Dispensing – With discharge assistant – Fluid pressure
Patent
1988-07-26
1989-10-24
Rolla, Joseph J.
Dispensing
With discharge assistant
Fluid pressure
22240218, B65D 8300
Patent
active
048756059
DESCRIPTION:
BRIEF SUMMARY
Field of the Invention
The present invention relates to a pressurised metering dispenser and to a holder and actuator for pressurised metering dispensers.
Background of the Invention
Metering liquid dispensers using gas pressure for discharging the liquid were invented in the 1950's. As with most common pressurised liquid dispensers, the liquid in such known metering dispensers is subdivided into minute droplets on leaving the dispenser, forming an aerosol.
The main use for such dispensers hitherto has been for administering metered doses of drugs for inhalation. Early forms of dispensers gave somewhat erratic metering, but improvements in valve designs and in formulations for the dispenser contents have led to pressurised metering liquid dispensers currently available which are capable of .+-. 1% on the nominal metered volume dispensed.
However, further variations occur during the period of use of a dispenser, reducing the overall dispensing accuracy to no better than .+-. 5%. One cause for this problem is that as the dispenser is used high vapour pressure components in the dispenser contents are preferentially discharged, and therefore depleted. Thus, when the dispenser is nearly empty the doses dispensed will have an increased concentration of low vapour pressure components, and the concentration of the active pharmaceutical ingredient may vary during the course of use of the dispenser.
A typical formulation in a known pressurised metering liquid dispensers used to administer pharmaceuticals for inhalation contains the pharmaceutical active ingredient, a mixture of propellents (typically fluorocarbons, 11, 12 and 114), a low volatility excipient and valve lubricant such as sorbitan trioleate and anti-oxidants, in solution in ethanol.
The dispensers perform their metering function by means of a metering chamber located within the dispenser and normally open to the main dispenser reservoir containing the formulation. When the dispenser is held in the correct position for use, the metering chamber is lowermost and filled with formulation. During actuation of the dispenser, the metering chamber is first closed from the main reservoir and then connected to a discharge passage. The pressure of the propellents contained in the formulation will then drive the contents of the metering chamber out through the discharge passage. As the formulation is released into the atmosphere, any propellents still in liquid form will tend to vaporise, assisting in the formation of the aerosol, and the ethanol solvent will also tend to evaporate. This evaporation tends to chill the discharge nozzle of the dispenser, and rapidly repeated discharges from the dispenser may result in the nozzle freezing.
In my co-pending application Ser. Nos. 8608571 and 8624064, it is suggested that a pressurised 1-shot metering dispenser may be used to deliver reagents during chemical analysis. It has also now been realised that there are many other situations in which it would be convenient to be able to deliver precisely metered volumes of liquid from a pressurised dispenser. For example, in many circumstances in medicine and chemistry it is necessary to prepare a sample before it can be analysed or studied. In such sample preparation, the sample may be diluted with distilled water or some other chemically pure diluant and stabilisers such as anti-oxidants, pH buffers etc may also be added. All of these must be added in precisely known quantities if accurate results are to be obtained from subsequent study or analysis.
Typically, the dispensing of accurate volumes in such circumstances is at present carried out using various types of pipettes and syringes. There are three main types of devices in use. The first are "air pipettes", in which a squeeze-bulb or syringe sucks up liquid by reducing the air pressure in the pipette, and then small amounts of liquid are dispensed by mechanically indexing a plunger. The second are positive displacement syringes, in which a plunger is brought up to the tip of the discharge nozzle and the syringe is fi
REFERENCES:
patent: 3092107 (1963-06-01), Froot
patent: 3367746 (1968-02-01), Maurukas
patent: 3796352 (1974-03-01), Morane
patent: 4673107 (1987-06-01), Obrist
Microvol Limited
Rolla Joseph J.
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