How do you change a bag filter?

  1. Close all valves at the inlet and outlet ports.
  2. Ensure that the housing is not pressurized, by opening the pressure release valve.
  3. Remove the clamp (for clamp top style housings) or loosen the bolts (for bolt-down top housings) at the top of the housing.
  4. Remove the top of the housing.
  5. Remove the T-bolt at the top of the interior of the housing, allowing you to also remove the diffuser plate.
  6. Remove the dirty bag filter.
  7. Place a clean bag filter into the strainer basket, being sure that the bag filter extends straight down through the strainer basket.
  8. Place the diffuser plate back on top of the new bag filter.
  9. Screw the T-bolt back into the housing (it may slide into grooves on the interior of the housing), and tighten.
  10. Place the top back onto the top of the housing.
  11. Reattach the clamp (for clamp top style housings) and tighten; or tighten the bolts (for bolt-down top housings)

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Should I be using a #2 or #4 size bag filter?

Virtually all industrial and commercial applications utilize trade size #2 or trade size #4 filters, which correspond with #2 and #4 size filter housings. The correct housing for an application is mostly determined by the flow rate.

A #4 size housing is appropriate for most applications up to 40 gpm, and a #2 size housing is appropriate for most applications up to 100 gpm. Multi-bag housings can generally handle flow rates greater than 100 gpm.

Learn more about choosing the correct size bag filter/housing here, or speak with a PRM filtration expert.

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What type of bag filter material should I use?

Choosing the appropriate bag filter material depends on a number of factors, primarily chemical compatibility and temperature.

Polyester Felt Filter Bags:

  • High dirt holding capacity
  • Removes solids and gelatinous particles
  • Low cost
  • Chemical compatibility with wide range of contaminants
  • Maximum Temperature: 275° F
  • Welded Seam

Nylon Monofilament Mesh Filter Bags:

  • Provide extra strength and abrasion resistance
  • Produce predictable results for consistent performance
  • Chemical compatibility with a wide range of contaminants
  • Maximum Temperature: 275° F
  • Sewn seam using 5-line system

Nomex High Temperature Filter Bags:

  • Removes solids and gelatinous particles
  • Maximum Temperature: 425° F
  • Sewn seam using 5-line system
 Polyester Felt Nylon Mesh Nomex Material
Mineral Acids Good Poor Fair
Organic Acids Good Fair Fair
Alkalis Good Good Good
Oxidizing Acids Good Poor Poor
Animal/Vegetable Petro Oils Excellent Excellent Excellent
Organic Solvents Excellent Excellent Excellent
Micro Organisms Excellent Excellent Excellent


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How long will my bag filter last?

The amount of contaminant as well as the micron rating of the bag will determine the life of the bag filter. Some applications may only allow the filter to last a few minutes, while other applications may be suited to last for weeks.

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When should I change the bag filter?

You need to be monitoring the inlet and outlet pressure on the vessel. The difference between the inlet and outlet pressure is referred to as “differential pressure” or “pressure drop”. You will want to change the bag filter when the differential pressure reaches a certain threshold that is dependent on your application or system. Often times this threshold can range from 5 to 15 psi. The manufacturer recommends changing your bag at <15 psi Δ. Pressure higher than this can lead to bag failure. PRM is expressly not responsible for all installations and any damages due to leaks, ruptures, bursts, explosions or other damages.

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Are bag filters reusable?

Most bag filters are intended to only be used one time, including all PRM filter bags. Cleaning the bag filter can cause unintended damage, resulting in a change in the end product and/or malfunctioning of the filter bag.

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How do I choose the correct ring material for a bag filter?

Chemical compatibility: Bag filter rings are typically either polypropylene, carbon steel or stainless steel. The ring material should be chemically compatible with your application.

Temperature: If you are running liquids over 190° F through the system, you will want to be sure that the temperature will not affect the polypropylene ring by melting or softening. A steel ring bag filter may be more appropriate for applications involving hot temperatures.

Incineration: Some bag filters are disposed of via incineration, in which case you would not want to use a steel ring.

PRM is in no way is responsible for the selection, suitability of, nor the material compatibility of materials being filtered through bag filters.

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What is the head loss across my bag filter housing?

An empty housing, at maximum flow rate, has no real measurable loss. With a clean bag(s), head loss is also negligible. It is not until the bag(s) begin to load that measurable loss occurs, increasing over time until the bag(s) needs to be changed.

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What is the maximum operating temperature of a bag filter housing?

The maximum operating temperature of a stainless steel or carbon steel bag filter housing is dependent on the type of bag filter material that will be used in the housing. A bag filter will begin to break down before any noticeable effects to a stainless steel or carbon steel housing.

PVC bag filter housings have a significantly lower maximum operating temperature compared their stainless steel and carbon steel counterparts. In general, PVC bag filter housings have a 100°-113°F maximum temperature rating, but be sure to check the exact specifications on the PVC housing in question.

Every bag filter has a specified maximum operating temperature. Most bag filters are rated for around 275°-300°F. If your application may exceed 275°F, High Temperature Nomex Filter Bags may be a good option.

You can always contact a PRM Filtration Expert for guidance in choosing the most appropriate bag filter housing and bag filter for your application.

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