If you have ever used liquid filtration equipment, you will know how convenient it can be! The ability to throw a filter in and have it work immediately is something that's easy to take for granted. When you forget about a filter bag, things can go wrong. From damaged equipment to slowed production, clogged filters can cause many problems. The most difficult part of bag filtration is knowing when to change liquid filter bags. In this blog post, we will discuss the recommended time to change liquid filter bags!
How Long Does Each Filter Bag Last?
While this is a common question, it is ultimately the wrong question to ask. There are so many factors that affect how long a filter will last. First of all, the type of liquid filter bag you are using will change how long you have between changeouts. Different micron sizes will produce different results, as will each possible material available. Another factor that will affect how long a bag lasts is the job itself. Flow rate, particle size, and countless other variables will affect how long you can use a filter bag.
The reason people ask this question so often is due to how convenient it would be if it had an answer. If we could tell you "change out your bag every 3 weeks," you would probably be more likely to buy filtration equipment. However, such a cut-and-dry answer just doesn't work in an industry with so many variables. Although determining when to switch out bags is not simple, it doesn't have to be difficult either.
How Do I Know When to Change the Filter?
While most people getting started with filtration assume they should use time to determine whether their filter needs to be changed out, the metric they should be paying attention to is pressure. As fluid passes through a filter, the pressure lowers. The difference between the entrance and exit pressure is called "differential pressure" or "pressure drop." The higher the differential pressure, the harder it is for fluid to get through the filter. If the differential pressure gets too high, you can risk quality of liquid passing through and structural integrity of the filter.
The recommended change-out differential pressure that companies typically quote is "between 20 and 25 psi." This is a good rule of thumb, but certain materials and flowrates make this number vary. Sometimes this number is even lower, so it's best to check the spec sheet and any notes from the manufacturer before you start using a filter. Many filters also have different flow rate and system pressure limits, so reading up on the filter before purchasing is always a good idea!
How to Measure Pressure Drop
Since differential pressure is such an important metric, you need to be able to reliably measure it. The most effective way to do this is to have two pressure gauges installed; one before the filter and one after. This allows you to track pressure drop accurately. There is some debate between using analogue or digital readouts, but that mostly depends on whether you have immediate access to power sources. Digital gauges allow for more accurate readings, but dealing with cables and extension cords can be a pain. Figure out what works best for you and give that a shot! Pressure gauges are typically installed directly into the pipeline, but certain filter housings will allow you to install them into the body of the housing. This means you won't have to drill into piping, which can be risky! For more info on measuring pressure, check out this article.
Now that you know the recommended time to change liquid filter bags (around 25psi differential pressure), you are ready to get started filtering all kinds of liquids. Just a reminder: be sure to check the technical details of any filter bags you use, as their differential pressure limits could be different than the standard.