Flyer
12-04-2010, 06:08 AM
DIY Super Venturi! Easy to make step-by-step guide!
http://www.youtube.com/watch?v=4czczYnuM_w&feature=player_embedded
This video is to demonstrate the function of the venturi design. As you can see, this venturi is mounted to the outlet of the pump (Laguna 2400). The pressure ratios are always more favorable for drawing air when using the inlet side of the pump. In this application, I would estimate around a 25% increase in airflow from using the suction side of the pump. It took 1min 34sec to empty the sack estimated at 2.4ft^3. This gives me a flow rate of about 91 SCFH. I would say this test is accurate to about 15% of true airflow, with all of the margin for error coming from my mathematical estimation of the volume of the bag. On the inlet side of the pump (if the pump was modified to avoid cavitation with large amounts of air), I think figures around 110-120 SCFH would be expected. Bubble size would also be much smaller of course from being chopped up by a mesh or needle wheel as well.
The Super Venturi
Venturis are essential to the function of some important pieces of hydroponic equipment. Reservoir tanks and cloners can improve from the use of a good venturi.
It's sometimes thought that to get the ideal shapes of a venturi, one would need to use a lathe, or a CNC mill. These certainly can produce a perfect venturi, but most folks don't have those machines laying around.
The purpose of this thread is to show how you can make nearly ideal venturis in any size or pressure ratio and flow requirement from just a few basic hand tools. They are also very clear, so you can watch the bubbles.
The tools used:
Drill and Drill bits (dulled edges for drilling acrylic)
Heat gun (you could use anything that will heat acrylic up enough to make a soft place)
Hacksaw
Pen
Glue
The materials:
Acrylic tubing in sizes that slip over each other. This means get something with an OD that equals another tube's ID. Often this just means you can grab a tube, and then grab the next size up. Most acrylic tubes are $4-15 depending on size.
Let's start:
Take your inside tube and roll it in your fingers in front of the heat gun. Check often to see when it become soft. If you get it too warm, the acrylic bubbles and becomes more brittle.
When the tube becomes soft, pull on the tube, and it slowly begins to stretch. Pull steady and even.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=876&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=876)
It stretches out nicely if you're careful. Keep holding pressure on the stretched tube or it will bunch up when it shrinks back. The greater the size ratio between the diameter and the contracted diameter will determine how hard the venturi is able to suck. If you have a lot of head pressure to fight, you will need to really shrink it down. If you have very little head, a less aggressive contraction will enable you to draw air and cause less water flow restriction. Since they are so quick and easy to make, I would recommend just trying a few designs to see what works best for your application.
When you see the shape you desire, it's helpful to blow to help cool the plastic faster. Not entirely needed, but your arms will get tired if you decide to stretch tubes about 50 times in a row while experimenting.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=877&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=877)
You will end up with a stretched tube. Unless you are crazy like me, you will just have a single tube in the size you need. I tried this with so many tubes so I could be sure that this method works well on both small and large tubing. It worked fine with all wall thicknesses and sizes of tubing I tried.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=866&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=866)
The next step is to mark a circle around the smallest diameter point. This is the point with the highest fluid speed. This gives it the lowest pressure. Look for whichever end has the most rapid increase in diameter, and make this the direction the air will move towards. Drill holes around this point, and then tip the spinning drill to the side so it cuts an angled hole in the venturi. Making a drill bit dull before trying this will help to avoid cracking.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=863&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=863)
I used a 1/16" bit for the smallest tubes, and up to 5/32" for the larger tubes. Remember, area increases at the square of radius, so a small increase in bit size has big effect on what a hole is able to flow.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=878&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=878)
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=879&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=879)
Next, cut some of the acrylic tubing from the bigger tube, drill an air hole in it, and slide it over the smaller venturi tube. You could tap this hole and thread in a nipple, or glue in your airline or smaller tubing or whatever best suits your application. Run a bead of glue around the seams of the larger and smaller pipe. This reinforces it and makes it strong, along with sealing the housing.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=880&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=880)
To mount them, you could use quality chunk of silicone tubing/hose and clamps like red dragon skimmers, or epoxy a plumbing union to each end. I would avoid wanting to glue them in place, as that would limit your ability to make changes if you desired.
NOTE:
A venturi of this style will be able to draw more air than a pump can handle without cavitation. A needle valve to limit the incoming air will likely be needed. This type of venturi will cause less flow loss and be capable of injecting much more air than a flow-nozzle type of injector that is most often seen in hydroponics. In other words, your venturi won't be limiting the amount of water pressure you are able to pump anymore. You will be limited by how much air your pump can handle before it chokes.
Most people would want 1/2, 3/4, 1" and 1.25" acrylic tubes (1-1.25" used in video). 1" was $8 for 6ft and 1.25" was $10.50 for 6ft. Not really something I would consider to be a cost prohibitive material to work with for most people. I bought mine from a plastic supply store, but I've seen them for sale in hardware stores, craft supply stores, hobby shops, and other places.
Enjoy your new Venturi!
http://www.youtube.com/watch?v=4czczYnuM_w&feature=player_embedded
This video is to demonstrate the function of the venturi design. As you can see, this venturi is mounted to the outlet of the pump (Laguna 2400). The pressure ratios are always more favorable for drawing air when using the inlet side of the pump. In this application, I would estimate around a 25% increase in airflow from using the suction side of the pump. It took 1min 34sec to empty the sack estimated at 2.4ft^3. This gives me a flow rate of about 91 SCFH. I would say this test is accurate to about 15% of true airflow, with all of the margin for error coming from my mathematical estimation of the volume of the bag. On the inlet side of the pump (if the pump was modified to avoid cavitation with large amounts of air), I think figures around 110-120 SCFH would be expected. Bubble size would also be much smaller of course from being chopped up by a mesh or needle wheel as well.
The Super Venturi
Venturis are essential to the function of some important pieces of hydroponic equipment. Reservoir tanks and cloners can improve from the use of a good venturi.
It's sometimes thought that to get the ideal shapes of a venturi, one would need to use a lathe, or a CNC mill. These certainly can produce a perfect venturi, but most folks don't have those machines laying around.
The purpose of this thread is to show how you can make nearly ideal venturis in any size or pressure ratio and flow requirement from just a few basic hand tools. They are also very clear, so you can watch the bubbles.
The tools used:
Drill and Drill bits (dulled edges for drilling acrylic)
Heat gun (you could use anything that will heat acrylic up enough to make a soft place)
Hacksaw
Pen
Glue
The materials:
Acrylic tubing in sizes that slip over each other. This means get something with an OD that equals another tube's ID. Often this just means you can grab a tube, and then grab the next size up. Most acrylic tubes are $4-15 depending on size.
Let's start:
Take your inside tube and roll it in your fingers in front of the heat gun. Check often to see when it become soft. If you get it too warm, the acrylic bubbles and becomes more brittle.
When the tube becomes soft, pull on the tube, and it slowly begins to stretch. Pull steady and even.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=876&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=876)
It stretches out nicely if you're careful. Keep holding pressure on the stretched tube or it will bunch up when it shrinks back. The greater the size ratio between the diameter and the contracted diameter will determine how hard the venturi is able to suck. If you have a lot of head pressure to fight, you will need to really shrink it down. If you have very little head, a less aggressive contraction will enable you to draw air and cause less water flow restriction. Since they are so quick and easy to make, I would recommend just trying a few designs to see what works best for your application.
When you see the shape you desire, it's helpful to blow to help cool the plastic faster. Not entirely needed, but your arms will get tired if you decide to stretch tubes about 50 times in a row while experimenting.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=877&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=877)
You will end up with a stretched tube. Unless you are crazy like me, you will just have a single tube in the size you need. I tried this with so many tubes so I could be sure that this method works well on both small and large tubing. It worked fine with all wall thicknesses and sizes of tubing I tried.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=866&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=866)
The next step is to mark a circle around the smallest diameter point. This is the point with the highest fluid speed. This gives it the lowest pressure. Look for whichever end has the most rapid increase in diameter, and make this the direction the air will move towards. Drill holes around this point, and then tip the spinning drill to the side so it cuts an angled hole in the venturi. Making a drill bit dull before trying this will help to avoid cracking.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=863&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=863)
I used a 1/16" bit for the smallest tubes, and up to 5/32" for the larger tubes. Remember, area increases at the square of radius, so a small increase in bit size has big effect on what a hole is able to flow.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=878&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=878)
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=879&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=879)
Next, cut some of the acrylic tubing from the bigger tube, drill an air hole in it, and slide it over the smaller venturi tube. You could tap this hole and thread in a nipple, or glue in your airline or smaller tubing or whatever best suits your application. Run a bead of glue around the seams of the larger and smaller pipe. This reinforces it and makes it strong, along with sealing the housing.
http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=880&thumb=1 (http://www.cannabis-world.org/cw/picture.php?albumid=101&pictureid=880)
To mount them, you could use quality chunk of silicone tubing/hose and clamps like red dragon skimmers, or epoxy a plumbing union to each end. I would avoid wanting to glue them in place, as that would limit your ability to make changes if you desired.
NOTE:
A venturi of this style will be able to draw more air than a pump can handle without cavitation. A needle valve to limit the incoming air will likely be needed. This type of venturi will cause less flow loss and be capable of injecting much more air than a flow-nozzle type of injector that is most often seen in hydroponics. In other words, your venturi won't be limiting the amount of water pressure you are able to pump anymore. You will be limited by how much air your pump can handle before it chokes.
Most people would want 1/2, 3/4, 1" and 1.25" acrylic tubes (1-1.25" used in video). 1" was $8 for 6ft and 1.25" was $10.50 for 6ft. Not really something I would consider to be a cost prohibitive material to work with for most people. I bought mine from a plastic supply store, but I've seen them for sale in hardware stores, craft supply stores, hobby shops, and other places.
Enjoy your new Venturi!