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Water pump action with lid off the tank


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Had a senior moment recently after filling the fresh water tank from winter emptying.


It did appear when priming the system that when the water tank lid is OFF and the tank is 'open to air' then the pump action is only pushing 40% or so, but when the lid is screwed on tight the pump works 100%.


Was this me, a fluke of nature or is the water system designed to advertise to the owner that the water container has a hole in it?

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Presumably this is a libby joke, but I'll treat it as if it were serious...


Your Rapido's fresh-water tank needs to be (and is) vented to atmosphere through a breather pipe. Otherwise your motorhome's diaphragm water-pump's vacuum-producing action could eventually prevent it sucking in water or (in theory at least) even cause the tank to collapse. Removing the tank's lid just produces a larger diameter 'breather', but otherwise can have no impact on the efficiency of the pump.


In fact, the reverse of your scenario MIGHT have some validity. Should the tank's breather pipe be obstructed, then the pump could begin to struggle as it fought against the partial vacuum built up within the tank. Removing the tank's lid would immediately restore full tank-breathing and allow the water-pump to work at maximum efficiency.


I suspect that it's your priming technique that has led you astray. That, at the start of the priming procedure you've concluded that your pump is functioning below par, when it's just at full stretch. At that stage you've happened to have had the lid of the tank off. Then you've come to the end of the priming procedure, when the pump is taking things easier: by which time you've replaced the tank's lid and made the mental leap that the pump's efficiency is linked to the tank's lid being off or on.


Off course it could possibly be that your water pump, after a period of enforced idleness, has needed some time to reach full working efficiency, or that there is something wrong with it. But your tank-lid theory is a non-starter - basically, it's you...!

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Sorry D its not an April fool, how dare you think I would do that.


I checked several times and it did operate just as I said. I could understand it if the opposite way round to indicate that an opening was present.


Thanks Brambles, at least someone's got his hat on straight this fine and sunny April fool's day. I will check the part number and report back.


Perhaps Derek's post was indeed an April fool in reverse?



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