How to Choose an In-line Filter – Operating Conditions
A look at how to match filter specs to your in-line filter needs.
We all realize that it is important to select the right filter so that something doesn’t go wrong later. For example, perhaps the efficiency of flow is too low. How do you know you made the right choice? Well, we already know about chemical compatibility requirements (see my previous post, How to Choose an In-line Filter – Chemical Compatibility). Now we need to think about operating conditions. I will go over flow rate, volume of solids, operating pressure and operating temperature in this post.
Filter flow rates show how much fluid, air or gas passes through the filter. These rates are based on testing under controlled conditions. Size of connections and housing size are important. But flow rate depends on two considerations, the size of the most restrictive flow path and how much flow the filter material or media allows.
Modular Check Valves
We've taken spring-loaded check valves to a whole new level. Mix and match imperial and metric connections. Watch the video.
More about filter media flow ratings
It is important for all of us to understand more about how filter media controls flow rate. The percent of open area (POA) of filter media and its total surface area may limit flow. The POA needs to be large enough to handle the expected flow through the filter. Low POA can still work if you use a filter with a larger surface area.
A note of caution
Relying simply on flow ratings could be risky. This is because these ratings are based on ideal test conditions. The best way to measure flow is to test samples in the actual process. Other variables that could influence flow when comparing flow ratings to actual flow include temperature and pressure.
Volume of Filterable Solids and Clogging
Please be sure the filter pores are the right size to catch the particles being filtered out. Manufacturers usually give filter pore sizes in microns. See our Mesh and Microns page for information about microns. More surface area means more solids are captured without clogging. Clogging reduces flow rate. Clogged filters increases pressure both across the filter and upstream of it. This reduces flow efficiency. It may cause filter failure too. Filter failure can damage downstream machinery. Choose filters with the right surface area and micron rating for your application. Then monitor those filters for clogging making sure that they are easy to service and/or replace.
Operating Pressure Ratings
Maximum operating pressure is the highest pressure that does not damage the filter media. Differential pressure is the difference in pressure between the filter inlet and the filter outlet. Burst pressure is the maximum pressure filter housings can handle before failing.
Why differential pressure matters
In general, differential pressure must exist for flow to take place. It makes sense then that more fluid could pass through a filter when pushed harder. Also, certain in-line components function properly for flow in one direction only. This means you probably will need to add check valves to protect filters from back flow. In addition, thick fluid can dramatically increase differential pressure across a filter. This pressure could become so high that flow rate is significantly reduced or even stopped. The pump might even be damaged.
Higher temperatures may lower filter pressure ratings. This is because higher temperatures can change chemical compatibility. It may also cause plastics to soften.
Now you can see why it is helpful to know flow rate, the amount of filterable material, operating pressure and operating temperature when choosing a filter.
- Too low a filter flow rate lowers efficiency and can cause component failure
- Poor filter operating and burst pressure choices cause other problems such as:
- Filter failure
- Component malfunction
- Catastrophic system failures
Think maximum operating pressure and burst pressure. And don’t disregard the effects of temperature both inside and outside the process.
Look for our upcoming blog article about filter connection types:
How to Choose an In-line Filter – Physical Connections
Have you had a particular difficulty in matching a filter to a process? Was pressure or flow rate your nemesis? Do you have any tips to pass on? Help us by telling others about what you learned.
Still have questions about how to select the right in-line filter for your application? If so, send me an email – email@example.com. You can also ask questions using the comments section below.
Previous posts in our How to Choose an In-line Filter series:
About the author
Steven C. Williams, BS, is the technical writer and an inbound marketing specialist at Industrial Specialties Manufacturing (ISM), an ISO 9001-2015 supplier of miniature pneumatic, vacuum and fluid circuitry components to OEM's and distributors all over the world. He writes on technical topics related to miniature pneumatic and fluidic components as well as topics of general interest at ISM.