Steam generator

Abstract: A steam generator has a base 1 and a lid 2, both injection mouldings. A heating element 6 is mounted in the base. A safety valve 13 is included in the lid and comprises a moulded plastics plunger 14 with a stem 15 and a head 16. The stem carries a circlip 17 and a spring 18 which biases the plunger downwards for captivation of an O-ring 19 between the head 16 and the lid around an aperture 20.

Description: Field of the Invention The invention relates to a steam generator particularly, though not exclusively, for use in a wallpaper steamer. Background of the Invention Wallpaper steamers are known for moistening old wallpaper so that it can be readily removed from walls prior to redecorating. CA-A-1,060519 describes a portable steam sauna tank having: a cast aluminium alloy base; a cast aluminium alloy lid sealingly carried on the base and including a steam outlet; a safety valve at a release aperture in the lid; and an electrical heating element. In a steam generator for a prior wallpaper steamer, which indudes a lid and a base of moulded plastics material, we provide a safety valve at a release aperture in the form of an automotive radiator cap. The present steam generator has been developed as a simpler, cheaper product. A steam generator according to the invention comprises: a base; a lid sealingly carried on the base and induding a steam outlet; a safety valve at a release aperture in the lid; and an electrical heating element mounted in the base; characterised in that: the lid is of a moulded plastics material and includes an outwards facing seat provided around the release aperture; and in that the safety valve has: a plunger with a head and a stem, the stem passing through the release aperture in the lid, an O-ring fitted on the stem for sealing abutment with the head and the seat, and a spring acting between the stem and the lid for biasing the head towards the aperture and causing the O-ring and the head normally to seal the aperture, and in that the seat tapers inwardly at a region thereof sealingly abutted by the O-ring. Preferably, the spring is a compression spring carried on the stem. Conveniently, the stem carries a fixture at its end remote from its head for holding the spring in compression. The fixture can be a spring clip, preferably a circlip. Preferably the plunger is of moulded plastics material. To help understanding of the invention, a specific embodiment thereof will now be described with reference to the accompanying drawings, in which:- The Drawings Figure 1 shows in a perspective view a wallpaper steamer including a steam generator of the invention and a wall plate; Figure 2 is an underneath plan view of the steam generator of Figure 1; Figure 3 is a cross-sectional view on the line III-III in Figure 2; Figure 4 is a rear view of the steam generator; Figure 5 is a scrap cross-sectional view on the line V-V in Figure 1 of an inter-engagement zone of the lid and base of the steam generator; and Figure 6 is a scrap underneath view in the direction of arrow VI of the detail shown in Figure 5. Referring to the drawings, the wallpaper steamer shown in Figure 1 comprises a steam generator G and a hollow-underside wall plate W interconnected by a pipe P. In use, water is boiled in the generator G to form steam which is led by the pipe P to the wall plate W for application to wallpaper to be steamed and stripped. The steam generator G comprises a base 1 and a lid 2, both being injection mouldings of plastics material, preferably heat stabilized polypropylene. The base has a central depression 3 in which an electrical heating element 4 is disposed and from which radiate a series of fins 5 for stability of the steam generator. The heating element 4 is of the type conventionally used in kettles. A stainless steel plate 6 is secured by the element's fitting 7 to extend between the element and the bottom wall 8 of the central depression to protect the latter in the event of the steam generator boiling dry. The lid 2 is domed slightly upwardly and has an integrally moulded central carrying handle 9, a filling inlet 10 with a pressure tight moulded plastics cap 11. Upstanding from the bottom of the base is a level indicating finger 12 which is visible through the inlet 10 with the cap removed. On the opposite side of the handle 9 from the inlet 10 is a safety valve 13 comprised of a moulded plastics plunger 14 with a stem 15 and a head 16. The stem carries a circlip 17 and a spring 18 which biases the plunger downwards for captivation of an O-ring 19 between the head 16 and the lid around an aperture 20. The spring is light, allowing the safety valve to open at 4 psig (approximately 0.25bar). The lid also incorporates a moulded, threaded outlet spout 21 to which the pipe P is connected by a union 22. Referring now to Figure 5 in particular, the engagement of the lid 2 with the base 1 will be described. Figure 5 shows the inter-engagement zone of the lid 1 and the base 2. In this zone the lid has an annular region 23 outwardly of which it has at an even radius a series of eight equally circumferentially spaced, downwardly depending individual engagement members 24. Discrete and outwardly from these downwardly depend outer location flanges 25, circumferentially occupying the spaces between the individual engagement members 24. Inwardly of the annular region 23 a circumferentially continuous, inner location flange 26 extends. In the interengagement zone, the base has an outwardly extending rim 27, having an annular recess 28 which provides a seat for a closed cell neoprene foam sealing ring 29, which on assembly, as shown in Figure 5, is compressed between the plain undersurface 30 of the lid at its annular region 23 and the recess 28. Above the surface 30, the lid has a first upstanding flange 31 for reinforcing it to exert compression on the sealing ring 29. A second reinforcement flange 32 extends around the lid radially further out above its engagement members 24. At the position of each lid-engagement member 24, an aperture 33 is provided in the rim 27 of the base 1, which rim otherwise extends out to a downwardly depending flange 34. Circumferentially positioned on each side of each aperture 33 is a radial web 35 extending between the sidewall 36 of the base 1 and the flange 34. The flange 34 has an outer step 37 for accommodating the outer location flanges 25 and providing a substantially flush exterior. The inner location flange 26 engages within the base sidewalls 36. Thus the lid is both centred on the base and stiffened in the inter-engagement zone. The lid-engagement members 24 each have an upwardly turned lip 38 on their radially outer surface with an engagement face directed away from the base. The flange 34 at the apertures 30 is in effect a series of base-engagement members 39, each of which has a downwardly turned lip 40 with an engagement face directed away from the lid. On assembly of the lid to the base, the lid-engagement members 24 flex inwardly and resiliently snap out when the lips 38,40 have passed and inter-engage at their engagement faces. This is the position shown in Figure 5, in which the sealing ring 29 is compressed. To resist unintentional disengagement of the lips 38,40 and their engagement members 24,39, the lid-engagement members 24 are provided on the inside with ribs 41 which at their surface 42 abut the base at the apertures 33. The inner edge of the apertures are stiffened by flanges 43, each of which is supported by two integral struts 44 extending back to the sidewall 36. It will be appreciated, from Figure 5 that the particular arrangement of the lid-engagement members 24 being discrete and with the lips 38 on their outer sides, that the moulds for both the base and the lid have no overhanging parts necessitating expensive, complex moving parts of the moulds.

Claims: A steam generator suitable for use in a wall paper steamer comprising:- a base (1); a lid (2) sealingly carried on the base (1) and including a steam outlet (21); a safety valve (13) at a release aperture (20) in the lid (2); and an electrical heating element (4) mounted in the base (1); characterised in that: the lid (2) is of a moulded plastics material and includes an outwards facing seat provided around the release aperture (20); in that the safety valve (13) has: a plunger (14) with a head (16) and a stem (15), the stem (15) passing through the release aperture (20) in the lid (2), an O-ring (19) fitted on the stem (15) for sealing abutment with the head (16) and the seat, and a spring (18) acting between the stem (15) and the lid (2) for biasing the head (16) towards the aperture (20) and causing the O-ring (19) and the head (16) normally to seal the aperture (20); and in that the seat tapers inwardly at a region thereof sealingly abutted by the O-ring. A steam generator as claimed in claim 1, characterised in that the spring (18) is a compression spring (18) carried on the stem (15). A steam generator as claimed in claim 2, characterised in that the stem (15) carries a fixture (17) at its end remote from its head (16) for holding the spring (18) in compression. A steam generator as claimed in claim 3, characterised in that the fixture (17) is a spring clip (17). A steam generator as claimed in claim 4, characterised in that the spring clip (17) is a circlip (17). A steam generator as claimed in any preceding claim, characterised in that the plunger (14) is of moulded plastics material. A steam generator as claimed in any preceding claim, characterised in that the head has a flat radially extending sealing surface against which the O-ring abuts. A steam generator as claimed in claim 7, wherein the said flat radially extending surface is of greater diametral extent than that of the O-ring.

Inventors: STEVENS PAUL, STEVENS, PAUL
Applicants: EARLEX LTD, EARLEX LIMITED
Application year: 1990
Main classification: F22B1
IPC codes: F22B37, F22B1