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Low-Speed Aerators

NSA Series Aerators

Surface mechanical aerators fall into two categories: high-speed aerators and low-speed aerators.
  • High-speed aerators use an electric motor to directly drive a pump impeller which pumps water up and sprays it out horizontally. While this design is inexpensive, it has low oxygen transfer efficiency because the pump impeller turns at higher-than-optimum aeration speed and wastes significant amounts of energy in moving water faster than needed.
  • Low-speed aerators are higher in efficiency than high-speed aerators because the aeration rotor operates near the optimum aeration speed. However, low-speed aerators are more expensive because they must use a gearbox to reduce motor speed to turn a large diameter aeration rotor. In addition, the gearbox is typically mounted a few feet above the rotor and requires a long and large shaft with substantial supporting bearings.

Before the DBS NSA was introduced to the market, a user had to weigh the benefits of long-term power
savings of the low-speed, high-efficiency aerator against the initial capital savings of the high-speed, low-efficiency aerator.

Now the DBS NSA low-speed aerator provides the best features of low-speed and high-speed aerators: HIGH-EFFICIENCY AT A LOW COST. The DBS NSA low-speed aerator is cost competitive with high-speed aerators and offers the efficiency and power savings of the low-speed aerator. The power savings can be significant, in the range of 20% or more.

NSA Technical Features

GEARBOX
The NSA aerator uses a planetary gearbox to drive the aerator rotor. This type gearbox is mass-produced and offers an excellent power/cost ratio. The gearbox is mounted directly in the aerator rotor. This unique arrangement provides a number of benefits:

  1. The gearbox operates partially submerged. Water flowing through the impeller cools the gearbox to near ambient temperature. The low operating temperature allows long oil life.
  2. The gearbox directly drives the rotor so there are no driveshaft or inherent driveshaft vibration problems common in traditional low-speed aerators.
  3. The gearbox and rotor assembly is attached to the electric motor by a "torque tube." This tube can flex laterally to dampen shocks caused by wave impact on the rotor.

ROTOR
A traditional high-efficiency back-curved radial blade rotor or a DBS advanced flexible radial blade rotor is available on the NSA. See details on the rotor page.

OIL CHANGE
With the oil change kit provided, oil change can be completed in about 15 minutes depending on the size of the aerator gearbox.

SUBMERGENCE ADJUSTMENT FOR FLOATING AERATOR

The exclusive "Rock and Adjust" joint (RA joint) permits easy submergence adjustment without using a crane.

OPTIONAL ELEVATION ADJUSTMENT STAND FOR BRIDGE-MOUNTED AERATOR

NSA bridge-mounted aerators are available with an optional elevation adjustment stand, which greatly simplifies installation.

Floating NSA Aerator

    Model
Horse-power
Service Factor1
O2/Hour2
ØA
1800 rpm input
ØA
1500 rpm input
B
ØC
Weight
hp
kw
60hz
50hz
lb
kg
in
mm
in
mm
in
mm
in
mm
lb
kg
NSA1-08 7.5 5.6 6.50 5.40 26 12 42 1,067 46 1,168 98 2,489 38 965 1,047 475
NSA1-10 10 7.5 4.90 4.06 35 16 46 1,168 49 1,245 98 2,489 38 965 1,112 504
NSA1-15 15 11 3.25 2.70 53 24 49 1,245 52 1,321 98 2,489 38 965 1,203 546
NSA1-20 20 15 2.44 2.03 70 32 52 1,321 57 1,448 98 2,489 38 965 1,253 568
NSA2-25 25 19 3.84 3.20 88 40 68 1,727 74 1,880 130 3,302 40 1,016 1,960 889
NSA2-30 30 22 3.20 2.67 105 48 72 1,829 78 1,981 130 3,302 40 1,016 2,100 952
NSA2-40 40 30 2.40 2.00 140 63 76 1,930 83 2,108 169 4,280 46 1,168 2,558 1,160
NSA2-50 50 37 1.92 NR 175 79 80 2,032 NR NR 169 4,280 46 1,168 2,682 1,216
NSA3-50 50 37 3.07 2.56 175 79 86 2,184 96 2,438 169 4,280 46 1,168 3,046 1,381
NSA3-60 60 45 2.56 2.13 210 95 88 2,235 99 2,515 169 4,280 46 1,168 3,264 1,480
NSA3-75 75 56 2.05 NR 263 119 91 2,311 102 2,591 169 4,280 46 1,168 3,500 1,587
NSA4-75 75 56 4.78 3.96 263 119 116 2,946 122 3,099 196 4,978 60 1,524 6,520 2,957
NSA4-100 100 75 3.59 2.97 350 159 122 3,099 130 3,302 196 4,978 60 1,524 6,847 3,105
NSA4-125 125 93 2.87 2.38 438 198 130 3,302 136 3,454 196 4,978 60 1,524 7,200 3,265
NSA4-150 150 112 2.39 1.98 525 238 136 3,454 144 3,658 196 4,978 60 1,524 7,700 3,492
NSA4-200 200 149 1.80 NR 700 317 144 3,658 NR NR 196 4,978 60 1,524 8,400 3,810
1 Minimum recommended service factor is 1.8. At 1.0 service factor, gears have a theoretical infinite life.
2 Under standard conditions. Performance under field conditions may vary.
NR: Not recommended.NSA4-200 200 149 1.80 NR 700 317 118 2,997 127 3,226 196 4,978 60 1,524 8,400 3,810


Bridge-Mounted NSA Aerator

Item
Description
1
 Mounting plate
2
 Electric motor
3
 Spool
4
 Rotor
5
 Gearbox

    Model
Horse-power
Service Factor1
O2/Hour2
ØA
1800 rpm input
ØA
1500 rpm input
B3
C
D
Weight
hp
kw
60hz
50hz
lb
kg
in
mm
in
mm
in
mm
in
mm
 in mm
lb
kg
NSA1-08B 7.5 5.6 6.50 5.40 26 12 42 1,067 46 1,168 13 330 20 508 1 25 659 299
NSA1-10B 10 7.5 4.90 4.06 35 16 46 1,168 49 1,245 13 330 20 508 1 25 724 328
NSA1-15B 15 11 3.25 2.70 53 24 49 1,245 52 1,321 13 330 20 508 1.25 30 815 370
NSA1-20B 20 15 2.44 2.03 70 32 52 1,321 57 1,448 13 330 20 508 1.25 30 865 392
NSA2-25B 25 19 3.84 3.20 88 40 68 1,727 74 1,880 19 483 30 762 1.5 40 1,515 687
NSA2-30B 30 22 3.20 2.67 105 48 72 1,829 78 1,981 19 483 30 762 1.5 40 1,655 751
NSA2-40B 40 30 2.40 2.00 140 63 76 1,930 83 2,108 19 483 30 762 2 50 2,113 958
NSA2-50B 50 37 1.92 NR 175 79 80 2,032 NR NR 19 483 30 762 2 50 2,237 1,015
NSA3-50B 50 37 3.07 2.56 175 79 86 2,184 96 2,438 19 483 30 762 2 50 2,237 1,015
NSA3-60B 60 45 2.56 2.13 210 95 88 2,235 99 2,515 19 483 30 762 2.5 60 2,605 1,181
NSA3-75B 75 56 2.05 NR 263 119 91 2,311 102 2,591 19 483 30 762 2.5 60 2,742 1,244
NSA4-75B 75 56 4.78 3.96 263 119 116 2,946 122 3,099 28 711 40 1,016 3 80 4,804 2,179
NSA4-100B 100 75 3.59 2.97 350 159 122 3,099 130 3,302 28 711 40 1,016 3 80 5,131 2,327
NSA4-125B 125 93 2.87 2.38 438 198 130 3,302 136 3,454 28 711 40 1,016 3 80 5,484 2,487
NSA4-150B 150 112 2.39 1.98 525 238 136 3,454 144 3,658 28 711 40 1,016 4 100 6,148 2,788
NSA5-200B 200 149 2.70 2.25 700 317 144 3,658 165 4,191 28 711 40 1,016 4 100 6,988 3,169
NSA5-250B 250 186 2.16 1.80 875 397 156 3,962 177 4,496 28 711 40 1,016 4 100 7,683 3,484
NSA5-300B 300 224 1.80 NR 1,050 476 165 4,191 NR NR 28 711 40 1,016 4 100 7,950 3,605
1 Minimum recommended service factor is 1.8. At 1.0 service factor, gears have theoretical infinite life.
2 Under standard conditions. Performance under field conditions may vary.
3 Bridge platform must have a hole larger than B dimension for installation.
NR: Not recommended.

NSA Aerator Lubrication

An oil change kit is provided with each NSA aerator. The kit includes oil pump, fittings, and the exact amount of synthetic oil for initial startup. Both removal and addition of oil is by pumping, similar to the oil change of a marine engine. The required oil volumes are as follows:
Model Oil Capacity
gallon liter
NSA1
NSA2
NSA3
NSA4
NSA5		 0.75
2.0
3.25
8
10		 2.8
7.6
12.3
30.2
37.8
Recommended oil change interval is every six months. Turn off the power before performing the oil change.


DBS High-Efficiency Aeration Rotors
Standard backward
curved blade rotor
DBS High-Efficiency Aeration Rotors
The aeration rotor is the device that does the work of pumping, mixing and aerating. Aeration rotors are commonly made of steel and have straight radial blades. "Top of the line" high efficiency rotors have backward curved blades that provide improved efficiency and a wider operating speed range. DBS offers two types of aeration rotors.

DBS Standard Aeration Rotor
The standard DBS aeration rotor uses fixed backward curved blades. These rotors are typically made from stainless steel and offer high pumping and aeration efficiency.

DBS Flexible Blade Rotor
This patented NSA aeration rotor uses cantilevered flexible radial blades. These blades are free to bend so when pumping loads are applied to the blades, they bend backward, assuming the desired curved profile at full speed and load. At less than full speed, the blades spring back and take on a more radial configuration. This change in profile is very important because the aeration rotor keeps the desired exit velocity of the water nearly constant over a wide speed range. This means that the aeration efficiency of the rotor is nearly constant over the operating speed range. The flexible blade aeration rotor is specifically beneficial in applications where a VFD controls the aerator to regulate oxygen levels in a lagoon or oxidation ditch.

From a rotor speed of 50% to 100%, the exit velocity "R" is nearly constant. As rotor speed increases from 50% to 100% the additional energy is put into pumping greater volumes of water, not into higher water velocity.

Installation

Floating NSA1 as shipped

Basic Installation and Erection Procedures

The NSA is shipped in modules and is easy to assemble in the field. It typically requires a crane and crew of two to four people, depending on size of the machine.

  1. Assemble the rotor.
  2. Position the drive mechanism on the rotor. Bolt the rotor to the drive mechanism.
  3. NSA1: bolt the arms to the center mechanism.
    NSA 2, 3 and 4: bolt the arms to the top lugs of the center mechanism.
  4. Install the lower link bars between the center mechanism and the arms.
  5. Bolt the float assemblies to the arms.
  6. Fill the gearbox with oil.
  7. Use the crane to place the NSA in the water. Hook up mooring and electric cable to the machine.
  8. Adjust floats for desired rotor immersion.

Floating NSA Aerator Mooring Options

General
Selection of a mooring arrangement is dependent on water level fluctuation, extreme weather, and the design of the aeration basin. Use the mooring accessories listed in the table below as minimum for normal applications. Applicable local, state and federal guidelines must be adhered to.

The key to mooring success is careful planning and engineering based on water level fluctuation, mooring distance, and weather conditions. Avoid any possibility of tangling the mooring cable in the rotor or rubbing and wearing damage to the cable.

Make sure the entire length of the mooring cable is visible. Use floats when the mooring cable is long. Three-cable mooring is preferred if the water level is stable. Two-cable mooring can better compensate for water level fluctuation, but the aerator tends to drift sideways when the mooring cables are long.

SHORE MOORING
A two-cable mooring system can be used when the aerator is close to shore. The minimum cable length is 10 feet (3 meters) plus the amount of water fluctuation squared.

POST MOORING
In large lagoons where distances prohibit mooring to shore, posts can be used for anchoring. The cable length can be calculated the same way as for shore moorings.

BOTTOM MOORING
If the mooring point is at the bottom of the basin, the mooring point and the trace of the mooring line must be flagged with floats. The minimum cable length is four times the basin depth plus the water fluctuation squared.

DIRECT POST MOORING
The arms of a floating aerator can be directly tied to the mooring posts. When this method is used, a sliding mechanism must be in place to compensate for water level changes.

Components
Mooring cable
Thimble/Cable clip
Shackle
Anchoring point
Specification
High Flex 304 stainless steel, 7 x 19 cable
Stainless steel
Stainless steel
Picture
Key variables
D
Breaking strength
S
Work load limit
Test force

in mm lbs N
in mm lbs N lbs N
Minimum Recommendation NSA1 0.19 5 3,700 16,444 For proper cable size 0.38 10 2,000 8,889 1,300 5,778
NSA2 0.25 7 6,400 28,444 0.38 10 2,000 8,889 4,000 17,778
NSA3 0.25 7 6,400 28,444 0.50 13 4,000 17,778 4,500 20,000
NSA4-75 to 125 0.31 8 9,000 40,000 0.63 16 6,000 26,667 10,000 44,444
NSA4-150 and up 0.38 10 12,000 53,333 0.75 20 8,500 37,778 14,000 62,222

Floating NSA Aerator Mooring Options

DBS "RaceTrack" Oxidation Ditch

Oxidation ditches are proven efficient and economical wastewater treatment systems that have been used for decades.   DBS Manufacturing Inc., has taken this proven technology and improved upon it by incorporating the new DBS Aerator technology.

DBS Racetrack Oxidation Ditches are powered with the patented NSA low-speed aerator.  These aerators provide high efficiency and long life at a substantially lower cost than competitive aerators.  And, maintenance parts are available worldwide. DBS Racetrack Oxidation Ditch aerators are equipped with the DBS stainless steel high efficiency backward curved aeration rotor.  This rotor maximizes pumping rate for superior mixing and aeration.

DBS Racetrack Oxidation Ditch offer guaranteed performance, not only for the mechanical equipment, but also for the biological process and ditch velocity.