Rotary kinetic fluid motors or pumps – Bearing – seal – or liner between shaft or shaft sleeve and... – Seal
Reexamination Certificate
1997-03-31
2001-09-11
Verdier, Christopher (Department: 3745)
Rotary kinetic fluid motors or pumps
Bearing, seal, or liner between shaft or shaft sleeve and...
Seal
C415S111000, C415S113000, C415S230000, C417S423110, C417S423120
Reexamination Certificate
active
06287074
ABSTRACT:
1. FIELD OF THE INVENTION
The present invention relates generally to rotating shaft devices, including motors, axles, centrifugal pumps, and more specifically to mechanical seals utilized in such devices.
2. BACKGROUND OF THE INVENTION
Rotating shaft devices are used extensively throughout the world, and have been improved many times over the course of many years. However, as described below with respect to centrifugal pumps, rotating shaft devices still have considerable problems which have not been resolved.
Centrifugal pumps typically contain an impeller coupled to a rotating shaft. In conventional centrifugal pumps a pumpable fluid (pumpate) is pulled into the eye of the impeller where the fluid is spun radially outwards into the volute space. Pressure builds in the volute space until the pressure is able to overcome the discharge resistance, at which point the pumpate exits the pump.
It is well known in the art to use either a soild or a hollow shaft, and to rotate the shaft using electromotive forces. Typically, a rotor is affixed to the outer circumference of the shaft of either configuration for this purpose, and the rotor is acted upon by a concentric stator. Either arrangement raises the possibility that some of the pumped fluid will leak from spaces between various stationary and rotating components.
It is known to eliminate the leakage problem by utilizing a canned pump (not shown). In such pumps the rotor and shaft bearings are contained within a “can” inside the pumpate flow stream. Canned pumps are typified by U.S. Pat. No. 3,667,870 to Yoshida, Canadian Pat. no. 733,312 to Penman, and more recently U.S. Pat. No. 5,356,273 to Nixon. While canned pump designs are effective in addressing the leakage problem, they are inherently inefficient because the wall of the “can” is interposed between the rotor and the stator. Such a design necessarily reduces the efficiency of electromagnetic energy transmission.
In centrifugal pumps other than canned pumps, leakage is commonly addressed using mechanical seals. Prior art
FIG. 1
depicts a generic centrifugal pump
110
having a rotating shaft
120
to which is affixed an impeller
130
. A rotor
140
is concentric about the rotating shaft
120
, and a motor stator
150
is concentric about rotor
140
. A volute
160
is held away from the motor assembly by close couple frame
111
. Volute
160
partially encloses the impeller
130
, and has suction inlet
15
and discharge outlet
165
. Fluid enters the pump in the direction of arrow
105
. Centrifugal pump
110
has a generic mechanical seal
110
A which includes non-rotating secondary seals
170
and
171
, and rotating secondary seals
172
and
173
. In the relationship shown, non-rotating secondary seal
170
seals non-rotating seal
171
, and rotating seal
172
seals rotating secondary seal
173
. A rotating pressure spring
174
biases seal
171
against seal
172
, and a spring cup
175
helps stabilize the pressure spring
174
.
For centrifugal pumps of the type shown in
FIG. 1
, there are logically only two categories of points A and B (shown) at which the seals can be positioned with respect to the rotating shaft
120
entering the volute to prevent leakage. In either position mechanical seals are positioned to provide a seal between the pressurized volute and the rotating shaft. Examples of such pumps are found U.S. Pat. No. 5,288,215 to Chancellor et al. (the '215 patent). In the '215 designs all of the fluid within the pressurized volute is prevented from recirculating back into the impeller suction eye. This provides a high degree of operational efficiency relative to pumps that allow pumpate recirculation lose optimum design efficiency through the pumpate recirculation.
Mechanical seals in centrifugal pumps are plagued with design problems because such seals necessarily involve at least two lap seal finished faces rubbing against each other. In
FIG. 1
, for example, seal
172
rubs against seal
171
, and such surfaces tend to wear out. This problem is especially acute where the pumpate includes suspended solids. Seal service life in conventional mechanical seals can also be reduced because of misalignment of the seal faces due to shaft deflection, and seal run out. One partial solution involves the placement of a “floating” or “intermediate” double faced seal between a rotating sealing surface and a stationary sealing surface. This can reduce the relative sliding speed between adjacent sealing surfaces to about one-half the speed encountered with a simple two-surface seal. Exemplary disclosures in this area are U.S. Pat. No. 4,351,533 to Moore and U.S. Pat. No. 4,266,786 to Weise. It is also known for seal designers to utilize a self-lubricating sealing material, which requires no lubricant. Such materials can be used as combination bearing-seals, and an example of such materials are described in U.S. Pat. No. 4,764,035 to Boyd.
Biasing of the seals against one another produces yet additional problems. Biasing is typically accomplished by spring loading one of the sealing surfaces, but may also be accomplished using another force such as fluid pressure as described in U.S. Pat. No. 4,707,150 to Graham Biasing of one sealing member against another is generally made axially but not radially.
It is known to incorporate several of the above-described improvements into a centrifugal pump having the first category of seals described above. The above-mentioned '215 patent, for example, describes a pump having an advanced axially biased floating seal. Despite all of these improvements, however, there is still a need to provide improved seals in a centrifugal pump. The above-described problems are largely echoed in other rotating shaft devices. Commonly used axles, for example, are typically supported by one or more lubricated bearings, which have sealing problems with respect to the lubricant.
3. SUMMARY OF THE INVENTION
The present invention provides for novel mechanical seals in which a non-rotating, axially slidable sealing member is biased against a sealing ring affixed to a rotating shaft.
In preferred embodiments the axial biasing, non-rotating sealing member additionally engages a second sealing member which is rotating with respect to the shaft. In particularly preferred embodiments relating to pumps, the biasing sealing members are positioned near the end of the motor housing or pump assembly, with a sealing ring interposed between a rolling bearing and the biasing sealing member.
REFERENCES:
patent: 2077881 (1937-04-01), Gits
patent: 2465499 (1949-03-01), Voytech
patent: 2549112 (1951-04-01), Miller
patent: 2653837 (1953-09-01), Voytech
patent: 2911241 (1959-11-01), Horvath et al.
patent: 2981558 (1961-04-01), Jensen
patent: 3079605 (1963-02-01), Thomas et al.
patent: 3218110 (1965-11-01), Conner
patent: 3540833 (1970-11-01), Talamonti
patent: 3667870 (1972-06-01), Yoshida et al.
patent: 3704020 (1972-11-01), Huhn
patent: 3746472 (1973-07-01), Rupp
patent: 4253713 (1981-03-01), Chambers, Sr.
patent: 5478222 (1995-12-01), Heidelberg et al.
patent: 5605436 (1997-02-01), Pedersen
patent: 5630699 (1997-05-01), Kirby et al.
patent: 539718 (1957-04-01), None
patent: 449584 (1913-08-01), None
patent: 719222 (1954-12-01), None
Fish & Associates, LLP
Nate International
Verdier Christopher
LandOfFree
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