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| My plant needs more air. Can I speed up my Sutorbilt 4M blower? I have a 7.5 hp motor. |
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| Possibly, but we need to know where the blower is operating within its design limits at this point in time. All of the Sutorbilt, Roots and M-D blowers commonly used in wastewater treatment operate within specific RPM and pressure ranges. With each revolution, a positive displacement blower takes in a given volume of air at a given altitude. The faster the blower turns the more air is moved. We can operate a 4M blower at 2500 RPM with a 3 hp motor or a 15 hp motor, and it will produce the same amount of air at atmospheric pressure. The actual amount of horsepower we need depends on the amount of backpressure at the blower discharge. Several conditions create backpressure in a blower system, some of which include: |
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- Each 2.31" of water over your diffusers creates 1 psi of backpressure.
- A rule of thumb is to add 0.5 psi backpressure if you have inlet and outlet silencers.
- The size of your air piping and the number of tees and elbows can make a difference if your pipe is small in relation to the volume of air being moved.
- Diffuser membranes may require 0.3 psi to open and function properly.
- Not having enough diffusers to utilize excess air can cause backpressure to rise.
- Dirty air filters can add load to a blower.
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| Total backpressure will determine how big a motor is required for operating a blower at a given RPM (CFM output). There is no substitute for having a good pressure gauge in your blower discharge line, which takes much of the guesswork out of trying to calculate total pressure losses. Before you call us, we strongly recommend that you install a gauge in your discharge line to measure actual system pressure. Additionally, using an ammeter to measure actual motor amp draw vs. maximum motor nameplate rating will let you know how much reserve capacity you have with your existing motor. |
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| We also need to know your existing sheave sizes so that we can determine exactly how fast the blower is turning in relation to its specified operating range. As a general rule we like to limit maximum blower rpm to 80% of maximum rated capacity if they are running long hours on a daily basis. |
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| Weighing all factors we can provide a reasonable estimate of how much extra capacity we can realize by increasing blower rpm with a sheave change or upgrading motor horsepower. |
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