Industrial Utility Efficiency    

Republic Manufacturing Delivers Food Grade Blower & Air Knife Systems

Blower & Vacuum Best Practices interviewed Republic Manufacturing VP of Sales & Marketing, Rich Leong

Good morning. Thank you for taking the time. To start things off, tell me a little about Republic Manufacturing.

Good morning. Republic Manufacturing has been in business since 1962. We draw on our experience and expertise to provide value, from the initial consultation to post-implementation support. Most of our products and systems are designed, manufactured, and tested at our headquarters in Dallas, Texas.

The company was originally a sheet metal fabricator, and quickly grew to become one of the largest in North Texas by intentionally adapting to the changing market conditions - offering products and services attractive to large corporations. The company became the in-plant contractor for these large corporations. 

In 1991, Republic took on the distribution of air moving equipment and the building of package systems. After a number of years as a distributor and repair center of all types of air moving equipment, Republic designed and manufactured its own centrifugal blowers and air knife drying systems, offering distinct advantages over existing systems within the industry.

Currently, our product range includes blowers, vacuum pumps, compressors, air knives, motors and systems. While many products are available for immediate shipment, Republic’s in-house staff of engineers can design custom options to meet the specifications necessary, utilizing state-of-the-art software and machinery. 

Republic Blower Kit

The Republic Regenerative Blower Kit is installed along with the VFD and HEPA filter.

I know there is a lot of interest in your regenerative blowers. Could you walk me through some of the main points for these products?

Absolutely! First, our line of regenerative blowers, also known as side channel blowers, are for vacuum or compressed air applications in both horizontal and vertical mounted positions. Airflow capabilities range from 50 to 776 CFM, vacuum capabilities from 47" to 236" of water (1.7 psi to 8.53 psi) and pressure capabilities up from 47" to 307" of water (1.7 psi to 11.09). TEFC electric motors are cUL and CE certified and come in single and three-phase, dual frequency and multi-voltage versions for worldwide applications. Horsepower ranges from 1/2 to 40 HP (from 0.4 to 30kW).

Regenerative blowers have the impeller directly connected to the motor shaft, and the blowers come as a single-stage (one impeller), double-stage (two impellers) or triple-stage (three impellers). The bearings are outside the compression chamber, ensuring maximum operational reliability under high differential pressure.


What is the biggest takeaway when comparing compressed air systems to your centrifugal blowers?

Our line of centrifugal blowers can provide a steady volume of air to supply energy-efficient pressure or vacuum. Air enters at the center of a spinning impeller, and is divided between the impeller’s vanes. As the impeller turns, it accelerates the air outwards using centrifugal force. This high-velocity air is then diffused and slowed down in the surrounding blower housing to create pressure. The pressure, or vacuum, offers a wide range of volumetric flows possible due to the geometry of the open impeller.

Centrifugal air is energy-efficient and inexpensive, especially when compared to compressed air as an alternative. Centrifugal blowers use much less horsepower to create flow, thus using less energy than compressed air. When replacing compressed air, centrifugal blowers can offer a payback of months or even weeks.

We currently have 6 centrifugal blowers ranging in size, in order to best fit our customer’s performance requirements. Horsepower options available range from 3 hp to 75 hp. A max flow of 500 cfm and a pressure rating of 103 inches of water (3.72 psi) can be achieved, or 4,000 cfm and a pressure rating of 165 inches of water (5.96 psi) depending on the model size.


In regards to drying applications, what makes air knives so different from something such as compressed air nozzles? What is the advantage to the air knife?

An air knife is a pressurized air plenum with a uniform continuous gap allowing pressurized air to exit in a laminar flow pattern. The exiting air velocity creates an impact air velocity directly onto the surface of the product to shear away moisture or particulates without mechanical contact. This impact air velocity can range from a gentle breeze, to greater than 40,000 feet per minute.

We incorporate a teardrop design to minimize the internal turbulence of air entering the knife, while projecting it in a highly controlled manner through the discharge. As air enters the knife, the lack of sharp edges within the knife minimizes pressure loss and turbulence, while the air moves along the walls and is concentrated at the discharge.

Compressed air is highly inefficient and very expensive for drying applications. The horsepower required to create the flow necessary to achieve some success in such applications consumes an exorbitant amount of energy. For example, consider a compressor air system used to dry product on a 36" length span of conveyor. Running 24/7, this system will cost over $1,434 per week to operate. However, utilizing a Republic Air Knife System costs only a little over $104 per week to operate. Not only is the Republic Air Knife System more efficient to operate than the compressed air system, but the results will also be much more impressive with a drier and cleaner product.


Why would less air equate to a higher quality finished product? More is better, right?

No, more is not always better. This is easiest to understand when we look at the relationship between pressure, flow and velocity.

Pressure is the measure of force applied on an area. Common units for pressure are inches of water (inH2O), or pounds per square inch (PSI). If an application is expected to have a high backpressure, the blower must be rated to operate at that pressure. This will determine the type of blower you should use in your application.

Flow is a measure of air output in terms of volume per a unit of time, measured as cubic feet per minute (CFM). Flow is critical when the air needs to fill a space. In all of these cases you need to supply a given volumetric flow rate continuously filling and replenishing the application space.

Velocity refers to how fast the air is moving in distance per unit of time, measured as feet per second. One example to better illustrate this, is a water blow-off system using air knives. In a blow-off system, the air is required to make physical contact with the surface water with enough force to knock the water free. The force comes from the air impacting at high velocity. Forcing a volume of air through a constricted outlet increases the velocity. While the air is moving very quickly, it is not necessarily at a high volumetric flow rate.

Compressed air commonly found in shops utilizes electricity to store energy as static pressure up to 200 PSI. When it comes to applications requiring any amount of laminar airflow, dynamic pressure is critical, both for functionality and cost efficiency. Although shop air is ideal for blow off or situations requiring short, powerful bursts of air, smooth flow at moderate pressures is preferable for an even distribution of air. Centrifugal blowers have high efficiencies and produce high velocity streams at moderate pressures, ensuring the right balance of flow and pressure is consistently applied to the end product.


Can you think of a recent example to further demonstrate the advantages of blower technology, where one might be overlooking its benefits and using compressed air instead?

Air knives are no stranger to the food industry. Canners, bottlers and food packagers in general have been using air knife systems to dry their products prior to secondary operations or shipment for years. However, we were recently approached to use air knives for a less traditional operation.

A national food company worked with Republic to provide a solution to a problem they were experiencing in their bakery. The bakery makes honey buns, cinnamon rolls and apple fritters. The baked goods travel along on a conveyor moving at a speed of approximately 45 feet per minute. The delicious treats are glazed by icing, dripping like a waterfall as they move along the conveyor.

Initially, the bakery tied into their compressed air system utilizing modular 2 1/2” compressed air knives rated at 12 CFM at 100 PSI each. The width of the production line was 24” requiring 12 of these air knives. The initial trial system had a manual flow control on it to limit the amount of compressed air contacting the product. It was immediately apparent this approach was not going to work effectively, was hard to dial in and would draw too much air off of their compressor.

The problem was two-fold: the icing was uneven and too thick. The bakery wanted Republic to create a solution to level the icing and smooth it over the entire baked good evenly. The bakery had nine production lines throughout the nation, requiring attention.

Our solution was to design an air knife system to level the icing consistently across the baked good. Republic prefers to couple air knives with centrifugal or regenerative blowers. These blowers are energy-efficient and inexpensive, especially when compared to compressed air as an alternative. They require much less horsepower to create flow, thus using less energy than compressed air. 

Republic Air Knife

The air knife is installed and piped to the blower with a food grade hose, immediately following the application of the icing.

Given the application, do these air knives comply with USDA, NSF and 3-A standards?

In this particular application, the low-pressure air coming from the air knives was in direct contact with the food. As such, the air knives needed to be sanitary, with no chance of harboring bacteria that could be transferred onto the food. We suggested using the Republic Food Grade Air Knives for this application. These air knives are specifically designed to comply with all USDA, 3-A, and ANSI/NSF/3-A Standards for use in meat, poultry, dairy and general food processing. The air knives were connected to food grade hoses using all stainless steel fittings.

The KPHRC500 regenerative blower pressure kit was used. This blower at maximum performance provides 2.74 psi and 221 cfm, requiring 3.4 horsepower, 6.0 Amp. In this case, the blower utilizes a variable frequency drive to turn adjust the flow to reach the sweet spot needed to level the icing. The actual flow needed varies, so the VFD provides more control of the airflow to the line operator. A HEPA filter helped ensure contaminants did not get into the airstream.

The Republic Food Grade Air Knives allow the customer to easily clean them as needed, and allow the necessary food plant inspections to be straightforward. All components, including the adjustable air knife brackets, must be USDA, 3-A, and ANSI/NSF/3-A compliant. This means they need to be easily cleanable, have no edges or pits where food could become trapped, and must be made all of food grade stainless steel. 

Republic Conveyor

The icing glaze drips like a waterfall along the conveyor.

The bakery’s new food grade air knife system was installed and was an immediate success. The product quality increased as icing was spread more evenly and to the desired level; thus, reducing waste of the finished product. However, a couple of unintentional benefits came with the new system. The excess icing removed from the product could be recaptured and reused; consequently reducing waste. In addition, the conveyor was cleaner, reducing the time needed for the staff to clean at the end of each shift.


Thank you very much for your time.

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