Cubic and rectangular metal tanks for places where a cylindrical tank will not fit: plant rooms, basements, rooftops and along walls. They fill the space completely and are simple to install, but their flat walls bulge under water pressure, which is why they are designed with stiffening sections and tie rods.
In a cylindrical tank, the water pressure pulls on the plate like a hoop, and even thin plate carries this tension well. A flat plate does not have this option; the water pressure bends it like a beam, and the bending stress in the plate is much higher than the tensile stress in a cylinder of the same thickness.
The solution is to shorten the span. Horizontal and vertical sections divide the wall into small panels, and each panel behaves like a small plate with close supports. In large tanks, internal tie rods tie opposite walls together so that the force on the whole wall is carried by tension in the rods instead of by the sections.
The figures that set the thickness and stiffening of a rectangular tank:
Pressure is higher at the bottom of the wall; that is why the sections are spaced closer at the bottom of the tank and further apart at the top.
| Feature | Rectangular tank | Cylindrical tank |
|---|---|---|
| Use of space | Complete | The corner space is left empty |
| Weight per litre | More | Less |
| Wall stiffening | Sections and tie rods | Usually not needed |
| Installation in tight spaces | Possible with the panel type | More difficult |
A tank full of water is heavy: each cubic metre of water weighs a tonne. On a rooftop or upper floors, the tank must sit on beams that transfer the load to columns or load-bearing walls. This must be coordinated with the structural engineer before ordering.
If the transport route or plant room door is narrow, a galvanized panel tank is the best option. The panels are transported separately and assembled on site.
A flat wall only stays sound with correctly designed stiffeners
A cylindrical tank needs the least plate for a given volume, but it does not always fit. In a plant room with a low ceiling and space along a wall, or on a rooftop where the load must be spread across the beams, a rectangular tank fills the space better and the pipe connections are simpler too.
The price of this convenience is more weight. A cylinder carries the water pressure through tension in the plate; a flat plate has to carry it in bending, which is why it bulges. Stiffening sections divide the wall into smaller panels, and the plate thickness is calculated from the size of these panels and the water pressure. We give the volume and wall pressure formulas in the article on rectangular tank volume calculation, and the online rectangular tank calculator works out the thickness and weight. If the tank is for drinking water, also see the water tank construction method and its food-grade coating.
Chosen by volume, use and transportability
Built in one piece in the factory and shipped ready to install. For small and medium volumes that fit through the door and along the transport route.
Galvanized panels are made separately and assembled on site with bolts and sealing tape. There is no size limit and it passes through narrow routes too.
For drinking water, the food industry and places where an internal coating is undesirable. No paint and low maintenance.
The main design parameters of a rectangular tank
From the space dimensions to the water-fill test
The wall of a rectangular tank is a flat plate under distributed pressure. The plate thickness is calculated from the size of the panel between sections and the water pressure at that depth, and the sections themselves are designed for bending. The water-fill test is the last check before delivery.
Where space is limited
Tell us the space dimensions, volume and transport route to receive proposed dimensions and a price for a rectangular tank.
The most common questions about rectangular tanks
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