In the development of specifications and in requesting vial quotations, consideration should be given to the following specifications and options:
Overall Length: Specify. The standard length tolerance is plus or minus .030 inches.
Diameter: Specify. The standard diameter tolerance is plus or minus .010 inches. Outside diameters are based on the availability of standard glass tubing from .175 to .787 inches.
Sensitivity: Specify sensitivity. Sensitivity normally runs from 5 to 600 seconds per graduation for precision vials and from 6 to 120 minutes for commercial vials.
Bubble Length: Specify either bubble length or index spacing.
Graduation: If applicable, specify design and type. Standard colors are red and black. Graduations are either printed, silk screened, or by decal. The decal and screen process result in a durable, baked ceramic line and are, therefore, recommended. The decal or screen process will be chosen based on the vial length and radius of the curve. Graduations are 2 mm or 0.1″ and are available in standard designs. (see Standard Graduation Chart and Recommended Bubble Sizes)
Glass: Borosilicate Glass (Pyrex®)
Fluid: Specify fluid and color. Various anhydrous fluids are available. The fluid used is determined by the application. Alcohols, ethers, and hydrocarbons are regularly stocked.
Polish: Specify if required for precision vials only. The inside surface of a precision vial may be polished for special applications. Polishing assures extremely smooth and accurate bubble movement.
Seal: Specify metallic seal or adhesive seal. Other seal types are in developmental stages.
Temperatures: Unless otherwise specified, bubble sizes are measured to 70-72 degrees F in temperature controlled room. However, in some instances, vials are called upon to withstand temperatures of minus 60 degrees to plus 200 degrees F. On equipment subject to higher than average temperatures consideration must be given to the ratio between bubble size and volume of fluid. When the ratio is correct, the vial will withstand the internal pressure developed by the expansion of the fluid.
Bubble Lengths: Incorrect bubble sizes often cause sluggishness and erratic movements. A bubble too small does not have enough inertia to give a correct reading. A bubble too large, especially in small diameter tubes, will drag on the sides of the tube, causing erratic and slow movements.
Heat and Light Rays: Heat and light from sources such as an operator’s body, fluorescent lamps incandescent bulbs, flashlights, etc., will often cause incorrect bubble readings in very sensitive vials. Precautionary measures should be exercised and means taken to shield vials from these conditions.
Static Electricity: Static electricity is often the cause of erratic bubble movements and bubbles that will not repeat consistently. This condition is frequently found in vials made of borosilicate glass.
Background: If required, specify color. Various backgrounds are available upon request. The available backgrounds are ceramic, enamel, sandblasted or aluminum coating. Backgrounds will reflect light and permit the bubble to read more easily for certain applications.