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.

 

[Baluncore]

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?

As a guide, let's say 20 drops per millilitre.
1.9 litre = 1900 millilitres = 38000 drops per hour.
That is 10.5 drops per second.
I guess your filter has become blocked by something in the water.
Are you able to clean the filter?

Domestic water pressure is usually about 4 atmospheres.
A pump can only suck 1 atmosphere.

If air contacts the filter material, it will be pulled through the filter much faster than water. The filter needs to be submerged.

Can you apply domestic water pressure to the filter input?

 

[sophiecentaur]

So would there be a way to make this work

It maybe that your filters are made of a flexible material which is squeezing tight with the increased water pressure and the filter could be 'blocking itself'. it can't be assumed that the system is linear.

You could experiment with a long pipe and vary the head between the supply container and the filter body. The flow would be proportional to head for normal pressures and then you may observe a sudden drop above a certain height. The effect could show itself with a head of about 1 Atmosphere (10m)

 

[sophiecentaur]

Domestic water pressure is usually about 4 atmospheres.

In UK the pressure is often only due to the height of the storage tank (say 10m). Higher in tall apartment blocks but do they not use a regulator?

 

[questions8938]

As a guide, let's say 20 drops per millilitre.
1.9 litre = 1900 millilitres = 38000 drops per hour.
That is 10.5 drops per second.
I guess your filter has become blocked by something in the water.
Are you able to clean the filter?

It isn't a case of cleaning or not, these are only a few months old and I do clean them every week or so when the flow rate drop (even lower than the piddling rate already), it is just how slow they filter as gravity filters are known to be slow. They are quite new. The few drops is normal for unpumped gravity filters.

This is actually exactly why I wanted to get a pumped one, since this low flow rate is excected from gravity filters and it has a very hard time keeping up with demand.

Domestic water pressure is usually about 4 atmospheres.
A pump can only suck 1 atmosphere.

If air contacts the filter material, it will be pulled through the filter much faster than water. The filter needs to be submerged.

This seems more the likely cause.

Can you apply domestic water pressure to the filter input?

Well that defeats the purpose as it is for filtering off-grid 'raw' water to make it potable but also the answer is no I can't as there is no mains water.

It maybe that your filters are made of a flexible material which is squeezing tight with the increased water pressure and the filter could be 'blocking itself'. it can't be assumed that the system is linear.

Actually the opposite, they are hard ceramic. If air sucks through easier than water, when both are competing, as explained by @Baluncore , that does sound plausible.

You could experiment with a long pipe and vary the head between the supply container and the filter body. The flow would be proportional to head for normal pressures and then you may observe a sudden drop above a certain height. The effect could show itself with a head of about 1 Atmosphere (10m)

Hmm this would classify as too much trouble to be worth it. There are also other constraints. This is in a campervan (RV for the americans), and a small one at that, so extremely limited space. Certainly no space for 10m apparatus, lol.

I just wanted to run through possibilities and if it makes more sense to just buy the ones that are made to run under pressure I will just do that.

In UK the pressure is often only due to the height of the storage tank (say 10m). Higher in tall apartment blocks but do they not use a regulator?

Don't know about that. Not my 'wheelhouse' as you yanks say.

 

[DaveC426913]

This is in a campervan (RV for the americans), and a small one at that, so extremely limited space. Certainly no space for 10m apparatus, lol.

Now don't give up too quick...
Are there many overpasses between your home and your fave campgrounds?
Have you measured them?

 

[sophiecentaur]

Now don't give up too quick...
Are there many overpasses between your home and your fave campgrounds?
Have you measured them?

I can just picture it in my mind.
"Police were called to an incident . . . . . . . ."

 

[Herman Trivilino]

the functionality seems the same as inline filters you put undersink.

Nope. Just nope. Pushing the water through faster, even if it produced water, the water would not be filtered.