A Steam Plant Component

The present invention relates to a steam plant component for installation in a steam plant, in particular a steam plant component incorporating a strainer screen for removing debris from steam or condensate flowing through the plant.

Steam plants operate to generate and transport steam under pressure to the point-of- use in various industrial processes. As part of the steam cycle, condensate is inevitably formed at various points in the plant, which is drained through steam traps. In any operating steam plant therefore, fluid in the form of steam and condensate is being transported around the plant at relatively high pressure.

The presence of loose scale, rust and other pipeline debris in a steam plant is commonplace. In order to prevent damage to the plant that might otherwise be caused by such debris being accelerated in the condensate or steam flow, this debris is effectively removed from the steam and/or condensate using strainer screens, which are designed to act as 'sieves' for the steam or condensate, arresting movement of the debris whilst nevertheless permitting the throughflow of steam or condensate.

Strainer screens are generally incorporated as part of a corresponding steam plant component installed in the steam plant, the component generally comprising a fluid inlet, a fluid outlet and a strainer chamber in-between the fluid inlet and outlet for accommodating the strainer screen. Fluid in the form of steam or condensate enters the steam plant component through the fluid inlet and exits the component through the fluid outlet, passing through the strainer screen along the way. The steam plant component may be a dedicated strainer or some other plant component such as a steam trap providing both a strainer function and a trap function. Where the component is a steam trap, the strainer chamber is usually situated upstream of the trapping components, and in particular upstream of any valve seat of the trap to prevent debris from reaching the trapping components.

The strainer screen itself is generally of very simple construction, typically comprising a perforated or wire-mesh screen spanning the cross-section of the relevant strainer chamber and having a straightforward shape such as a regular cylindrical shape (angled to the direction of steam flow so as to span the cross section of the strainer chamber).

It is an object of the present invention to seek to provide a steam plant component incorporating an improved strainer screen.

According to the present invention there is provided a steam plant component configured for installation in a steam plant carrying steam or condensate, the component defining a strainer chamber having a fluid inlet and a fluid outlet for passage of said steam or condensate through the steam chamber, the strainer chamber accommodating a strainer screen having a convoluted configuration.

The strainer screen may be generally cylindrical and incorporates circumferential corrugations forming a series of circumferential ridges and valleys along the longitudinal axis of the strainer screen.

The opposite faces of each ridge may be parallel to each other.

The strainer screen may be a perforated screen, in which case the perforations may be circular and may be 0.8mm to 3mm wide. Alternatively, the strainer screen may be a mesh screen, for example a 40, 100 or 200 mesh screen. In any case, the strainer screen may be formed from any suitable material such as stainless steel or Monel®.

The screen may be of generally cylindrical configuration, with axially extending pleats forming ridges and valleys as viewed from the exterior of the screen. The opposite faces of each ridge may be parallel to each other.

The screen may have an axially extending opening over part of its periphery, bounded by screen edges situated at or near the radially outermost regions of respective ridges.

At least one axial end of the screen may be closed.

The steam plant component may be a strainer or a steam trap, for example a float trap, which incorporates a strainer, Thus, for example, a steam trap may comprise a single body which accommodates a steam trap mechanism and also includes a strainer chamber provided with a strainer screen.

According to another aspect of the present invention there is provided a float operated valve mechanism comprising a valve element which is movable into and out of engagement with a valve seat, the valve element being connected for actuation to a float lever by a connecting arm, the float lever carrying a float and being pivotable about a fulcrum, the moment arm between the fulcrum and the line of action of a buoyancy force on the float, acting through the centre of buoyancy of the float, being greater than the moment arm between the fulcrum and the line of action of a force applied at a pivotal connection between the lever arm and the connecting arm in a direction corresponding to opening movement of the valve element, the mechanism including a counterweight which generates a moment about the fulcrum in the sense opposite to that generated by the weight of the float.

The float operated valve mechanism seeks to address a problem associated with float traps.

Thus, a fundamental problem associated with float traps is that a significant part of the force arising from the buoyancy of the float is used to overcome the weight of the float. Consequently, not all of the buoyancy force is available to open the valve. When used in pressurised systems such as steam traps, floats must be strong enough to withstand the pressure of the steam to which they are subjected. In practice, this means that floats are made from strong materials, such as stainless steel, and need to have a significant wall thickness, for example in the range 0.5 mm to 2.0 mm. As a result, the efficiency of the float, in terms of the ratio of the buoyancy available to operate the valve to the total buoyancy of the float, can be less than 50% and sometimes significantly so.

It is desirable for float traps to have as large a discharge orifice as possible, so that accumulated condensate can be discharged quickly. Since the valve element must be displaced from the valve seat against the pressure within the chamber, an increased discharge capacity requires a greater buoyancy force. This, in turn, requires a larger float, leading to the need for a larger chamber to accommodate the float. It would therefore be desirable for the discharge orifice to be as large as possible, while keeping the overall dimensions of the float trap as small as possible.

In the present float-operated valve mechanism, the weight of the float is counterbalanced by the counterweight, so that near to the full buoyancy force

generated by the float can be employed to displace the valve element away from the valve seat.

The valve element may be mounted on a carrier which is pivotable with respect to the valve seat, in which case the connecting arm may be pivotably connected to the carrier. The valve element may have a spherical surface which is engagable with the valve seat.

In one embodiment, the counterweight may be mounted on the float lever at a position on the opposite side from the float of a vertical plane containing the fulcrum. However, in practice this can result in the counterweight being situated above the valve seat, and will move upwardly as the float descends. If the mechanism is to be installed within the chamber of a float trap, the size of the chamber may need to be increased to accommodate the movement of the counterweight.

In an alternative embodiment, the counterweight is mounted on a counterweight arm which is rigidly connected to the carrier in such a way that the counterweight acts on the carrier in the direction to displace the valve element away from the valve seat. The counterweight can thus be situated on the same side as the float of the vertical plane containing the fulcrum.

The carrier may be pivotably mounted with respect to the valve seat by a pivot shaft, in which case the counterweight arm may be connected by the same pivot shaft to the carrier, and a locking pin may be provided at a position spaced from the pivot shaft to secure the counterweight arm against rotation relatively to the carrier about the pivot shaft. The locking pin and the pivot shaft may be parallel to each other, and situated on opposite sides of the valve seat.

The locking pin may also extend through the connecting arm, so as to provide the pivotable connection between the carrier and the connecting arm.

The counterweight may be formed in various different ways. For example, it may comprise a separate component secured to the counterweight arm, or it may be formed integrally with the counterweight arm, for example by casting both components from a suitable material such as steel.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a partial cross-sectional view showing a strainer screen employed in a Y- type strainer;

FIGURE 2 is a cut-away view of a float trap;

FIGURE 3 is a diagrammatic side view of a float operated valve mechanism of the float trap of figure 1 ;

FIGURE 4 shows a strainer screen employed in the float trap of Figure 1 ;

FIGURE 5 corresponds to Figure 3, but shows an alternative embodiment of the float operated valve mechanism;

FIGURE 6 shows an end-on perspective view of a strainer screen located within the strainer chamber of a float trap: and

FIGURE 7 corresponds to an isometric drawing of the strainer screen shown in Figure 6.

Figure 1 shows a steam plant component, in this case a dedicated strainer 100.

The strainer 100 comprises a strainer body 100a of generally conventional Y-shaped construction incorporating a fluid inlet in the form of a steam inlet 102, a fluid outlet in the form of a steam outlet 104 generally aligned with the steam inlet 102, and a blind cylindrical "pocket" 106 which diverges from the outlet 104 along the direction of steam flow A and forms a strainer chamber 108 in between the inlet 102 and the outlet 104.

A strainer screen 110 is accommodated in the strainer chamber 108.

The strainer screen 110 comprises a sheet material, for example stainless steel or Monel®, which is perforated by holes (not shown) of sufficiently small size to allow the strainer screen 110 to intercept and arrest movement of debris incident on the strainer screen 110, while nevertheless permitting relatively free flow of fluid through the

strainer screen 110. The perforations may circular and each perforation may be 0.8mm to 3mm wide.

The strainer screen 110 is generally cylindrical, but with a convoluted configuration incorporating a series of circumferential corrugations 112. The corrugations 112 form a series of alternating circumferential ridges 114 and valleys 116 along the longitudinal axis B of the strainer screen 110, giving the strainer 110 a "ribbed" appearance as shown in Figure 1.

Typically the strainer screen may have an axial length of 46 to 298mm, and the ridge to ridge pitch of the corrugations may independently be in the range 5 to 20mm, more specifically 8 to 15mm. The diameter of the strainer screen may be in the range 18 to 208mm.

It will be appreciated from Figure 1 that each ridge 114 and valley 116 is defined by a circular arc of 180°, so that the flanks of each corrugation between the respective ridge 114 and the corresponding valleys 116 are parallel to each other.

The strainer screen 110 sits co-axially in the cylindrical strainer chamber 108 and extends back towards the inlet so as to span the cross-section of the strainer chamber 108, thus ensuring that steam passing through the inlet 102 and exiting the outlet 104 passes through the screen 110 along the way.

The screen 110 may be open at each axial end. When installed in the strainer chamber 108, the lower end (as seen in Figure 1) is closed by a cap 118. The upper end of the screen 110 seats against internal surfaces of the body 100a. Consequently, incoming flow enters the strainer screen 110 through its top end, and then passes through the perforations to flow towards the outlet 104. The cap 118 may be removed so that the screen 110 can be extracted for cleaning or replacement.

The strainer 100 is configured for installation in a steam plant between two sections of a steam pipeline (not shown) using attachment flanges 114, 116, associated with the inlet 102 and outlet 104 respectively; the flanges 114, 116 may be fixedly attached to corresponding flanges on the pipeline sections (not shown) in conventional manner to secure the strainer 100 between the pipeline sections. With the strainer 100 thus installed, fluid, primarily steam in this case, flowing from one of the pipeline sections to

the other of the pipeline sections enters the strainer 100 through the steam inlet 102, passes through the strainer chamber 108, where the strainer screen 110 acts to 'sieve' debris from the steam, and then exits through the outlet 104.

It will be appreciated that the convoluted configuration of the strainer screen 110 provides a relatively large surface area for the size of the strainer screen 110, thus tending to optimise the flow capacity of the strainer 110 and minimise the pressure drop across the strainer 110 as a function of the overall size of the strainer 110.

Figure 2 shows a steam plant component in the form of a float trap, comprising a casing 2 defining a chamber 4. The chamber 4 has an inlet 6 and an outlet 8. The inlet 6 opens into a strainer chamber 10; the strainer chamber 10 also has an outlet (also not shown in Figure 2) that communicates with the chamber 4.

A strainer screen 12 is accommodated in the strainer chamber 10; the strainer screen 12 is not illustrated in Figure 2 for the purposes of clarity, but is shown clearly in Figure 7. In common with the strainer screen 110 previously described, the strainer screen 12 comprises a sheet material, for example stainless steel or Monel®, which is perforated by holes (not shown) of sufficient size to intercept solid matter passing through the inlet 6, while permitting relatively free flow of fluid, primarily condensate in this case, through the strainer chamber 10. By way of example, the perforations in the strainer may be circular, having a diameter of approximately 0.5 to 3mm.

As shown in Figure 7, the sheet material of the strainer screen 12 is folded into a generally cylindrical, convoluted configuration of non-circular form, giving the strainer screen 12 a somewhat star-shaped configuration as viewed from the end. Thus, the strainer screen 12 has a plurality of pleats in the sheet material, which define alternate valleys 40 and ridges 42. The ridges 42 form radially extending arms 38, each of which has opposite sides 44 that are parallel to each other.

At one side, the strainer screen 12 has an axially extending opening 46, defined between edges 48 along the ridges 42 of respective half-arms 50.

The strainer screen 12 shown in Figure 7 is open-ended, the strainer being closed by contact with the ends of the strainer chamber 10. In other embodiments, one or both ends of the strainer screen 12 may be closed by end panels.

The strainer screen 12 is positioned within the strainer chamber 10 so that the opening 46 faces the inlet 6. Consequently, condensate flowing into the strainer chamber 10 enters the interior of the strainer screen 12 and flows through the perforations into the valleys 40 between the arms 38. The condensate flows axially along the valleys 40 into the chamber 4.

A cap 54 closes the end of the strainer chamber 10 away from the chamber 4, but can be removed to permit withdrawal of the strainer screen 12 for cleaning or replacement.

For use, the float trap is installed in a steam plant at a position below a device, such as a heat exchanger (not shown), in which steam is utilised for heating purposes. Condensate forming as a result of loss of heat from the steam drains to the inlet 6 and flows under gravity into the strainer chamber 10, where the strainer screen 12 "sieves" the condensate to remove debris, and out into the chamber 4.

In common with the strainer screen 110, it will be appreciated that the strainer screen 12 advantageously has a relatively large screening area in relation to its overall (volumetric) size.

Referring back to Figures 3 to 5, the chamber 4 itself accommodates a float operated valve mechanism 14 (see Figures 3 and 5). The mechanism 14 comprises a valve unit having a housing 16 secured to the casing 2 at the chamber end of the outlet 8. The housing 16 has an internal passage communicating with the outlet 8, the end of this passage situated within the chamber 4 being provided with a valve seat 18.

A float lever support 20 is secured to the valve housing 16 and supports a float lever 22 for pivotal movement about a float lever pin 24, serving as a fulcrum. The float lever 22 carries a float 26 at one end and a counterweight 28 at the other end. The centre of buoyancy of the float 26 is indicated at 27.

A valve element 30 is mounted on a valve element carrier 32, which is pivotably connected to the float lever support 20 by a pivot pin 34. A connecting arm 36 is pivotably connected at its ends to the float lever 22 and the carrier 32, by pivot pins 38, 40, respectively.

It will be appreciated that, since the chamber 4 is connected to the live steam pipework, it is maintained at the system pressure. As condensate builds up in the chamber 4, the float 26 rises, pivoting about the pivot pin 24. The resulting movement of the float lever 22 is transmitted by the connecting arm 36 to the valve element carrier 32. The carrier 32 is thus pivoted to the right, as seen in Figure 2, retracting the valve element 30 from the valve seat 18. The accumulated condensate in the chamber 4 can then flow through the valve seat 18 and the valve housing 16 to the outlet 8 under the action of the system pressure in the chamber 4. The float 26 then falls again, so closing the valve element 30 against the seat 18, allowing condensate to accumulate again within the chamber 4.

It will be appreciated that the moment arm between the centre of buoyancy 27 of the float 26 and the fulcrum constituted by the pivot pin 24, measured in the horizontal direction, is significantly greater than the moment arm between the fulcrum 24 and the line of action of the force applied at the pivot pin 38 to the connecting arm 36 owing to the movement of the float arm 22. There is thus a significant multiplication of the buoyancy force acting on the float 26 as it is applied to the carrier 32. Furthermore, the counterweight 28 applies to the float arm 22 a moment in the same direction as the buoyancy force acting on the float 26. The mass of the counterweight 28 is selected so that it counterbalances, at least partly, the weight of the float 26 and the part of the float arm 22 situated on the float side of the fulcrum 24. Consequently, the full buoyancy force applied to the float 26, multiplied by the linkage including the connecting arm 36, acts on the valve element 30. It will be appreciated that additional force multiplication is achieved because the moment arm between the valve element 30 and the pivot pin 34 is much smaller than that between the pivot pin 40 and the pivot pin 34.

Consequently, the buoyancy of the float 26 is sufficient to withdraw the valve element 30 from the seat 18 against the differential pressure acting on the valve element 30 in the direction towards the valve seat 18.

Figure 4 shows an alternative configuration for the float operated valve mechanism 14. Parts corresponding to those shown in Figures 1 and 2 are identified by the same reference numbers. In the embodiment of Figure 4, the float lever 22 extends generally only to one side of the pivot pin 24 and carries the float 26. The counterweight 28 is carried on a separate lever 56 which is connected to the carrier 32 by the pivot pin 34 about which the carrier 32 is pivotable relative to the valve seat support 20. The lever 56 is cranked, and as shown in Figure 4 it extends upwardly from the pivot pin 34 to the

pivot pin 40 which extends through the carrier 32 and the counterweight lever 56. The pivot pin 40 thus serves as a locking pin to secure the counterweight in a fixed orientation with respect to the carrier 32. In the illustrated embodiment the pin 40 serves both as the locking pin and as the connection pin between the connecting arm 36 and the carrier 12. In other embodiments, these can be performed by separate pivot pins.

In operation, rising of the float 26 acts, as before, on the carrier 32 through the connecting arm 36 to exert an opening moment on the carrier 32. By contrast with the embodiment of Figures 1 and 2, there is no counterweight mounted directly on the float lever 22. Instead, the counterweight 28 acts directly on the carrier 32 to assist the buoyancy force exerted on the float 26, thereby counterbalancing the weight of the float 26.

In the embodiment of Figure 4, the counterweight is in the form of a cylindrical mass, and may be manufactured by cutting an appropriate length of bar stock which is subsequently secured, for example by welding, to the counterweight arm 56. In an alternative embodiment (not shown) the counterweight 28 may be formed integrally with the arm 56, for example by casting from a suitable material such as steel.

Although each of the strainer screens 110 and 12 are perforated screens, they might alternatively be wire mesh screens, for example a 40, 100 or 200 mesh screen.