Aeration System Operation

General Description
Culver Lake experienced poor clarity in the latter 20th century due to algae densities that interfered with recreational activities. In the early 1990’s, a layer aeration system was installed to prevent recirculation of internal phosphate, oxygenate the hypolimnium and to provide improved habitat for fish. The aeration system is composed of an air supply system, interconnecting air lines and the in-lake aerators consisting of 1-hypoliminetic unit (Hypo), 2-layer aeration units (L1, L2) and 1- continuous mixing diffuser (CMD).

Air Compressor Description
There are two compressors, 10-30 and 10-40. They are Sulair screw driven compressors. The unit closest to the door is the 30 HP, the other being a 40 HP unit. Their rated capacity at standard conditions is 140 CFM and 160 CFM respectively. The rated discharge pressure is approximately 110 PSIG. These units are air cooled and require about 3700 CFM of cooling air from the Club House basement. Ventilation of this area must be maintained while the units are in service by making sure enough windows are open at the snack counter end of the basement and along the front.

Starting One Compressor
After a power loss, both compressors will be shutdown. Do not start any compressors until all supply valves located near the floor are closed and their associated regulators are closed by unscrewing the stems. Start the compressor. The pressure reducing valves and the flow meters will immediately pressurize and the compressor will begin to cycle. Both Layer and Hypo. units are suspended from the bottom and require the slow, gradual introduction of air. See explanation under “Starting a layer Aerator”

Starting Second Compressor
Before starting a compressor while the aeration system is functioning (other compressor in service), the aeration manifold supply pressure must be near 105 – 110 PSIG. This is accomplished by slowly unscrewing aeration pressure regulators on all aerators (this reduces air flow) until all airflows are sufficiently reduced to allow the manifold supply pressure to be in the above range. Maintain enough air flow so that the submerged aerators continue bubbling action and do not sink. Make sure the compressor discharge valve (near floor behind the unit) is fully open. Start the compressor. Begin to slowly increase aeration flow by screwing in on the regulators. Bring them back up gradually until all flows are set to the desired level. Do not exceed 100 CFM on the layer units.

Starting a Layer Aerator

The layer aeration units are in a resting position when they are not supplied with air. If air is applied suddenly, the chains securing the aerator to its anchors experience shock loading that in the past have sustained anchor attachment failures including main anchor bracket failure. To avoid this from happening, air to the aerator must be introduced very slowly at first. This will gradually bring the aerator up to its operating elevation and place less stress on the anchoring system. Below is the recommended procedure to start an aeration unit.

Both shut-off valves on the aerator (top and bottom) should be initially closed. Verify that the air regulator is backed off (unscrewed). One or both compressors are to be started (described above). Next, gradually open the top aerator plug valve to pressurize the air regulator. Open the bottom aerator valve gradually. If you hear air flow when opening the bottom valve, close this valve and unscrew the regulator to close the regulator and prevent air flow to the aerator. Repeat opening the bottom valve. If air flow is again heard, this could indicate that the pressure regulator is faulty. In this case, air flow to the layer unit (or any other device with a similar regulator probem,) will need to be controlled by the outlet valve near the floor.

Once both inlet and outlet valves are open and there is no air flow to the aerator, begin to introduce air to the aerator by gradually opening (screwing in) on the air pressure regulator. The flowrator will bounce off zero and you will hear some flow. Once bubbles are visible on the surface, continue to gradually increase air flow to the aerator until the desired air flow is achieved. Total time to do this should take approximately 10-15 minutes.

Single Air Compressor Operation
Occasionally single air compressor operation occurs when one unit is “down” for maintenance or when the aeration air demand does not require two compressor operations. Single compressor operation will save power. We determined that wide open compressor operation (maximum air flow) occurs when the aerator manifold pressure is about 95-100 PSIGand the compressor is not cycling (loading and unloading). If aerator air flow demand is less than supply capability, the air compressor inlet control valve will begin to close when the discharge line pressure is at 110 PSIG and above. The discharge line pressure will fall when the the compressor inlet control valve is wide open under a condition where airflow demand exceeds compressor capacity. If one compressor is operating under this condition, it might be advisable to start the second compressor.

High Temperature Operation Difficulties
The compressors are protected by a thermal protection switch located under the compressor in the oil line. This will prevent damage to the machine and undue over-heating the oil. The thermal switch, located at the discharge of the compressor, will trip the 480V breaker at a temperature of 240F. Thermal gauges that register sump temperature are close in temperature but notably inaccurate. Usually, they read higher then the actual temperature. A portable infrared thermometer is more accurate. The lubricant used in these machines begins to degrade when oil temperature exceeds 200F. For every 10F above 200F, the oil service life is halved. Check for adequate oil level at this time. You must shutdown the compressor to see oil in the sight glass. Unless a leak develops, it is rarely necessary to have add oil. We have found that cleaning the coolers (oil and air) and making sure there is adequate air circulation is the best way to reduce oil temperature. Once or twice during the season, if high oil temperature operation is observed (> 210 F), the compressor should be shut down and the coolers should be cleaned with a degreaser and the compressed air wand. When annual maintenance is performed, the coolers should be removed and power washed. Another potential source of high temperature is the thermal by-pass valve leaking back to the supply side of the cooler. These valves were removed and the lines plugged in July 2006 as a trial to circumvent this problem. (Note the 30 HP bypass valve was reinstalled in August 2017) While the unit is shutdown, before any work is started, make sure the compressor discharge valve is closed and that no person accidentally pushes any buttons. For extended maintenance or when ever the control panel door is opened, it is advisable to open the 480V switch for the compressor. Hang a note on the switch.

Oil Separator
The oil separator, a white box mounted near the wall, receives condensate from the after cooler. The water is piped to the separator via PVC piping along the floor to the separator box then to the outside after passing through the oil absorbent disc. This disc must be replaced on a weekly basis or whenever it becomes oil soaked. Occasionally check the 55 gallon drum oil level. Have Airmatic or an authorized waste oil vendor dispose of the oil when the drum is full. If air is passing the water traps and entering the separator, this indicates the float valves need to be replaced.

Routine Checks
A periodic check of the equipment can prevent potential problems down the road. A log of pressures, temperatures and flows is helpful. Although the compressors are designed to shutdown automatically if there is over pressure, high current and high temperature, it is advisable to check the compressor room for leaks, adequate oil level and unusual noise. The aerator flows should be monitored and adjusted as directed by Bob Kortmann. If there is a need for a service call, the Normanoch Secretary and or the Director who is assigned responsibility for the aeration system should be called. A “work to do” list should be kept so that service can be arranged. Log any observations for future reference.

Paul Sutphen
Revised Sept. 2017