GB2323351A - Valves for pressurised dispensing containers - Google Patents

Abstract

This invention relates to valves for pressurised dispensing containers with particular reference to improved sealing arrangements. The invention discloses a metering valve (10) for use with a pressurized dispensing container. The valve (10) comprises a valve stem (11) co-axially slidable with a valve member (12). The valve member (12) and valve stem (11) define an annular metering chamber (13). First and second annular seals (17, 18) operative between the valve member (12) and the valve stem (11) to seal the annular metering chamber (13) therebetween. The first seal (17) being located at a discharge end of the valve stem (11), in which the valve stem (11) has an annular flange (20). The flange (20) has a transverse face on which is an annular lip (30 figure 2). The transverse face being directed towards the first seal (17). The valve (10) further comprising a spring member (25) located between the valve stem (11) and valve member (12) so as to bias the valve stem (11) into a non-dispensing position in which the annular lip is in sealing contact with the first seal (17).

Description

IMPROVEMENTS IN VALVES FOR PRESSURISED DISPENSING CONTAINERS The invention relates to improvements in valves for pressurised dispensing containers with particular reference to improved sealing arrangements.

Pressurised dispensing containers are used for dispensing a wide variety of products from mobile to viscose liquid products, powdered products and the like and typically employ a liquid propellant such as a hydro-carbon or fluoro-carbon having sufficiently high vapour pressure at normal working temperatures to propel the product through the valve. These are commonly used for dispensing pharmaceutical medicament.

Conventional metering valves for use with pressurised dispensing containers comprise a valve stem co-axially slidable within a valve member defining an annular metering chamber. "Inner" and "outer" annular seals are operative between the valve stem and the valve member to seal the metering chamber therebetween. The valve stem is hollow and comprises a flange, whereby in a non-dispensing position of the valve stem, the flange is held in sealing contact with the outer seal to prevent leakage of propellant between the valve stem and outer seal, and the metering chamber is connected to the container and charged with product therefrom. The valve stem is generally movable against the action of the spring to a dispensing position, wherein the metering chamber is isolated from the container and vented to atmosphere for the discharge of product.

The valve is usually held in place with respect to the container by a closure which is crimped to the container. A seal, or gasket which is usually made of elastomeric material, is compressed between the container and the closure to prevent leakage of the contents. The efficiency of the sealing arrangement is particularly important to prevent the leakage of propellant. Although such leakage from medicinal aerosols no longer causes environmental and safety hazards as the new HFA propellants used are environmentally friendly, where CFC propellants are used it is vital to prevent leakage to avoid such hazards. For all aerosols, regardless of the propellants used, it is also important that leakage of the contents of the dispensing container is minimal to prevent loss of contents ensuring that sufficient product is available after storage to meet label claims and that the ratio of propellant product remains constant.

Dispensing containers are often used to dispense, among other products, powdered medicaments which are stored in the container suspended in the liquefied propellant. The powdered medicament is dispensed from the container, on actuation of the aerosol, together with the propellant as the propellant boils off. A particular leakage problem has been found to occur in aerosols dispensing certain types and concentrations of powdered medicaments, especially where the medicament is finely powdered. The problem, known as "in-use leakage", occurs due to deposition of the powdered medicament on the surfaces of the metering valve through continued use. The deposition of powdered medicament occurs on all surfaces exposed to the propellant-medicament suspension including the flange of the valve stem and the outer seal. When the powdered medicament is deposited on the flange and the outer seal, the powder creates a poor sealing surface.

The force of the spring is unable to effectively compress the powder into the surface of the outer seal leading to the flange not fully contacting the outer seal. Thus, propellant can pass out of the metering chamber between the outer seal and the flange.

Various improvements have been proposed to deal with leakage problems via the seal between the container and the enclosure, as described in International patent specification WO 94/25373, GB-A2307278 and unpublished application GB9523457.1.

However, it is an object of the present invention to propose a modified valve arrangement which provides improvement in sealing to prevent leakage via the aperture in the ferrule or closure through which the valve stem protrudes, especially where powdered medicament-propellant suspensions are used.

According to the present invention there is provided a metering valve for use with a pressurised dispensing container, the valve comprising a valve stem co-axially slidable within a valve member, said valve member and valve stem defining an annular metering chamber, first and second annular seals operative between the valve member and the valve stem to seal the annular metering chamber therebetween, the first seal being located at a discharge end of the valve stem, in which the valve stem has an annular flange, said flange having a transverse face on which is an annular lip, said transverse face being directed towards the first seal, the valve further comprising a spring member located between the valve stem and valve member so as to bias the valve stem into a nondispensing position in which the annular lip is in sealing contact with the first seal.

In a first version the annular lip has a substantially square cross-sectional form.

In a second version the annular lip has a substantially triangular cross-sectional form.

In a third version the annular lip has a substantially rounded cross-sectional form.

Preferably the annular lip and annular flange are selected from one of acetal, nylon, polyester or metal.

A particular embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of a known metering valve; Figure 2 is a cross-sectional side elevation of a valve stem for use with a metering valve according to the present invention; Figure 2a is an enlargement of the ringed section of Figure 2; Figure 2b is an enlargement of the ringed section of Figure 2 showing an optional formation of lip; Figure 2c is an enlargement of the ringed section of Figure 2 showing a further optional formation of lip; Figure 3 is a plan view of the valve stem of Figure 2; and Figure 4 is a cross-sectional side elevation of part of a metering valve according to the present invention.

As shown in Figure 1, a typical metering valve 10 includes a valve stem 11 which protrudes from and is axially slidable within a valve member 12, the valve member 12 and valve stem 11 defining therebetween an annular metering chamber 13. The valve member 12 is located within a valve body 14 which is positioned in a pressurised container (not shown) containing a product to be dispensed. The metering valve 10 is held in position with respect to the container by means of a ferrule 15 crimped to the top of the container and sealing being provided between the valve body 14 and container by an annular gasket 16. The ferule 15 has an aperture 28 through which one end 19 of the valve stem 11 protrudes.

A pair of seals 17, 18 of an elastomeric material extend radially between the valve stem 11 and the valve member 12. The "outer" seal 17 is radially compressed between the valve member 12, valve stem 11 and ferrule 15 so as to provide positive sealing contact to prevent leakage of the contents of the metering chamber 13 between the valve stem 11 and the aperture 28. The compression is achieved by using a seal which provides an interference fit on the valve stem 11 and/or by the crimping of the ferrule 15 onto the pressurised container during assembly. The "inner" seal is located between valve member 12 and valve body 14 to seal an "inner" end of the metering chamber 13 from the container contents.

The end 19 of the valve stem 11 is the discharging end of the valve stem 11 and protrudes from the ferrule. The end 19 is a hollow tube, which is closed off by a first flange 20 which is located within the metering chamber 13. The hollow end 19 of valve stem 11 includes a discharge port 21 extending radially through the side wall of the valve stem 11. The valve stem 11 further has an intermediate section 22, extending between the first flange 20 and a second flange 26. The intermediate section 22 is also hollow between the flanges 20, 26 and defines a central passage. It also has a pair of spaced radial ports 23, 24 which are interconnected through the central passage. The second flange 26 separates the intermediate section 22 of the valve stem 11 and an inner end 27 of the valve stem 11.

A spring 25 extends between the second flange 26, and a shoulder defined by the valve body 14 to bias the valve stem 11 in a non-dispensing position in which the first flange 20 is held in sealing contact with the outer seal 17. The second flange 26 is located outside the metering chamber 13, but within the valve body 14.

The metering chamber 13 is thus sealed from the atmosphere by the outer seal 17, and from the pressurised container to which the valve 10 is attached by the inner seal 18. In the illustration of the valve 10 shown in Fig. 1 radial ports 23, 24 together with the central cavity in the intermediate section 22 of the valve member 11 connect the metering chamber 13 with the container so that in this non-dispensing condition the metering member 13 will be charged with product to be dispensed.

Upon depression of the valve stem 11 relative to the valve member 12 so that it moves inwardly into the container, the radial port 24 is closed off as it passes through the inner seal 18, thereby isolating the metering chamber 13 from the contents of the pressurised container. Upon further movement of the valve stem 11 in the same direction to a dispensing position the discharge port 21 passes through the outer seal 17 into communication with the metering chamber 13. In this dispensing position the product in the metering chamber 13 is free to be discharged to the atmosphere via the discharge port 21 and the cavity in the hollow end 19 of the valve stem 11.

When the valve stem 11 is released, the biasing of the return spring 25 causes the valve stem 11 to return to its original position. As a result the metering chamber 13 becomes recharged in readiness for further dispensing operations.

Figures 2 and 2a illustrate in cross-section the upper hollow end 19 of the valve stem 11 for use in a metering valve according to the present invention.

The first flange 20 is modified to provide a lip 30 on its upper transverse face. The lip is "raised" from the transverse face, and has a cross-sectional form which is either substantially triangular, rounded, or square as shown in Figures 2a, 2b and 2c. When the spring 25 biases the valve stem 11 into the non dispensing position, the lip 30 is pushed into sealing contact with the outer seal 17.

The force of the spring 25 causes the lip 30 to deform the outer seal 17 as shown in Figure 4. The reduced area of the lip 30 in contact with the outer seal 17 means that for a given spring force the pressure exerted on the outer seal 17 by the flange 20 and the deformation of the outer seal 17 is proportionally greater compared to a conventional flange 20 with a flat transverse face.

The increased deformation of the outer seal 17 means that an improved seal between the outer seal 17 and flange 20 is achieved even where the outer seal 17, flange 20 and lip 30 have been coated by a deposit of powdered medicament.

The cross-sectional shape of the lip 30 is not critical as long as the surface area contactable with the outer seal 17 is sufficiently small to achieve the desired pressure increase.

Typical materials for the lip 30 and flange 20 include acetal, polyester, nylon and stainless steel.

Claims (6)

CLAIMS:-

1. A metering valve for use with a pressurised dispensing container, the valve comprising a valve stem co-axially slidable within a valve member, said valve member and valve stem defining an annular metering chamber, first and second annular seals operative between the valve member and the valve stem to seal the annular metering chamber therebetween, the first seal being located at a discharge end of the valve stem, in which the valve stem has an annular flange, said flange having a transverse face on which is an annular lip, said transverse face being directed towards the first seal, the valve further comprising a spring member located between the valve stem and valve member so as to bias the valve stem into a nondispensing position in which the annular lip is in sealing contact with the first seal.

2. A metering valve as claimed in claim 1, wherein the annular lip has a substantially square crosssectional form.

3. A metering valve as claimed in claim 1, wherein the annular lip has a substantially triangular crosssectional form.

4. A metering valve as claimed in claim 1, wherein the annular lip has a substantially rounded crosssectional form.

5. A metering valve as claimed in claim 1, wherein the annular lip and annular flange are selected from one of acetal, nylon, polyester or metal.

6. A metering valve substantially as hereinbefore described with reference to and as shown in the accompanying drawings.