SEALING THE FATE OF BATTERIES

A sealing system promotes the change to closed cell batteries in vehicles

Maintenance-free, closed cell batteries require venting valves in order to ensure their proper function over prolonged periods. The demands made on such components are very high. If the valves do not close correctly, the cell will dry out in a relatively short time or will be destroyed by the ingress of oxygen from the air.

A further difficulty is posed by the opening characteristic of the valve. If the opening pressure limit is exceeded as a result of a jammed valve, there is a risk of structural damage in the cell, possibly even complete destruction.

Effectively venting the closed-cell battery was a problem until the Busak+Shamban design team developed the Ventseal, (Figure 1) a patented valve that seals whilst permitting the opening and re-sealing of the battery, as required.

Each version of the Ventseal allows integration into existing grooves, avoiding major modifications to the battery. Furthermore, tests have shown that the battery provides tightness up to 10 times greater than comparable solutions.

The continuous sealing edge closes a pressure chamber from the atmosphere. As pressure is built up, the geometry of the sealing lip profile changes. Above a given pressure, the Ventseal opens via the sealing edge of the control surface where the wall thicknesses are lighter.

Figures 2 and 3 show the contact pressure curve of the Ventseal in comparison with the conventional geometry of a valve seal. With the same radial preloading force, a higher maximum contact pressure is achieved with the seal because of its smaller sealing surface. As a result, a better sealing effect is gained. Adhesion phenomena are effectively minimised by the very small and linear sealing surface.

The sealing edge of the seal also produces a defined opening behaviour. As pressure drops, the closing process begins, ie, the opening cross section is reduced. On reaching the closing pressure, the Ventseal is technically closed tight, ie, the sealing edge of the control surface is again in contact with the mating surface.

Figure 1: The Ventseal has been developed for closed cell batteries

Figure 2: Optimum compression curve of the Ventseal

Figure 3: Unfavourable compression curve of a conventional elastomer valve

Figure 4: The Ventseal family can be used in a variety of different applications

{{Busak+ShambanTel: 0121-744 1221Enter 424}}