Abstrict A flow meter assembly includes a flow meter for use in a sanitary
process environment. The flow meter includes a flow tube having
an end which includes a first gasket lip and a first abutting face.
A sealing flange mates with the flow tube and includes a second
gasket lip and a second abutting face configured to abut against
the first abutting face. A gasket provides a seal between the first
and second gasket lips. The first abutting face and second abutting
face limit compression of the sealing flange.
Claims 1. A flow meter assembly comprising; a flow meter for use in a
sanitary process environment, the flow meter including a flow tube
having an end which includes a first gasket lip and a first abutting
face; a sealing flange having a bore extending therethrough configured
to mate with the flow tube, the sealing flange including a second
gasket lip and a second abutting face configured to abut against
the first abutting face; and a gasket configured to provide a seal
between the first gasket lip and the second gasket lip; wherein
the first abutting face and the second abutting face are configured
to limit compression of the sealing flange.
2. The apparatus of claim 1 wherein at least one of the flow tube
and sealing flange is threaded for use in coupling the flow tube
and sealing flange together.
3. The apparatus of claim 1 including a threaded nut configured
to couple the flow tube and the sealing flange together.
4. The apparatus of claim 1 including a flange extension coupled
to one of the first and second abutting faces and having a length
which limits the compression of the sealing flange.
5. The apparatus of claim 4 wherein the flange extension couples
to the first abutting face and the flow tube.
6. The apparatus of claim 4 wherein the flange extension couples
to the second abutting face and the sealing flange.
7. The apparatus of claim 1 including a void region between the
flow tube and the sealing flange.
8. The apparatus of claim 7 wherein the gasket is partially positioned
in the void region.
9. The apparatus of claim 1 wherein the gasket has a cross section
in the shape of a "T".
10. The apparatus of claim 1 wherein the gasket comprises an elastomer.
11. The apparatus of claim 1 wherein the gasket comprises a fluorocarbon.
12. The apparatus of claim 1 wherein the gasket comprises a single
component.
13. The apparatus of claim 1 wherein compression of the gasket
is less than about 25%.
14. The apparatus of claim 1 wherein compression of the gasket
is less than about 20%.
15. A method for coupling a flow meter to a sanitized process,
comprising: providing a first gasket lip and a first abutting face
on a flow tube of the flow meter; providing a sealing flange having
a bore extending therethrough and having a second gasket lip and
a second abutting face configured to abutt against the first abutting
face; and placing a gasket between the first gasket lip and the
second gasket lip to provide a seal therebetween; compressing the
gasket between the first gasket lip and the second gasket lip; and
limiting the compression applied to the gasket by abutting the first
abutting face against the second abutting face.
16. The method of claim 15 wherein at least one of the flow tube
and sealing flange is threaded for use in coupling the flow tube
and sealing flange together.
17. The method of claim 15 including a threaded nut configured
to couple the flow tube and the sealing flange together.
18. The method of claim 15 including a flange extension coupled
to one of the first and second abutting faces and having a length
which limits the compression of the sealing flange.
19. The method of claim 18 wherein the flange extension couples
to the first abutting face and the flow tube.
20. The method of claim 18 wherein the flange extension couples
to the second abutting face in the sealing flange.
21. The method of claim 15 including a void region between the
flow tube and the sealing flange.
22. The method of claim 21 wherein the gasket is partially positioned
in the void region.
23. The method of claim 15 wherein the gasket has a cross section
in the shape of a "T".
24. The method of claim 15 wherein the gasket comprises an elastomer.
25. The method of claim 15 wherein the gasket comprises fluorocarbon.
26. The method of claim 15 wherein the gasket comprises a single
component.
27. The method of claim 15 wherein compression of the gasket is
less than about 25%.
28. The method of claim 15 wherein compression of the gasket is
less than about 20%.
Description BACKGROUND OF THE INVENTION
[0001] The present invention relates to flow meters of the type
used for measuring flow of process fluid in sanitary process environments.
More specifically, the present invention relates to a seal used
to couple the flow meter to process piping.
[0002] The term "industrial process" generally refers
to automated, or semi-automated processes which are used for the
manufacture or distribution of various materials or compositions
such as natural gas, crude oil, paper pulp, etc. In an industrial
process, remote field devices are used to measure and/or control
operation of the process. For example, process variable transmitters
are used to measure process variables such as pressure, temperature,
flow, etc. The measured process variable is transmitted to another
location for monitoring or for use in controlling the process. Process
control units such as a valve, a boiler, or the like, can be used
to control the process in response to the measured process variable.
[0003] Typically, such field devices communicate with a process
controller located remotely, for example in a process control room.
The communication can take place using various known techniques
such as a two wire process control loop. Typical two wire process
control loops use a single pair of wires to carry both information
to and/or from the field device along with power for use in powering
the field device. One example process control loop is a 4-20 milliAmps
process control loop in which a process variable or process set
point is represented be a current level which ranges between 4 milliAmps
and 20 milliAmps carried on the wire pair. Other process control
loop configurations employ digital signals to carry information.
These include the HART.RTM. protocol and the FieldBus protocol.
[0004] One particular type of industrial process is frequently
referred to as a "sanitary process". Sanitary processes
are used when the process materials must remain pure and not be
exposed to contamination during processing. For example, food and
pharmaceuticals are typically processed in a sanitary process environment.
[0005] The various components used to implement a sanitary process
must not be a source of contamination to the process materials.
For example, any surfaces of the components in the sanitary process
should not corrode or otherwise introduce contaminants into process
materials. For example, the materials used to make surfaces of the
conduits and field devices which come into contact with the process
must not corrode or otherwise contaminate the process fluid. In
other instances, the components which contact the process materials
can be lined with a desired material which is selected so as not
contaminate the process.
[0006] Because the number of materials which can be used in sanitary
industrial processes is limited, it is often the case that a preferred
material for a particular component can not be used. Or, in some
instances, the use of a particular component for a specified purpose
is limited. For example, one standards body known as the European
Hygienic Equipment Design Group (EHEDG) sets forth specific requirement
for the performance for a particular flow meter (between 1'' and
4'' diameter) flow tube. These specifications require the flow meter
to operate over a temperature range. The varying temperatures can
cause degradation in some components such as gaskets. One way to
reduce degradation to gaskets is to limit the amount of compression
a gasket can be placed under in such a configuration. One technique
used to address this design constraint is to use a special metal/elastomer
gasket. This gasket is configured with a metal ring that prevents
the gasket from being compressed beyond the specified limit. The
gasket material is bonded to the metal ring. However, such a configuration
is complex and difficult to manufacture.
SUMMARY OF THE INVENTION
[0007] A method and apparatus for a flow meter assembly of the
type which includes a flow meter for use in a sanitary process environment
are provided. The flow meter has a flow tube with an end which includes
a first gasket lip and a first abutting face. A sealing flange having
a bore is configured to mate with the flow tube. The sealing flange
includes a second gasket lip and a second abutting face configured
to abut against the first abutting face. A gasket provides a seal
between the first and second gasket lips. The first abutting face
and second abutting face are configured to limit compression of
the sealing flange.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a perspective view of a flow meter assembly for
use in a sanitary process environment.
[0009] FIG. 2A is a side cross sectional view showing a flow meter
tube, sealing flange and gasket of the flow meter assembly in FIG.
1.
[0010] FIGS. 2B and 2C are perspective exploded views of the sealing
flange and gasket assembly of the flow meter illustrated in FIG.
1.
[0011] FIGS. 3a and 3b are side cross sectional and front plan
views of a coupling portion of the sealing flange shown in FIGS.
2A, 2B and 2C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] FIG. 1 is a perspective view of a flow meter assembly 10
in accordance with the present invention for use in a sanitary process
environment. Flow meter assembly 10 includes a magnetic flow meter
12 having a flow tube 14. The flow meter 12 is configured to measure
flow of process fluid through the flow tube 14. The flow tube 14
is coupled to sealing flanges 16 using a gasket arrangement in accordance
with the present invention described below in more detail. The sealing
flanges 16 include fitting ends 22 which are in accordance with
an industry standard coupling for use in coupling the flow tube
14 to process piping 18 which carries process fluid (not shown).
Although a standardized coupling 22 is shown, one is not required
and the coupling technique can be in accordance with any desired
configuration.
[0013] Flow meter 12 is illustrated as a magnetic flow meter. A
magnetic flow meter is a known technology in which magnetic coils
are used to induce a magnetic field in a process fluid. Electrodes
in the process fluid are used to sense a voltage potential which
arises in the fluid due to the applied magnetic field. The magnitude
of the voltage potential is related to the flow rate of process
fluid through the tube. Although the present invention is described
with reference to magnetic flow meter, it is not limited to such
a configuration and may be implemented with other types of field
devices.
[0014] Flow meter 12 is illustrated as coupling to a two wire process
control loop 20. In some configurations, circuitry in the magnetic
flow meter 12 can be wholly or partially powered with power received
from the process control loop 20. However, in a more typical configuration,
a separate power source is used to power the flow meter 12.
[0015] FIG. 2A is a cross sectional view and FIGS. 2B and 2C are
perspective exploded views of flow tube 14 and sealing flange 16
which illustrate one configuration of the present invention. As
illustrated in FIGS. 2A, 2B and 2C, a gasket 50 is used to seal
the coupling between the sealing flange 16 and the flow tube 14.
As mentioned in the Background section, certain sanitary process
standards limit the amount of compression which can be applied to
gasket 50. As discussed in the Background section, in some sanitary
process installations, a device such as a flow meter assembly must
be capable of operation over a temperature range. As the temperature
of the device varies, components of the device expand and contract
causing stressed to be applied to gaskets in the device. These stresses
can cause cracks and ultimate failure of the gaskets. One way to
reduce the damage to the gasket caused by the temperature induced
stress is to limit the compression which can be applied to the gasket.
In one specific implementation, the compression of the seal is limited
to less than 25%. In another configuration, the compression is limited
to less than 20%. As discussed below, the present invention is configured
to provide sufficient compression on to gasket 50 to allow the gasket
to effectively seal the sealing flange 16 to the flow tube 14 without
exceeding the compression limitations set forth in various industry
standards.
[0016] Gasket 50 can be of any appropriate material. However, in
example embodiments, gasket 50 comprises ethylene propylene, viton.RTM.
(available from DuPont Dow elastomers L.L.C. of Wilmington, Del.),
silicone or a fluorocarbon.
[0017] Flow tube 14 includes a gasket lip 52 and sealing flange
16 includes a similar gasket lip 54. A void region 56 extends circumferentially
around lips 52 and 54. As illustrated in FIG. 2 a cross sectional
view of gasket 50 has a "T" configuration with the lower
portion of the "T" fitting between lips 52 and 54 and
the upper cross section of the "T" fitting into void 56.
The seal provided by gasket 50 is achieved in the region where the
gasket 50 abutts the gasket lips 52 and 54 along the lower portion
of the "T" and along the top portion of the "T".
[0018] Flow tube 14 includes an abutting surface 60 and sealing
flange 16 includes an abutting surface 62 which are configured to
abut each other as illustrated in FIGS. 2A, 2B and 2C. Surfaces
60 and 62 limit the spacing between sealing flange 16 and flow tube
14 and thereby limit the maximum compression which can be applied
to gasket 50. In the configuration illustrated in FIGS. 2A, 2B and
2C, abutting surface 62 is formed from flange extension 66 which
extends over gasket 50 forming void 56. However, this is simply
one example and other configurations are within the scope of the
present invention. The flange extension can be coupled to sealing
flange 16 or flow tube 14 or can be carried partially on both flange
16 and tube 14. The amount of compression on gasket 50 is a function
of the cross sectional thickness of gasket 50 between lips 52 and
54 and length of flange extension 50. A nut 70 is configured to
be threadably received on threads 72 of flow tube 14 to cause sealing
flange 16 to be secured against flow tube 14 along gasket 50 and
faces 60 and 62. Other techniques can be used to couple flange 16
to flow tube 14 and the invention is not limited to the nut 70 illustrated
in FIGS. 2A, 2B and 2C. In another example, a spanner may be used.
[0019] In one specific embodiment, the amount of compression which
can be applied to gasket 50 is limited to less than 25% and more
specifically less than 20%. However, any compression limitation
can be selected as desired.
[0020] The sealing flange 16 and flow tube 14 can be of any appropriate
material in accordance with sanitary process environment requirements.
If a suitable material is not available, a coating can be applied
to exposed surfaces to prevent process fluid from contacting the
underlying material.
[0021] FIGS. 3a and 3b show side cross sectional views and front
plan views of a coupling portion 76 of sealing flange 16. Coupling
portion 76 can be formed integrally with the remainder of sealing
flange 16 or can be a separate component which is mounted, for
example, by welding, to form the entire sealing flange 16. As illustrated
in FIGS. 3a and 3b, face 62 void 56 and gasket lip 54 are formed
in concentric circles. Coupling portion 76 can be formed of any
appropriate material for use in a sanitary processing environment.
One example material is stainless steel, such as 316L.
[0022] Although the present invention has been described with reference
to preferred embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention. Although the present invention
has been described with a flow meter assembly, and specifically
a magnetic flow meter assembly, the invention can be used with any
field device for use with a sanitary process environment. |