Top 5 questions to ask before purchasing a fume hood blower

Certain products in a laboratory require a remote blower in order to operate. Choosing the correct blower makes a huge difference in how that piece of equipment performs. For example, if a motor with the wrong horsepower is chosen, it may not pull enough air through the fume hood to contain effectively, putting personnel at risk of breathing hazardous fumes &#; precisely what the fume hood was created to avoid!

For more information, please visit HAIYANG.

Answer these five questions to make your blower choice an easy one:

1. What blower construction materials do I need?

Three common materials for blowers are:

• Coated Steel
• Fiberglass
• PVC

If you aren&#;t sure what type you need, a good rule of thumb is to match it with the fume hood liner material.

If the chemicals used in your applications are non-corrosive, such as Butane, a coated steel blower can be used. For moderately corrosive chemicals, such as Acetone, use a fiberglass blower. And for very corrosive chemicals, usually strong acids such as Hydrofluoric Acid, use a PVC blower.

2. How many operating speeds does my blower need?

Two very different types of blowers cover a wide range of applications:

• Belt-Driven (single speed)
• Intelli-Sense Multi-Speed Blower (up to three speeds)

The Belt-Driven Blower is good for laboratories that operate constant volume fume hoods. It is offered in coated steel, fiberglass, and PVC construction, and many of these models are offered in Explosion Proof (EP) construction.

The Intelli-Sense Multi-Speed Blower is good for small laboratories that are looking for energy efficiency. The largest operating expense for many laboratories is exhausting tempered air out of the fume hood. This blower was designed to alleviate the burden of those high energy costs. It can be programmed to operate at up to three different speeds using a control box located on top of the fume hood, making this blower incredibly versatile. A night set-back mode can be set to allow the fume hood to operate at low speeds, using the least amount of air required, when the fume hood is not in use, while still maintaining negative pressure within the fume hood to ensure back draft prevention. This blower is not available in EP construction.

3. Where should my blower be mounted?

Typically blowers are mounted on the rooftop so that the exhaust stack can be oriented vertically, allowing harmful fumes to exhaust and travel with higher elevation trade winds, carrying the vapors away from the surrounding environment.

Consider what is being exhausted and how it is being exhausted. For example, you would not want to allow acid vapors to flow over a parking lot, possibly harming vehicles below. Nor would you want the vapors to exhaust out of the side of the building if there is an air conditioning unit a short distance away.

Plan carefully to ensure that vapors are exhausted properly.

4. What should I consider when planning my ductwork?

The material and design of your ductwork are key to providing a safe exhaust system. The material of the ducting must be compatible with local fire codes, and also compatible with the chemicals your ductwork will be exposed to. The two most common types of duct are Type 1 PVC (great for use with corrosives) and 316 Stainless Steel (great for use with solvents). If you have both solvents and corrosives, you may have to make concessions based on the most aggressive chemicals used; however, Type 1 PVC is very versatile.

Accessories that may be added to your system include a damper to control airflow, flexible duct to reduce vibration, and a Zero Pressure Weathercap to exhaust the air vertically without stoppage. These are options that help the fume hood and blower operate at optimum levels.

With some applications, such as Acid Digestion or Perchloric Acid, ductwork may require a wash-down system in order to neutralize acid remnants. This will require a drain system connected to the hood and blower so that wash water can drain properly. Another consideration with these wash-down systems is to plan to run ductwork at an angle, not at a 0-degree horizontal, to allow water to easily wash down the system and drain into the fume hood&#;s drain trough.

5. How do I choose the right size of blower?

The relationships between static pressure, volumetric flow, and the RPM at which any blower can operate can be expressed by a blower curve chart. You could simply choose to leave the blower sizing up to a fume hood expert, but here is a basic run-down:

All fume hoods and ductwork systems create static pressure (or resistance), typically measured on an Inches of Water Gauge (in. w.g.) scale. The static pressure from all components is taken into account to ensure the blower can overcome the static pressure. The factors of a duct run include:

• Duct diameter
• Duct length
• Number of elbows and degree of bend (e.g. Two 90 degree elbows)

The velocity the fume hood is going to be operating at, and the corresponding sash height are also required pieces of information in order to size the blower most accurately.

After all of the information is compiled, all of the static pressure of the components can be added together and compared with the volumetric flow that matches the velocity. Then we can tell what blower will work with your fume hood.

Here is an example of a blower curve:

If your position is not within an available blower curve, a damper can fine-tune your operating position. The damper will create more static pressure, and lessen the volumetric flow of air (CFM).

Those are the top 5 questions to ask before purchasing a blower for a fume hood. For help answering any of these questions or for other information on fume hoods and blowers, you can contact me online, or call the Labconco at 1-816-333-.

Let Scout&#; lead you to the right Labconco enclosure for your application.

My FAQs

GENERAL FANS

What does the term &#;fan arrangement&#; mean?
Fan Arrangement refers to the way the fan is set up for operation.  The NYB website new user support page has a list of arrangements with pictures.  In addition to arrangement, rotation and discharge are needed to describe the fan.

How is rotation specified?
View the fan from the drive side.  Rotation (clockwise or counterclockwise) is specified from this point of reference.  The fan will have a rotation arrow on it when it ships from the factory.  More explanation is available on the NYB website new user support page.

How is discharge specified?
The term used to describe the orientation specifies the angle of the air blast from the fan discharge.  The terms are up blast and down blast;  top or bottom horizontal blast; and angular up blast and angular down blast.  The angular versions often require the angle to be specified. More information (with pictures) is available on the NYB website new user support page.

What is the best material choice from my fan?
A material choice should be made that does not limit fan operation at the maximum operating speed and temperature.  The material must also be compatible with the chemistry of the flue gas being handled.  Fan material should meet or exceed the properties of the ductwork associated with the fan system.  It is better to specify the minimum material properties required and allow NYB to recommend any upgrades needed for a more successful installation.

How can I get a drawing or performance curve for my fan?
The New York Blower website has a tool called Drawings on Demand that allows people to input the NYB shop number and get a drawing of an existing fan.  The shop number is available on the fan nameplate or order acknowledgment.   When a fan is selected on the NYB webpage, using Fan to Size Online&#; (F2SO), a fan performance curve and preliminary drawing may be obtained for the fan chosen in the selection program.  Instruction may be found on the final selection page.

FAN PERFORMANCE

Why do I need a safety factor on fan performance?
The main reason to add a safety factor to fan performance (safety factor is often called test block) is to ensure good process control at the maximum expected operating condition.  Ten percent added to fan volume and 20 percent added to fan pressure are customary.

How can I increase my fan&#;s capacity?
The only way to increase fan capacity is to increase fan speed or size.  The equations known as The Fan Laws govern how a fan behaves at other speeds and sizes.  A copy of The Basic Fan Laws  is available on the NYB website.  Increasing fan performance will also increase fan power, making sure there is sufficient motor capacity before making changes. 

What is a fan performance curve?
A fan performance curve is a graphic representation of the results of a series of capacity tests on a specific fan.  It defines the volume range and what pressure is produced at each volume.  It also shows a graphic representation of the power required for each volume and pressure.  The curve will include fan speed and inlet density and the effect of any accessories specified for the fan. 

Contact us to discuss your requirements of Custom Blower Fan. Our experienced sales team can help you identify the options that best suit your needs.

What is a system resistance curve?
A system resistance curve is a graphic representation of a series of operating points that define the pressure a system requires to operate properly over its volume range.

FANS AND SYSTEMS

How do fans and systems interact?
If you overlay fan performance and system resistance curves, their intersection defines the point of expected fan operation.

What are the different types of systems?
There are three basic system types:  The most common is the parabolic system.  In the parabolic system, pressure increases with the square of increasing volume.  This means the pressure increases by a factor of four when the volume doubles.  Hybrid systems are the second most often seen.  In hybrid systems, there is a fixed pressure drop plus a parabolic pressure curve.  This is seen in systems with pressure-controlled scrubbers or baghouses that automatically clean to a specified pressure drop.  The last type of system is the constant volume system.  The volume remains the same in these systems, but the pressure increases with time as the system becomes plugged. This type of systems is found in cement kiln ID fans with preheaters and papermill recovery boiler ID fans. 

FAN MECHANICS- BEARINGS

What types of bearings are available?
Most fans employ ball bearings or spherical roller bearings, or a combination of the two.  Many of the standard choices are influenced by fan size and drive type.   Many specialty bearings are available as options.  Feel free to make your preferences known. 

What are the best bearings for my fan?
The bearings that come with your fan are specifically designed for it.  There are other choices available if you have a specific preference for a type of bearing housing or a specific lubrication protocol.   Feel free to make your preferences known. 

Are bigger bearings better?
Generally not.  Most fan bearings are lightly loaded. Ball and roller bearings tend to skid through the load zone at very low loads instead of rolling. This can lead to high temperature operation and potential failure.

When do water-cooled sleeve bearings make sense?
Water-cooled sleeve bearings make sense for high speed or high temperature applications and very large fans. 

What is a tunnel bearing and how can it help?
A tunnel bearing (two-bearing housing) is very useful for high speed service in small fans.  The bearings are located close together in a single housing, which facilitates alignment, reduces shaft size and increases bearing loads.  The tunnel bearing also allows the use of some specialty bearings not available in pillow block configurations.

LUBRICATION

What is the best bearing lubricant?
Most fan bearings are lubricated with a lithium-based, NLGI grade 2 grease.  There are also mineral oils that can provide slightly higher speeds, but these require special bearing housing choices.  The temperature limit for these lubricants is about 160 F.  There are high temperature (synthetic) greases and oils that can be employed when higher operating temperatures are expected.

When do I need a circulating oil system?
Circulating oil systems are used when expected bearing operating temperatures are too high for most lubricants.  A lubrication system provides auxiliary cooling and storage capacity that can make a  positive difference in bearing operation.  Lubrication units are also good choices when there is no cooling water available for sleeve bearings.  Most lubrication sets use pressurized oil feed and gravity return.  They also feature instrumentation that can advise when the oil temperature is too high or flow is interrupted. 

Lubrication Aids
Several automated grease and oil lubrication systems are designed to keep bearings lubricated for fans in locations that are difficult to reach. These can be inexpensive solutions to problems.  They also help control random lubrication patterns. 

TYPES OF FAN DRIVES  - V-Belt Drives
V-Belt drives are adjustable speed drives where the speeds are set based on the motor speed and the diameter ratio of the sheaves on the fan and motor.  The sheaves are connected with a set of matched belts with v-shaped cross sections, so if looking to change the speed, the sheave system must also be changed. These drives are generally used on fans with motor sizes below 200 hp,  Most fans designed for v-belt drives use spherical roller bearings to handle the loads from the belts. 

Direct Drives
Direct drive fans operate at motor speeds and are directly connected to the motor with a flexible coupling.   Many of these fans need specialty bearing on the low load side because its low radial load is susceptible to skidding through the loads zone.  Some sort of damper control systems are usually used to control the process.

Variable Speed Drives
Variable speed drives are set up like direct drives, but use a specialty electrical system to vary fan speed in order to control the process.  This is the most efficient form of fan control. 

FAN ACCESSORIES

What are the different types of Dampers?
There are two optimum locations for fan dampers.  These are at the fan inlet and outlet.  External inlet dampers and inlet box dampers control the fan based on pre-spinning the inlet air to reduce fan pressure and power consumption.  Most of these dampers have blades that operate in parallel with each other.  External inlet damper blades are arranged in a radial fashion at the fan inlet duct. Outlet dampers bolt to the fan outlet to add pressure to the system to adjust flow.  The blades may be parallel or opposed, with opposed (counter-rotating) blades providing the best control.  Outlet dampers adjust the system to the fan.

How do I choose the right damper?
Inlet damper control provides the best operating efficiency for direct drive fans.  If the process gas is sticky or corrosive, an inlet box and inlet box damper may be the best choice because all the damper bearings are outside the airstream.   Outlet dampers are customary for small fans because they are not expensive and their total power consumption is small. 

Do I need a damper actuator?
It is possible to manually set a damper and lock it in position if the process does not require adjustment.  If the intention is to control the fan and system automatically, an actuator with a positioner is necessary.  If the desire is to isolate the systems remotely, an on-off damper actuator is a reasonable choice. 

Do I need flex joints on my fan?
In general, flex joints are a good idea.  They minimize vibration transmission between the fan and its ductwork and facilitate fan installation and duct alignment.  In very low pressure or dirty gas systems, flow liners are also a good choice.  If the fan inlet or outlet is not connected to a duct, flex joints are not required at that point.

What are the different types of shaft seals?
Shaft seals keep the fan airstream inside and help isolate it from the atmosphere.  They are not required but are generally employed on larger fans.  Ceramic felt and Teflon shaft closures are the least expensive options.   There are several version of labyrinth seals which are available, including mechanical seals which feature a single or double carbon rings.  The double carbon ring seal may be arranged for a purge between rings to ensure there is no migration between the atmosphere and airstream. 

What is the purpose of an Inlet box?
An inlet box allows the air or flue gas to enter the fan from the top or side (perpendicular to the shaft) rather than from an open inlet (parallel to the shaft.)  This can help with fans that have flow coming from above.  Fans that have a bearing on each side of the rotor need an inlet box to keep the bearings out of the gas stream.  Corrosive Gas streams may need an inlet box to keep inlet box damper bearings out of the airstream. 

What instruments can I put on a fan?
There are many options.  Damper position feedback, bearing temperature and bearing vibration are the most commonly used.  Shaft speed transmitters are also sometimes used.  There are also flow and pressure transducers that can provide information about fan capacity, pressure and power. 

Do I need instruments on my fan?
Fans in critical service need feedback to the operators at the control center.  Critical service means that if the fan stops, the process stops, as well.

If your question is still not answered, feel free to reach out to us at 800.208. for assistance.

If you want to learn more, please visit our website Ceiling Fan Wholesale.