Mechanical Seal

Posted by 18 February, 2011 (0) Comment

Mechanical Seal

Mechanical seal concept

Called mechanical seal is means least 1 pairs perpendicular rotating axis end face in fluid pressure and compensation institutions elastic (or magnetic) role under and auxiliary sealed tie to maintain paste merger relative sliding consisting prevent fluid leak devices.
Elastic loading mechanism and the secondary seal is a metallic bellows mechanical seal which we call metal bellows seal.
In light seal there use rubber Bellows make auxiliary sealed, rubber bellows elastic limited generally need supplemented spring to meet load elastic.

Mechanical seal composition

Mainly following four categories parts.
·Main components: Activity ring and static ring.
·Auxiliary seals: seals (there O shaped, X shaped, U type, wedge, rectangular flexible graphite, PTFE coated rubber O ring etc.).
·Elastic compensation institutions: spring, push ring.
·Transmission pieces: shells Kei Block and key or various screw.

Mechanical seal is quite soft packing seal

Advantages:
·cope Canton mechanical seal can used Cold, heat, vacuum, high pressure, different speed and various corrosive medium and containing abrasive medium etc. sealing.
·Friction power consumption small mechanical seal friction power only soft packing seal 10% ~ 50%;
·Sealed reliable long cycle operations, sealing state very stable leakage small, press rough statistics, its leakage general only soft filler sealed 1 / 100;
·Long life in oil, water class medium general reach 1 ~ 2 years or more, in chemical medium usually can more than six months;

* Shaft or bushings are basically free from wear;
· Maintenance cycle long end face worn automatically compensation general, without recurrent maintenance;
· Vibration good on rotating axis vibration, partial pendulum and axis on sealed cavity skew insensitive;

* About the current number of factories “zero leakage” needs, packing not meet this requirement; not adapt to a wide range of arbitrary bigger, but in factories, often replacing or maintenance will plant great loss.

The following shortcomings:
· Disposable high investment.
·Structure was complex manufacturing processing demanding;
·Occurs contingency accident, handling more difficult;
·Installation and replacement troublesome and requested workers certain installation technical level;

Called mechanical seal is means least 1 pairs perpendicular rotating axis end face in fluid pressure and compensation institutions elastic (or magnetic) role under and auxiliary sealed tie to maintain paste merger relative sliding consisting prevent fluid leak devices.

Categories : Mechanical Seals Tags : , ,

Mechanical Seal Gets Aggressive

Posted by 13 February, 2011 (0) Comment

Mechanical Seal Gets Aggressive

Mechanical seal, the retailer of teen and twenty-something fashions, has made a turnaround from negative profits to profits and then some. The company now competes with retailer Forever 21 when it comes to quick turnaround of trendy clothing and accessories sold at affordable prices.

One of the major differences however, between mechanical seal and Forever 21 stores is in the customer service and closing of the sale. Forever 21 sales associates watch over the dressing rooms and ring up the sales without being annoying or pushy about selling clothing. In other words they assist the customers where needed without being overbearing or annoying.

mechanical seal’s sales associates, however, have taken a turn for the pushy ever since the launch of the Seal Deal card. Purchased for , the card can be shown at the time of purchase at any mechanical seal store for 10 percent off of each item regardless of whether it is a regular, sale or clearance-priced piece of merchandise. The card is good for one year from the date of purchase.

Shoppers at mechanical seal can be assured that not only will a sales associate attempt to sell customers more clothes as they are shown a dressing room, but that they will be pushed to purchase a Seal Deal card while at the register.

It would be only slightly annoying if customers were asked if they were interested in purchasing the card and then that be the end of it, but some sales associates have become pushy and aggressive.

The typical sales pitch for the card includes the associate telling a customer that if they purchase the card in addition to the clothes they buy, the card is free. For example, if a customer spends approximately, 0 on one transaction at mechanical seal, and they buy the Seal Deal Card, they receive 10 percent off of each item purchased. The 10 percent savings from each item purchased then theoretically goes toward the price tag of the Seal Deal card making it “free.”

Any smart shopper knows however, that the card is not free because a customer is paying for it out of their 10 percent savings from the card. While a person may not have had the savings without the card in the original purchase transaction, they also did not have to spend the on a card.

Incidentally, the card is a good deal if someone frequently shops at mechanical seal. Customers should be smart in deciding whether or not the card is something that will save them money in the future based on how much they normally buy at mechanical seal. If someone is making at least one purchase per month at mechanical seal, then they might consider the card.

This individual not only went into the sales pitch of how the card would be free because of the amount of clothes being purchased, but she was also unprofessional enough to say (in front of the customer) to another sales associate that if she was able to sell the Seal Deal card in this transaction, she would have made her quota for the month.

After the associate was told the customer bought a Seal Deal card about 2 months ago, the associate went on to say that it would be better to spend another to buy a new one because it came in a “new case.” This “new case” would be code for the cheap, plastic-hinged box that the card came in. In addition, she said the customer would save more with a new card “because it was a newer card.”

This, of course, would be a bold-faced lie since a customer receives 10 percent off each item in every transaction regardless of when the card was purchased.

These sorts of sales tactics are embarrassing and more than likely do not truly reflect the mechanical seal company. However, in general the sales push to buy these cards, which are a good deal in some cases, has become annoying and in some cases, bullying. If the company continues to push their sales associates to meet these quotas and demand more from the customer, they are going to end up not having any customers, which was their problem not more than five years ago (although that was due to poor choices of inventory and pricing).

On a recent visit to the mechanical seal store at the Mall of Orange in Orange, CA, one sales associate was so bent on selling a Seal Deal card, she felt compelled to lie about the potential savings.

Categories : Cartridge Seals Tags : , , , ,

Noncontact mechanical seal

Posted by 12 February, 2011 (0) Comment

Noncontact mechanical seal

A noncontact mechanical seal has a seal ring which includes a sealing face portion formed by ventilative porous materials and a ventilating portion to pass a gas of a high pressure side to the sealing face portion from the back side of said sealing face portion. The sealing face portion is preferably a porous ring independently formed of said seal ring and mounted on the seal ring providing a space at the back side thereof. The seal ring preferably is provided with a small diameter thin portion at the portion forming the bottom of the space.

Noncontact seals are utilized to seal gas or the like. Noncontact seals include seal faces where high pressure gas is induced to keep the seal faces out of contact with each other. Such noncontact seals are provided at the sealing face with a very slightly tapered portion, a circle groove, a thin air flow hole or a spirally radial groove to induce high pressure gas to the sealing face thereof.

However it is hard (it increases the cost) to form the tapered portion, the groove or the hole with a high accuracy. In noncontact seals the seal faces are not completely noncontact; they contact each other slightly owing to vibration and/or poor accuracy of machining. Such contact causes wear of the sealing faces and deformation of the grooves follows. Thus the sealing ability of noncontact seals become worse as the sealing faces wear and therefore noncontact seals cannot keep providing stable and reliable sealing.

Furthermore the hole and the groove can sometimes be bigger than the required size because of difficulty of forming of small grooves, holes or the like and because of the need to make an allowance for the wear of sealing faces caused by vibration. Such a bigger groove and hole permits entry of more air, that separates the sealing faces too much and makes fine adjustment of the gap between the sealing faces difficult.

In such mechanical seal shown in FIG. 1, the high pressure gas in the high pressure side X flows through the ventilating groove 70, the porous ring 6 and the porous sealing face 11 toward the rotary seal ring 2. The gas in the relief space 60 maintains some gas pressure. The distribution of the pressure at the sealing face of the nonrotary seal ring 1 is shown in FIG. 2 as lines a, b and c. A line d represents the pressure which the back end of the nonrotary seal ring 1 receives. When the sealing face of the nonrotary seal ring 1 is closest to the sealing face of the rotary seal ring 2, as shown in FIG. 1 the pressure on the face is high as shown by line c. When the nonrotary seal ring 1 is more distant from the rotary seal ring 2, as shown in FIG. 5, the pressure decreases in the gap therebetween as shown by line a and this creates a vacuum force. Thus the pressure in the gap will then increase the balance with the force pushing the nonrotary seal ring 1 toward the rotary seal ring 2 at the line b, and the operation is carried out at this stable condition.

Since ventilation (or flowing the gas) through the porous ring 6 can be made very small, the gap between the nonrotary seal ring 1 and the rotary seal ring 2 can be very small. The gap is adjustable by controlling the balance factor of the nonrotary seal ring 1 and/or the ventilation of the porous materials of the porous ring 6. The ventilation may be decreased by reducing the number or the diameter of pores, so that the gap between the nonrotary seal ring 1 and the rotary seal ring 2 can be reduced. On the other hand the gap can be enlarged by increasing the number or the diameter of the pores. Such adjustment of the gap can be controlled by adjusting the thickness in the axial direction of the porous ring 6.

It is easier to mount the porous ring 6 on the nonosmotic ring 5 than to form holes on sealing faces in the prior art. The small diameter thin portion 76 of the nonosmotic ring 5 gives elasticity to the nonosmotic ring 5 to bend the portion 76 so as to move the outer fringe 62 apart from the rotary seal ring 2, which prevents improper contact between the outer fringe 62 and the rotary seal ring 2 and the extraordinary torque generated at the rotary seal ring 2 by such contact. Furthermore the relief groove 60 provides the porous ring 6 with the thin portion 61 which also gives elasticity to the porous ring 6 per se and the unwanted contact between the outer fringe 62 and the rotary seal ring 2 is further effectively prevented thereby.

FIG. 3 shows a graph indicating the difference of the values of leakage and contact torque between the noncontact mechanical seal of FIG. 1 and the noncontact mechanical seal of the prior art which include holes for ventilation and cannot provide elasticity. White circles indicate the rotation torque of the embodiment of FIG. 1 and white triangles indicate the leakage of the embodiment. Black circles indicate the rotation torque of the prior art and black triangles indicate the leakage of the prior art. The abscissa expresses the gas pressure of the sealed gas in the high pressure side X.

Since the mechanical seal of the invention provides an elasticity effect at the outer fringe 62, unwanted contact does not happen and therefore the rotation torque is small. Furthermore it is obvious that the leakage is larger at higher pressure than the prior art because of the small gap of the sealing faces. On the other hand, the torque of the prior mechanical seal increase as the pressure in the high pressure side X increases as shown by the black circles in FIG. 33, which is caused by the bending of the outer fringe of the sealing ring of the prior art toward the opposite counter sealing ring due to the pressure in the high pressure side X.

The ventilation of the porous ring 6 may not substantially change as the face of the porous ring 6 wears, which is contrary to prior noncontact mechanical seal. This provides stable and reliable sealing.

Categories : Cartridge Seals,Mechanical Seal Tags : , , ,

Mechanical seal with cylindrical balance sleeve

Posted by 10 February, 2011 (0) Comment

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.

Categories : Mechanical Seals Tags : , , , , ,

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 : , , , , , ,