many conventional mechanical seals can be used as single stage seals or in a multiple stage seal assembly.
In a common type of mechanical seal, one of the seal rings is constructed of a relatively brittle, soft material, such as carbon, whereas the opposing ring is constructed of a harder material, such as titanium carbide, silicon carbide, and thelike. In many of these seal assemblies, the carbon ring is "backed up" by a back-up ring constructed of a harder material, such as a stainless steel. The mating faces of the relatively brittle, soft seal ring and the back-up ring are lapped, so thatthe carbon ring becomes stuck or "married" to the back-up ring. Because of the difference in the modulus of elasticity between the two materials of the seal ring and the back-up ring, i.e., carbon with a modulus of about 2×106 to about4×106 and 18-8 stainless steel with a modulus of about 30×106, a compressive load on the mated rings will cause the carbon ring to shrink more diametrically than the back-up ring. The carbon ring, being married to the back-up ring,will shrink more at its seal or running face, so that this face becomes concave which seriously affects the sealing area of the distorted face, leading perhaps to failure of the seal. The compressive load is mainly due to excessive differentials of thepressures on the inside and outside surfaces of the married rings, which frequently exist in the before-enumerated pumps.
Zobens, U.S. Pat. No. 4,174,844, describes a mechanical seal for high pressure sealing applications having a carbon seal ring, supported on a rigid backing ring, in sliding contact with a seal ring of dissimilar material. A barrier is providedin overlying relation to the outer circumferential surface of the carbon ring to separate this surface from exposure to the pressure exerted by the sealed fluid. There is no communication between the inner and outer circumferential surfaces of thecarbon ring to equalize the pressures on these surfaces, nor is there any attempt to equate the axial pressures.
Martinson, U.S. Pat. No. 4,272,084, describes and claims a multi-stage mechanical seal assembly for pumps of the kind before enumerated. However, the problem of seal ring distortion is not discussed, no back-up ring of a high modulus ofelasticity axially abutting a seal ring of a lower modulus of elasticity is used.
Wiese, the applicant herein, in earlier U.S. Pat. No. 3,813,103, discloses a mechanical seal assembly in which the back-up ring has a marginal portion exposed in a pressure chamber in the seal housing, and the nonrotatable seal ring (backed upby the back-up ring) is ported to allow flow of fluid into the pressure chamber from between the sealing faces to reduce the distortion of the back-up ring and the stationary seal ring.
While the latter may be effective for some installations, it has not been found to be effective where the pressure differentials are as experienced in pumps of the type above described.
Wiese, in U.S. Pat. No. 4,114,900, teaches a mechanical seal in which a rotatable seal ring is provided with an internal radial, annular chamber exposed to low pressure fluid via a radial passage, such that high pressure on the seal ring at aseal face distorts the ring and causes it to be convex. The degree of convexity determines the leak rate across the seal faces. There is no attempt to eliminate distortion of one seal ring; distortion of the seal ring is actually caused by theconstruction.
The mechanical seal assembly of this invention comprises the combination of a rotatable seal ring and a stationary seal ring, the seal rings having seal faces which oppose one another and across which the flow of a fluid from a high pressure zoneto a low pressure zone along the rotatable shaft is substantially prevented. The rotatable seal ring, in the preferred embodiment, is made of a carbide material, and the stationary seal ring, or at least its seal face, is made of a softer material, suchas carbon. The stationary seal ring has a rear face mating with a face of back-up ring and the back-up ring is supported for limited axial movement on a cylindrical balance sleeve surrounding the shaft. The balance sleeve has a stepped outer surfaceand there is provided an annular surface exposed to high pressure fluid. The balance sleeve is received in a cylindrical cavity in a seal flange of a housing and is biased by fluid pressure on its annular surface to insure its seating in the cavity. The back-up ring and the stationary seal ring are resiliently urged toward the rotating seal ring by a plurality of coil springs.
The mechanical seal assembly of this invention is constructed in such a manner to substantially, if not totally, eliminate compressive loads on the outer periphery of the softer seal ring which causes distortions and deflections of this seal ringand leads to failure of the seal assembly. This is accomplished by encircling the softer seal ring and its back-up ring with a cylindrical member, and by providing one or more passages in the seal ring and back-up ring subassembly to insure equalizationof fluid pressures on their inner and outer surfaces. The fit of the cylindrical member around the seal ring and its back-up ring is such to permit fluid to exist therebetween and the outer surface of the cylindrical member is exposed to the highpressure fluid. Also, the seal ring and back-up ring subassembly is constructed so that axial fluid pressure on the back-up ring is sufficient to insure sealing of the mating faces of the soft seal ring and the back-up ring, and to limit thetransmissions of deflections of the back-up ring to the softer seal ring. Axial fluid pressures on the opposite sides of the stationary seal ring are substantially balanced, which insures little, if any, deflections of the softer seal ring which couldbe caused by axial pressure differentials.
About the Author
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.
how can i know the size of a side seal plastic bag ?
You actually could measure it with a tape measure!!!!
Comments
Leave a Reply