Dual-chamber bottles, mainly used to make a mixture of two liquid ingredients ending up in one liquid. I wrote about these in a previous article and they are not the subject I want to write about today. I want to talk about fixed-dose dispensing technology, which mainly is realised by using dual-chamber bottles, of which one chamber holds the liquid and the second chamber is used as a fixed measuring cup, from which the liquid is dispensed.
There are many variants. Not only the bottle incorporating two chambers, but also the bottles with an insert in the neck, which acts as a fixed-dosing dispenser. Furthermore we see the fixed-dose caps topping off a bottle neck.
In this and next articles I will show a variety of systems used to allow the consumer to (more or less) accurately dispense a pre-set volume of liquid.
In general the fixed-dose dispensing technology relates to an (inexpensive) dosing bottle which consistently can dispense exact same volumes of liquid. To reach this goal often a dosing chamber is located inside the body of the bottle and which communicates with the bottle opening. When the bottle is tipped forward, only the liquid in the dosing chamber is dispensed, without any other liquid being able to flow into the dosing chamber from inside the bottle. When the bottle is tipped back into its vertical position, the dosing chamber re-fills. There are several other techniques as we will see.
Detergents, washing powders, pesticides, fertilizers, syrups, and many other liquids are frequently presented to the consumer in a container, which incorporates a feature which assists in pouring from the bottle a predetermined volume of liquid. A typical example of a measuring device for dispensing fluids is a large cap on top of a liquid detergent bottle, where the cap is hollow or concave in construction and is adapted to be used upside-down as a measuring cup so that the consumer can pour out or measure a controlled dose of detergent. Sometimes the bottle is adapted with a moat and drainback hole so that residual fluid dripping from the interior of the cap can flow back into the bottle rather than down the outside of it after the dose has been dispensed and the cap has been returned to the top of the bottle.
One disadvantage of dosing in this manner is that the dosing operation is physically awkward because one needs two hands for operation. Moreover the dosing is often improperly carried out as the accuracy of the dose depends on the user, while it also leaves the consumer with the risk of spilling liquid during dosing.
Furthermore, with concentrates in particular, there is a real danger of under-dosing or over-dosing because the measuring cup can easily be filled to above or below the dosing mark in haste, or depending on the ergonomic (or lack thereof) design of the bottle of the dexterity of the user.
The structural designs of fixed-dose dispensers have shown us a number of solutions for more conveniently dosing a volume of liquid from a bottle by, in one form or another, equipping such bottles with a dosing chamber. Bottles of this type are all based on some same physical principles.
And don’t think that the “single-dose-at-a-time technology” is a recent development. It reaches back for many decades, so let’s start with a look at an invention from 1960 (US Patent 3107031) by John David Adams. It doesn’t give the most accurate dose of liquid, but is a very simple and low-cost solution.
The John David Adams invention
After filling the bottle with liquid an L-shaped tube is inserted into the bottle. The top of the tube provides a substantially fluid-proof seal between the tube and the neck of the bottle. The level of the liquid in the tube, when the bottle is in upright position is at approximately the upper wall of the tube’s base, as shown in image, due to the atmospheric pressure on the surface of the liquid within the tube and the substantial absence of pressure on the surface of the liquid within the bottle itself.
When the container is tilted, the liquid in the base portion of the tube, when the container was upright, passes through the tube and the bottle neck in a measured quantity, as only that quantity leaves the bottle because the liquid level in the bottle is below the inflow opening of the base portion, when pouring.
Grosso modo this construction guarantees that the same quantity is measured out each time the bottle is tilted.
One disadvantage of this solution is that, when the level of liquid in the bottle falls to the top edge of the part of the L-shaped tube disposed horizontally in the bottle, the doses become smaller and smaller, because at the level of the dosing chamber, liquid is captured from the bottom part of the bottle out of the range of the dosing chamber. As a result, it is impossible to empty the bottle (with a flat bottom) completely. There will always be a certain volume that remains outside the dosing tube, except when the L-shape is embedded in a groove in the bottom of the bottle.
In the following invention from 2002 by Ulrich Loertscher (US patent 6378741) the mentioned disadvantage is claimed to be eliminated. The Loertscher dosing bottle also has a very simple construction, is extremely inexpensive to manufacture, and allows the consumer to reliably and conveniently dose a fixed volume of liquid.
The Ulrich Loertscher invention
This dosing bottle is comfortable with regard to handling and dosing liquids. To carry out a dosing operation, the bottle can be held with one hand and simply tipped forward from the upright position to the pouring position. For each new dose it simply has to be returned to the upright position and then tipped forward again into the pouring position. Each such dosing operation dispenses a consistently fixed quantity of liquid, until the bottle is empty.
The inventor intended the bottle to be made in one piece from plastic through a blow moulding or injection moulding process, using one or several mash seams or a constriction in the bottle walls to form, at the bottom of the bottle, a separate dosing chamber with an opening, passing through the inside of the bottle. The dosing chamber communicates with an outlet tube, which runs through the inside of the bottle to the bottle neck so that whenever the bottle is tipped forwards from an upright position into a pouring position, only the liquid in the dosing chamber can flow out of the bottle.
The bottom of the bottle is essentially moulded into two feet, of which one foot, forms the dosing chamber. Connected in leak-proof fashion with the bottle neck is outlet tube, which passes through the inside of the bottle at an angle and opens just below the top edge of the dosing chamber. Between this bottom opening of the outlet tube and the adjacent inside wall of the bottle there is a space which serves as an opening, connecting the inside of the bottle to the dosing chamber.
When the bottle is upright, the top edge of the bottom opening of the outlet tube defines the level of liquid in the outlet tube. More liquid does not flow through the opening into the outlet tube, which is prevented by the partial vacuum formed above the level of the liquid in the bottle as liquid drains into the dosing chamber. Simultaneously, atmospheric pressure takes effect in the outlet tube to counteract any increase in the level of liquid.
From all the hundreds and hundreds patents filed about this subject I selected just two more examples, which I will describe in the next article. After that we move to the market and have a look at fixed-dose dispensing bottles and inserts as offered by several companies, among them the Vetnil two-chamber dispensing bottle, the Twin Neck Bettix Bottles and the Greiner-Bark dispensing bottle. Furthermore we will describe some dispensing caps, as the Freehand and the Suredose.
to be continued