Frequently Asked Questions – Filtration
Q: What types of filtration media does Scott Labs offer?
Scott Laboratories offers filter sheets and modules for depth filtration and cartridge filters for depth and absolute filtrations. We also offer filter equipment such as pressure leaf filters, cartridge housings, plate and frame filters and more.
Q: What are the basic types of filtration and how do I know when to use each type?
There are two main categories of filtration, depth filtration and surface filtration.
- Depth filtration removes particles from your product within the depth structure of the filter medium itself. The filter media in depth filtration will be many times thicker than the particle sizes that are being removed. Depth filtration is required when high solids removal is required. Filtrations wil occur within an established micron retention range. Tighter filtration will occur at lower flow rates, while looser filtration will occur at greater flow rates.
- Surface filtration can be either absolute or nominal with a minimal depth capacity. Surface filtrations consist of a thin membrane or a thin membrane covered with polypropylene or polyethersulfone. Surface filtration relies on liquid pressing through an array of small gaps of a certain absolute maximum size in the surface of a membrane. Prior filtration with a depth filter is usually required to prevent clogging the surface of a membrane filter. Absolute filtration is useful for sterile filtration at the bottling line and at times when you require precise accuracy of filtration to limit risk.
Q: What is the range of micron retention using depth filtration?
Scott Labs stocks depth filter sheets from 55 microns down to .2 micron. Depth filter cartridges are available from .8 microns to greater than 10 microns.
Q: What Sheet Filter should I use?
Q: What is a "micron" and what does it mean to me?
A micron is one one-millionth (0.000001) of one meter. Bacteria are typically less than one micron in their largest dimension. Human hair is 60 to 80 microns and the smallest visible object is about 40 microns across. "Sterile" filtrations generally involve depth filtration media (normally a depth filtration sheet and possibly a depth cartridge) followed by an absolute membrane. Depth filtration at sterile micron retentions may be desirable prior to sterile membrane filtration in order to protect the membrane cartridge. The membrane filter then becomes your insurance policy to ensure near absolute exclusion of particles smaller than the membrane rating.
Q: What is differential pressure?
Differential pressure is the difference between the pressure in the system before fluid reaches the filter and the system pressure after the fluid flows through the filter. As the filter clogs, differential pressure increases.
Q: What puts the "depth" in a depth filter?
Like Theseus and the Minotaur, particles moving through a depth filter are caught within a labyrinth of channels, destined to never escape. Whether constructed of diatomaceous earth, polymers or even glass, depth filtration is based on trapping particles larger than the filter's porosity rating within a matrix of nearly infinite passageways. Certain filter media, like some pad filters, also exhibit a positive ZETA potential that attracts and holds particles exhibiting a certain charge. These two attributes allow depth filtration to retain a large number of solids for effective and economic filtrations. However, when solids are trapped in the depth of a filter, this also makes back flushing a moot point.
Q: How long will my filters last?
Filter life is expressed in terms of time or volume filtered between changes of filter media or filter elements. A filter's life span will depend upon the solids load and conditions of filtration (i.e. flow rate, density and temperature). Laboratory numbers will not reflect real life numbers. Laboratory numbers might be useful for comparison, but actual experience with the product under real life operation conditions will provide the best determination of filter media life.
Q: In sheet filtration, does the liquid pass through all of the sheets in the filter?
No, each drop of liquid passes across only one sheet of filter media and into the stream of filtered product headed to the receiving vessel. Put differently, more filter sheets means more capacity.
Q: What does "code" mean when referring to cartridge filters?
The code of a filter is related to the filter housing and the receptacle in which the filter element will fit. They must match! It also refers to the configuration at the closed end of the filter element. For example, a code 7 filter element will have a bayonet (insert and turn to lock) fitting on one end and a spear point on the other end. Please call for technical assistance if you are not sure which code you need.
Q: What is a "two-stage filtration" on a plate and frame filter?
This feature involves a diversion chamber placed in the middle of the filter pack, which causes the filtration fluid to be diverted into a second filtration stage. This allows winemakers to accomplish two filtration stages in a single process. Typically, the sheet filter must already be predisposed for this type of use as specific valving is a must.
Q: What is meant by "Sanitary Execution" on a plate and frame filter?
"Sanitary Execution" refers to the configuration and attachment method of portings on the filter. This style will allow for complete dissasembly of parts for detailed cleaning and sanitization. This also makes possible a two-stage filtration, with the use of a diversion chamber, as portings may be removed and reattached on the movable head. While "Sanitary Execution" is neccesary for two-stage filtration, it is also a desirable standard feature as it will enchance overall winery hygiene.
Q: Do I need to completely load my filter with filter sheets every time I filter?
No, for smaller volume filtrations you can reduce the number of plates and therefore sheets. Plates must be removed, or added, two at a time. For very small numbers of plates a ram extension might be necessary to fully close down on the remaining plates.
Q: How do I determine which type of filtration best meets my needs?
Methods of filtration are best decided by addressing a number of variables. These variables include the typical solids content of your product, the period of production in which you filter, available operating staff, and total product to be filtered during a work shift. In deciding which type best fits you, please contact us for technical advice or ask the Scott Laboratories sales representative in your area.
Q: What is Cross flow filtration?
Cross flow filtrationm in wine can be described as the tangential flow of wine accross a membrane surface. Simply put, wine constantly brushes the filter surface, cleaning it, while also migrating through to the clean end as opposed to passively "Dead End" filtrations solids, cross flow is constantly cleaning and rejuvenating itself as the filtration progresses.
Q: What would I use Cross flow for?
The benefit od Cross flow is that you can filter relatively high solids wine with very little labor input. Cross flow machines can be run automatically for long periods of time to process large quantities of product without supervision. This makes Cross flow an excellent candidate for pre membrane filtration.
Q: What media do I use with Cross flow?
Velo Cross flow units use hollow fiber PES media that should have a working life of 5-8 years in normal conditions. The membranes are easily regenerable and an effective substitute for DE and other bulk filter media.
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