GB2474237A

GB2474237A - Valve for steam trap

Info

Publication number: GB2474237A
Application number: GB0917451A
Authority: GB
Inventors: Tom Vivian; brian Chu
Original assignee: Spirax Sarco Ltd
Current assignee: Spirax Sarco Ltd
Priority date: 2009-10-06
Filing date: 2009-10-06
Publication date: 2011-04-13
Anticipated expiration: 2029-10-06
Also published as: US20110084222A1; US9200752B2; JP2011080594A; EP2360415A2; JP5714860B2; GB2474237B; GB0917451D0

Abstract

A valve element for a steam trap comprises an expansion chamber in the form of a metallic bellows 32 having a variable axial length and having first and second ends sealed with first and second end caps 34, 36 respectively. A valve closure member 58 is provided on the second end cap and is arranged to cooperate with a valve seat (26, Fig. 4). A first guide member 38 is coupled to the first end cap and axially extends into the bellows and a second guide member 40 is coupled to the second end cap, axially extends into the bellows and cooperates with the first guide member. This allows relative axial movement between the first and second end caps 34, 36 but restricts relative radial movement between the first and second end caps. This ensures that the valve closure member 58 seats properly on the valve seat 26.

Description

VALVE ELEMENT FOR A STEAM TRAP

The present invention relates to a valve element for a steam trap, in particular, a valve element comprising an S expansion chamber having a variable axial length.

Steam traps are commonly used in steam systems, in which circumstances they are usually referred to as steam traps.

Their function is to discharge condensed water from the system without allowing steam to escape. If steam is lost from the system, this represents a waste of energy. Steam traps thus commonly comprise a valve which is responsive to the presence of condensate or steam in the vicinity of the valve, so that the valve opens when condensate is present and closes when steam is present.

One type of steam trap, known as a balanced pressure steam trap, comprises a valve body having an inlet and an outlet which are in fluid communication with a valve body chamber. Located within the valve body chamber is a valve element which includes a metal bellows having a valve closure member which cooperates with a valve seat to open and close the valve. The metal bellows is deformable in the axial direction (i.e. the valve opening and closing direction) and has a bellows cavity which is filled with a fluid/gas mixture.

When the temperature of the bellows is cooled by condensate, the volume of the fluid/gas mixture reduces and the bellows axially contracts, moving the valve closure member away from the valve seat and allowing the condensate to exit through the outlet. When the condensate has been discharged, the steam enters the valve body chamber and increases the temperature of the bellows. This causes the fluid/gas mixture to expand and the bellows axially expands, thus pressing the valve closure member against the valve seat and preventing steam from leaving the system through the outlet.

The temperature differential between the temperature of saturated steam and the temperature when the valve operates is controlled by the liquid/gas mixture. The optimum differential allows the trap to quickly remove condensate without wasting steam.

The metal bellows of a known steam trap is made from a number of metal disks which are welded to one another. Whilst this produces a satisfactory component, the manufacturing procedure is time consuming. Further, the gaps between the metal disks forms crevices. If the gaps are small they can be difficult to clean and bacteria can grow.

Metal bellows are known which are made from a single piece of material by deforming the material to produce corrugations which provide the bellows configuration. Such bellows lack rigidity in the radial direction, and consequently have not been considered suitable for steam trap applications, in which precise alignment of the valve closure member with the valve seat is required.

Accordingly, embodiments of the present invention aim to address at least some of the above problems to some extent.

According to an aspect of the present invention there is provided a valve element for a steam trap comprising: an expansion chamber having a variable axial length and having first and second ends sealed with first and second end caps respectively; a valve closure member on the second end cap; a first guide member coupled to the first end cap and axially extending into the expansion chamber; a second guide member coupled to the second end cap, axially extending into the expansion chamber and cooperating with the first guide member to allow relative axial movement between the first and second end caps but to restrict relative radial movement between the first and second end caps.

Preferably the expansion chamber is a metal bellows. The metal bellows may be preformed from a single piece of material.

In a preferred arrangement the first and second guide members are a rod and a corresponding sleeve within which the rod is located and can axially slide. The sleeve may be coupled to the first end cap and the rod may be coupled to the second end cap.

Preferably the valve element further comprises a fluid passageway extending from outside the expansion chamber to inside the expansion chamber which arranged for filling the expansion chamber with fluid during manufacture, wherein the fluid passageway is sealed to prevent fluid exiting the expansion chamber. The fluid passageway may be sealed by a plug fitted into the fluid passageway. The fluid passageway may be at least partially sealed using a sealing cap fitted over the end of the fluid passageway. The fluid passageway may open into the interior of the sleeve.

Preferably the valve element further comprises a mounting member coupled to the valve element for mounting the valve element in a valve body. The valve element may be pivotable with respect to the mounting member.

The present invention also concerns a steam trap comprising a valve element in accordance with any statement herein.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 schematically show a cross-sectional view of a steam trap according to an embodiment of the invention; Figure 2 schematically shows a plan view of the steam trap of Figure 1; Figure 3 schematically shows the valve element of Figure 1; and Figure 4 schematically shows the steam trap of Figure 1 with the valve in the closed position.

Figures 1 and 2 show a balanced pressure steam trap 10 including a valve. The steam strap 10 comprises a valve body 12, a valve element 30 and a clamp 60.

The valve body 12 comprises a first upper part 14 having an inlet 16 and a second lower part 18 having an outlet 20.

An annular seal 22 is located between the first and second parts 14, 18 which are held together by the clamp 60. The valve body 12 defines a valve chamber 24 which is in fluid communication with the inlet and the outlet 16, 20. The second part 18 also comprises a valve seat 26 in the vicinity of the outlet 20.

Figure 3 shows the valve element 30 outside of the valve body 12. The valve element 30 comprises a pre-formed metal bellows 32 that is deformable, and therefore has a variable length, in the axial direction. The bellows 32 is formed from a tubular element which is deformed to produce an axially extending series of circumferential corrugations. The corrugations have a radiussed profile, making them easy to clean. A first upper end cap 34 seals a first upper end of the bellows 32 and a second lower end cap 36 seals a second lower end of the bellows 32, thereby defining a bellows cavity 33. The bellows cavity 33 is filled with a liquid and gas mixture, the ratio of which is critical to the operation of the valve steam trap. The upper end cap 34 has a first axially extending guide member 38 that extends into the bellows 32 and the lower end cap 36 has a second axially extending guide member 40 that extends into the bellows 32.

An axially extending mounting projection 42 is provided on the first end cap 34 and is located within an opening 46 in a mounting member 44. The mounting member 44 comprises an annular flange 43 and a number of fluid passageways 45. The diameter of the opening 46 in the mounting member 44 is larger than the diameter of the mounting projection. Further, the thickness of the mounting member 44 is less than the length of the mounting projection 42. This allows a small amount of movement between the mounting member 42 and the bellows 32.

A bore axially extends through the mounting projection 42, upper end cap 34 and first guide member 38. The bore comprises a first bore 48 of a first diameter extending through the mounting projection 42, upper end cap 34 and a portion of the length of the first guide member 38, and a second bore 50 of a second larger diameter extending along the remaining portion of the first guide member 38. The change in diameter between the first and second bores 48, 50 results in an annular shoulder 52. The end of the first bore 38 is sealed using a ball 54, which is pressed fitted in, and a sealing cap 56 which is welded onto the mounting projection 42. The sealing cap 56 has an external diameter that is larger than that of the opening 46 in the mounting member 44 and therefore retains the bellows assembly on the mounting member 44. However, because the length of the mounting projection 42 is greater than the thickness of the mounting member 44, there is free play in the connection between the mounting member 44 and the bellows 32, enabling the bellows 32 to pivot to a small extent relatively to the mounting member 44. The first bore 48 is further provided with two fluid passageways 49, in the form of two bores, that extend in the radial direction in opposite directions from one another.

These passageways provide fluid communication between the first bore 48 and the bellows cavity 33.

The second guide member 40 is in the form of a rod and is located within the second bore 50 of the first guide member 38, which is in the form of a sleeve. The outer diameter of the second guide member 40 is slightly smaller than the internal diameter of the second bore 50 and therefore the first and second guide members 38, 40 can slide axially, but not radially, with respect to one another. This in turn allows the first and second end caps 34, 36 to move axially, but not radially, with respect to one another.

The lower end cap 36 is provided with a valve closure member 58, which in use cooperates with the valve seat 26 to open and close the valve. The operation of this will be described in more detail below.

The valve element 30 is manufactured by welding the first and second end caps 34, 36 onto the first and second ends of the metal bellows 32, ensuring that the second guide member 40 is located within the second bore 50 of the first guide member 38. The bellows 32 is then compressed in the axial direction so that the second guide member 40 abuts the annular shoulder 52. The bellows cavity 33 is then filled with a Jcnown quantity of liquid. This may be done by injecting a known quantity of liquid into the first bore 48, which enters the bellows cavity 33 via the fluid passageways 49, or by completely filling the bellows cavity 33 with liquid and then removing a known quantity of liquid, to be replaced by air.

In a particularly preferred embodiment, the fluid passageways 49 are positioned such that when liquid is injected into the first bore 48 the bellows cavity 33 fills up leaving a gas pocket in the bellows cavity 33 above the top of the fluid passageway. Appropriate positioning of the fluid passageways 49 ensure that the size of the gas pocket in the bellows cavity 33 provides a suitable gas to liquid ratio for operation.

Once the bellows cavity 33 has been appropriately filled with fluid, the ball 54 is inserted into the top of the first bore 48. The ball 54 is force fitted into the first bore 48 and provides a hermetic seal. The mounting projection 42 is located in the opening 46 in the mounting member 44 and the sealing cap 56 is laser welded to the top of the mounting projection 42. The ball 54 prevents fluid from evaporating during welding of the sealing cap 56. This results in a good weld.

The assembly of the bellows 32 and the end caps 34, 36 can be manufactured with ease and at speed when compared to the prior art. This is because the bellows 32 is pre-formed and it is therefore not necessary to edge weld a number of metal disks together.

The valve element 30 may either be retrofitted into the valve body 12 of an existing steam trap 10, to replace a previous valve element of a different kind, or a new steam trap 10 can be supplied with the valve element 30 already installed. The process for installing the valve element 30 is as follows. The upper and lower valve body parts 14, 18 are separated and the valve element 30 is positioned on the lower part 18 with the annular flange 43 resting against an annular surface 19 of the lower part 18. The upper part 14 is then placed on top of the lower part 18 with the annular disposed therebetween. The clamp 60 is then clamped around the upper and lower parts 14, 18 in order to hold them together.

The steam trap 10 is typically provided at a lower region of a steam system. During normal operation the steam trap 10 is in the operative condition shown in Figure 4. In this configuration the valve closure member 58 is in intimate contact with the valve seat 26 and therefore there is no fluid flow through the valve. Condensate that has collected in the system will flow through pipeworic (not shown) into the inlet 16 and will collect in the chamber 24. The temperature of the condensate causes the temperature of the fluid/gas mixture in the bellows cavity 33 to reduce which causes the volume of the bellows cavity 33 to reduce. This reduction in internal volume causes the valve closure member 58 to move axially away from the valve seat 26. As a result, the condensate is able to flow through the outlet 20. Once all of the condensate has been discharged through the outlet 20, steam will enter the chamber 24 and the temperature of the fluid/gas mixture in the bellows cavity 33 will increase which in turn causes the volume within the bellows cavity 33 to increase, thus pressing the valve closure member 58 against the valve seat 26. This closes the valve and prevents the passage of steam through the outlet 20.

The cooperation of the first and second guide members 38, ensures that the valve closure member 58 can only move in the axial direction with respect to the first end cap 34.

This is because the first and second guide members 38, 40 prevent the bellows 32 from bending along its length. This ensures that the valve closure member 58 seats properly on the valve seat 26 to ensure a fluid tight seal. The small amount of clearance at the connection between the bellows 32 and the mounting member 44 enables the bellows 32 to pivot to allow for manufacturing and assembly tolerances, and ensures that the valve closure member 58 seats properly on the valve seat 26 to ensure a fluid tight seal. For example, if the valve S closure member 58 is slightly misaligned with the valve seat 26, when the valve closure member 58 contacts the valve seat 26 the tapered nature of the closure member 58 causes it to self-seat' by moving radially, and aligning itself with the valve seat 26.

The use of pre-formed bellows 32 results in a steam trap having fewer crevices than prior art steam traps which use a bellows 32 formed by welding a number of metal disks together. This makes the steam trap 10 according to the above embodiment particularly suitable for applications where hygiene is particularly important. This is because there are fewer crevices within which bacteria may be trapped and grow.

The steam trap operates close to saturated steam temperature across a pressure range allowing cooler condensate to drain from the system while retaining hotter steam in the system.

Claims

CLAIMS: 1. A valve element for a steam trap comprising: an expansion chamber having a variable axial length and having first and second ends sealed with first and second end caps respectively; a valve closure member on the second end cap; a first guide member coupled to the first end cap and axially extending into the expansion chamber; a second guide member coupled to the second end cap, axially extending into the expansion chamber and cooperating with the first guide member to allow relative axial movement between the first and second end caps but to restrict relative radial movement between the first and second end caps.
2. A valve element according to claim 1, wherein the expansion chamber is a metal bellows.
3. A valve element according to claim 2, wherein the metal bellows is preformed from a single piece of material.
4. A valve element according to any preceding claim, wherein the first and second guide members are a rod and a corresponding sleeve within which the rod is located and can axially slide.
5. A valve element according to claim 4, wherein the sleeve is coupled to the first end cap and the rod is coupled to the second end cap.
6. A valve element according to any preceding claim, further comprising a fluid passageway extending from outside the expansion chamber to inside the expansion chamber and arranged -10 -for filling the expansion chamber with fluid during manufacture, wherein the fluid passageway is sealed to prevent fluid exiting the expansion chamber.
7. A valve element according to claim 6, wherein the fluid passageway is sealed by a plug fitted into the fluid passageway.
8. A valve element according to claim 6 or 7, wherein the fluid passageway is at least partially sealed using a sealing cap fitted over the end of the fluid passageway.
9. A valve element according to any of claims 6 to 8 when appended to claim 4 or 5, wherein the fluid passageway opens into the interior of the sleeve.
10. A valve element according to any preceding claim, further comprising a mounting member coupled to the valve element for mounting the valve element in a valve body.
11. A valve element according to claim 10, wherein the valve element is pivotable with respect to the mounting member.
12. A steam trap comprising a valve element in accordance with any of claims 1 to 11.
13. A valve element or steam trap substantially as described herein with reference to the accompanying drawings.