Learn About Aquaculture
HERE YOU CAN LEARN ABOUT ALL ASPECTS OF AQUACULTURE
Aspirators and agitators are the aeration devices most commonly used on hauling tanks when the stocking densities do not require the use of pure oxygen. Agitators use a small motor (normally 12V) to spin a paddle which is in the water. The paddle splashes the water, which adds oxygen and removes carbon dioxide. Aspirators also use a small motor, which spins a small venturi device. Air is pulled down through the shaft and exits the venturi underwater, causing a draft of bubbles. Agitators are the best choice for heavy stocking loads because they transfer more oxygen than aspirators. Aspirators are a good choice for smaller stocking densities, and they are much quieter than agitators.
The measurement of total dissolved gas pressure (TGP) can be a very important factor in aquaculture. When the total pressure of all gases in the water exceeds the ambient atmospheric pressure at the water's surface, supersaturation exists. The effect of excessive supersaturation on fish has been well documented and has caused massive fish kills.
Supersaturation can be caused by numerous man-made and natural sources including:
- Dam spillways that allow a high-volume discharge to plunge air deep into the receiving water.
- Water pump inlets that suck air, putting that air under high pressure in the piping (this is all too common).
- Naturally high levels of nitrogen that can be found in well water.
- Algae blooms that can cause supersaturated levels of oxygen.
- Temperature changes, which affect the saturation level. Simply heating the water can cause lethal supersaturation.
You will only know if your pump is working too hard by measuring the pump motor amp draw at the motor. If it is drawing more amps than the full load amps (FLA) rating on the motor label, there is a serious risk of burning out the motor. To reduce the amp draw, do one of three things: get full voltage to the motor by using heavier wiring, restrict the pump discharge or trim the impeller.
- Check the voltage at both the pump and the source. If it is less than 5V (or more) at the pump, a heavier gauge wire will reduce the voltage drop and, thus, the amp draw.
- Pump discharge can be restricted by using a valve, but there is a risk of someone opening the valve later. In place of a valve, use a permanent restriction, such as a reducer fitting in the discharge pipe.
- To trim the impeller, remove the pump case (volute) and very carefully trim 1/8" off the impeller diameter. In some cases, this can be done by very carefully holding a file to the impeller while the pump is on. Put the pump back together and test the amp draw again. Repeat the trimming procedure until the desired amp draw is achieved. Remember that trimming reduces the gpm.
To be absolutely certain that motors won't fail due to excessive amp draw, always check volts and amps at the motor while the pump is running at full load. In many places with 110-120V service, a voltage variation from 105 to 126 may occur. A motor's amp draw will be the highest when the voltage is the lowest, so check the full load amps when the facility's voltage is lowest and while all other equipment on that circuit is in use.
"My motor is running too hot to touch. Is this a problem?"
The old "Too-Hot-To-Touch" test no longer applies, due to the improved materials now used in motor manufacturing.
The best way to determine if a motor is operating properly is to check the ampere (amp) draw. Each motor has a nameplate listing full-load amps (FLA). If the tested amp draw does not exceed the nameplate rating, its internal or external cooling fan is working (if so equipped), and the ambient air temperature around the motor is below 104°F (40°C). The motor is probably not running hot, even though it is too hot to touch.