Mechanical Seal

Noncontact mechanical seal

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.

whatis a mechanical seal?

Question by sandeep d: whatis a mechanical seal ?
used in centrifugal pumps.

Best answer:

Answer by dawnsdad
It is a seal that separates the motor housing from the wet end of the pump. It is installed behind the impeller. Since the impeller must be surrounded by water and is also connected to the motor (which cannot be wet), a mechanical seal is used to prevent water from leaking from the pump volute (were the impeller is located), down the motor shaft. It allows the motor shaft to rotate without leaking.

Add your own answer in the comments!

BSM Pump 713-9507-270 #4 Mechanical Seal Unit Reviews

BSM Pump 713-9507-270 #4 Mechanical Seal Unit

• “BSM PUMP” MECHANICAL SEAL
• Units #4

“BSM PUMP” MECHANICAL SEAL

Units #4

Price: $ 100.08

Related Mechanical Seal Products

Arrangement in connection with mechanical seal

An arrangement in connection with a mechanical seal includes at least two sliding surfaces pressing against each other, which are arranged to seal a gap between a rotating and a non-rotating machining part, and mechanism for providing a sealing fluid flow cooling the sliding surfaces. To provide an optimal consumption of sealing fluid, a valve mechanism is arranged to the mechanism for providing the cooling sealing fluid flow, the valve mechanism being arranged to react to the temperature of the seal and to open and close the flow of sealing fluid according to the cooling need.

The method of controlling sealing fluid flow according to seal cooling need, comprising: providing at least two sliding surfaces pressing against each other, which are arranged to seal a gap between a rotating and a non-rotating machine part, providing means for providing a sealing fluid flow cooling the sliding surfaces, and providing a valve means arranged in connection with the means for providing a cooling sealingfluid flow, the operation of the valve means being based on a memory metal element that is arranged to react to the temperature of the sealing fluid and to open and close the sealing fluid flow according to a cooling need, wherein the valve means isintegrated to the mechanical seal.

Mechanical seals are commonly used in different technical fields to seal gaps between a rotating and a non-rotating machine part. Examples of such rotating and non-rotating machine parts and gaps between them include the body and shaft of apump, for instance process pump, and the gap between them that needs to be sealed so that the pumped process fluid cannot leak out through the gap between the pump shaft and the pump body. The sealing is done between two exactly opposing slidingsurfaces that rotate against each other. In normal use, a mechanical seal naturally also heats up, in which case it is cooled by a fluid flow on the opposing side to the seal. Water, for instance, is used as the coolant. Mechanical seals often alsocontain a second sliding surface pair on the atmospheric side, in other words on the outside, to seal any leakage of sealing fluid to the atmosphere.

Critical operating values in the operation of a mechanical rotary shaft seal include pressure, temperature and a few other factors. Pressure includes the pressure of the sealed product, the pressure inside the seal, or the sealing fluidpressure, the ratio of the above-mentioned pressures with respect to each other, and any changes occurring in the pressures.

As regards temperature, the related issues are the temperature of the sealed product, the temperature of sealing fluid, the temperature of the environment, the temperature of the parts of the seal, especially the sliding surfaces, and any changesin temperature.

Mechanical rotary shaft seals are cooled by means of a sealing fluid that flows continuously through them. The flow is in some cases limited, i.e. the flow is adjusted in such a manner that cooling is sufficient for the conditions prevailingduring the adjustment. In some cases, the water connection from the seal is plugged completely. These solutions use a sealing water adjustment and control unit, for instance, to adjust the flow and pressure of the sealing water of the mechanical seal. The apparatus comprises a flow meter and any necessary adjustment devices for adjusting the flow and pressure of the sealing water.

The flow rate of sealing water is determined using the above-mentioned arrangement. One important task of the sealingwater is to cool the mechanical seal, as stated above. It is, however, difficult to adjust the flow of the sealing water to be optimal according to the temperature of the outflowing sealing water. The above-mentioned solution helps find out the amountof used sealing water, but, for safety, water consumption is often adjusted to be too high.

Further, there is the problem that if the flow of the sealing water is adjusted to be low, the flow orifice is easily blocked by particles in the water, eventhough the orifice were designed to allow water impurities to pass. Flow low-limit alerts caused by orifice blockage are also problematic in practice. Plugging the sealing water outflow connection provides good conditions for a mechanical seal, butthis arrangement does not provide heat removal from the seal. If the temperature rises higher than the temperature designed for a mechanical seal, the seal may suffer damage. The solution is thus not suitable for situations, in which the temperature ofthe seal rises easily. An advantage of the solution is naturally that it does not waste expensive sealing water.

The mechanical seal comprises two sliding surfaces pressing against each other, which are arranged to seal the gap between the rotating and the non-rotating machine part. The seal further comprises an input unit and an output unit for directingcooling sealing fluid to and from the mechanical seal. The seal may also comprise a second sliding surface pair to seal any leakage of sealing fluid to the surroundings.

Seals and Sealing Handbook, Fifth Edition

Seals and Sealing Handbook, Fifth Edition

Wherever machinery operates there will be seals of some kind ensuring that the machine remains lubricated, the fluid being pumped does not leak, or the gas does not enter the atmosphere. Seals are ubiquitous, in industry, the home, transport and many other places. This 5th edition of a long-established title covers all types of seal by application: static, rotary, reciprocating etc. The book bears little resemblance to its predecessors, and Robert Flitney has re-planned and re-written every aspe

List Price: $ 192.00

Price: $ 145.00