Why does this not produce water pressure?

[questions8938]

I have a gravity water filter and rather than pay $$$ to buy an undersink pumped one I thought I could try and add a pump to the existing one instead but it is not working for some reason I can't figure out why.

You can see images of it here.

There is a top chamber where you place water with the filter 'candles' which have spigots in the bottom where the water slowly drips through.

What I tried is adding blanking grommets to the other 3 holes leaving only one filter candle and attaching a plumbed pipe to the last spigot beneath which goes to the pump. As far as I can tell the connection is sealed but when I turn on the pump it doesn't pump anything or just a pathetic drip but mostly just air.

I can't figure out why it doesn't pull the water through? as the functionality seems the same as inline filters you put undersink. I am guessing it is mostly pulling are since the candle isn't completely seal and submerged like with the undersink ones?

So would there be a way to make this work or am I better just shelling out the $$$ for the 'proper' ones?

If they needed to me totally submerged all the time to work I don't see that as very practical given the design so not sure if it would be worth trying to figure out vs just getting the proper ones?

 

[Baluncore]

What is the normal flow rate through the filter, when only gravity is present.

 

[questions8938]

What is the normal flow rate through the filter, when only gravity is present.

Something like 1.9 litres per hour I think they rate it at per hour but in practice I have found it far lower. It is just a few drips every few seconds.

I am thinking the pump is sucking air through the candles mostly rather than water due to not being fully submerged? I am wanting to know if there might be a way to get around this. It would have to be full all the time to fully submerge them but I think this goes against the design since they are meant to empty into the lower chamber, like a sand timer and I would be having to make other chambers to keep the main one full which then gets convoluted.