Railway tank car having a heating system with internal heat transfer panel

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of railway tank cars and, in particular, to a railway tank car having a lading heating system.

BACKGROUND OF THE INVENTION

Railway tank cars may be used to move hazardous and non-hazardous liquid or semi-liquid bulk freight of all types including, but not limited to: liquified petroleum gases; liquified gases (e.g., carbon dioxide); chemical intermediates; polymers; antiknock compounds; anhydrous ammonia; chlorine, alcohol, vegetable and fish oils; fruit juices; wine and syrups. Modern tank cars are typically designed without center sills and rely on the structural strength of the tank to transmit draft and buffing forces. Many of the tank cars currently in use can carry in excess of one hundred tons and often have a thirty-thousand gallon capacity. Tank cars which are either heated, pressurized, lined, or a combination of these features, are available to shippers.

Heated tank cars may be used to carry liquids which are highly viscous at low temperatures. Heating panels, internal pipes, or heating coils, may be applied within or external to the tank car in order to increase the temperature of the lading, during unloading operations. These panels, coils or pipes may be fed by a heating fluid such as steam, hot water or hot oil.

Heating panels, and their associated piping and coils which carry the heating fluid, decrease the capacity of the railway car by decreasing the available volume within the tank. The specific configuration of heating panels and associated coils may also affect the performance of the tank car during unloading. For example, many tank cars distribute heat disproportionately to the contents of the car. Accordingly, a portion of the contents may become overheated, which may be detrimental to certain liquids which may solidify or caramelize. Underheated contents will not unload efficiently. A combination of these factors may lead to a phenomenon referred to as “heel” wherein solidified contents remain within the car after unloading and decrease the overall capacity of the car. Heel is also detrimental to heat transfer of the piping and coil system and may contaminate subsequent lading within the tank car.

Traditional interior piping and exterior coil configurations do not efficiently distribute the heating fluid throughout the system. Furthermore, improper drainage of the heating fluid and/or condensate by-product can lead to failure of the heating system.

SUMMARY OF THE INVENTION

In accordance with teachings of the present invention, disadvantages and problems associated with previous heated railway tank cars have been substantially reduced or eliminated.

In one embodiment of the present invention, a railway tank car including a tank coupled with first and second stub sill assemblies may be provided. The stub sill assemblies may each be coupled with associated railway car truck assemblies. A tank defined in part by a generally elongate hollow cylinder having first and second ends with first and second heads mounted respectively thereon, may also be provided. In a particular embodiment, one or more heat transfer panels may be disposed within the cylinder adjacent the first and second heads. Each of the heat transfer panels may communicate with respective pluralities of heat transfer ducts, operable to provide a heating medium to the first and second heat transfer panels.

In another embodiment, a first support member may be disposed within the cylinder, intermediate a discharge valve of the tank, and head. A second support member may also be disposed within the cylinder, intermediate the discharge valve and an opposing head. Each support member may provide support for, and maintain their respective heat transfer panels in a spaced relation with a lower portion of the cylinder.

In still another embodiment, each support member may comprise an arcuate shaped bar disposed axially along the lower portion of the cylinder along a plane approximately perpendicular to a longitudinal centerline of the cylinder. Alternatively, each support member may comprise a generally arcuate shaped angle disposed in a similar manner as described above with respect to the bar.

In yet another embodiment, each heat transfer duct may be disposed upon an exterior portion of the cylinder, being in fluid communication with the heat transfer panels.

A technical advantage of the present invention includes a lading heating system which minimizes any reduction in available volume for carrying lading in the tank car. The reduced size of the heat transfer panels and the exterior location of the heat transfer ducts provides for maximum capacity of the interior of the tank. Also, placing the heat transfer ducts on the exterior of the tank maximizes heat transfer at the bottom of the tank and increases the efficiency of the heating system. This allows for a reduction in overall weight of the heating system, thereby increasing payload capacity.

Another technical advantage of the present invention includes the increased strength of the railway tank car provided by the installation of the support members, heat transfer ducts, coils and heat transfer panels. The location of the support members on the tank shell, near the heads, provides support to the tank where the highest train loads are supplied to the tank, at the end of the draft sill. Also, the ducts, coils and heat transfer panels provide support and increase the moment of inertia of the tank.

Still another technical advantage of the present invention includes the increased duct width and reduced duct height which spread the heating media into a thin film over a larger area, thereby increasing the heat transfer efficiency. The increased duct width also reduces the number of ducts required to efficiently cover the desired heating surface.

Yet another technical advantage of the present invention includes the reduction and/or elimination of heel. Accordingly, heat transfer is accomplished more efficiently without the loss of volume typically accompanied by heel, and lading contamination is substantially reduced.

Other technical advantages are readily apparent to one of ordinary skill in the art from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be acquired by referring to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein:

FIG. 1

is a schematic drawing illustrating a side view of a railway tank car incorporating teachings of the present invention;

FIG. 2

is a schematic drawing with portions broken away illustrating a cross-section of a portion of the railway tank car of

FIG. 1

;

FIG. 3

is a schematic drawing illustrating a top view of a heat transfer panel for use within the teachings of the present invention;

FIG. 4

is a schematic drawing with portions broken away illustrating heat transfer panel and piping configurations of the railway tank car of

FIG. 1

;

FIG. 5

is a schematic drawing with portions broken away illustrating a cross-section through line

5

—

5

of

FIG. 4

;

FIG. 6

is a schematic drawing with portions broken away illustrating a connection between a heat transfer panel and railway tank car;

FIG. 7

is a schematic drawing with portions broken away illustrating the piping configuration at a central portion of the railway tank car of

FIG. 1

;

FIG. 7A

is a schematic drawing with portions broken away illustrating an alternative embodiment piping configuration for the central portion of the railway tank car of

FIG. 1

;

FIG. 8

is a schematic drawing with portions broken away illustrating a cross-section through lines

8

—

8

of

FIG. 7

;

FIG. 9

is a schematic drawing illustrating a top view of a valve heating donut suitable for use within the teachings of the present invention;

FIG. 10

is a schematic drawing illustrating a cross-section through lines

10

—

10

of

FIG. 9

;

FIG. 11

is a schematic drawing with portions broken away illustrating an alternative embodiment piping configuration suitable for use with the railway tank car of

FIG. 1

;

FIG. 12

is a schematic drawing with portions broken away illustrating a cross-section taken through lines

12

—

12

of

FIG. 11

; and

FIG. 13

is a schematic drawing illustrating a side view of a support member, suitable for use within the teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention and its advantages are best understood by referring to

FIGS. 1-13

of the drawings, like numerals being used for like and corresponding parts of the drawings.

Referring to

FIG. 1

, a railway tank car is provided and generally designated by the reference numeral

30

. Tank car

30

includes a tank

32

mounted upon a pair of stub sill assemblies

34

and

36

. A tank cradle

38

couples tank

32

with body bolster

39

. Similarly, tank cradle

40

couples tank

32

with body bolster

41

. Body bolsters

39

and

41

are coupled with truck assemblies

42

and

44

, respectively. The structural strength of tank

32

may be relied upon to transmit draft and buffing forces from the ends of the draft sills to tank

32

.

Tank car

30

of the present invention may be used to transport a variety of hazardous and non-hazardous liquid or semi-liquid bulk commodities of all types. Liquid commodities may be loaded within tank

32

through an associated tank manway

46

. Unloading of the lading may be accomplished by gravity-flow through discharge valve

48

. In another embodiment, the discharge valve may be located practically anywhere upon tank

32

, for example, upon upper portion

61

of tank

32

. Tank

32

may also be pressurized to assist in unloading of the lading. Tank car

30

includes various safety appliances including, but not limited to ladders, handholds, rails, steps, operating platforms and safety valves. Depending upon the specific application and/or the type of commodity involved, tank car

30

may be heated, pressurized, lined or any combination of these features. For example, when tank car

30

is used to transport lading which is highly viscous at low temperatures, tank car

30

may be heated in order to efficiently discharge the lading through discharge valve

48

.

Tank

32

is generally defined by an elongated hollow cylinder

50

having a first end

52

and a second end

54

. At the lower portion of cylinder

50

, tank

32

may slope gradually toward discharge valve

48

from each head

56

and

58

. Similarly, the configuration and slope of an upper portion

61

of cylinder

50

may conform to the configuration and slope of lower portion

60

. A head

56

is disposed upon cylinder

50

at first end

52

. Similarly, a head

58

is disposed upon second end

54

of cylinder

50

. Heads

56

and

58

, and cylinder

50

at least partially define generally enclosed tank

32

and protect lading contained therein from ambient environment. Discharge valve

48

may be disposed upon tank

32

intermediate end heads

56

and

58

on a lower portion

60

of cylinder

50

. Manway

46

may be disposed upon an upper portion of cylinder

50

, also intermediate heads

56

and

58

.

Referring now to

FIGS. 1-4

, a heat transfer panel

62

may be disposed within tank

32

adjacent head

56

. A top view of heat transfer panel

62

is illustrated in FIG.

3

. Heat transfer panel

62

includes a first end

64

which may contact head

56

adjacent to and spaced both horizontally and vertically from lower portion

60

of cylinder

50

. First end

64

of heat transfer panel

62

may be secured to head

56

by welding. Edges

67

and

69

of heat transfer panel

60

may include forty-five degree chamfers to form “knife-edges,” at the point of contact with first end

52

of cylinder

50

, and head

56

.

Heat transfer panel

62

generally tapers inward along walls

70

and

72

from first end

64

to second end

74

. Second end

74

is generally spaced from lower portion

60

of cylinder

50

, and supported by a back support

76

. The height of back support

76

may be selected to allow heat transfer panel

62

to slope downward from first end

64

to second end

74

, toward discharge valve

48

. Accordingly, an angle &thgr; is formed between heat transfer panel

62

and an imaginary longitudinal horizontal central axis X of cylinder

50

. The slope of heat transfer panel

60

, defined by angle &thgr;, promotes flow of liquid lading within tank

32

from first end

52

toward discharge valve

48

during unloading.

Heat transfer panel

62

is supported in a spaced relation from cylinder

50

at its second end

74

, by back support

76

. Back support

76

may include an arcuate shaped member which generally conforms to the lower portion

60

of cylinder

50

(FIG.

13

). Back support

76

extends axially along cylinder

50

, generally perpendicular to longitudinal horizontal axis X. Heat transfer panel

62

may be welded to back support

76

adjacent second end

74

of heat transfer panel

62

. Similarly, back support

76

may be welded to the lower portion

60

of cylinder

50

, intermediate head

56

and discharge valve

48

. In another embodiment, the support member may be formed as an integral component of the heat transfer panel, during fabrication of the heat transfer panel. In the same embodiment, only one weld would be required, at the juncture of the heat transfer panel and lower portion

60

of cylinder

50

.

Back support

76

provides additional strength to cylinder

50

and therefore increases the ability of tank

32

to withstand external forces due to impact, squeeze and vacuum conditions. Traditional railway stub sill tank cars are weakest at the points of their tank at the end of the draft sill assemblies. Back support

76

provides additional reinforcement from which any type of stub sill tank car may benefit. Back support

76

may be selected from various structural materials and configurations. In the illustrated embodiment, back support

76

includes a one and one-half inch thick steel bar, of a generally “half-moon,” arcuate shape (FIG.

13

). In another embodiment, back support

76

may include a 3×2×½″ angle having a first leg fastened to the lower portion

60

of cylinder

50

, and a second leg providing support to second end

74

of heat transfer panel

62

, thereby maintaining heat transfer panel

62

in a spaced relation with cylinder

50

. An angle back support may provide a thirty percent (30%) greater fatigue life than a bar back support. In still other embodiments, support member

76

may include any type of structural support including, but not limited to, tube steel and “I” beams.

A second heat transfer panel

80

may be disposed within second end

54

of cylinder

50

in a similar manner as heat transfer panel

62

. Heat transfer panel

80

is installed similarly, and essentially a mirror image of heat transfer panel

62

. Accordingly, only heat transfer panel

62

and its associated ducts and coils will be described in detail except where otherwise appropriate. Heat transfer panels

62

and

80

may be installed within tank

32

during fabrication of railway tank car

30

. Alternatively, existing tank cars may be retrofit to include heat transfer panels

62

and

80

of the present invention, at a reasonable cost.

In the illustrated embodiment of

FIG. 4

, heat transfer panels

62

and

80

are of the mini-panel type, and are disposed at the ends of tank

32

only. In practice, heat transfer panels of various sizes and configurations may be provided within the teachings of the present invention. For example, heat transfer panels associated with railway tank car

30

may be provided of a length approximately one-half of the length of tank

32

. In this embodiment, heat transfer panels would extend from each head

56

and

58

, and terminate adjacent discharge valve

48

. Alternatively, heat transfer panels of any intermediate size may also be provided.

Referring now to

FIGS. 5-7

, a plurality of heating coils

82

,

84

, and

86

may be welded to an underside

78

of heat transfer panel

62

. Heating coils

82

,

84

and

86

extend approximately the entire longitudinal length of heat transfer panel

62

and include a slope &thgr; with respect to longitudinal axis X. In one embodiment, heat transfer panel

62

may be rolled from a one-quarter inch thick ASTM A-572, Grade 50, Type 2 material, or equal. Heating coils

82

,

84

and

86

may be welded to underside

78

and formed from the same material as heat transfer panel

62

. Heat transfer ducts, including ducts

94

,

96

and

98

, which will be described later, in more detail, may also be formed of a similar material.

In the illustrated embodiment, heating coil

84

functions as a steam supply intake and distributes steam to heat transfer panel

62

. Steam enters heat transfer panel

62

through a supply manifold

88

, which is located adjacent second end

74

. Steam travels the longitudinal length of heat transfer panel

62

from second end

74

to first end

64

. A transfer conduit

90

collects steam and condensate from heating coil

84

and distributes the steam and condensate to heating coils

82

and

86

. Accordingly, heating coils

82

and

86

function as condensate return lines and distribute steam and condensate to return manifolds

91

and

92

, respectively. The constant flow of steam and condensate through heat transfer panel

62

and heating coils

82

,

84

and

86

maintain heat transfer panel

62

at an elevated temperature. As such, heat is subsequently transferred to the lading within tank

32

to raise the temperature of the lading for efficient unloading.

Manifold

88

establishes fluid communication between heating coil

84

and steam supply duct

94

. Similarly, return manifold

91

establishes fluid communication between heating coil

82

and steam return duct

98

. Return manifold

92

establishes fluid communication between heating coil

86

and steam return duct

96

.

In operation, the heating fluid, for example steam, may enter steam supply duct

94

from an inlet

100

located adjacent discharge valve

48

. Steam will then travel within steam supply duct

94

from inlet

100

toward supply manifold

88

, and enter heat transfer panel

62

. As previously discussed, steam will be distributed throughout the transfer panel

62

and condensate will be returned from return manifolds

91

and

92

to steam condensate return ducts

98

and

96

, respectively. Condensate will then travel within steam return duct

96

from return manifold

91

to a “T” connector

102

located adjacent discharge valve

48

. Condensate is then discharged through outlet

104

of “T” connector

102

and enters a one-inch pipe

106

which carries condensate to a valve heating donut

108

.

In a similar manner, condensate exiting condensate return manifold

92

will travel through steam return duct

96

to a second “T” connector

110

, which forms a condensate return. Condensate exits “T” connector

110

through outlet

112

and into one-inch pipe

114

, for distribution to valve heating donut

108

. Condensate is collected within valve heating donut

108

in order to increase the temperature of discharge valve

48

for efficient unloading of the lading within tank

32

. Condensate traveling through valve heating donut

108

will ultimately be discharged to the atmosphere through a two inch outlet pipe

116

.

The configuration of heat transfer panel

80

and its associated coils, ducts, and piping are configured and operate similarly to the description above. Steam enters steam intake duct

120

through a steam inlet

122

for distribution to steam intake

124

of heat transfer panel

80

. Steam enters steam supply coil

126

through intake manifold

124

for distribution to steam return coils

128

and

130

. Steam and condensate are delivered to condensate return ducts

132

and

134

through return manifolds

136

and

138

, respectively. Steam and condensate are then distributed through steam return ducts

132

and

134

to “T” connectors

102

and

110

, respectively. As previously discussed, steam and condensate are transferred through outlets

104

and

112

to pipes

106

and

114

, and ultimately reach valve heating donut

108

. Again, condensate is ultimately released to ambient environment through outlet pipe

116

.

Additional valves, steam traps and restrictors may be included within the piping configuration of

FIG. 4

, within the teachings of the present invention. For example, one-quarter inch restrictors may be located on each condensate manifold

91

,

92

,

136

and

138

. Such restrictors operate similarly to steam traps, and increase the pressure of steam within heat transfer panels

62

and

80

, to achieve higher temperatures. Similarly, a three-eighth inch restrictor

117

may be located upon outlet pipe

116

. The restrictor at each location function as non-mechanical steam traps, and reduce the flow of steam and condensate in order to increase the heating effect. It will be recognized by those of ordinary skill in the art that the size of ducts, coils, pipes and restrictors may be significantly altered within the teachings of the present invention. Accordingly, steam traps may also be placed at any or all of these locations.

In the illustrated embodiment, steam is used as the heating medium and condensate is therefore produced as the steam cools. It will be recognized by those of ordinary skill in the art that other heating media may be used in lieu of steam, within the teachings of the present invention. Furthermore, although this description and figures describe the approximate location at which the steam condenses, this location may be altered significantly by many external factors, and remain within the teachings of the present invention.

FIG. 7A

illustrates an alternative embodiment piping configuration adjacent discharge valve

48

. In this embodiment, “T” connectors extend into a valve heating donut

49

without intermediate piping. Steam and condensate traveling through “T” connectors

202

and

210

enter an annular fluid passageway

51

within discharge valve

248

. Steam is then discharged from valve heating donut

49

, through condensate discharge

216

. Surrounding discharge valve

248

with heating fluid increases the temperature of the lading nearest discharge valve

248

and enhances the flow of fluid lading through discharge valve

248

during unloading. Additional details regarding valve heating donut

49

are illustrated in

FIGS. 9 and 10

.

The configuration of ducts

94

,

96

, and

98

, coils

82

,

84

and

86

, and heat transfer panel

62

may be referred to as a “three pass” system, primarily because of the existence of three ducts

94

,

96

, and

98

serving the transfer panel

62

. Limiting the amount of ducts

94

,

96

, and

98

to three provides many advantages over traditional railway tank car heating systems. For example, heating is accomplished much more quickly and efficiently in a “three pass” system. Steam has less distance to travel and arrives at each point within the system much more quickly. Also, the reduced number of ducts, reduces the overall weight of railway tank car

30

and provides for reduced time and complications of fabrication. Less parts and pieces are required for assembly of the system. Also, by reducing the overall linear footage of ducts

94

,

96

, and

98

, leakage points and other points of failure are significantly reduced. In order to thoroughly and efficiently heat lading within tank

32

, the size, and/or diameter of ducts

94

,

96

, and

98

may be increased. The location of ducts

94

,

96

and

98

provide for simplified identification of leaks and points of failure, and simplified repair and retrofit. In one embodiment, ducts

94

,

96

, and

98

may be provided with approximately an eight-inch diameter and extend approximately fourteen and one-half feet longitudinally.

The installation of back support

76

, heat transfer panel

62

and its associated coils and ducts increase the overall strength of tank

32

. For example, the strength of cylinder

50

is dependent upon many factors including the thickness of material, strength of material, diameter of cylinder

50

, and the distance between supports, for example truck assemblies

42

and

44

. In general, the strength of cylinder

50

will increase with an increase in the thickness of material used to fabricate cylinder

50

, and/or a decrease in the diameter of the cylinder, all other factors being equal. Similarly, the thickness of tank

32

is proportional to the cross-sectional area of tank

32

. Ducts

94

,

96

and

98

and/or the installation of heat transfer panel

62

substantially increases the moment of inertia (cross sectional area x distance squared from the neutral axis). The larger the moment of inertia of tank

32

, the greater the ability of tank

32

to withstand large external forces due to impact, squeeze and draft pull conditions. Accordingly, tank

32

may withstand loads that cause fatigue failure, and also resist buckling loads. In one embodiment, the stress at the inboard termination of the stub sill reinforcing plate may be reduced by twenty to twenty five percent, as opposed to a tank without heat transfer panels. In fact, cars of older design may be substantially strengthened by adding heat transfer panels and their associated back supports, coils and ducts.

Referring now to

FIGS. 11 and 12

, an alternative duct configuration suitable for use with heat transfer panels

62

and

80

is provided. In this embodiment, heat transfer panels

62

and

80

function similarly and generally form mirror images of one another. Accordingly, the operation of heat transfer panel

62

will be described in detail only, except where otherwise appropriate. Heat transfer panel

62

includes heating coils

82

,

84

and

86

, in fluid communication with one another through transfer conduit

90

. As described above with respect to

FIG. 4

, steam enters heat transfer panel

62

through supply manifold

88

. Condensate leaves heat transfer panel

62

through a pair of return manifolds

91

and

92

.

The heating, or heat transfer duct configuration illustrated in

FIGS. 11 and 12

may be used for high viscosity lading which requires additional heating prior to unloading. Steam enters this system through a steam intake

150

located adjacent discharge valve

148

. Steam supply duct

152

carries steam from steam intake

150

to supply manifold

88

of heat transfer panel

62

. Steam supply duct

152

generally includes an elongate, half-oval which extends approximately one-half the length of railway tank car

30

. Steam return ducts

154

and

156

are in fluid communication with return manifolds

91

and

92

, respectively. Steam traveling through steam return duct

154

encounters a one-hundred eighty degree elbow

158

, which diverts steam/condensate into condensate return duct

160

. Another one-hundred eighty degree elbow

162

forms a fluid pathway between condensate return duct

160

and condensate return duct

164

. Condensate return duct

164

carries condensate for collection at a Tee connector

166

which is located adjacent discharge valve

148

, intermediate heat transfer panels

62

and

80

. Condensate is discharged from Tee connector

166

through condensate return

168

.

In a similar manner, condensate traveling through steam return duct

156

encounters a one-hundred eighty degree elbow

170

, which diverts condensate to condensate return duct

172

. Another one-hundred eighty-degree elbow

174

provides fluid communication between condensate return duct

172

and condensate return duct

176

. Condensate collected at Tee connector

178

is discharged through condensate return

180

. Distribution of condensate around discharge valve

148

, and the ultimate discharge of condensate from railway tank car

30

is similar to that described above with regard to FIG.

4

.

Condensate bypass

182

provides fluid communication between one-hundred eighty degree elbow

158

and Tee connector

166

. Similarly, a second condensate bypass

184

provides fluid communication between one-hundred eighty degree elbow

170

and Tee connector

178

. Bypasses

182

and

184

improve the heating and efficiency of the heating duct system by providing for the rapid transfer of steam and condensate throughout. Also, bypasses

182

and

184

provide a more efficient method for purging the system of condensate.

In the current state of the art, railway tank car heating systems may include ducts and coils located entirely within, or entirely external to the car. For the purposes of this specification, ducts and coils may be used interchangeably to refer to any fluid pathway for the transfer of steam, condensate or other heating media. In the illustrated embodiment, coils were used to describe fluid pathways, or conduits, associated with the heating panels, while ducts were used to describe the pathways, or conduits associated with the tank. This distinction was made for purposes of clarity only. The hybrid distribution of coils and ducts described within this specification provides many advantages over such systems. By placing ducts, for example,

94

,

96

and

98

on the exterior of tank

32

, significant savings in volume is realized within tank

32

, and the capacity of tank

32

is thereby increased. The installation of heat transfer panels

62

and

80

within tank

32

increases the overall structural strength of tank

32

near its ends

52

and

54

, nearest the most critical areas. Also, the location of panels

62

and

80

inside tank

32

improves the efficiency of heat distribution between heat transfer panels

62

and

80

and lading contained within tank

32

.

In one embodiment of the present invention, each heating coil and heating duct may include a one-inch positive slope, end-to-end. In excess of 500 lineal feet of coil and duct may be provided, establishing a heating area of approximately 300 square feet.

In the illustrated embodiment, heat transfer panels

62

and

80

are generally spaced from tank

32

to avoid contact. This reduces the heat loss associated with the direct contact of tank

32

through cradles

38

and

40

, bolsters

39

and

41

, and truck assemblies

42

and

44

. The location of heat transfer panel

62

and

80

concentrates heat in the bottom and ends of the car to promote rapid fluidizing of the lading without causing “hot spots” and subsequent burning of the lading.

Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.