Valve Seat Differences 1

[ohiowater]

Can someone provide a synopsis on the direct differences between resilient seated valves and metal seated valves (or provide a link to a good site that describes the differences between the two)? What is the primary initiative to choosing one type or another for water (or wastewater) treatment plants and distribution systems?

 

[hydrae]

Resilient seat valves are latest and greatest item for waterworks valves, been out for about 20-30 years, which is still considered newfangled to some operators
smooth waterway, dutile iron, (lightweight and strong) easy to replace the disk (as if anyone needs to). If there is debris in the pinch area, the rubber (resilient seat) will deform to attempt a seal, otherwise flushing can clear the debris. Stem sealing is by o-ring so near zero maintenance on the packing gland.

Metal seated valves have been on the block for the past 100 years, they still work, (if you know how to operate them)
Issues, there is a groove in the waterway that get cloggled with debris. Regular exercise will keep the waterway clear, proper operation when the valve is needed will get a decent seal. The trick is to use the water to wash away the debris. They were built stout, servicing them is possible, the seats can be machined and disks, gears, threads and linkage replaced. The stem seal is typically packing which needs to be kept wet to maintain the seal, (another proper operation requirement). There are tools that can replace the packing though the valve box without having to dig up the valve.

I choose RSV unless the client does not want that newfangled gadget.

Hydrae

 

[gerhardl]

As this is a question boarded on this forum (and not valve engineering) the question is pretty much answered by hydrae above.

The answer would have been different if you wanted to include process industry, higher pressures and other media.

From a European point of view there would be no doubt selecting resilient seated valves for all normal water distribution applications, up to the largest, and up to and including at least pressure class PN25 (250MWC).

For on/off valves it would be more a question of finding the construction and type of valves with the lowest cost over lifetime (expected and wished lifetime and maintenance and operational cost considered), and construction suited to piggable or not piggable pipelines.

Typical choices would be for drinking water:

Soft sealed wedge gate valves for street distributions up to PN16 and 200 to 250 mm.

This type further in size and pressure class oft only if piggable (but not exclusively this reason).

Centric BFL soft sealing on building distribution nets and smaller sizes of this for water purifying plants, mixed with soft sealed gate-valves.

Double eccentric soft sealed BFL valves for larger sizes and if critical (bursting protection valves), mixed up with the shorter lifetime centric BFL valves.

In reality the picture is more complex than this and mixed up in different valvetypes and constructions for checkvalves, regulating valves, motorized valves etc., but I can,t think of a single valvetype I would recommend metal seated within water or water purifying.

Wastewater would have soft sealed knifegate valves in addition to soft sealed gate valves, very seldom eccentric plug-valves for water in Europe.

 

[mkred]

Is there a big cost difference between the two?

 

[gerhardl]

Which two in which context ? (size, pressure class, application, placement, expected lifetime requirement, consequences if failure, geographical area - eg. market availability and price competition)?

 

[bimr]

Resilient seated valves are typically installed in the municipal business:

http://www.eng-tips.com/viewthread.cfm?qid=223891&page=10