What is the Difference between Mesh and Micron? How Do I Know Which Sanitary Screen Gasket to Pick?

March 28, 2014
Sanitary Screen Gaskets

Sanitary Screen Gaskets

One of the more popular items we get requests through our website for are sanitary screen gaskets. Screen gaskets are used in a variety of applications, including to protect fill and finish equipment, spray balls, pumps, and spray nozzles. While we’ve discussed gasket material selection in previous posts, this post will focus on the filter screen ratings and the difference between micron and mesh.

So what is mesh and how is it determined? It’s pretty easy, actually. Simply count how many openings there are in one inch of screen. The number of openings is the mesh size. So a 120 mesh screen has 120 openings per linear inch. A 250 mesh screen will have 250 openings per linear inch. As it applies to filter media, wire mesh measures the number of wires (or threads) per linear inch, not the size of the size of the holes between them. As the mesh rating goes up, the number of wires per inch goes up, and the size of particles that can pass through the screen goes down. It is important to note, however, that because wire mesh is count of a number of threads and is determined in part by wire size, mesh size is not a precise measurement of particle size.

This begs the question, what is the highest mesh size we can attain? For all practical purposes, 400 mesh is the highest. Beyond 400 mesh, filter media is normally defined only in microns. This is because as the filter weave gets finer, the wires get closer together, and there is almost no space between them. A micron rating for a fluid filter is a generalized way of indicating the ability of a filter’s ability to remove contaminants by the size of particles it is exposed to. In sum, the finer the filter, the lower the micron rating. To achieve low micron ratings, many screen gaskets will use a mesh screen with a filter cloth backing. This allows screen gaskets manufacturers to offer screen gaskets as large as 6” with media as fine as 10 micron.

So now that we’ve figured out what the rating means, let’s talk about go applications for sanitary screen gaskets, or more specifically, bad applications for screen gaskets. Screen gaskets are great for protecting sensitive pieces of process equipment, such as spray balls, pumps, and filling needles. Contrary to popular belief, they are NOT designed to replace inline, wye, or basket strainers. For this reason, most sanitary gasket manufacturers don’t advertise a maximum differential pressure rating of their screen gaskets. There are many factors that can lead to fouling and failure of screen gaskets and ultimately screen gaskets are designed to provide protection and should be used as a safeguard, NOT AS A FILTER. If you really want to know what the differential pressure for your screen gasket is, contact Holland and we can work with you on some differential pressure testing. Monitoring differential pressure will help us predict failure and identify when a screen has fouled.

Other variations of sanitary screen gaskets include perforated plate and sock screen gaskets. Perforated plate gaskets will have plates with larger holes, while sock screen gaskets insert into the line and increase surface area in applications with high levels of particulate and where screens are prone to fouling. All screen gaskets are available in USP Class VI FKM, EPDM, PTFE, and metal detectable flavors. They are available in ½”-6” and we have even developed custom, small diameter O rings with imbedded screens. All screens are 316 stainless steel and some screens are available in Teflon.
For more information and help with you next screen gasket information, contact a Holland Sales Engineer today.