GB2340477A

GB2340477A - Metering valve

Info

Publication number: GB2340477A
Application number: GB9821418A
Authority: GB
Inventors: Richard John Warby; Anthony Stanford
Original assignee: Bespak PLC
Current assignee: Consort Medical PLC
Priority date: 1998-08-13
Filing date: 1998-10-01
Publication date: 2000-02-23
Anticipated expiration: 2018-10-01
Also published as: GB2340477B; GB9817685D0; GB9821418D0

Abstract

A metering valve is provided for use in a pressurised dispensing container, the metering valve comprising a valve member 1 co-axially slidable within an annular metering chamber 13 defined between the valve member and a substantially cylindrical chamber body 2. The metering valve further comprises an outer seal 4 operable between the valve member and an outer end portion of the chamber body to seal an outlet duct 9 of the valve member when the valve member is in its inoperative position. The valve member being slidable to an operative position in which the contents of the metering chamber are dischargeable in use via the outlet duct. The outer seal has an outer diameter between 8.17mm and 8.43mm and an inner diameter between 2.69mm and 2.84mm. An inner seal 5 has an outer diameter of between 7.87 and 8.13mm and an inner diameter of between 2.69 and 2.84mm. These dimensions allow the valve member to move without being impaired and provide effective seals.

Description

1 2340477 METERING VALVE This invention relates to metering valves for

pressurised dispensing containers.

Pressurised dispensing containers are typically used to dispense formulations in aerosol form using a propellant which is volatile at normal temperature and pressure. As well as the propellant the formulation includes a product to be dispensed and may include other additives such as surfactants, antioxidants and flavourings all of which are mixed with the liquid propellant which remains in liquid phase by virtue of excess vapour pressure within the container. The propellant may be present with or without a co is solvent. Metering valves are utilised to dispense measured volumes of this liquid and comprise a metering chamber with inlet and outlet valves controlled by displacement of a valve member which defines an outlet duct.

Operation of the metering valve requires the chamber to be filled via the inlet valve, the inlet valve then closes and the output valve opened such that the contents are expelled by boiling off propellant in response to the chamber being vented to atmospheric pressure.

One problem associated with metering valves of the type described above is improper dose retention in the metering chamber due to "drainback" through the inlet valve. Such Ildrainbacku leads to an incorrect dosage of medicament being delivered to the user of the metering valve upon actuation.

Another problem associated with metering valves of the type described is "continuous spraying" whereby leakage of propellant and medicament suspended or dissolved therein occurs between an inner end 2 portion of the valve member and an inner seal during actuation, in particular when the valve member is fully depressed and the metering chamber is venting.

Leakage at the inner seal position at this time results in propellant and product entering the metering chamber from the container as the original contents are being dispensed. This results in overdosing. Such "continuous spraying" may be overcome by adjusting the inside diameter of the inner seal. However, a further problem has been found to occur where the inside and outside diameters of the seals are adjusted to create too much sealing pressure between the moving valve member and the seals which results in failure of the is valve member to return to its initial position properly after actuation of the metering valve.

A further problem associated with metering valves of the type described is "static leakage" whereby propellant is lost by leakage via the inner and outer seals.

Accordingly the present invention provides a metering valve for use in a pressurised dispensing container, the metering valve comprising a valve member co-axially slidable within an annular metering chamber defined between the valve member and a substantially cylindrical chamber body, the metering valve further comprising an outer seal operable between the valve member and an outer end portion of the chamber body to seal an outlet duct of the valve member when the valve member is in its inoperative position, the valve member being slidable to an operative position in which the contents of the metering chamber are dischargeable in use via the outlet duct, wherein the outer seal has an outer diameter of between 8.17 and 8.43mm and an inner diameter of between 2.69 and 2-84mm.

The present invention is concerned with improving the performance of the metering valve.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:- Figure 1 is a sectional elevation of a metering valve according to the present invention; and Figure 2 is an enlarged sectional view of the encircled portion of Figure 1.

The metering valve of Figure 1 comprises a valve member 1 which is axially slidable within an annular chamber body 2 mounted coaxially within a valve housing 3.

An outer seal 4 and an inner seal 5 of elastomeric material extend radially between the valve member 1 and the chamber body 2.

(Throughout the description, unless otherwise indicated, the terms "inner" and "outer" indicate relative positions along the axis of the metering valve such that "innerff implies proximal to the container and "outerm implies distal with respect to the container).

The outer seal 4 is radially compressed between the chamber body 2 and the valve member 1 so as to provide positive sealing contact, the compression being achieved by dimensioning the outer seal such that it is an interference fit on the valve member 1 or by axially compressing the outer seal by crimping onto a container (not shown) a ferrule 6 which secures together the valve housing 3, the chamber body 2 and the outer seal 4 during assembly.

An upper end portion 7 of the valve member 1 is tubular and hollow but closed internally at a location corresponding to an external radially projecting - 4 flange 8. A discharge port 9 is defined in the upper end portion 7 at a location immediately above the flange 8 so as to extend radially into communication with the interior of the upper end portion.

Also formed in the valve member 1 is an inlet passage comprising a pair of axially spaced radial ports 10 and 11 which are interconnected through a central cavity 12 within the valve member.

An annular metering chamber 13 is enclosed between the chamber body 2 and the valve member 1 and is normally sealed from the atmosphere by the outer seal 4 when the valve member 1 is in its inoperative position (as shown in Figure 1). In the configuration shown in Figure 1, the radial ports 10 and 11 together is with the central cavity 12 connect the metering chamber 13 with the interior of the container so that the metering chamber 13 would in this configuration be filled with fluid material to be dispensed when the container and valve are held in an inverted position in which the valve member 1 is pointing downwardly.

Upon depression of the valve member 1 relative to the valve housing 3, the radial port 10 becomes sealed by the inner seal 5 so that the metering chamber 13 is isolated from the interior of the pressurised container. Upon further depression of the valve member 1 into its operative position, the discharge port 9 moves into a position in which it communicates between the metering chamber 13 and the hollow interior of the upper end portion 7 of the valve member thereby constituting an outlet duct such that the pressurised material within the metering chamber 1 is discharged to the atmosphere by virtue of the rapid expansion of volatile propellant on being exposed to atmospheric pressure. Upon returning the valve member 1 to its inoperative position as shown in Figure 1, the metering chamber 13 becomes recharged in readiness for further dispensing operations.

A return spring 15 extends in compression between the valve housing 3 and a second flange 14 of the valve member, the bias provided by the spring being operable to hold the flange 8 in sealing contact with the outer seal 4.

It is known for the axially spaced radial ports and 11 to have a typical diameter of 0.62 mm.

However, it has been found that "drainback" of propellant and medicament suspended or dissolved therein can occur through holes of this size. In the present invention the radial ports 10 and 11 are dimensioned to have a nominal size of approximately 0.4 mm diameter. It has been found that reducing the diameter of the ports io and 11 in this way improves dose retention in the metering chamber 13 by providing greater capillary retention across the holes. This increased dose retention has been found to be particularly advantageous where the propellant used with the metering valve comprises any of the propellants in the HFA family. Typically, these include 134A and 227. The HFA propellant may be present with or without ethanol as a co-solvent.

The compression of the inner seal 5 between the chamber body 2 and the valve member 1 has been found to be important to prevent "continuous spraying" whereby leakage of propellant occurs between the inner seal 5 and valve member 1 during actuation of the metering valve. The dimensioning of the inner seal 5 is critical in preventing "continuous spraying". If the pressure of the seal between the inner seal 5 and the valve member 1 is insufficient "continuous spraying" will occur upon actuation of the metering valve. Conversely, if the pressure of the seal between the inner seal 5 and the valve member 1 is too great, movement of the valve member 1 past the inner seal 5 is inhibited and the return movement of the valve member 1 after actuation of the metering valve to the configuration shown in Figure 1 may be impaired or even prevented. According to the present invention it has been found that an inner seal 5 having an inner diameter of between approximately 2.84 and 2.69 mm and an outer diameter of between approximately 8.13 and 7.87 mm and an outer seal 4 having an inner diameter of between approximately 2.84 and 2.69 mm and an outer diameter of between approximately 8.43 and 8.17 mm used with a valve member 1 with external diameter of between approximately 3.20 and 3.15 mm provides is sufficient sealing pressure between the seals and the valve member 1 to prevent "continuous spraying" yet still allow acceptable movement of the upper end portion 7 of the valve member 1 past the seals during actuation of the metering valve.

Another means of ensuring acceptable movement of the valve member 1 is to increase the return spring force. This may be utilised separately or in conjunction with adjustments to the inner and outer dimensions of the seals 4 and 5. It has been found that increasing the return spring force to between 20 and 25 Newtons promotes acceptable movement of the valve member 1.

"Static leakage" of propellant from the metering valve 13 by-passing the outer seal 4 and inner seal 5 may occur between actuations of the metering valve if the axial compression of the outer seal 4 and inner seal 5 is not sufficient. According to the present invention it has been found that altering the axial dimensions of the chamber body 2 can be utilised to increase the axial compression of the outer seal 4 and I- inner seal 5. A particularly advantageous means of achieving this is as shown in Figures 1 and 2 wherein the "inner" end of the chamber body 2 comprises a stepped profile 20. Preferably, the step 20 has an axial dimension of 0.25 mm. This step 20 effectively increases the axial length of the chamber body 2 held between the outer seal 4 and the inner seal 5. This results in an increased axial compression of both outer seal 4 and inner seal 5 thereby reducing static leakage of propellant. The provision of the step 20 is advantageous in that it may be provided by adjusting only the mould tool ejectors used to form the chamber body 2 hence avoiding the requirement to provide new moulds for manufacturing the chamber body is 2 according to the present invention. This reduces the manufacturing cost of the metering valve.

The present invention has particular application to pharmaceutical metering valves in which the volume of the metering chamber 13 is typically of the order of 25 to 100 micro litres.

The present invention is suitable for use with formulations including products such as medicaments having one or more active ingredients. It is particularly suitable for active ingredients such as P-adrenorector agonists (for example, salbutamol and terbutaline), anti-cholinergics (for example, atropine and ipratopium), steroids (for example, beclomethasone and budesonide), di-sodium chromoglycate and nedocromil sodium.

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Claims

1. A metering valve for use in a pressurised dispensing container, the metering valve comprising a valve member co-axially slidable within an annular metering chamber defined between the valve member and a substantially cylindrical chamber body, the metering valve further comprising an outer seal operable between the valve member and an outer end portion of the chamber body to seal an outlet duct of the valve member when the valve member is in its inoperative position, the valve member being slidable to an operative position in which the contents of the metering chamber are dischargeable in use via the is outlet duct, wherein the outer seal has an outer diameter of between 8. 17 and 8.43mm, and an inner diameter of between 2.69 and 2.84mm.

2. A metering valve as claimed in claim 1 wherein the metering valve further comprises an inner seal operable between the valve member and an inner end portion of the chamber body wherein the inner seal has an outer diameter between 7.87 and 8.13mm and an inner diameter between 2.69 and 2.84mm.

3. A metering valve as claimed in any preceding claim wherein the metering chamber further comprises an inlet duct of diameter 0Amm.

4. A metering valve as claimed in any preceding claim wherein the metering valve further comprises spring means to bias the valve member into the inoperative position and wherein the spring means has a spring force of between 20 and 25 Newtons.

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