Air admittance valve

This invention relates to valves used for admittance of atmospheric air into an upper end of a pipe, and is particularly but not exclusively applicable to the control of air flow in stack pipes forming part of household toilet and drainage systems.

It is the object of the present invention to provide an air admittance valve of improved construction which can be fitted to the normally open upper end of a stack pipe and which is so arranged as to normally close the end of the stack pipe under conditions of atmospheric or greater- than-atmospheric pressure in the stack pipe, but to open to admit atmospheric air upon the occurrence of even a very small less-than-atmospheric pressure in the stack pipe.

The valve of the present invention is of the kind comprising: <ul id="ul0001" list-style="none"><li>(i) a body having an upper opening and a lower end opening,</li><li>(ii) an internal portion in said body positioned between its upper and lower end openings, and bounding an internal chamber which has only a first opening directed towards the upper end opening of the body and a second and lateral opening in the body,</li><li>(iii) a valve element to seat removably on said internal portion to open and close said first opening of the internal chamber,</li><li>(iv) guide means acting between said internal portion and the valve element, to guide the valve element during lifting and lowering thereof, (v) a cap threadedly engaged in airtight manner on the body and closing the upper end opening thereof. Such a valve is known from DE-C-51130.</li></ul>

According to the present invention a valve of the kind set forth in the preceding paragraph is characterised in that: <ul id="ul0002" list-style="none"><li>(a) said body is tubular and has a side wall which defines said upper end opening and said lower end opening,</li><li>(b) said internal portion is an internal wall positioned in the body intermediate its upper and lower end openings, said internal wall including a first portion which extends from the side wall of the body partly across the interior of the body, and a second integral wrapper portion which is co-extensive with the first portion and together therewith defines within the body said internal chamber,</li><li>(c) said internal chamber has its first opening bounded by the wrapper portion, and its second opening provided in the side wall of the body,</li><li>(d) said valve element seats on said wrapper portion such that when said valve is in its closing position said first and second internal wall portions and said valve element collectively close off said internal chamber from the remainder of the interior of the body,</li><li>(e) the guide means comprise a guide element on said first wall portion extending centrally towards the first opening of the internal chamber, and a hollow depending stem on the valve element engaged with clearance over and slidable on said guide element.</li></ul>

The valve element is advantageously of relatively large area and light weight, so as to be readily operable, against gravity, by even small amounts of negative pressure occurring in the stack pipe. Preferably, the tubular body is of circular section, and the valve element and said first opening of the internal chamber have a diameter which is at least half of the diameter of the body.

To enhance the air-tight sealing engagement of the valve element with the valve seat, it may have secured at its underside a flexible and resilient sealing diaphragm, and in a preferred form this is a thin disc or annulus of rubber or like flexible material. Where a sealing diaphragm is provided, such diaphragm may be secured to the under side of the valve element by a circular spring clip or equivalent means engaged on the stem and abutting the underside of the diaphragm.

In a preferred embodiment of the valve, the body comprises a portion having the internal walling, and a cap and cover portion which is removably engaged in air-tight manner on that portion. By way of example the portion of the body may have an open upper end which is externally threaded, and the cap portion is correspondingly internally threaded below a plane top wall thereof closing the upper end of the body. A preferably inclined, e.g. frusto-conical, skirt depends from said plane top wall, e.g. to somewhat below the level of the second opening of the internal chamber, and is spaced externally all about the side wall of the body. Preferably also, a seal may be provided between the lower part of the body and the cap, e.g. a rubber or like ring engaged in a circular recess in the upper end of the lower part of the body and positioned to be compressed between the body and the cap.

Figure 5 is an axial section, to a smaller scale, to show air flow through the valve under conditions of negative pressure in the stack pipe.

Referring to figure 1, the valve comprises a main body 1 which is of greater internal and external diameter at its lower part so as to permit engagement over the open upper end of a stack pipe 7, and presents a shoulder 1a which limits engagement onto the stack pipe 7.

At its upper end the body 1 is externally screw threaded to receive an internal screw threading at the upper interior of a retaining cap and cover 2. Internally of its screw threading the upper end of the body 1 is recessed circumferentially and axially to provide a seating 1b for a resiliently compressible sealing ring 4 which can become tightened between the cap 2 and the body 1 when the cap has been fully tightened onto the body, and thereby forms an air-tight seal between the cap and the body.

Internally, the body 1 is formed with a partial transverse wall which firstly passes across at a slight upward inclination 1c to the horizontal and then extends upwardly by a part-cylindrical portion 1d so as to bound an internal chamber 1e which opens upwardly to the top part of the body 1 through a circular opening 1f, and which also opens laterally of the body 1 to the exterior, at 1g.

On the inclined portion 1 of the transverse wall there is provided a fixed guide pin 8 which is coaxial with the circular opening. On the guide pin 8 there is engaged, as a loose sliding fit, the hollow stem of a valve plunger 3 which overlies the circular opening. To provide an air-tight seal between the plunger 3 and the circular opening, the plunger 3 is provided at its underside with a flexible and resilient diaphragm 5 which is retained.

An embodiment of air admittance valve in accordance with the invention is hereinafter particularly described with reference to the accompanying drawings, wherein: <ul id="ul0003" list-style="none"><li>Figure 1 is a perspective elevation, with the parts shown in axially separated condition, of the valve;</li><li>Figure 2 is an axial section of the valve, seen engaged on a stack pipe;</li><li>Figure 3 is a side elevation of the valve, with part shown broken away to reveal internal details;</li><li>Figure 4 is an axial section, to a smaller scale, to show the effect of air pressure on the valve, under conditions of normal or positive pressure in the stack pipe; on the hollow stem by means of a resilient star locking washer 6 forced onto the stem.</li></ul>

Referring to figures 4 and 5, and assuming that the valve has been positioned on the open upper end of a stack pipe, the normal condition of the stack pipe is that its internal pressure will remain at atmospheric, or may be slightly positive, i.e. greater than atmospheric. The pressure in the stack pipe is present also in the upper part of the valve body 1 and will be applied against the upper face of the valve plunger 3. The underside of the valve plunger 3 is exposed to atmospheric pressure through the lateral opening. Accordingly, there is a differential of pressure tending to force the plunger 3 onto its seating, and thereby seal the stack pipe against outflow of air or gas.

Referring now to figure 5, upon the occurrence of a negative, i.e. less than atmospheric, pressure in the stack pipe, the upper surface of the plunger 3 is subjected to less than atmospheric pressure, whilst its underside is subjected to atmospheric pressure. Accordingly there is now a pressure differential tending to liftthe plunger 3 off its valve seating, and the valve opens to admit air from the exterior. Air enters the valve through the lateral opening, as shown by the arrows in figure 5, and passes into the upper part of the body 1 and then into the stack pipe.