Our new article concludes the series of valve sealing solutions and adds to those previously published in our blog “Some sealing solutions in valves”.”, “Certified O-rings for valves.“ , “Elastomers resistant to aggressive fluids in valves”.” y “Recommended sealing materials for valve seats.”.
In today's article we take a closer look at another aspect of the valves, the options available for the valves. flat gaskets to be installed in split body valves and between stem and handwheel.
Index
Valve gasket materials
The operating conditions of the valve, primarily the process fluid and temperature, restrict the material options for flat gaskets. The most commonly used materials are graphite, PTFE, stainless steels or nickel-based alloys.
Graphite flat gaskets
The graphite has the following advantages:
- Economical price
- Up to 450º C for fluids and for steam, the maximum temperature is 650º C.
However, it raises the problem that does not have good chemical resistance against oxidizing media and can adhere to its housing, making it difficult to maintain the equipment. Graphite is the preferred filler material for spiral wound gaskets although it can also be used as a flat gasket with a stainless steel metal insert.
PTPE flat gaskets
The PTFE enjoys a almost universal chemical resistance but its service temperature is limited to +260 ºC. In addition, the material suffers creep (the nominal joint thickness is not maintained) and has a coefficient of expansion that should not be underestimated.
Of the two limitations, creep is by far the more serious. To overcome this, there is a variant of the PTFE which involves a mechanical treatment (calendering) that significantly corrects the creep of the PTFE virgin. It is the Gylon®, PTFE, the restructured PTFE of Garlock, The third generation of this material is now being marketed. This material is characterized by its excellent behavior against steam, the gasket does not stick to the housing and has no difficulty to be cut from sheets. In the coming weeks we will be presenting in our blog the 3rd generation of Gylon®.
For valves with spiral wound seals that are subject to vibration or when the temperature or pressure is very high, it is recommended that the seal be replaced by a grooved metal gasket, type Kammprofile. However, another more interesting option to that of spline wear, is that of the corrugated and flexible metal, capable of absorbing movements. The gasket can also have a graphite coating that copies the flange but is recommended for use in oxidizing media.
The manufacturer Revoseal has patented a graphite-filled corrugated metal gasket that, once assembled, encapsulates the graphite and acts as a secondary seal. This gasket combines the strengths of the Kammprofile gasket and the conventional corrugated metal gasket.
Flat gaskets in stainless steel or nickel-based alloys
There is a wide range of metals for flat gaskets such as:
- Stainless steels (300 series).
- Nickel-based alloys (Incolloy®, Hastelloy®).
- Nickel-chromium austenitic base alloys (Inconel®).
- Nickel-copper alloys (Monel®), among other materials.
You can contact us at 93 863 32 77 or send an email to infoweb@epidor-srt.com and we will study together the most appropriate solution to your problem. Get to know all our engineered sealing solutions in our catalog.