When designing a liquid filtration system that will utilize bag filtration there are two broad categories to choose from: Standard (or ‘trade size’) filter bags or a custom filter bag design.
The advantage to using a standard product, of course, is lower cost, shorter lead-time, and an array of interchange options. The downsides are that a standard product may not be well suited to the application; standard products may not have the material selection, performance, or features required for the application; the standard product may not fit an existing vessel or integration requirement; or there may be an inherent desire to have a unique or otherwise proprietary product.
It is worth considering trade size filter bag for new applications. For very low volume applications, an off-the-shelf product may be the only cost-effective solution. Below are several details related to standard filtration bags.
Active trade size designations and the overall dimensions are shown in the table below. The most common product configurations are available for purchase here.
|Trade Size||Nominal Diameter||Nominal Length||Notes|
“PP/SS” refers to either a polypropylene or stainless ring that are hemmed into the top of the bag. The hemmed in ring will fit most industry-standard bag filter housings of the stated size.
The molded flanges are generally polypropylene made to fit specific styles of filter housings. It is important to note the difference between the flanges and the polypropylene ring. If you need help identifying your flange, please send us a picture and whatever other details you can provide. There are some less-common flanges that we can provide by request.
“DS” is a bag with a drawstring at the top. These bags can be cinched onto a feed pipe or folded over an open-top vessel and cinched to the outside (much like a trash bag installed in a trash can) so that liquid can be poured into the filter.
Trade size filter bags are produced continuously in large quantities. Many industrial processes rely on bag filtration and need to consistently change out the filter bags. Bag filters and housings are most effective for course filtration where heavy particulate loading is present in higher-flow rate applications. Bag filters generally should not be used as the primary filter when high-efficiency filtration is required. However, bag filters can be excellent pre-filters in systems with high efficiency filters downstream of the bag filters.
Please be aware that there are some proprietary (manufacturer specific) configurations that are very similar to – but ultimately incompatible with – the industry-standard filter bags. In general, Filter Products Company can provide the vast majority of liquid filter bag configurations and we can often provide guidance on proprietary and manufacturer-specific variants of these types of products.
If a standard configuration product will not work for your application, Filter Products Company would be happy to review your application and design a custom filter bag with you.
When developing a custom product, here are some tips to keep the cost down:
- Stay with a “pocket” or “sock” shape with a radiused bottom (or “toe”) when possible. Adding a disc or flat bottom to the bag can increase the price.
- Use a round bag cross-section with a consistent diameter when possible.
- Design the bag so that the fully laden weight of the bag and contents do not require handles, lifting loops, reinforcing straps or multiple layers of fabric.
- If the application requires a closure mechanism, keep it as simple as the application will allow.
- Specialized materials of construction increase prices.
- More individual pieces of fabric and greater complexity drive up the cost of a filter bag.
- Bigger bags cost more not only because of the additional material, but the additional time to cut and sew large configurations.
Large volumes, like those associated with Original Equipment Manufacturer specified products, can help offset many of the costs associated with custom designs.
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