Flange: most flanges thickness will be smaller than the thickness in the standard to save cost, but some flanges are too thin to resist the working pressure.

Some flanges are painted, except customer required, some flanges material is ductile iron instead of carbon steel. In order to cover the air holes during casting manufacturing, they will paint. Carbon steel flange price is higher than ductile iron flanges.

Rubber: EPDM maybe the most popular rubber all around the world, in fact, only the content more than 45%, the features will be very good, the price is also higher, many suppliers declare that their rubber is EPDM, after testing, there is a little even no EPDM content, only testing, you can find the truth. There are many suppliers add a lot of reclaimed rubber, the finished bellow is very hard, the movement is very little.