Bladder and pillow tanks are used to store liquids

Bladder and pillow tanks are used to store liquids, sometimes for short periods of time. A great deal of confusion surrounds the nomenclature surrounding bladders and pillow tanks. In short a pillow tank is a type of bladder. Bladders generally can be made as pillow tanks (take their name from their shape and form) or as shaped bladders (made to fit a particular shape).

Pillow tanks are a self supporting bladder and do not have walls as such. To get height they effectively steal some material from the top and bottom of the bladder giving that traditional curved shape towards the middle along the length of the bladder most particularly. The maximum fill height of any pillow tank is primarily a function of its width and to a lesser extent the length. For example a bladder sized to suit a truck bed (2.4m wide) is limited to about 0.7m max fill height.

Since pillow tanks are self supporting, the material that they are made from needs to be very strong as the pillow tank, is under constant load (hoop stress) similar to that of a circular tank.  This fact limits the fill heights of pillow tanks, irrespective of the bladder width to in most cases 1.3m – 1.5m in height. The other thing with pillow tanks is that due to their curved shape on the length, width and height, the capacity (stored volume) of a pillow tank is about 70% that of a rectangle with the same maximum dimensions. Since pillow tanks are self supporting and the material is under constant load, their life is limited. They are in reality designed for short term but repeated use.

Pillow tanks are sometimes deliberately made quite oversize and are fitted into tanks of various shapes or shipping containers. These oversize bladders then tend to follow the shape of the surrounding structure. Pillow tanks generally are cheaper to produce than shaped bladders. Fabric Solutions Australia can and has made pillow tanks from about 50 litre capacity to 1000 kL capacity.  The larger bladders tend to be for water storage while the fuel, sewerage and chemical storage pillow tanks tend to be restricted to about 100 kL maximum size.

Bladders, as in shaped bladders on the other hand, are made to fit the shape of the surrounding structure. At Fabric Solutions Australia we have made shaped bladders to fit into the keel of yachts, fit into the companionway on large yachts, to fit into shipping containers, under seats and in floor wells of vehicles etc. These bladders often used to s tore fuel, sewerage, grey water or potable water. A common application for this style of bladder is to repair existing leaking tanks. The tank forms the structure and takes the load so there is no restriction as to the height of the bladder. These bladders are often strange shapes to suit the tanks they are repairing. Shaped bladders only follow the shape of the structure and if used without surrounding structure will tend to sit low and flat. There is really no size limitation on shaped bladders as long as the surrounding structure can take the loads, the bladder can be fitted correctly and fully supported.

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