Sink Floats

What are Sink Floats?

Sink floats are used to discernibly measure and observe a liquid's density. The sink floats are small amber glass capsules that are weighted and air tight. Sink floats have been calibrated at 73.4ºF in order to measure a specific liquid density.

Sink floats are dropped into  liquid and then the position of the sink float is observed.

• If the sink float stays suspended in the liquid the density of the liquid and sink float are the same.
• If the sink float sinks, the liquid is less dense than the sink float.
• If the sink float floats, the liquid is more dense than the sink float.

Sink floats can also be observed and recorded over time. Any change in the sink float's position indicates a change in the liquid's density.

How to Use One, Two, or Three or More Sink Floats

1 Sink Float: Using a single sink float will provide the most exact management when the sink float is suspended in the fluid. Using a single sink float can show the minimum density when the fluid is higher and a maximum density when it is lower. If observing density changes, a sinking sink float indicates a drop in fluid density and a floating sink float indicates a rise in density.

2 Sink Floats: If it is important to keep a liquid within a specific density range, an easy solution is to use two sink floats. When the fluid is within the correct density range one sink float will sink and one will float. If both sink floats float or sink, it indicates that the liquid is no longer in the desired range.

3+ Sink Floats: Liquid density varies with temperature changes. Bringing a liquid to different temperatures can take time. An alternative solution is to select sink floats for the liquid's temperature. Use the chart below to select that sink float for the desired temperature.

Temperature	Sink Float gm/cc
21.1ºC (70ºF)	2.225 Sink Float
22.7ºC (73ºF)	2.220 Sink Float
24.4ºC (76ºF)	2.215 Sink Float
26.1ºC (79ºF)	2.210 Sink Float

For Example if a liquid is 75ºF, by using sink floats 2.215 and 2.220 the minimum and maximum acceptance limits would be set. Or, if all four sink floats in the chart above were used for 75ºF the density would be acceptable if two sink floats sank and two floated.

What Applications Use Sink Floats?

Diamond Identification: In the diamond mining process many minerals and crystals are extracted along with diamonds. In order to separate the desired diamonds from the other materials a density liquid is prepared. If the desired diamonds range from 3.5 - 3.55 a liquid with density of 3.5 would cause the diamonds to sink and all other crystals and minerals to float.

Soldering Flux: When using fluxes with automatic soldering equipment, the diluents and solvents slowly evaporate and need to be refilled to keep the fluidity consistent. During application flux solids are used up and need to be replenished. Since there are detectable variations between the stable (more dense) components and the lighter solvent, density is frequently utilized to control fluidity. Sink floats are designed to keep an eye on densities and notify the user as soon as there is a change in density or when fluidity might become a problem.

Contamination Control: Tiny amounts of liquids may be carried into the density liquid that is separating the materials. A change in density brought on by the addition of pollutants will be detected by monitoring using sink floats.

Purity Control: When the purity of a liquid product is linked to its maximum or lowest density, a well chosen sink float will show whether the required purity has been attained or has been altered due to deterioration or contamination.

Making / Adjusting Density Liquids: By combining carefully chosen liquids until the right sink float stays afloat in the liquid, density liquids can be created. As a monitor, the same sink float can be kept in the liquid, and if the density of the liquid changes, modifications can be made by changing the temperature or adding the proper end member.

Quality Control of Ceramic Parts Dielectric Properties: Dielectric constants are impacted by pressed parts' porosity, or air inclusion. Parts with high air inclusions can be separated with the application of density liquids. A single sink float would provide crucial control, while two sink floats would provide a limited range of control, saving the operator time when modifying the density of the liquid while preventing the potential of an abrupt change in density occurring without the operator's knowledge.

Solution Prep Concentration Control: One or two sink floats can be used to adjust the concentration when creating a solution from a concentrate when the diluent's density differs from the concentrate's density.

Separating Gems: Given the knowledge of the gem density, a density liquid or set of liquids that fall in between the densities of the gems to be separated can be chosen. A pair of sink floats will require less operator attention than a single sink float to manage the liquid. The pair of sink floats that offers the greatest range of liquid fluctuation consistent with clear stone separation should be chosen.

Separating Liquid from Solvent: When a minimum or maximum density is reached in a solvent-based manufacturing process where the solvent is distilled off, a sink float can be utilized to signal the event. The difference in density between the product and the solvent determines the accuracy. Distillation would go on until a sink float either simply sinks, simply floats, or remains suspended; alternatively, one sink float sinks and one floats to define an acceptability density range.

Reaction Concentration Control: A test using a carefully chosen sink float will indicate when concentration has fallen below the minimal threshold when a reaction process consumes a material in solution and the drop in concentration alters density.