Venturi and Needle Wheel Skimmers
Two of the Most Popular Skimming Technologies Explained
Jason Kim, president of AquaC, helps readers understand the difference between these two popular skimmer technologies for the marine aquarium.
Protein skimmers are considered essential equipment by most marine aquarists. They work on a relatively simple principle, which Jason Kim of AquaC explains: “Proteins and other molecules (fish and coral waste, uneaten food, etc.) are attracted to the surfaces of air bubbles inside a protein skimmer. As the bubbles rise, these waste products accumulate and become concentrated, eventually leading to a nasty foam that is skimmed off and discarded.” In this article, Kim weighs some of the pros and cons of venturi driven protein skimmers and the closely related needle wheel skimmers.
“Most skimmers are cylindrical in shape and utilize a similar overall body design,” points out Kim. “The main difference between brand A and brand B is in the method of air injection. Air-driven and venturi skimmers were the only real options until the mid 90's,” recalls Kim. “That's when downdraft skimmers became popular and their introduction coincided with the explosion of the reef tank craze.” Today, Kim thinks it’s really a choice between venturi driven, spray injection, and needle-wheel.
Venturi Driven Protein Skimmers
Venturi driven protein skimmers inject small air bubbles into the skimmer chamber through the venture valve. These bubbles create a sort of whirlpool effect in the chamber, which increases contact time. Venturi driven skimmers don’t require a separate air pump since the venture valve is responsible for injecting the bubbles. The downside here is that venturi skimmers need high pressure, dedicated pumps (usually powerheads when used in-sump) that can deal with back pressure in order to function well. Some Venturi driven skimmers come with pumps, others don’t. Even the ones which are sold with pumps are sometimes paired with pumps that are not powerful enough to make the skimmer run at maximum efficiency—always check with the manufacturer. Also take into account the heat the pump will add to the system. You will need to clean the venturi valve from time to time by reaming it, but other than that, they are pretty maintenance free.
Needle-Wheel Skimmers
Most needle wheel protein skimmers are just venturi skimmers with a so-called “needle wheel” impeller. A venturi valve is still used to inject the air—the difference is that the water is then drawn through the needle wheel impeller, which chops the incoming bubbles into a fine mist. “These needle-wheel impellers can really hack bubbles apart,” says Kim, “which is great since small bubbles are ideal for efficient skimming. The better needle-wheel skimmers on the market are notorious for building a dense, milky froth. This makes for efficient skimming in a relatively compact package.” The needle wheel skimmer’s efficiency is largely responsible for its huge popularity. Given that this pump is really a venturi hybrid, it has the same downsides as those listed above for venture driven skimmers. Kim also cautions against needle wheel skimmers' low rate of air and water flow. "A needle-wheel impeller is designed to chop up air bubbles, and it doesn't do a very good job at moving water flow," Kim says. "Venturi and spray-injection skimmers driven by pumps with normal impellers move a lot more water flow. That offers some advantages, especially on large tanks."
The next article in this series will look at how the spray injection skimmers that Kim introduced in late 1998 are different from both venturi and needle wheel skimmers.
Additional Resources:
Kim on Protein Skimmers - Jason Kim Walks the Aquarist through the Basics of Skimming (Part 1)
Venturi and Needle Wheel Skimmers - Two of the Most Popular Skimming Technologies Explained (Part 2)
Spray Injection Protein Skimmers - AquaC's Patent Process Relies on Brute Force (Part 3)
An Article on Sump-Based Filtration in General
