VENTURI MODIFICATIONS - UPDATE FOR 2005

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Update for 2005

This photo was taken about June 2005 and shows some well established
plants in the top of the bio-filter. These are still in their pots to assist easy removal.

This year (Spring 2005) I have made a few changes to my setup. I have found that Ziks design (click here to see Ziks design) of venturi works very well in the top of my bio-filter, and it allows frequent and easy cleaning of the venturi - something I couldn't do as quickly with my own design.

Conversely I have found that my own design of venturi works very well in the pond itself (see further below).

The new-cut scourer pad filters in the bio-filter with the Zik design of venturi aerating the water.	Close-up of the Zik-type venturi, with a piece of green-scrubby acting as an air and noise filter.
The length of hosepipe fits snugly into the 22mm standard plumbing pipe. I have not glued it because it means its dead easy to remove the venturi to clean the teeth every week, although often it works for 2 or 3 weeks without any attention. Again its just a case of listening for poor performance.	Close-up of the Zik type of toothed venturi. This really swirls and chops the air into the water as it passes, and makes quite a loud noise. I have since slightly reduced the length of the teeth because I found that over time the force of the water bends the teeth ! Making them a bit shorter makes them more robust and improves the venturi action.

Cleaning and Adjusting the Venturi

Having the piece of green scouring pad as an air-filter is also necessary to cut down the noise, because when its going it really makes a good swooshing sound. Every few days I check the venturi for blockages from any muck that has come from the pump. I simply pull the green pipe out, and clean it off, making sure the teeth are good and clean. I leave the pump running while I do this (the water just overflows out of the white pipe while I clean the tooth-pipe). When I put it back together I insert the the green pipe (making sure I've put the green side of the teeth facing the side that the water enters, with the white side of the teeth facing the way the water goes into the bio-filter), and slowly push it downwards until I see the water start to get sucked down, and then the venturi suddenly kicks into action again. I then adjust it for the most powerful draw on air. I want a balance of allowing the best water rate through, but also achieving a good aerating effect. The trick is to listen! Push the green pipe all the way down until it touches the bottom, then lift it very slowly up until the venturi effect starts to lose power, then push it back down a bit. This allows the fastest water flow. Now make a final adjustment by rotating the green pipe very slightly to offset its angle against a straight thru flow of water by about 10-15 degrees. You will hear the swooshing sound become slightly more intense, and this creates a swirling effect in the bottom of the venturi which really mixes the air into the water.

Tip for Adding Bacteria to your Bio-Filter You can insert a funnel into the venturi pipe and then pour mixtures directly into the bio-filter chamber. For example a fresh bacteria mix at the start of the year, or whenever you want to give it a boost. This gets thoroughly mixed into the water passing through the bio-filter by literally injecting the solution right into its heart. This really helps jump-start the bacteria colony in your bio-filter.

Venturi Silencer - Up Periscope

That venturi can sure make a lot of noise when its running! And on a beautiful sunny afternoon when you're lazing in the garden by the pond you just want to hear the sounds of the birds, insects and water trickling lazily down your stream. You certainly don't want to hear the constant whooshing of your venturi.

So I constructed a better silencer than the simple wad of scouring pad that I had stuck in the top of the venturi hoze (photo above). Its a simple extension to the venturi tube, which is a loose push-fit over the top of the venturi hoze. I sprayed it with green paint to make it blend in with the plants. I call it my periscope silencer.

"Up Periscope!"

The periscope silencer is filled with some green scouring pad cut and folded into a cylinder shape so that it pushes into the 22mm piping. This scouring pad acts like a baffle and helps to reduce the noise, whilst also acting as a filter to prevent insects or dust being drawn into the venturi. The black fitting is a spare top insert for a bell-effect water fountain, which inserts nicely into the scouring pad. It doesn't have to be a tight fit. The idea is just to give a cap to protect the opening of the pipe, and further block the noise, while allowing easy airflow.

The main upright of the periscope is likewise filled with a cylindrical shaped fold of scouring pad. The whole periscope, with its 90 degree bend, scourer pads and the black plastic insert all work to cut down the noise dramatically, in fact so much that you can now only hear the venturi if you are close to it.

Silence is golden.

Venturi in da Pond

This is my own design of venturi (originally described on my Build a DIY Venturi for a Pond Bio Filter page) which I now use attached to a second Hozelock pump. This sits on a shallow shelf of the pond, just below the surface of the water. It creates a tremendous swirl of air and water, which the fish love to play in, and it creates very good circulation in the pond. This in itself helps keep muck and silt waterborne for longer so that the main pump can send it to the bio-filter.

And here it is in action...... (ugh, look at all that horrible slimy blanket weed, this was in the Spring before the biological processes in the pond had kicked in to reduce the algae).

It works on a timer to come on from 10am to 3pm to give current, and oxygenate the water.

This particular venturi was originally in my bio-filter, but then I changed to the Zik design for my bio-filter, and put my design for the venturi in the pond.

The Venturi in da Pond uses a Hozelock Cascade 2000 Low-Voltage (24v) pump (2000 litres/hour or 0.55 litres/second).

Look at the photo and I'll explain a few points about it:-

On the left of the photo you have the Cascade 2000 with its standard pipe and valve fittings that comes with the pump and normally feed a fountain and flexible hose to other water features (2 valves).

The bottom valve controls flow to the venturi pipe.

The top valve would normally control flow vertically upward to a fountain head. The valve is a simple butterfly valve that is unable to shut-off fully, hence a piece of cork in the top of the up-pipe to block it up completely because the pump is quite a decent little fella and even with the butterfly shut it would shoot a little spout up the sides of the valve! Obviously I want all the power to go to the venturi.

So the water passes to the right, thru the venturi and out of a nozzle of 22mm pipe from the T-piece used for the venturi.

The bottom valve has a barb fitting which flexible hose is normally attached to, so I have used a short length of black plastic 25mm piping which has a tight fit on the barb, then the 22mm piping entry pipe of the venturi is clamped into the black plastic tube using a jubilee clip.

In operation I occasionally clean the plastic cage around the pump which prevents too much crap from going into the pump, but I have found it performs satisfactorily without cleaning for several weeks.

Venturis operate easier the shallower they are, but oxygenate better the deeper they are, so the strength of the pump you employ will determine how deep you can put it.

Obviously the small green air-intake tube (electricians earth-wire sheathing) must be above water to take in air, and if you were to put it deeper you might need to rig up something to keep it at the surface.

This venturi works very well and my fish enjoy it very much.

In summer it is often better to run a venturi at night because that is when oxygen levels can drop, but I personally feel that night-time is rest-time for the fish and they probably prefer motionless water.

The choice of whether you run the pump at night probably depends on how many fish you have in your pond and therefore how much oxygen they use up, and whether you have any other oxygenation methods such as a stream, waterfall or air-stones.

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