GB2394759A - A bimetallic condensate trap with a plate spring - Google Patents

Abstract

A condensate trap comprises a bimetallic device 26 which, at elevated temperatures, applies a closing force to a valve element 20. The stack 26 acts on an abutment 52 through a plate spring 42. An increase in pressure and temperature after the valve element 20 has contacted its seat 64 causes the spring 42 to be deformed into a conical shape. Consequently, the closing force applied to the valve element 20 increases with temperature in a manner corresponding to the steam saturation line.

Description

A BIMETALLIC CONDENSATE TRAP

This invention relates to a bimetallic condensate trap.

5 Condensate traps are more usually referred to as steam traps, since they are commonly used in systems utilising steam, in order to remove condensed steam from the system. Steam traps respond to the presence of condensate so that they open to discharge condensate 10 when condensate is present at the trap, and close when steam is present.

There are many different control mechanism for steam traps. One mechanism uses a bimetallic control device 15 such as is disclosed in US 6158664. This device comprises a stack of bimetallic elements which tend to expand or contract in the lengthwise direction of the stack as the temperature changes. One end of the stack engages an abutment, while the other engages a valve 20 element which can move into and out of engagement with a seat. When the stack of bimetallic elements is cold, for example when it is surrounded by cool condensate, the valve is open. As the temperature increases, the bimetallic elements deform to increase the length of 25 the stack, so closing the valve. When the valve is closed, increasing temperature will increase the force with which the valve element is held against the seat, and consequently will increase the upstream pressure required to force the valve element away from the seat 30 to allow flow through the valve.

In a conventional steam trap having a bimetallic operating device made up of circular elements, the force applied by the bimetallic device to the closed

valve element is directly proportional to the temperature. This is represented by the line A in Figure 1. Figure 1 also shows the steam saturation line S. and it will be appreciated that, with 5 increasing pressure, the line A lies further and further below the steam saturation line S. The steam saturation line S represents the temperature, for any given pressure, at which condensate will form.

10 Thus, it will be appreciated from Figure 1 that at, for example, a pressure of 16 bar, condensate will begin to form at a temperature above 204.38 C, but the valve will not open to discharge condensate until the temperature of the condensate has fallen to 140 C.

In some circumstances, such performance is useful, for example in steam tracer lines which are used to maintain the temperature of a primary process fluid line. In such applications, it is desirable to extract 20 as much energy as possible from the steam and, after condensation, from the resulting water.

However, in some applications, it is desirable for condensed water to be discharged from the system as 25 soon as it forms, in order to maintain efficiency and to avoid detrimental effects such as water hammer in the pipework of the steam system.

Consequently, it would be desirable for the steam trap 30 characteristic to follow the steam saturation line S more closely.

US 6158664 attempts to achieve this by the use of bimetallic elements which have projecting arms of

different lengths. Thus, as the temperature increases, the longer arms of adjacent bimetallic elements come into contact with each other, applying a.relatively weak force to the valve element so that the valve will 5 open at a lower pressure than would be achieved using circular bimetallic elements. As the temperature rises, the other arms progressively come into contact with each other, so increasing the force applied by the metallic element and increasing the pressure at which 10 the valve will open. Such a steam trap achieves a characteristic approximately as shown by the line C in Figure 1. It will be noted that line C is made up of three straight portions, with gradient changes at approximately 3.5 bar and 15 bar.

While the characteristic of a steam trap constructed in accordance with US 6158664 approximates to the desired curve B. the bimetallic elements, because of their complex shape, are relatively expensive. They also 20 tend to have a larger diameter than corresponding circular bimetallic elements, which requires a larger housing for the steam trap with associated additional expense. 25 An alternative technique for matching the steam trap performance to the steam saturation line S is to provide a coil compression spring between the bimetallic stack and the abutment, so that the initial closing force is imposed by the spring as the stack 30 expands. This provides a relatively steep straight line increase of temperature until the spring is fully compressed, "hereafter the characteristic corresponds to line A, but at a higher temperature. Consequently,

only a very rough approximation to the line S is achieved. According to the present invention there is provided a 5 condensate trap comprising a valve element which is movable in to and out of sealing contact with a valve seat, the valve element being controlled by a bimetallic device which acts through a spring against an abutment, the spring having a spring characteristic 10 such that the spring rate increases as the spring is deflected from a relaxed configuration, corresponding to an open position of the valve element with respect to the seat, to a fully deflected configuration corresponding to a closed position of the valve element 15 with respect to the seat.

The spring is preferably in the form of a plate which is acted upon by the bimetallic device and the abutment in such a way that, in its relaxed configuration, it is 20 substantially flat but, as it is deflected, it assumes a generally conical configuration. The plate may have a central aperture, and it may have a substantially continuous outer periphery and a substantially continuous inner periphery, one of which peripheries 25 engages the abutment and the other of which is acted upon by the bimetallic device. In a preferred embodiment, the spring comprises a continuous circular outer peripheral region and a continuous circular inner peripheral region extending around a central aperture, 30 the outer peripheral region and the inner peripheral region being interconnected by a plurality of arms, which may be disposed radially.

The arms may vary in width along their length, for example they may taper in the radially outwards direction, in order to achieve desired spring characteristics. The spring preferably engages the abutment at its outer periphery, and is acted upon at its inner periphery by the bimetallic device. There may be a spacer disposed between the bimetallic device and the inner periphery 10 of the spring.

The abutment is preferably fixed with respect to the seat, and may be provided on a valve seat body in which the seat is formed. In such a case, the valve seat 15 body may be provided with an inclined region in the form of a conical chamfer on which the inner periphery of the spring rests when the spring is in its fully deflected configuration.

20 The bimetallic device may comprise a plurality of stacked bimetallic elements, which may each have a circular outer periphery. In such an embodiment, one end of the stack acts on the spring, while the other end of the stack engages the valve element, for 25 example, by way of a valve stem which extends from the valve element through a central aperture of the stack.

The valve seat body preferably comprises a condensate passageway which extends from an external surface of 30 the valve seat body, at which the passageway opens into a chamber accommodating the bimetallic device, to a valve passage in which the valve seat is situated. A flushing passageway may be provided between the

condensate passageway and an end face of the valve seat body over which face the spring lies.

The valve element may comprise a head disposed in the 5 valve passage downstream of the valve seat, with respect to the normal direction of condensate flow in operation of the condensate trap, which is situated in a region of the valve passage which diverges in the downstream direction. This head, when acted upon by 10 fluid flowing through the valve seat when the valve is open, provides additional force in the valve opening direction to increase the flow rate through the valve.

For a better understanding of the present invention, 15 and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a graph showing the steam saturation line 20 and the characteristics of various steam traps; Figure 2 is a sectional view through a steam trap; Figure 3 is an enlarged view of part of the steam trap 25 of Figure 2; Figure 4 is a further enlarged fragmentary view of part of the steam trap; and 30 Figure 5 is a face view of a component of the steam trap; and Figure 6 corresponds to Figure 5 but shows an alternative component.

i The steam trap shown in Figure 2 comprises a main body 2 having inlet and outlet connections 4 and 6. A cap 8 is fitted to the body 2 to define a chamber 10. A 5 passage 12 connects the inlet connection 4 to the chamber 10, and a valve arrangement 14 controls communication between the chamber 10 and the outlet connection 6. The valve arrangement 14 comprises a valve seat body 16 which is fitted into a screw 10 threaded bore 18 in the body 2. A valve element 20 is situated within a valve passage 22 in the valve seat body 16. The valve element 20 has a valve stem 24 which extends through the passage 22 into the chamber 10. Within the chamber 10, there is a bimetallic device 26 assembled from a stack of bimetallic elements 28 in the form of circular discs each having a central aperture through which the valve stem 24 extends. The 20 bimetallic discs 28 are disposed face-to-face in pairs or in groups of four, in such a way that, upon an increase in temperature, the discs 28 of each pair adopt a cupped configuration with the concave face directed towards the other disc 28 of the pair.

25 Consequently, an increase in temperature causes the stack 26 to increase in length is unrestrained or, if restrained, to generate a greater force. Spacers 30 are disposed at intervals through the stack 26, and end spacers 32, 34 are disposed respectively at the upper 30 and lower ends of the stack, as viewed in Figure 2.

The spacers 30 allow condensate to permeate between the sets of discs 28 to improve heat flow between the condensate and the discs. The lower end spacer 34

provides a clearly defined zone of action on the spring 42 of the force applied by the stack 26.

The upper end spacer 32 is situated between the upper 5 endmost disc 28 and a nut 38 which serves to adjust the position of the valve element 18 with respect to the upper endmost disc 28. The nut 38 is situated within a circular recess 40 in the cap 8 to support the upper end of the stem 24.

The lower spacer 34 is situated between the lowermost end disc 28 and a spring 42. The spring 42 is shown in face view in Figure 5. It is of circular configuration having a central aperture through which the valve stem 15 24 extends. The spring 42 comprises a continuous outer peripheral region 44 and a continuous inner peripheral region 46, each in the form of a circular annulus.

These two regions 44, 46 are interconnected by radial arms 48 left between four generally quadrant-shaped 20 apertures 50. The spring 42 may be formed by stamping from a sheet of spring steel.

An alternative spring 42' is shown in Figure 6. This spring has only three arms 48' distributed equally 25 around the axis of the spring. Each arm 48' reduces in width in the radially outward direction from the inner peripheral region 46' to the outer peripheral region 44'. This configuration provides an improved spring characteristic of force versus deflection, compared 3 0 with the spring of Figure 5. The varying width of the arms 48' equalises stresses in the spring as it deflects, and so increase the force that the spring can accommodate before the elastic limit of the material of the spring is reached.

r The outer peripheral region 44 of the spring 42 rests on an annular abutment 52 formed on the valve seat body 16 as shown more clearly in Figure 3. The lower spacer 34 engages the inner peripheral region 46 of the spring 5 42. The annular abutment 52 surrounds a depression 54 in the end face of the valve seat body 16 so that, in the relaxed configuration of the spring 42 as shown in Figure 3, the inner peripheral region 46 of the spring 42 is supported above that end face by the arms 48.

The valve passage 22 comprises different sections of different diameter. Adjacent the end face provided with the depression 54, there is a bearing section 56 which supports the valve stem 24 for longitudinal 15 movement. Below the bearing section 56 there is an enlarged region 58 which is connected to the exterior of the valve seat body by an inclined condensate passageway 60 which emerges, as seen in Figure 2, into the chamber 10. A flushing passageway 62 extends 20 between the end face of the valve seat body 16 and the condensate passage 60, and consequently opens into the depression 54 beneath the spring 42.

The enlarged passage section 58 terminates at a valve 25 seat 64, below which there is a cylindrical chamber 66 which is connected to the outside of the valve seat body 16 by way of a downwardly divergent passage section 68. The valve element 20 terminates at its lower end in a head 70 having a tapered surface 72 30 corresponding to that of the divergent passageway 68.

As shown in Figure 4, the bearing passage 56 opens into the depression 54 at a shallow chamfer 74. The angle of this chamfer is such that, if projected radially

outwardly, the chamfer surface would pass close to the abutment 52. In the embodiment shown in the drawings, the angle of the chamfer is 160 inclusive.

Consequently, as the inner peripheral region 46 of the 5 spring 42 is displaced downwardly under the action of the bimetallic stack 26 acting through the lower end spacer 34, this inner peripheral region 46 will make face-to-face contact with the surface of the chamfer 74, so avoiding the creation of undesirable stresses 10 within the material of the spring 42. Additional stresses are also avoided by forming the abutment 52 as a convex curve to allow the outer peripheral region 44 of the spring 42 to roll over the curve as the spring 42 is deflected. The depth of the depression 54 and 15 the dimensions of the spacer 34 are closely toleranced in order to achieve a reproducible characteristic of the spring 42 as it is deflected from the relaxed, flat configuration as shown in Figure 3 to the fully deflected configuration in which the inner peripheral 20 region 46 engages the chamfer 74.

In operation, assuming a starting condition in which the steam trap is cold, the valve will be in the condition shown in Figure 2, in which the valve head 20 25 is spaced downwardly from the seat 64, so enabling flow through the valve 14. The bimetallic elements 28 are generally flat and unstressed, as is the spring 42.

Flow therefore takes place through the steam trap through the inlet connection 4 to the outlet connection 30 6, by way of the chamber 10, the passageway 60 and the passage 22. This flow includes the discharge of any condensate which may be present upstream of the steam trap, and the inclination of the passageway 60 improves the flow of condensate from the chamber 10.

r When steam reaches the steam trap, the bimetallic elements 28 will respond to the increase in temperature by adopting a concave configuration, so extending the 5 length of the stack 26. Since the bottom end of the stack is supported, through the end spacer 34, on the spring 42, the increasing length of the stack 26 will raise the nut 38, so taking with it the valve element 20. Eventually, the valve element 20 will contact the 10 seat 64, so lightly closing the passage 22. However, an adequate pressure difference between the chamber 10 and the downstream side of the valve 14 (ie the outlet connection 6) will force the valve open by deflecting the spring 42.

As the temperature within the chamber 10 rises higher, the increasing length of the stack 26 will deflect the spring 42 so increasing the closing force applied to the valve element 20 and consequently increasing the 20 pressure difference required to open the valve 14.

Eventually, the spring 42 will be deflected so that its inner periphery 46 contacts the chamfer 74. When this happens, any further increase in the force retaining the valve element 20 against the seat 64 arises from 25 increasing stress in the bimetallic elements 28.

If condensate reaches the chamber 10, it will eventually cool the bimetallic elements 28 sufficiently to allow the pressure difference between the chamber 10 30 and the outlet connection 6 to overcome the biasing force on the valve element 20 so that the condensate will be discharged.

Referring to Figure 3, once the valve head 20 has moved off the seat 64, flow through the passage 58 into the chamber 66 will impinge on the head 70. In addition, the pressure in the chamber 66 will rise, the effect 5 being to increase the downwards force on the valve element 20. As a result, a relatively large valve opening will be achieved to enable rapid discharge of condensate. The tapers of the passageway 68 and the head 70 ensure that, as the valve element 20 is pulled 10 from the seat 64, the restriction between the head 70 and the passageway 68 decreases. Thus the flow will not be stalled, as it would be if the surface 72 and the wall of the passageway 68 were parallel to the axis of the stem 20.

When the condensate has been discharged, steam will enter the chamber 10, and the resulting temperature increase will cause the valve to close.

20 The cooperation between the nut 38 and the recess 40 supports the upper end of the stem 24. This avoids misalignment of the stem 24 in the event of offset forces being applied by the stack 26. Such misalignment would increase friction between the stem 25 24 and the bearing section 56, and would result in increased wear of the stem 24.

The spring 42 has a force/deflection characteristic (i.e. a spring rate) which increases as the spring is 30 deflected from the flat unstressed configuration shown in Figure 3 to the fully deflected configuration in which the inner periphery 46 lies against the chamfer 74. More specifically, the force/deflection characteristic has the following form:

t pa= Ed][(h-si h-)t+t3] (l_V2)Ma2 2 where V = Poisson's ratio; M is a constant related to the ration a/b; a = outer diameter; 5 b = inner diameter; h = conical height with no load (O if flat as in the present embodiment); t - thickness.

10 From this equation, it can be appreciated that P is proportional to 63 which means that the condensate discharge temperature curve (B in Figure 1) has a gradually decreasing gradient until the spring 42 is fully compressed into the conical shape at which the 15 inner periphery 46 abuts the chamfer 74. Thereafter, the load, as applied by the bimetallic stack 26 alone, increases linearly with temperature. The transition between these two characteristics takes place, in the embodiment represented in Figure 1, at approximately 15 20 Bar.

Consequently, the use of the spring 42 which deflects from a flat relaxed state to a conical form provides an overall temperature/pressure characteristic which 25 approximates closely to the steam saturation line S. As a result, the pressure upstream of the steam trap will be sufficient to cause the valve 14 to open to discharge condensate soon after the condensate forms, and after it has caused a temperature drop of less than 30 20 C.

Claims (1)

1. A condensate trap comprising a valve element which is movable into and out of sealing contact with a valve 5 seat, the valve element being controlled by a bimetallic device which acts through a spring against an abutment, the spring having a spring characteristic whereby the spring rate increases as the spring is deflected from a relaxed configuration, corresponding 10 to an open position of the valve element with respect to the seat, to a fully deflected configuration, corresponding to a closed position of the valve element with respect to the seat.

15 2. A condensate trap as claimed in claim 1, in which the spring is a plate spring.

3. A condensate trap as claimed in claim 2, in which the spring is substantially flat in the relaxed 20 configuration and of generally conical form in the fully deflected configuration.

4. A condensate trap as claimed in claim 2 or 3, in which the spring has outer and inner regions, one of 25 which is supported by the abutment, and the other of which is acted upon by the bimetallic device.

5. A condensate trap as claimed in claim 4, in which the spring has a central aperture surrounded by the 30 inner region of the spring.

6. A condensate trap as claimed in claim 5, in which the outer and inner regions each comprise a continuous circular annulus.

/ 7. A condensate trap as claimed in claim 6, in which the outer and inner regions of the spring are interconnected by a plurality of radially extending 5 arms.

8. A condensate trap as claimed in claim 7, in which the width of each arm decreases in the radially outward direction. 9. A condensate trap as claimed in any one of claims 4 to 8, in which the outer region is supported by the abutment and the inner region is acted upon by the bimetallic device.

10. A condensate trap as claimed in any one of claims 4 to 9, in which a stop surface is provided for engagement by the region of the spring acted upon by the bimetallic device, when the spring is in its fully 20 deflected configuration.

11. A condensate trap as claimed in claim 10, in which the stop is fixed with respect to the abutment.

25 12. A condensate trap as claimed in claim 10, in which the stop comprises an oblique surface, a projection of which passes substantially through a surface of the abutment which is engaged by the spring.

30 13. A condensate trap as claimed in any one of the preceding claims, in which the valve seat and the abutment are provided on a valve seat body.

14. A condensate trap as claimed in claim 13 when appendant to any one of claims 9 to 12, in which the stop is provided on the valve seat body.

5 15. A condensate trap as claimed in claim 13 or 14, in which the abutment is annular, and surrounds a depression in a face of the valve seat body.

16. A condensate trap as claimed in claim 15, in which 10 the valve seat body comprises a condensate passageway providing communication through the valve seat body to the valve seat, a flushing passageway being provided which extends from the condensate passageway to the depression surrounded by the abutment.

17. A condensate trap as claimed in any one of the preceding claims, in which the bimetallic device comprises a stack of bimetallic elements.

20 18. A condensate trap as claimed in claim 17, in which each bimetallic element comprises a circular disc.

19. A condensate trap as claimed in claim 17 or 18, in which one end of the stack is operatively connected to 25 the valve element, the other end of the stack acting on the spring.

20. A condensate trap as claimed in claim 19, in which the said one end of the stack is operatively connected 30 to the valve element by a valve stem which extends from the valve element and passes through the spring and the bimetallic elements.

21. A condensate trap as claimed in any one of the preceding claims, in which the valve element is provided with a head having a diameter greater than that of the valve seat, the head being disposed in a 5 passage which is downstream of the valve seat with reference to the normal flow of condensate through it, the passage being divergent in the downstream direction. 10 22. A condensate trap substantially as described herein with reference to, and as shown in, the accompanying drawings.

I g Amendments to the claims have been filed as follows CLAIMS

1. A condensate trap comprising a valve element which is movable into and out of sealing contact with a valve 5 seat, the valve element being controlled by a bimetallicdevice which acts through a plate spring against an abutment, the spring being disposed so that, in opertion, it becomes increasingly dished as it is stressed, and having a spring characteristic whereby 10 the spring rate increases as the spring is deflected from a relaxed configuration, corresponding to an open position of the valve element with respect to the seat, to a fully deflected configuration, corresponding to a closed position of the valve element with respect to 15 the seat.

2. A condensate trap--as claimed in claim 1, in which the spring is substantially flat in the relaxed configuration and of generally conical form in the 20 fully deflected configuration.

3. A condensate trap as claimed in claim 1 or 2, in which the spring has outer and inner regions, one of which is supported by the abutment, and the other of 25 which is acted upon by the bimetallic device.

4. A condensate trap as claimed in claim 3, in which the spring has a central aperture surrounded by the inner region of the spring.

5. A condensate trap as claimed in claim 4, in which the outer and inner regions each comprise a continuous circular annulus.

6. A condensate trap as claimed in claim 5, in which the outer and inner regions of the spring are interconnected by a plurality of radially extending arms. 7. A condensate trap as claimed in claim 6, in which the width of each arm decreases in the radially outward direction. 10 8. A condensate trap as claimed in any one of claims 3 to 7, in which the outer region is supported by the abutment and the inner region is acted upon by the bimetallic device.

15 9. A condensate trap as claimed in any one of claims 3 to 8, in which a stop surface is provided for engagement by the region of the spring acted upon by the bimetallic device, when the spring is in its fully deflected configuration.

10. A condensate trap as claimed in claim 9, in which the stop is fixed with respect to the abutment.

11. A condensate trap as claimed in claim 9 or 10, in 25 which the stop comprises an oblique surface, a projection of which passes substantially through a surface of the abutment which is engaged by the spring.

12. A condensate trap as claimed in any one of the 30 preceding claims, in which the valve seat and the abutment are provided on a valve seat body.

13. A condensate trap as claimed in claim 12 when appendant to any one of claims 8 to 11, in which the stop is provided on the valve seat body.

5 14. A condensate trap as claimed in claim 12 or 13, in which the abutment is annular, and surrounds a depression in a face of the valve seat body.

15. A condensate trap as claimed in claim 14, in which 10 the valve seat body comprises a condensate passageway providing communication through the valve seat body to the valve seat, a flushing passageway being provided which extends from the condensate passageway to the depression surrounded by the abutment.

16. A condensate trap as claimed in any one of the preceding claims, in which the bimetallic device comprises a stack of bimetallic elements.

20 17. A condensate trap as claimed in claim 16, in which each bimetallic element comprises a circular disc.

18. A condensate trap as claimed in claim 16 or 17, in which one end of the stack is operatively connected to 25 the valve element, the other end of the stack acting on the spring.

19. A condensate trap as claimed in claim 18, in which the said one end of the stack is operatively connected 30 to the valve element by a valve stem which extends from the valve element and passes through the spring and the bimetallic elements.

20. A condensate trap as claimed in any one of the preceding claims, in which the valve element is provided with a head having a diameter greater than that of the valve seat, the head being disposed in a 5 passage which is downstream of the valve seat with reference to the normal flow of condensate through it, the passage being divergent in the downstream direction. 10 21. A condensate trap substantially as described herein with reference to, and as shown in, the accompanying drawings.