How to Select a Filter for your Blower

 

Can you quote me the filter for a 56 URAI blower?  What filter goes on a 616 RAM blower?

A question we get frequently is which filter goes with a specific blower model.  Unfortunately it’s not so simple, but fortunately there are lots of right answers to that question!

 

First, let’s talk about why’s it’s not an easy answer.

In a pressure or vacuum system, air filters are placed before the inlet of the blower to filter out any particles and debris that could be sucked into the blower.  The purpose of the filter is to ensure an unrestricted flow of clean air to feed the blower.  Unrestricted is the key word.  The filter will have a maximum level of airflow it can handle before the pressure drop starts to increase.  The additional pressure drop will increase the load on the blower which will increase the temperature rise which will reduce performance and may eventually fail the blower.

Positive displacement blowers can move a LOT of air, so the main goal when selecting a filter is to pick one that can handle the amount of air that is moving through the blower system.

There are a number of manufacturers who make filters for blower systems.  Between the different manufacturers there are hundreds of different options for filters that have different connection sizes, filter element sizes, filter element materials, and maximum flow capacities. Which one is right for your system will depend on your application, how you plan to connect it to the blower, and what your maximum flow could be.

Selecting a filter for your blower

  I’m replacing an existing filter      I am installing a new blower system

Replacing an Existing Filter Element

If you just need a new filter element for your existing filter, then you don’t need to worry about going through a selection process to pick a model that will work for your system.  That part was done when your system was installed, so all we need to do now is identify your current filter.

The air filter typically consists of a metal housing with a replaceable filter element inside.  The filter housing is usually cylindrical with a removable lid at one end.  First take a look all the way around the filter housing.  These will often have a nameplate attached that shows the model of the filter and/or the element inside.

If you can’t find identifying information on the outside of the filter housing, open it up and take a look at the replaceable element inside.  These may have a model number marked at one end.

If there are no identifying marks or ID plates on either the housing or the element, it would be worth checking to see if you have a manual or spec sheet that came with the original system.

Once you have exhausted all other options, it’s time to pull out a camera and measuring tape.  Photos of the filter housing and element may help provide clues to which manufacturer made the filter,  which filter series it belongs to, and possibly which filter media the element contains.  Measurements of the filter element—including the length, outer diameter, and inner diameter—as well as the connection size where the housing is attached to the blower or inlet pipe can also help narrow down the possible options. View available blower filter assemblies and filter elements.

Inlet filters are an important component in every blower system to protect the blower from damage leading to eventual failure. Inlet filters are usually cylindrical and can be found mounted directly to a blower or farther away on the inlet line.
Manufacturers typically include a nameplate on the housing to specify the model of the filter. Some filter elements are also marked with identifying information on one end. A manual or spec sheet for the overall blower system would also include info about the filter.
Providing measurements of the element—including the length/height, outer diameter, and inner diameter, as well as the connection size of the filter housing—can narrow down which filter is installed with your blower system.

Sizing a New Filter for a Blower System

To correctly size a new filter, we’ll need to determine what type of filtration is needed and make sure that the model we select can handle the maximum amount of airflow that will be moving through the system.

Selecting a Filter Style

Do you have a pressure system or a vacuum system?  Blowers can be used to push air through a pressure system or suck air through a vacuum system.

In a pressure application, inlet filters are typically used to filter air coming from the immediate area around the blower or from outside of a building or equipment enclosure.  These filters remove dust, pollen, and other particles from the air before it reaches the blower. Depending on your installation, the filter hood may also prevent loose objects or even rain from getting into the blower as well.

In a vacuum application the blower is pulling air through a piping system which means it’s very important to filter out any process material that could inadvertently get into the line.  Powders, fibers, and other particulates that reach the blower can damage the blower’s internal components or build up inside the unit, changing the clearances of the blower lobes, eventually leading to failure.

Take a look at this photo gallery to see examples of common filter styles for pressure and vacuum blower applications.

 

2.5" compression coupling installed on a 45 URAI blower pressure package
Before reaching the blower on this pressure package, the air passes first through the inlet filter and then a silencer.
Inline vacuum filters
The inline filters on these vacuum packages also feature differential pressure gauges for monitoring.
On this compact pressure package, the filter is mounted directly to the inlet of the blower.
4" compression coupling installed on a 409 RAM blower pressure package
Air enters into this vacuum filter from above and exits out to the blower at a 90 angle.
Custom stainless steel inline filters with ceramic coating
These custom inline vacuum filters were made from stainless steel and finished with a ceramic coating for a harsh application. The inset shows the interior view.

Filter or Filter Silencer?

During operation blowers create a good amount of noise, so silencers are generally needed to reduce the noise level. How much that sound needs to be reduced is usually determined by where the blower is operating and its proximity to people. Blower filter housings that have additional silencing features built in are referred to as Filter Silencers.  If the blower has separate silencers, it may be unnecessary for the filter to also provide silencing.

The first image below shows a blower package that has a separate silencer at both the inlet and discharge of the blower and a standard filter for air intake.  In the second image a filter silencer is pictured on the right; the sound is reduced as the air passes through metal tubes before reaching the filter media. The final image shows a blower package with a filter silencer directly connected to the blower inlet.

Airflow Capacity

Positive displacement blowers are preferred in a wide range of applications because they provide a constant, high volume of airflow, regardless of changes in pressure.  As we touched on above, the filter in your blower system must be able to allow enough volume of air to pass through the system unrestricted.  If the filter is not designed for a high enough volume of air, or if the filter becomes dirty and clogged, the pressure drop in the blower system will increase.  That PD blower is going to keep moving the same volume of air even if the inlet pressure changes.  Additional pressure drop will increase the load on the blower, which will increase the temperature rise, which will reduce the blower’s performance and may eventually lead to failure.

The volumetric flow of air passing through a blower system is measured in CFM (Cubic Feet per Minute), or m3/hr (Cubic Meter per Hour) across the pond. If you designed the blower system, then you know how many cubic feet of air per minute (CFM) to plan for.  If not, then we can just look at the maximum airflow for your blower model and select a filter that can handle as much airflow as the blower.  From a performance standpoint, it’s never a bad idea to size a filter that can handle more airflow than expected.

 

Blower Filter Selection Examples

Let’s look at a few different examples that all feature a 45 URAI blower driven by a 10hp motor. The 45 URAI has a 2.5″ inlet connection and is rated for a maximum airflow of 395 CFM. All of these example pressure packages have a configuration we refer to as P1 which includes a filter/silencer at the blower inlet, followed by a silencer, relief valve, and check valve underneath the mounting base on the discharge side of the blower.

Looking at the operating conditions for this application, we can see that the air volume at the inlet will be 173 ACFM, so we need a filter that can handle at least that much flow. Since it will be connected directly to the blower, first we’ll look at models that have a 2.5″ MPT connection that can screw directly into the 2.5″ FPT blower connection. We selected the FS-231P-250, a filter/silencer model with a 2.5″ MPT connection and a max flow of 195 CFM.

Operating conditions:
Inlet Volume: 173 ACFM (150 SCFM)
Site Elevation: 500′
Barometric Pressure: 14.4 PSIA
Inlet Temperature: 100˚F
Inlet Pressure Drop: 0.3 psi
Inlet Pressure: 14.1 PSIA
Discharge Pressure: 6.0 psig
Blower Differential Pressure: 6.5 psi

Design Speed 1995 RPM (55% of maximum)
Discharge Temperature: 197˚F
Discharge Volume: 139 ACFM

In this next package we have more flow entering the system at 225 ACFM. This is over the max flow limit for all of the 2.5″ filters so we’ll need to move up a size to find a filter model with a higher flow capacity. For this package we selected the CCS-3 filter/silencer model that has a max flow of 275 CFM. A reducing bushing and pipe nipple are used between the 2.5″ FPT blower connection and the 3″ FPT filter connection.

Operating conditions:
Inlet Volume: 225 ACFM (208 SCFM)
Site Elevation: 50′
Barometric Pressure: 14.67 PSIA
Inlet Temperature: 85˚F
Inlet Pressure Drop: 0.3 psi
Inlet Pressure: 14.37 PSIA
Discharge Pressure: 6 psig
Blower Differential Pressure: 6.5 psi

Design Speed 2411 RPM (67% of maximum)
Discharge Temperature: 173˚F
Discharge Volume: 180 ACFM

Our final example has an oversized blower. While we would normally use a smaller blower for these operating conditions, the customer’s speed requirement dictated the use of a 45 URAI. The inlet volume is only 93 ACFM, so we were able to use a less expensive 2″ filter, the FS-230P-200, that can handle a max airflow of 135 CFM. A reducing bushing and pipe nipple connect the 2.5″ FPT blower connection and the 2″ MPT filter connection.

Operating conditions:
Inlet Volume: 93 ACFM (80 SCFM)
Site Elevation: 500′
Barometric Pressure: 14.4 PSIA
Inlet Temperature: 100˚F
Inlet Pressure Drop: 0.3 psi
Inlet Pressure: 14.1 PSIA
Discharge Pressure: 6.0 psig
Blower Differential Pressure: 6.5 psi

Design Speed 1333 RPM (37% of maximum)
Discharge Temperature: 197˚F
Discharge Volume: 77 ACFM

Filter Media

One final decision when selecting a blower filter is which media will filter the air. The efficiency of the media, the cost of replacement, and the frequency filter changes will be required should all be considered.  Most filter manufacturers offer filter elements in the following three media options.  Efficiency data varies by manufacturer so check the spec sheets if this is important for your application.

Paper 
– Pleated paper; Most efficient and most economical
– Typically treated as disposable, but can be cleaned with compressed air
– Media efficiency: 99.5% on 2 microns; 97% on 1 micron

Felt
– Durable pleated polyester felt
– Can be cleaned and reused a number of times
– Media efficiency: 99% on 10 microns

Wire
– Galvanized wire-mesh with corrugated construction
– May be cleaned and reused indefinitely; must be treated
– Media efficiency: 90% at 20 microns

 

 

 

A brand new filter should have a pressure drop of between 2 to 3″ w.c. (water column). Once the pressure drop exceeds 10 to 15″ w.c., the filter should be replaced or changed.

A simple differential pressure gauge can be mounted to the outside of the filter housing to visually indicate when the filter is in need of maintenance or replacement.  Many filter housings come standard with a port where the gauge can be screwed in; if not, it can be added.

Want to keep learning?  Check out our article on how to size a blower silencer!

Browse our available filter options.see filters
Lindsey Marshall
AUTHOR
Lindsey Marshall

Combining deep knowledge of the blower industry with many years of B2B marketing experience from the digital agency world, Lindsey is the driving force behind pdblowers.com.

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