GB2495523A - Steam trap - Google Patents

Abstract

A steam trap 10 comprises an inlet 103 and an outlet 105 terminating at a valve seat 220. A valve member 600 is provided which is moveable between a closed position in which flow between the inlet 103 and the outlet 105 is restricted and an open position in which fluid can flow between the inlet 103 and the outlet 105. The steam trap 10 further comprises a bimetallic venting ring 400 which is in contact with a body 200 at three discrete angularly spaced contact positions (418, Fig. 8) and which is arranged to change in shape in response to temperature changes. In response to a particular temperature drop, the venting ring 400 changes in size and cooperates with the body 200 so that it moves the valve member 600 away from the valve seat 220 to an open position.

Description

STEAM TRAP

The invention relates to a steam trap, in particular, although not exclusively, to a thermodynamic steam trap.

The main function of a steam trap is to drain condensate from a steam line in which the trap is connected. However, it is also desirable to discharge air and other non-condensable gases which may collect in the steam line. For example, when steam is first turned on to a cold plant, there is usually a considerable volume of air which should be purged out as quickly as possible so as to quickly raise the plant to the desired operating temperature.

In a thermodynamic steam trap there is a floating disc that serves as a valve member, mating with concentric seat rings below the disc to control communication between an inlet to the trap and a discharge outlet from the trap. When steam is first turned on, the disc is raised by the pressure, and air in the line is discharged. The cold condensate which follows is also discharged. As the condensate temperature and pressure rises, flash steam is formed under the disc and the velocity of this passing below the disc towards the outlet increases, lowering the pressure under the disc so that the disc is drawn towards the seat rings. At the extreme circumference of the disc the velocity is less and there is a pressure build-up in a chamber above the disc until, at a point when the condensate temperature has approached that of steam, the flash-produced pressure in the chamber above the disc, acting on the large overall area of the disc, overcomes the inlet pressure (which acts on a smaller area of the disc) and the disc snaps shut against the seat rings to prevent further flow.

Deprived of further flash steam, the temperature and pressure in the chamber above the disc falls, the inlet pressure asserts itself and the valve opens for the cycle to be repeated. However, if considerable amounts of air are encountered in the chamber as opposed to steam, so-called "air-binding" may occur, that is the trap may become held closed for long periods by air caught in the chamber above the disc. This phenomenon is discussed in some detail in GB 1,178,160.

In a thermodynamic steam trap described GB 1,178,160 there is a bi-metallic ring, which either expands or contracts on cooling, co-operating with an inclined surface such that the ring is displaced to lift the disc valve member off its seat arrangement on cooling of the bi-metallic ring below a certain temperature. This helps to override the effect of all trapped in the chamber above the disc. Whilst this arrangement may be satisfactory, it may be difficult to manufacture the bi-metallic ring to the appropriate tolerance required such that the ring does not become stuck on the inclined surface.

Another approach to the problem of air-binding is radially to groove the sealing face of the disc to provide an air-bleed from the chamber above the disc. The problem then arises that controlling steam can also bleed away and additional measures have to be taken to deal with this.

GB 2,163,832 attempts to deal with this problem by providing a valve member with a bypass path which allows fluid communication between the chamber and the outlet. A bi-metallic member is provided which opens and closes the bypass path in response to temperature changes, thereby allowing the pressure above the valve member to be reduced when the steam trap is cooled. Whilst this arrangement is satisfactory, the valve member is relatively expensive and complicated to manufacture.

It is therefore desirable to provide an improved steam trap that may be more reliable and less expensive to manufacture.

In a broad aspect the invention relates to a venting ring for a thermodynamic steam trap which is arranged to be in contact with a body of the steam trap at three discrete angularly spaced contact positions and which is arranged to change in size and/or shape in response to temperature changes. The venting ring is arranged to rise and fall in response to temperature changes so that when the venting ring cools below a certain temperature, the ring lifts a valve member of the steam trap off a valve seat.

Since the venting ring is in contact with the body, which may be a valve seat body, at three discrete contact positions, it is not necessary to manufacture the ring to such a high tolerance and there will always be a circle that passes through the three contact positions. Further, even if the venting ring expands or contracts in a non-uniform manner, the radius of the circle passing through the three contact positions will change, thereby ensuring that the ring moves. Three discrete contact positions may be the most beneficial arrangement. However, it should be appreciated that more than three discrete contact positions could be used. For example, there may be four, five, six, seven or eight discrete contact positions.

According to a first aspect of the invention there is provided a steam trap comprising: an inlet and an outlet terminating at a valve seat; a valve member moveable between at least a closed position in which flow between the inlet and the outlet is restricted and at least one open position in which fluid can flow between the inlet and the outlet; and a venting ring which is in contact with a body at at least three discrete angularly spaced contact positions and which is arranged to change in size and/or shape in response to temperature changes; wherein in response to a particular temperature drop, the venting ring changes in size and/or shape and cooperates with the body so that it moves from an operating position to a cold position in which it moves the valve member away from the valve seat to an open position. This arrangement allows the steam trap to vent air from the steam system during start-up when the steam trap is cold. When the steam trap heats up during normal operation, the venting ring changes its size and/or shape and cooperates with the body to move to a position in which it does not cause the valve member to be in the open position. The use of a number of discrete contact positions between the venting ring and the body reduces the likelihood of the venting ring becoming stuck in a particular position.

The venting ring may directly act on the valve member, or it may indirectly act on it through another component such as a valve washer.

The valve member may be located on a substantially horizontal valve seat. The venting ring may be disposed below the valve seat. The valve member may be located in a chamber.

The venting ring may be substantially coaxial with the body. The venting ring may be substantially coaxial with an axis of chamber, which may be coaxial with an axis of the body.

The angle of the smallest circular arc passing through the contact positions may be greater than 180°. The angle of the smallest circular arc may be at least 200°, for example it may be approximately 240°. The contact positions may be irregularly spaced or regularly spaced. The contact positions may be approximately 120° apart from one another.

The change in size and/or shape of the venting ring due to a temperature change may cause the circumradius of the three contact positions to change. The change in size andfor shape of the venting ring due to a temperature change may cause the radius of a circle inscribed in the venting ring to change.

The venting ring may be a bimetallic ring. The venting ring may be an open ring. The venting ring may be an open ring with a circumferentially extending gap. The bimetallic ring may be composed of two strips of metals, each with different coefficients of thermal expansion. The venting ring may be configured to expand in response to a temperature increase, and contract in response to a temperature decrease.

Alternatively the venting ring may be configured to contract in response to a temperature increase, and expand in response to a temperature decrease.

The contact protrusions may have a circumferential length. The contact positions may comprise a circumferentially extending length of a contact protrusion. A contact position may be defined by several closely spaced discrete contact protrusions.

The contact protrusions may be integrally formed with the venting ring. The contact protrusions may be separately attached to the venting ring. The venting ring may have outer radial portions between the contact protrusions. The venting ring may be integrally formed. The outer radial portions may have a radius of curvature that is larger than that of the contact protrusions.

The body may comprise a frustoconical surface which the venting ring is in contact with. The frustoconical surface may be an inner frustoconicat surface or an outer frustoconical surface. The body may be a valve seat body comprising the valve seat, the valve seat body having an outer frustoconical surface which the venting ring is in contact with. The frustoconical surface may be coaxial with an axis of the body, and/or with an axis of the chamber.

The invention also concerns a steam system comprising at least one steam trap in

accordance with any statement herein.

The invention also relates to a venting ring for use with a steam trap in accordance with

any statement herein.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 schematically shows a perspective view of a steam trap in accordance with an embodiment of the invention; Figure 2 schematically shows a cross-sectional view of the steam trap of Figure 1 when the steam trap is cold and with the valve disc in an open position; Figure 3 schematically shows a cross-sectional view of the steam trap of Figure 1 when the steam trap is hot and with the valve disc in an open position; Figure 4 schematically shows a cross-sectional view of the steam trap of Figure 1 when the steam trap is hot and with the valve disc in the closed position; Figures 5 and 6 schematically show a previously considered venting ring; Figure 7 schematically shows a perspective view of the venting ring of the steam trap of Figure 1; Figure 8 schematically shows a plan view of the venting ring of Figure 7; and Figures 9 and 10 schematically show the venting ring of Figure 7 in use and undergoing non-uniform expansion.

Figure 1 shows generally at 10 a thermodynamic steam trap comprising a main body 100 having an inlet port 102 and outlet pod 104. The trap 10 further comprises a cap 3o2which is threadedly attached to the main body 100 to define a chamber therebetween and a cover 300 which sits over the cap.

As shown in Figure 2, the main body 100 comprises a base 106, to which the cap 302 is threadedly attached and a valve seat body 200 that projects into the chamber 500.

The valve seat body 200 is substantially cylindrical and an upper surface of the valve seat body 200 provides a substantially circular valve seat 220. An annular groove 230 is provided in the upper surface of the valve seat body 220. The inlet port 102 leads to an inlet 103 which is coaxial with the axis Aol the valve seat body 200 and axially extends through the base 106 and the valve seat body 200 to terminate at the valve seat 220. An outlet 105 extends from the outlet port 104 through the base 106 and the valve seat body 200 at an angle and opens into the annular groove 230, thereby terminating the outlet 105 at the valve seat 220. The annular groove 230 separates the valve seat into two concentric valve seat surfaces.

The steam trap 10 further comprises a valve member 600 which is in the form of a disc.

The valve member 600 is disposed above the valve seat body 200 and is arranged to cooperate with valve seat 220 to open and close the steam trap 10. The diameter of the valve member 600 is larger than that of the valve seat 220 and therefore overlaps the edge of the valve seat 220. When the valve member 600 is in contact with the valve seat 220 (as shown in Figure 4) it is in the closed position and prevents fluid flow from the inlet 103 to the outlet 105. When the valve member 600 is raised from the valve seat 220 (as shown in Figures 2 and 3) it is in an open position and allows fluid flow between the inlet 103 and outlet 105.

The valve seat body 200 comprises a frustoconical outer surface 217 that is towards the bottom of the body 200 adjacent to the base 106. The frustoconical surface 217 tapers towards the top. The steam trap 10 also comprises a venting ring 400 which is positioned around the frustoconical surface 217 of the valve seat body 200 and is therefore disposed beneath the valve member 600. A venting washer 420 is provided which is positioned around the valve seat body 200 and rests on the venting ring 400 below the valve member 600.

In this embodiment, the venting ring 400 is an open bimetallic ring that contracts as it cools and expands as it is heated. The venting ring 400 cooperates with the frustoconical surface 217 of the body 200 so that when it contracts it rises towards the valve seat 220, and when it expands it falls towards the base 106. The venting ring 400 is configured so that below a certain temperature, for example below 120°C, it rises above a particular position such that the venting washer 420 projects above the level of the valve seat 220 to lift the valve member 600 away from the valve seat 220 to an open position. This is shown in Figure 2. As the temperature of the venting ring 400 increases, it expands until it falls to a position such that the venting washer 420 no longer projects above the level of the valve seat 220 and therefore the valve member 600 can move to a closed position. This is shown in Figure 4.

The cap 302 is substantially axisymmetric about the axis A, and comprises a top 310 and a circumferentially extending side wall 320. The lower end of the side wall 320 is threaded so that the cap 302 can be threadedly attached to main body 100.

The cylindrical side wall 320 defines an upper section 324 of the cap 302 having a first diameter and defines a lower section 326 of the cap having a second larger diameter.

An annular shoulder 328 joins the upper and lower sections 324, 326. The vertical position of the shoulder 328 is a shod distance above the vertical position of the valve seat 220. The valve member 600 is positioned within the upper section 324 which has a diameter that is slightly larger than that of the valve member 600. The upper section 324 therefore limits the horizontal movement of the valve member 600. The venting ring 400 and the venting washer 420 are disposed within the lower section 326. The diameter of the lower section 326 is larger than that of the venting ring 400 and therefore does not inhibit the expansion and contraction of the ring 400. However, the diameter of the lower section 326 is only slightly larger than the outer diameter of the venting washer 420 and therefore limits the horizontal movement of the washer 420.

The annular shoulder 328 restricts the vertical movement of the venting ring and washer 400, 420.

In use, the steam trap 10 is connected in a steam system with the inlet port 102 connected to a steam line and the outlet port 104 connected to a discharge. With reference to Figures 3 and 4, during normal operation, the steam trap 10 is at a relatively high temperature Ti and therefore the venting ring 400 is in an expanded configuration in which it has a first diameter dl. The venting ring 400 therefore sits on the frustoconical surface 217 of the valve seat body 200 at a vertical position vi with respect to the base 106 where the diameter of the frustoconical surface 217 is of a first diameter di. At this vertical position vi of the venting ring 400, the upper surface of the venting washer 420 does not project above the level of the valve seat 220.

Therefore, the venting washer 420 does not interfere with the valve member 600. As shown in Figures 3 and 4, the diameter dl of the venting ring 400 is such that the position vi is at the junction between the frustoconical surface 217 and the upper surface of the peripheral region of the base 106. The venting ring 400 is configured so that over the normal operational temperature range it always has a radius greater than a certain threshold such that it sits at a vertical position in which the venting washer 420 does not project above the valve seat 220. As can be seen from Figure 3, during normal operation the valve member 600 can move to an open position in which it is raised trom the valve seat 220 in order to allow condensate to be discharged from the steam system. As shown in Figure 4, in order to prevent the loss of steam from the steam system, the valve member 600 sits on the valve seat 220 to prevent fluid flow between the inlet 103 and outlet 105.

Referring back to Figure 2, during start-up, the steam trap 10 is at a relatively low temperature T2 and therefore the venting ring 400 is in a contracted configuration in which it has a second diameter d2. The venting ring 400 therefore sits on the frustoconical surface 217 at a vertical position v2 with respect to the base 106 where the diameter of the frustoconical surface 217 is of a second diameter d2. At this vertical position v2 of the venting ring 400, the upper surface of the venting washer 420 projects above the level of the valve seat 220. The venting ring 400 in conjunction with the venting washer 420 therefore acts to lift the valve member 600 off the valve seat 220 and moves it to an open configuration. This allows any air trapped in the system to be purged and therefore overcomes the problems of "air binding". The venting ring 400 is configured so that at low temperatures, when it is desirable to purge air from the system, the venting ring 400 always has a radius less than a certain threshold such that it sits at a vertical position in which the venting washer 420 projects above the level of the valve seat 220 to lift the valve member 600 to an open configuration.

In summary, the venting ring 400 is configured so that below a threshold temperature Tt it has a radius that is less than a certain radius rt such that it sits above a certain vertical position vt with respect to the base so that the venting washer 420 projects above the level of the valve seat 220 to move the valve member 600 to an open configuration. This ensures that below the threshold temperature Tt the steam trap is open and air can be purged from the system. The corollary of this is that the venting ring 400 is configured so that above the threshold temperature Tt it has a radius that is greater than a certain radius rt such that it sits below a certain vertical position vt so that the venting washer does not project above the level of the valve seat 220. This ensures that above the threshold temperature Tt the steam trap 10 opens and closes normally to allow condensate to be discharged from the system.

The threshold temperature Tt will typically be just below the normal operational temperature so that during start-up the steam trap 10 is forced open by the venting ring 400 to allow air to be vented from the system, and so that during normal operation the venting ring 400 will not interfere with the valve member 600. For example the threshold temperature Tt may be approximately 120°C.

As discussed above, the vertical position of the venting ring 400 on the frustoconical surface 217 depends on the radius of the venting ring 400. If the venting ring 400 is always a perfect circle then this is easily defined. However, it can be difficult to manufacture a venting ring 400 that is perfectly circular, and furthermore it can be difficult to ensure that the venting ring 400 always expands and contracts in a uniform manner.

Figures 5 and 6 show a previously considered venting ring 700 that does not fall within the scope of the invention. The venting ring 700 is an open bimetallic band that is arranged to contract when cooled, and expand when heated. The vertical position of the venting ring 700 on the frustoconical surface 217 depends on the radius of an inscribed circle within the venting ring 700. An inscribed circle is the largest circle that fits within the boundaries of another geometric shape. As can be seen from Figure 5, at ambient temperature Ta the open-band venting ring 700 is the arc of a circle having a radius ra. Since the venting ring 700 is the arc of a perfect circle, the inscribed circle 702 also has a radius ra. Therefore, at ambient temperature the venting ring 700 sits on the frustoconical surface 217 at a vertical position where the radius of the frustoconical surface is also ra.

However, as shown in Figure 6, if the venting ring 700 is heated to a temperature Th it may expand in a non-uniform manner. This may be due to non-uniform heating, non-uniform material properties, or non-uniform manufacture, for example. As can be seen from Figure 6, the non-uniform expansion may cause only the left-hand portion 701 of the venting ring 700 to expand. Despite the expansion of the venting ring 701, the radius of the inscribed circle 702 does not change. In this scenario, the venting ring 700 would not move to a different vertical position on the frustoconical surface, despite expanding due to a temperature increase. This may cause the venting ring 700 to become stuck in a particular position. For example, the venting ring 700 could become stuck in a raised position in which the venting washer lifts the valve member 600 away from the valve seat 220 to an open configuration. This could mean that when the steam trap 10 is operating at the operational temperature, for example in the range between 120°C and 450°C, the steam trap 10 would be open and would therefore allow useful steam to be lost from the system.

Figures 7 and 8 illustrate the venting ring 400 of Figures 2-4 which falls within the scope of the invention.

The venting ring 400 is an integrally formed open band that generally extends in the circumferential direction and which has a gap between its two ends. The venting ring 400 is bimetallic and therefore comprises two metals having different coefficients of thermal expansion such that the ring expands and contracts in response to temperature changes. In this embodiment, the venting ring 400 contracts upon cooling and expands upon heating. The venting ring 400 is provided with a wear resistant and corrosion resistant coating, such as a coating formed by electroless nickel plating. This ensures that the venting ring moves smoothly on the frustoconical surface 217 of the valve seat body.

The venting ring 400 comprises three angularly spaced contact protrusions 412 that extend radially inwardly with respect to the remainder of the venting ring 400. Each of the contact protrusions has a contact surface 415 that is circumferentially extending over approximately 10. In this embodiment the contact protrusions are spaced from one another by approximately 120 and are therefore equally spaced. The venting ring 400 also comprises two outer radial portions 414 that extend between the contact protrusions 412. The outer radial portions 414 are positioned radially outwards with respect to the contact protrusions 412.

As described above with reference to Figure 2, the venting ring 400 is disposed within the chamber 500 and is located around the frustoconical surface 217 of the valve seat body 200 so that it is substantially coaxial with the body 200. Each of the three contact protrusions 412 radially extends inwardly towards the frustoconical surface 217 and the contact surface 415 of each protrusion 412 is in contact with the frustoconical surface 217 at a discrete contact position 418. As can be seen from Figure 8, the contact position is circumferentially extending and in this embodiment corresponds to the circumferential length of the contact surface 415 of the contact protrusions 412.

In this embodiment, the contact protrusions 412 are distributed around the venting ring 400 such that the smallest circular arc passing through all of the contact protrusions 412 is greater than 180°. This ensures that the venting ring 400 is supported around its full circumferential extent and is substantially coaxial with the axis of the valve seat body 200. Another way of expressing this is that there is at least one contact protrusion 412 on each side of any diametric line of the venting ring 400.

The venting ring 400 will sit on the frustoconical surface 217 at a vertical position where the radius of the frustoconical surface 217 is the same as the radius of the circle that passes through the contact surfaces 415 of the contact protrusions 412. This circle will be referred to as the circumscribed circle or circumcircle of the three contact protrusions 412 and the radius of this circle will be referred to as the circumradius. As the venting ring 400 is cooled, the circumradius will reduce and therefore the venting ring 400 will rise, and as the venting ring 400 is heated, the circumradius will increase and therefore the venting ring 400 will fall.

References to the venting ring 400 expanding or contracting are references to the venting ring 400 changing shape such that the size of the circumscribed circle or circumcircle of the three contact protrusions 412 expands or contracts.

As can be seen from Figure 9, at ambient temperature Ta the circumradius of the three contact protrusions 412 is ra and therefore the venting ring 400 sits on the frustoconical surface 217 at a vertical position where the radius of the frustoconical surface is also ra.

As shown in Figure 10, if the venting ring 400 is heated to a temperature Th it may expand in a non-uniform manner such that only the left-hand portion 401 of the venting ring 400 expands. Despite this non-uniform expansion, the circumradius of the three contact protrusions 412 increases to rh. The venting ring 400 therefore moves to a vertical position on the frustoconical surface where the radius is rh.

The use of three contact protrusions 412 which contact the frustoconical surface 217 at three discrete angularly spaced contact positions ensures that any expansion or contraction of the venting ring 400, uniform or non-uniform, causes the circumradius of the three contact protrusions 412 to change. This ensures that the venting ring 400 will move on the frustoconical surface 217 in response to a temperature change, even if the venting ring 400 has non-uniform properties. Since the circumradius will change in response to a temperature change, the chances of the venting ring 400 becoming stuck in the raised position in which it lifts the valve member 600 away from the valve seat 220 to an open configuration are vastly reduced. Therefore, the loss of valuable steam from the system through the steam trap 10 can be avoided.

This is in contrast to the venting ring 700 described with reference to Figure 5 and 6 in which it cannot be guaranteed that non-uniform expansion or contraction of the ring results in a change in the inscribed circle. As described above, this may result in the venting ring 700 becoming stuck in a particular position, such as in a position in which it lifts the valve member 600 away from the valve seat 220.

The radial distance between the contact surfaces 415 of the contact protrusions 412 and the inner surface of the outer radial portions 414 is chosen such that over the operational temperature range the outer radial portions 414 will not come into contact with the frustoconical surface 217. This means that the inscribed circle within the venting ring 400 will always be the circumcircle passing through the three contact protrusions 412.

The design of the venting ring 400 allows it to be manufactured with ease and to a lower tolerance which results in a steam trap that is less expensive. It may be possible to retrofit steam traps having a conventional venting ring 700 with an improved venting ring which contacts a body at a discrete number of angularly spaced positions.

Although it has been described that the venting ring 400 has three contact protrusions 412 contacting the frustoconical surface at three discrete contact positions, it should be appreciated that the venting ring may have more than three contact protrusions, and may in some embodiments contact the body at more than three discrete contact positions. For example, the venting ring 400 may have at least four contact protrusions 412. Two of the four contact protrusions 412 may be close together so that in effect they contact the body at a single contact position that is circumferentially extending.

Alternatively, the four contact protrusions may contact the body at four discrete contact positions 418. Whilst it would no longer be possible to guarantee that the circumradius of the venting ring 400 would change in response to any temperature change, it would represent a significant improvement over the arrangement of Figures 5 and 6 in which there is effectively an infinite number of contact positions. This arrangement would therefore mitigate the effect of non-uniform expansion or contraction. In summary, the venting ring 400 may have any suitable number of contact protrusions.

Although it has been described that the contact protrusions 412 extend radially inwardly and cooperate with a frustoconical surface, it should be appreciated that in other embodiments the venting ring and the frustoconical surface may be arranged differently. For example, the frustoconical surface 217 may be an inner frustoconical surface which is wider at its upper end, and the contact protrusions 412 may extend radially outwardly. In another arrangement, the venting ring 400 may have inclined protrusions that are arranged to cooperate with an edge of a body.

Claims (2)

1. <claim-text>CLAIMS1. A steam trap, comprising: an inlet and an outlet terminating at a valve seat; a valve member moveable between at least a closed position in which flow between the inlet and the outlet is restricted and at least one open position in which fluid can flow between the inlet and the outlet; and a venting ring which is in contact with a body at three discrete angularly spaced contact positions and which is arranged to change in shape in response to temperature changes; wherein in response to a particular temperature drop, the venting ring changes in shape and cooperates with the body so that it moves from an operating position to a cold position in which it moves the valve member to an open position.</claim-text> <claim-text>2. A steam trap according to claim 1, wherein the venting ring is substantially coaxial with the body.</claim-text> <claim-text>3. A steam trap according to claim 1 or
2. 2. wherein the angle of the smallest circular arc passing through the contact positions is greater than 1800.</claim-text> <claim-text>4. A steam trap according to any preceding claim, wherein any change in shape of the venting ring due to a temperature change causes the circumradius of the contact positions to change.</claim-text> <claim-text>5. A steam trap according to any preceding claim, wherein the venting ring is bimetallic.</claim-text> <claim-text>6. A steam trap according to any preceding claim, wherein the venting ring is an open ring.</claim-text> <claim-text>7. A steam trap according to any preceding claim, wherein the venting ring is arranged to contract in response to a temperature drop and expand in response to a temperature rise.</claim-text> <claim-text>8. A steam trap according to any preceding claim! wherein the venting ring comprises three angularly spaced contact protrusions which contact the body at the three contact positions.</claim-text> <claim-text>9. A steam trap according to claim 8, wherein the contact protrusions have a circumferential length.</claim-text> <claim-text>10. A steam trap according to any preceding claim, wherein the body comprises a frustoconical surface which the venting ring is in contact with.</claim-text> <claim-text>11. A steam trap according to any preceding claim, wherein the body is a valve seat body comprising the valve seat, the valve seat body having an outer frustoconical surface which the venting ring is in contact with.</claim-text> <claim-text>12. A steam strap according to any preceding claim, wherein the venting ring is provided with a wear and/or a corrosion resistant coating.</claim-text> <claim-text>13. A steam trap according to claim 12, wherein the coating is formed by an electroless nickel plating process.</claim-text> <claim-text>14. A steam trap substantially as described in with reference to Figures 1-4 and Figures 7-10.</claim-text> <claim-text>15. A steam system complising at least one steam trap in accordance with any preceding claim.</claim-text> <claim-text>16. A venting ring for use with a steam trap in accordance with any one of claims 1-14.</claim-text>