Filtration can be intimidating. There's a lot of jargon, marketing, and confusing terminology. We talk to customers about cartridge filters every day, and want to help make things a little easier to understand. Here are some questions we get most often. As always, though, if you want some one-on-one assistance feel free to give us a call.

Without further ado, our most frequently asked cartridge filter questions:

How many gallons can I filter before I need to change out a cartridge?

This is the question we get most frequently. It's also the most challenging one to answer accurately. There's no one-size-fits-all answer. It depends on a lot of variables, some of which are difficult (or costly) to calculate.

How long filters last depends on:

  • The filter's micron rating
  • Its efficiency at that micron rating
  • Its surface area
  • What percentage of solids are in the solution you're filtering
  • The size of those solids
  • And more…

While it may be possible to calculate all of these values, it's usually more trouble (or expense) than it's worth. Most of our customers just run trials with a few types and sizes of filters at first. After all, even if you have a 30" housing, you can just get a few 10" filter cartridges and test those at first.

After you run a trial you'll get a feel for how your product reacts to filtering. Then you'll be in a position to get a standard operating procedure that you can run each time you need to filter.

In short, we can't always tell you exactly how long filters will last. But we can tell you how often we observe our customers buying replacement filters. Small to mid-size facilities tend to purchase a few filters every 6-8 months or so. Larger facilities may purchase every 1-2 months.

Are cartridge filters cleanable and reusable?

Yes, most of the Graver filters we carry are cleanable and reusable. Here are instructions from Graver. These instructions discuss cleaning, sanitizing, and storage protocols.

Not all filters are cleanable or reusable. Many filters—particularly melt blown or string-wound depth filters—are intended for a single use only. We don't sell this style. They are usually not very accurate or efficient, and they have low dirt-holding capacities.

Do 30" filters work better than 10" or 20" filters?

There should be no observable difference in performance between filters of different lengths. Longer filters will get you more on-stream life, and higher flow rates. But in terms of general performance there is no difference between different filter lengths.

Which direction should liquid flow through a filter: outside-in, or inside-out?

The filters we sell are designed to have liquid flowing from the outside-in. Your product should fill up the filter housing, flow through the filter, and exit out through the bottom center of the filter.

How do I know when a filter is clogged?

Graver lists recommended change-out pressures for their filters. Your filter housing likely has a pressure gauge on top. If not, we recommend something like our Filter Housing Topper Assembly that measures pressure and lets you bleed out excess air in the housing.

The gauge on top of the housing (or at it's inlet) will tell you the pressure that is required to push liquid through the filter. As the filter gets clogged, it will require more pressure to push through. This is a sign that the filter is working as intended to remove particles.

Most Graver filters are considered clogged at around 30-35 psid. So, assuming that your source and destination tanks are not pressurized or under vacuum, the pressure you read at the inlet is the total differential pressure (psid). Once the gauge reaches 35 psi, it's time to change out the filter. You may be able to get a bit more life out of it through cleaning and regeneration.

How do I store my filters when they're not in use?

If you are planning on using the filters again in less than a couple of weeks, you can store them in a sterile liquid solution. Some customers use neutral grain spirits or acidic solutions, for example. We sell a Filter Cartridge Storage Tube for just wet filter storage.

To keep filters from growing any microorganisms, you should change out the storage solution after a couple of weeks if you end up not needing to use them.

If you know you won't be filtering again for a long time, it's better to thoroughly clean and completely dry your filters, then store them in a sealed bag somewhere sterile. A freezer is great, if you have space in one.

What micron size filters should I buy?

This is another question we frequently hear that is difficult to answer accurately. It all depends on what you're trying to achieve.

First things first: it helps to understand how large—or small, more accurately—a micron is. Let's get some scale.

Most people can only see individual particles that are 40–50 microns or larger. A hair on your head is probably about 70–100 microns across, for reference.

The vast majority of filters we sell are in the 0.45 to 10 micron range. This means they're filtering out large visible particles. They're also filtering out sub-visible particles. A lot of haze/cloudiness particles occur in the < 10 micron range. Although you can't see these particles individually, when enough of them are together you can see them as haze.

So, if you're just trying to filter out big visible particles you can get a filter in the 10 micron or larger range. QMC is probably a good choice.

If you're trying to filter for haze or cloudiness you'll want something in the 1–5 micron range. Again QMC will work. You may want to try GFC. Its glass fiber composition helps attract haze-forming colloids.

If you need to filter out spoilage micro-organisms, you pretty much need ZTEC WB. 0.45 microns is sterile grade for these microbes.

If you are using a sterile filter you will also want to protect it. Sterile filters are extremely accurate, but have low dirt-holding capacities and will clog quickly without adequate protection. QSL is a great choice as a prefilter. It has an outer depth-filter layer and an inner absolute filter layer that protects a 0.45 micron filter like ZTEC WB.

I need to filter, but I don't want my product to lose flavor. What should I do?

We hear this concern a lot; particularly from distillers who are concerned that filtration will strip flavor or odor from their product.

In reality it is very difficult to remove flavor from a product through normal micro-filtration. Elements that contribute to flavor are typically in solution. They will pass right through any filter because they are liquids. It takes nano-filtration or ultra-filtration (e.g. reverse osmosis) to strip certain flavors from a product. These are much smaller sizes than the cartridge filters we offer, and typically require specialized equipment to operate.

So why do people get concerned about stripping flavors? As noted above, much of what happens in filtration takes place at the micron and sub-micron scale. These are sizes that are too small to see. Consequently, there can be a lot of fear, uncertainty, and doubt about what's actually happening during filtration. Rest assured, removing flavors from a product through barrier filtration alone would be really, really tough to do.

All that said, we encourage you to try and carry out a blind taste test of your product filtered with filters at different porosities to see if you can distinguish the difference.

QMC, GFC, ZTEC WB…Which should I buy?

We sell Graver cartridge filters. Graver makes filters in their Delaware manufacturing plant. They're exceptionally high-quality, and less expensive than competing filters. Graver doesn't employ an enormous, high-pressure sales force, nor do they import their filters from overseas. Consequently, they are able to offer high quality filters that are reasonably priced.

That said, their filter names are a bit confusing. Here is an overview of the filter styles we offer, and what we feel they're best for.

  • QMC: This is a general-purpose polypropylene depth filter in the 0.2–10 µm range. With 95% accuracy, it's ideal for just about any general purpose filtration task. Since it's not absolute-rated, you can't use it for true sterile filtering, but for clarification and bug catching it's ideal. It is likely our most popular filter because of its versatility.
  • ZTEC WB: ZTEC WB is an absolute-rated membrane filter for wine & beer that is made from asymmetric PES (polyether sulfone). The most popular size we sell to wineries & breweries is 0.45 µm, which is the size where spoilage organisms occur. It is a true sterile filter that can be integrity tested
  • QSL: QSL filters are designed specifically as a prefilter for a 0.45 micron ZTEC WB filters. Since ZTEC WB is an ultra high-efficiency membrane filter, it is more prone to clogging. You need to protect it with a prefilter. QSL has an external depth filter layer and an internal membrane filter, providing extra protection downstream. If you're sterile filtering, we highly recommend using QSL in front of the final filter.
  • GFC: GFC is made from borosilicate glass fiber that carries a slight ionic charge. This makes it great for haze filtration. It is one of the most popular spirits filters we sell for this reason. It is only available in 1 µm, but this happens to be a popular size for general purpose filtration anyway. Consequently, we sell many of these filters to distilleries.
  • WaterTEC: You must pre-wet membrane filters with water prior to using them. However, the rinse water may contain particles that can prematurely clog your filter. WaterTEC is specifically for filtering water, and is great for extending the lifespan of your sterile filter, like ZTEC WB so that it doesn't get clogged accidentally before you introduce your product.
  • PME: PME is an economy-grade sterile filter. Filters broadly fall into two categories: absolute (a.k.a sterile or membrane) and depth (a.k.a. prefilters). PME is a depth filter, but it acts like a membrane filter. It has a very high accuracy, but you can't claim that it's a true sterile filter. It's also only available in 12-packs.
  • TefTEC: These filters are made from hydrophobic teflon. That means they resist water and liquid. They're not for liquid filtration at all. They're for gas and air filtration. If you're running a bottling line and need the compressed air or gases to be free of particles so that they don't accidentally get introduced to the product, these are the solution.
  • QXL: QXL is a depth filter made from a very thick, lofty material. It's great for more viscous products like oils and syrups.

Let us know if you have any questions that weren't answered here!