Solberg - Inlet Filters/Silencers, Vacuum Filters, Air/Oil Separation

Air Filtration Rules of Thumb
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General: For peak output performance from a compressor, blower, vacuum pump, engine, or any other machine that consumes air, one must have clean, unrestricted air. Filters were born out of this basic need. Proper Filtration can help stabilize the working environment within a given piece of equipment even when the external conditions may be quite severe. A critical component in creating the right working conditions is the sizing of the Filter. With the correct Filter size, one’s piece of equipment will operate smoothly over a significant period of time.

A major factor in filtration and filter sizing is Air Velocity through a given media. Generally, the slower the Velocity of air through a media the higher the filter efficiency and, conversely, the lower the pressure drop. This translates into optimizing an air system’s performance, which is a major goal in any system.

Rule of Thumb #1: Always begin with the filter cartridge requirements when sizing a Filter Housing. Once the appropriate element has been selected then move on to the housing requirements.

Rule of Thumb #2: Always ask or specify a filter based on a micron rating with Filtration efficiencies. (Stating that one has or needs "a 5-micron filter" alone for example is misleading or confusing as no efficiency rating has actually been specified. A 5-micron filter at 97-% efficiency can be less efficient than a 10-micron filter at 99.7% efficiency!) For proper air system performance in light and industrial duty environments, a filter with a minimum of 99.7% filtration efficiency at 10 micron is required.

Rule of Thumb #3: Size your filter correctly by understanding the impact air velocity through a media has on efficiency and pressure drop. Maintain the suggested Air-to-Media ratios listed below based on the external environment listings and Filtration efficiency needs.

Suggested

Filtration Efficiency Requirements 99.7-% efficiency or better @	Environmental Conditions	Air to Media Ratio
Industrial Grade 10-micron Paper	Light Duty (clean, office/warehouse-like)	20 to 30 CFM: 1 ft²
	Industrial Duty (workshop, factory-like)	10 to 15 CFM: 1 ft²
	Severe Duty (Foundry, Construction-like)	5 to 10 CFM: 1 ft²
Industrial Grade 10-micron Polyester	Light Duty (clean, office/warehouse-like)	40 to 50 CFM: 1 ft²
	Industrial Duty (workshop, factory-like)	30 to 40 CFM: 1 ft²
	Severe Duty (Foundry, Construction-like)	15 to 25 CFM: 1 ft²
Industrial Grade 4-micron Polyester	Industrial Duty (workshop, factory-like)	15 to 25 CFM: 1 ft^2*
Industrial Grade 4-micron Polyester	Severe Duty (Foundry, Construction-like)	10 to 15 CFM: 1 ft^2*
Industrial Grade 1-micron Polyester	Severe Duty (Foundry, Construction-like)	5 to 10 CFM: 1 ft^2*
Industrial Grade 0.3-micron HEPA Glass	Industrial Duty (workshop, factory-like)	5 to 7 CFM: 1 ft^2*
Industrial Grade 0.3-micron HEPA Glass	Severe Duty (workshop, factory-like)	3 to 5 CFM: 1 ft^2*

Notes:

Ratios are based on the assumption that one wants to maintain the same pressure drop (or less) as the 10-micron elements listed above.
Air to Media ratios are our suggested ratios. Some catalog items, because of customer demand, have resulted in ratios that are higher than our suggested ratios. In those cases, the life expectancies of the elements are reduced.

Example: A reciprocating (piston) air compressor will be installed in a cement pit. The compressor is a 25HP unit with a 1-1/2" inlet connection for air. The inlet airflow is 80CFM(136 m³/hr). It is feared that very fine cement dust (approximately 1-4 micron) will destroy the compressor very quickly. What filter should be offered?

Based on Rule of Thumb #2, an Industrial Grade 4-micron Polyester or an Industrial Grade 1-micron Polyester would be two immediate choices. For the 4-micron Polyester, an element with 5 to 8 ft² of media should be used while for the 1-micron polyester; an element with 8 to 16 ft² of media should be used.

Rule of Thumb #4: Pressure Drop is also caused by the dirt holding capacity of the element. As the element fills up with dirt, the pressure drop increases. The ratios that were listed in Rule of Thumb #2 also take into account the desire to select a Filter that minimizes the maintenance required during the lifetime of the machine. It is important to document the Pressure Drop of a given Filter when it is clean and then replace it (or clean it) when the pressure drop increases by 10-12 inches WC from the original reading.

Rule of Thumb #5: The inlet connection greatly influences the overall pressure drop of the Inlet Filter System. To minimize the restriction contributed by an Inlet Filter, a velocity of 6,000 ft/min or less is suggested through the outlet pipe. The below table lists the suggested flows based on this Rule.

Pipe Size (inches)	Airflow	Pipe Size (inches)	Airflow	Pipe Size (inches)	Airflow
¼"	6 CFM	1 ¼"	60 CFM	6"	650-1100 CFM
3/8"	8 CFM	1 ½"	60-80 CFM	8"	1440-1800 CFM
½"	10 CFM	2"	60-135 CFM	10"	1800-3300 CFM
¾"	20 CFM	2 ½"	80-195 CFM	12"	2600-4700 CFM
1"	20-35 CFM	3"	200-300 CFM	14"	4700-6000 CFM
		4"	300-520 CFM
		5"	500-800 CFM

Rules of Thumb for Sizing Coalescing Filters for Vacuum Pumps
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General: Recent developments in product design allow for the possible selection of Oil Mist Exhaust Filters based on the type of equipment being used. It is, for the first time, possible to identify the appropriate grade of aerosol discharge filter because of the extensive research completed by the Solberg R&D Department. Please follow the below rules to correctly size your Oil Mist Exhaust Filter. If further consultation is required, please contact Solberg Mfg., Inc. or Dan Bott of our Vacuum Systems consulting service will be pleased to return your call.

Rule of Thumb #1: Forget all that you know about air/oil separators for Compressed Air Systems, as such systems repeatedly fail in a vacuum pump application. The first consideration is to determine the type of Vacuum Pump being used. The particle size distribution and mass of oil aerosol discharging from a vacuum pump is as varied as the number of separator tank designs utilized by the industry. The main pump types are Rotary Vane, Rotary Screw, Rotary Piston, Liquid Ring, and Reciprocating Vacuum Pumps. Each type of pump produces its own specific oil discharge characteristics and requires the appropriate media make-up to effectively capture and drain oil aerosols.

Rule of Thumb #2: Determine the type of oil being used in the vacuum pump. Trade names, viscosity/grade of oil, and the lubricant base (mineral, synthetic, etc.) are all useful in determining the discharge aerosol characteristics.

Rule of Thumb #3: Determine how much oil the pump consumes under normal operating conditions. Typical consumption rates are gallons or liters per hour. The amount of oil consumed is typically the amount of oil being discharged.

Rule of Thumb #4: Pump operating cycles including vacuum range, temperature fluctuations, contaminant gases or vapors, and hours of operation per day/week. Also, determine the maximum pressure drop or filter restriction the system will allow.

Rule of Thumb #5: Determine the operating temperature at the discharge connection. If it is above +220 ° F, methods of cooling the aerosol should be considered.

Rule of Thumb #6: Note the Horsepower of the pump, the outlet connection, and the SCFM.

Rule of Thumb #7: When an external unit is to be used as the primary or sole air/oil separator in a system, a multi-stage Severe Duty system is required.

Rule of Thumb #8: In the case where an existing air/oil separator (internal or external) is already used, it is important to specify the desired goal for a second filter. Is it planned to have a multi-staged system for severe or extreme duty applications, or is there a requirement for exceptionally clean discharge air? If a multiple stage system is needed, try to identify the primary stage unit and the purpose for the second stage.

Rule of Thumb #9: Consider where to install the Filter. Where possible it is best to install in moderate temperature (+35 to +100 ° F) environments and avoid freezing conditions to ensure the oil drains freely without causing undue backpressure to the Vacuum Pump.

Once as much information as possible is obtained, send the data to Solberg Manufacturing, Inc. for our review and/or review our data sheets in the Product-by-Product Line section of our webpage. You’ll find our data sheets under "Oil Mist Exhaust Filters".