GrahamC Posted January 17, 2012 Report Share Posted January 17, 2012 I have a venturi port on my submersed filter that allows air to be mixed in with the filter output. But I noticed that it stops working if I submerse the filter too much below the water line. Since the air line hose length is not changing, and atmospheric pressure is constant, then it must be the increased water pressure that is limiting the water flow and reducing the negative pressure at the venturi port? Quote Link to comment Share on other sites More sharing options...
supasi Posted January 17, 2012 Report Share Posted January 17, 2012 You answer your own questions Quote Link to comment Share on other sites More sharing options...
CodKing Posted January 17, 2012 Report Share Posted January 17, 2012 +1 :thup: Quote Link to comment Share on other sites More sharing options...
zuri08 Posted January 17, 2012 Report Share Posted January 17, 2012 +2 :slfg: Quote Link to comment Share on other sites More sharing options...
GrahamC Posted January 18, 2012 Author Report Share Posted January 18, 2012 So, if that is correct, how does one calculate how deep one can immerse a filter and still have the venturi still work? I presume that the variables are water depth, rated litres per hour flow, and diameter of the outflow, diameter and length of the airline tubing .... Quote Link to comment Share on other sites More sharing options...
blueether Posted January 18, 2012 Report Share Posted January 18, 2012 All of that, pluss probably the most important thing would be how well designed the venturi is Quote Link to comment Share on other sites More sharing options...
livingart Posted January 18, 2012 Report Share Posted January 18, 2012 So, if that is correct, how does one calculate how deep one can immerse a filter and still have the venturi still work? I presume that the variables are water depth, rated litres per hour flow, and diameter of the outflow, diameter and length of the airline tubing .... just move it up and down till you are happy with it Quote Link to comment Share on other sites More sharing options...
GrahamC Posted January 18, 2012 Author Report Share Posted January 18, 2012 That won't work if I am looking to buy a filter for this purpose Quote Link to comment Share on other sites More sharing options...
Insect Direct Posted January 18, 2012 Report Share Posted January 18, 2012 can always just hook an air pump up to it. that really boosts the bubbles i have one on a pond pump, the air thing came with a cheap little internal filter and had same problem when using that in deepish water, also as soon as it got slightly clogged it would stop working. with it on the pond pump it can go at least 30cm deep and still go hard, no air pump either. Quote Link to comment Share on other sites More sharing options...
CodKing Posted January 18, 2012 Report Share Posted January 18, 2012 can always just hook an air pump up to it. that really boosts the bubbles +1 Get yourself a valve (http://www.tails.co.nz/fish/filters-airstones-and-pumps/plastic-airvalves), a couple of blobs of hot glue and you've got control. Quote Link to comment Share on other sites More sharing options...
spoon Posted January 18, 2012 Report Share Posted January 18, 2012 if you want a pump that makes heaps of air bubbles make your own venturi (google diy epoxy venturi) and use a really grunty pump it would possibly be noisy Quote Link to comment Share on other sites More sharing options...
GrahamC Posted January 18, 2012 Author Report Share Posted January 18, 2012 I want to be able to recirculate the air at the top of a bottomless tank so external air pumps will not work as they will introduce air into the system dropping the water level. Based on my experience so far, I suspect the pump itself will need to be outside the water column to reduce the water pressure. Quote Link to comment Share on other sites More sharing options...
livingart Posted January 18, 2012 Report Share Posted January 18, 2012 aah, more info makes it clearer Watson Quote Link to comment Share on other sites More sharing options...
Insect Direct Posted January 18, 2012 Report Share Posted January 18, 2012 if you put the airline inside a slightly larger pipe down to just above pump, seal it so no water in large pipe. may work? or would pressure come up pump... Quote Link to comment Share on other sites More sharing options...
GrahamC Posted January 18, 2012 Author Report Share Posted January 18, 2012 I think it is water pressure on the pump itself ...so that there is greater resistance to outflow. With this the water velocity drops, and so the negative pressure at the venturi port drops. Quote Link to comment Share on other sites More sharing options...
Squirt Posted January 18, 2012 Report Share Posted January 18, 2012 How deep is this pump? I never notice too much difference in flow when I change the height of the pump. Quote Link to comment Share on other sites More sharing options...
GrahamC Posted January 18, 2012 Author Report Share Posted January 18, 2012 It's a tank maid, and currently it's just under the water line with the output at 5 cm below that ... Quote Link to comment Share on other sites More sharing options...
alanmin4304 Posted January 18, 2012 Report Share Posted January 18, 2012 I would have thought that the pressure difference between the inlet and outlet would be the same regardless of the depth of the pump so it should not make any difference, only if the outlet was raised above the water level and increased the operating head. Quote Link to comment Share on other sites More sharing options...
Warren Posted January 19, 2012 Report Share Posted January 19, 2012 I would have thought that the pressure difference between the inlet and outlet would be the same regardless of the depth of the pump so it should not make any difference, only if the outlet was raised above the water level and increased the operating head. +1 Must have a poorly designed venturi (or none at all). Most pumps just have a hole and call it a venturi... It needs a properly shaped tube sticking down into the pump flow outlet to be called a venturi. Got a photo of it? Quote Link to comment Share on other sites More sharing options...
GrahamC Posted January 19, 2012 Author Report Share Posted January 19, 2012 I think youre right... it's just a hole with a shaped cone to plug the air hose to it ... Quote Link to comment Share on other sites More sharing options...
alanmin4304 Posted January 19, 2012 Report Share Posted January 19, 2012 I am no engineer but have seen engineers I worked with build them to extract the magic metal from rivers on the west coast. There is a whole formulae for getting them to work well. Quote Link to comment Share on other sites More sharing options...
blueether Posted January 20, 2012 Report Share Posted January 20, 2012 It needs a properly shaped tube sticking down into the pump flow outlet to be called a venturinot quite true, needs a velocity increase through a bore diamator change to be call a venturi :sage: Edit: Just lookd up the max head for a water driven venturi and it is 0.46 psi or 13 inchs of water Quote Link to comment Share on other sites More sharing options...
alanmin4304 Posted January 20, 2012 Report Share Posted January 20, 2012 There are a number of factors as well as a reduction in bore diameter that are required to make a good venturi as I understand it. Quote Link to comment Share on other sites More sharing options...
Warren Posted January 20, 2012 Report Share Posted January 20, 2012 not quite true, needs a velocity increase through a bore diamator change to be call a venturi :sage: Yup, and and a properly shaped tube sticking down into the pump flow outlet will do exactly this... Quote Link to comment Share on other sites More sharing options...
Cricketman Posted January 20, 2012 Report Share Posted January 20, 2012 surely changing air pressure would also come into effect? especially in NZ where we are so close to the sea... (compared to a higher altitude) :dunno: Quote Link to comment Share on other sites More sharing options...
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