Standard duty polyethylene or plastic tanks usually have a specific gravity of 1 (SG 1) and these are suitable for storing water. Poly tanks for storing other liquids must be chosen according to the specific gravity of the liquid.
Good quality plastic tanks are excellent storage containers for water and most chemicals including acids, chlorine, bleaches and fuel. When considering which poly tank to use, the specific gravity of the liquid should be known.
Simply put, poly tanks with a higher specific gravity rating is designed for heavier duty containment and will have thicker walls than another plastic tank made from the same material but with a lower specific gravity rating. As an example, a polyethylene tank that has a specific gravity of 1.6 (heavy duty) will be stronger and more durable than a tank that has a specific gravity of 1.4 (medium duty) or 1 (standard duty). Most poly tanks for storing rainwater or water have an SG equal to 1 – this is fine for normal situations. However, if the tank may be subjected to abuse/rough treatment (e.g. where animals may rub against it or in the case of a transporter tank that will be towed over rough roads), it may be wise to choose a poly tank with a higher specific gravity rating. More raw material is used to manufacture poly tanks with higher specific gravity ratings so the cost of these tanks rises according to the increase in the tanks’ specific gravity ratings.
Calculating Specific Gravity (Relative Density)
The Specific Gravity – SG – of a liquid is a dimensionless unit defined as the ratio of density of the liquid to the density of water at a specified temperature. Specific Gravity of a liquid can be expressed
SG = ρ / ρH2O (3)
SG = specific gravity
ρ = density of fluid or substance (kg/m3)
ρH2O = density of water (kg/m3)
It is common to use the density of water at 4 oC (39oF) as reference – at this point the density of water is at the highest – 1000 kg/m3or 62.4 lb/ft3. The SG of water is 1.
Example – Specific Gravity of Muriatic acid (Hydrochloric acid – HCL)
If the density of this concentration of HCL is 1191 kg/m3, 1.191 grams per cubic centimeter (cm3), 1.191 kilograms per liter, or 1.191 metric tons per cubic meter – the specific gravity of HCL is:
SG = (1191 kg/m3) / (1000 kg/m3) [water density is 1000 kg/m3]
This means that a chemical poly tank that has an SG of 1.2 or more, should be chosen.
In some cases, the specific gravity of certain liquids is less that an SG of 1 but it is still recommended that medium duty poly tanks be chosen due to the hazardous nature of the liquid. An example would be fossil fuels such as paraffin or petrol that have SG’s of less than one. The environmental (and safety) threat that fuels pose should the tank be breached, makes it a wise decision to choose a medium duty chemical storage tank or even a heavy duty tank if rough handling is envisaged.
JoJo Tanks in South Africa manufacture three main versions of most of the vertical, horizontal and silo tanks, i.e. standard duty water tanks (SG 1), medium duty chemical tanks (SG 1.4) and heavy duty chemical tanks (SG 1.6).
Click on the links below to view the wide range of JoJo water tanks, JoJo chemical tanks, JoJo septic tanks, JoJo silo tanks and JoJo steel tank stands as well as many other high quality JoJo Tanks products.
JoJo Tanks South Africa offer a wide range of products such as plastic water tanks and chemical tanks to suit every household, business or agricultural need, including silo tanks and silo tank stands as well as other high quality JoJo Tanks products. See JoJo Tanks’ VERTICAL TANKS, HORIZONTAL TANKS (transporter tanks), STEEL TANK STANDS and OTHER JOJO PRODUCTS and see JoJo Tanks’ NEW 6000 LITRE UNDERGROUND TANKS. Also see our FAQ and WATER TANK PRICES.