vents on flexible water tanks

Mine "vents" through the manual sink tap, oh and also expands to lift up the cushions beneath which it sits. There needs to be a vent to allow air in when the water is pumped out from the bottom.
 
Flexible water tanks fall into two distinct types.

Pillow tanks .. designed like a pillow and intended to go flat as they empty, These do not have a vent. Filler and outlet are usually on the top surface.

Shaped tanks .. three dimensional tanks with top, bottom and sides. These are not intended to go flat as they empty ... they should roughly retain their shape and large ones may be supported to prevent them collapsing .... They must be vented in the same way as a rigid tank.

If the shaped tanks collapse as they empty they tend to fold and crease in the same places every time and eventually may fail at these points.

I had a shaped tank that did not have a vent .... it lasted about 3 years. I now have a pillow tank which has been in use for over 25 years
 
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catmandoo said:
Why is it necessary to plumb in the vent on a flexible water tank ?
Click to expand...

It depends also on the geometry of the tank when intalled. On our old Sadler 29 with a roughly cylindrical tank, although the inlet was at the top of the tank a considerable amount of air was carried in with the water and this formed a large bubble of its own. One of the duties of the crew was to "burp" the tank before finally filling up.

A better solution would have been to vent the tank with a small bored tube within the water inlet but I never got round to fitting one.
 
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