For anyone attending a vacuum truck sale, the most commonly found holding tank shape has always been cylindrical with rounded ends. From the looks of it, this particular shape doesn’t appear very practical in terms of volume when compared to a square version. While it is true that a square holding tank with a similar length, height and width can hold more content, there are good reasons why these tanks are not cylindrically shaped.
Although maximizing holding capacity is definitely a top design consideration, a more important reason why these tanks are cylindrical is because of the structural requirements for maintaining shape and integrity. A vacuum truck tank works by drawing air inside via a pump; a suction hose is connected to an inlet port that goes directly into the holding tank. The pump can suction so much air that it creates a vacuum throughout the length of the entire system including the suction hose and tank.
Relationship of Shape and Strength
The vacuum generated from the pump is so strong that it could literally collapse a tank out of its original shape. A cylindrical shape is ideal because it evenly distributes the force on all sides of the holding container, which does not leave any weak points that could collapse when vacuum pressure inside the tank increases.
When the vacuum is in use, there is a negative pressure constantly pulling on all sides from within. If the holding container were square, the flat side would be much weaker than its edges because there is no structure supporting it from the inside; such weak points could easily cave in under extreme negative pressure. On the other hand, a round shape has higher structural integrity than a flat shape. So the curved shape of the metal gives it structural resistance from the strong force within the curve, making it less prone to collapse.
As for the oblong-shaped tank seen mostly on fuel tankers, although it is more resistant than a square one, it still doesn’t offer the same structural integrity for vacuum applications and should not be considered when selecting from a vacuum truck sale. Remember than the fuel inside a container applies a positive pressure to the walls so that the shape can perfectly support such force. A vacuum’s force is applied negatively and inwardly, so an oblong shaped tank will have a weak spot on the flatter sides, making it susceptible to collapse.
In addition to shape considerations, there are other important features that allows a holding tank to withstand extreme vacuum forces.
- Metal Thickness – The holding tank metal sheets are a 1/4 inch thick while water tanks have metal sheets that are 1/8 of an inch thick, making the vacuum truck holding tank heavier but more durable.
- Vacuum Relief Valve – Even with a thicker metal plate, structural failure can still occur; this is why tanks are equipped with a relief valve to ease pressure should it reach dangerous levels. The relief valve kicks in automatically at a predetermined level.
- Primary Shutoff – The primary shut off is a valve that closes the port leading to the pump if the tank fills to a certain level to prevent overfilling the holding tank and debris getting sucked through the pump.
A vacuum truck sale holding tank shape is an important safety feature. Although appearing inefficient, it is actually an optimal shape for maintaining structural integrity and resisting damage caused by high levels of vacuum forces. So keep on rounding out those holding tanks and never let them be square!
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