Wafer or Lug? 1

[Foxtrap]

Howdy,

I am new at picking valves. I don't know if I have enough information to pick the right one. I was asked to find quotes for an 8" butterfly valve, sour-trimmed, air actuated to be used in an abrasive service application. As I started researching them I have discovered some two types of bodies, the wafer and the lug. Does anyone have any recomendations?

Thanks,

Foxtrap

 

[askmeaboutvalves]

HelloFoxtrap,
With respect to your application, the wafer valve is typically used between two raise flaced flanges and then all-thread is used to "sandwich" the butterfly valve between the flanges. The pressure of the nuts on the backside of the flange squeeze the gaskets into the face of the body and hold it in place. This is a common installation. The lugged version has drilled and tapped, or threaded ports that would match the bolt circle of the mating flange, thus allowing the use of a bolt to hold the valve in place. This is typically used in whats called an end of line servive, where you might want to isolate a pump or piece of equipment. This configuration allows you to remove the downstream flange and leave the upstream flange attached to the butterfly valve and isolating the pressure in the line.
Bottom line, if you want to be able to remove one of the flanges and retain pressure upstream, you need a lugged version.
Sour trim and abrasive service, need special attention (NACE) and hard facing on disc edge and seating. In some cases, you may need hardened body and sealed bearings to keep contaminants out of the bearings.
Hope this helps.
Bob

 

[GeoSmith]

For the sour trim and abrasice service, it is not good to use the triple-offset butterfly valve? AM I right?

 

[TBP]

Unless there's some special reason to use wafer style, anybody involved with maintenance, will prefer lug style for the reason "askmeaboutvalves" gives.

 

[joeswoes]

The body connections are irrelavent to your application. Makes sure valve is installed with stem horizontal to keep the stem seals clean of any settled debri. Also, watch out for surface treatments on discs as their great while they last and a slurry can get to the base metal quickly. Depending on your expected life, there's dozens of ways to skin this cat. UHMWPE plastic is an outstanding abrasion-resistant material, as are many rubbers.

 

[Foxtrap]

I was reading further into valves and there was a note that wafer was not good for between slip-on or threaded flanges because of the possibility of not having a complete seal. I was wondering if because this is a H2S service that it was common to use the lug style?

Geosmith: Why is a triple offset valve bad for abrasize and sour service?

Is there any more things I should be taking into account?

Thanks for your help to far?

 

[NGiLuzzu]

Foxtrap,
if You use tripple-offset metal-seated design (there are many discussions about that within this site, such as thread408-135872, thread408-126483 and others...), in addition to the sealed bearings and the horyzontal installation already mentioned, I'd suggest to make sure - if possible - that the valve is installed with the "flat face" of the conical seat below and the "inclined face" above (so that the possible solid particles accumulation may be removed more easily by the opening and closing movements of the valve disc itself...).

A solid seal ring (if the sealing element is on the disc) in a properly hardened or coated material may also be useful.

Hope this helps, 'NGL

 

[JimCasey]

I'm a lot more concerned about your application than I am about wafer or lug connection. To paraphrase what was stated earlier: Lugged valves are for the guys who work with them, wafer valves are for purchasing clerks.

Butterfly valves in abrasive slurries can be great or they can be a disaster. The original rubber-lined butterfly valves were developed for cement dust. A cast-iron vane and a rubber liner lasts pretty well in that application. There are also rubber-encapsulated vanes to protect against abrasion. They make tires out of rubber...abrasion resistance is one of the primary reasons. Automotive brakes are made of cast iron for the same reason. The best trick for ruber-lined valve in abrasives is to undercut the vane: i.e. to reduce slightly the diameter of the vane, so that the vane does not grind grit against the seat with ans much force as a standard-fit valve would.

What is the temperature of your application?
What is the flowrate in your application/line-size/velocity?

High-performance (double-offset) valves are not as successful in abrasive services as symmetrical butterflies. The seating surface on an HP valve is narrow and must be polished. Turning the vane with the finely-polished edge facing directly into the abrasive flow results in the finely-polished surface not being there for you when you need the valve to shut off. The seats are usually convoluted to be process-energized. Packing the convolutions with abrasive fines does not contribute to their successful functioning.

Triple-offset valves seat without wiping action, so they tend to trap chunks between teh vane and seating surface. There is an active sealing member in most TO valves (One MFR calls it a lamellar ring) , and the crevice between the active sealing member and its holder can pack with fines. Again, if this gets chewed up in the open position, the valve will leak when you try to close it.

If your slurry temperature is compatible with elastomers, use a rubber-lined valve.
Try to keep the velocity between the values where the particles drop out, and an upper limit of around 12 FPS.

Earlier advice about having the stem horizontal is valid. ALSO put the actuator on the left side (looking downstream). Actuators customarily open CCW, so this installation will push back/dislodge/flush the settled layer of sludge at the bottom of the line as the valve opens.

One other trick is to put a 1" thick steel plate in the pipe upstream of the valve, in the same plane as the open vane. This will work like an inertial cleaner, deflecting the larger chunks and allowing the open vane to stay in its protective "wake". This will protect the LE of the vane and help extend the life of the valve. It needs to be as close as possible to the valve, but make sure you can get the vane completely open.

If the service is too hot for elastomers, think about a ceramic ball valve instead.

 

[Foxtrap]

Is a butterfly valve the way to go? Is abrasive service too hard on the vane and seal seat to be effective without having to replace it all the time? Should I really consider a knife valve? I was looking at previous threads and found one on the knife valve. They were specifically saying "for use in slurry applications".

I unfortuately I wasn't made familar with the application except a few details, the ones forementioned and that it is Ø8" and should have class 150 flanges (or BC).

Thanks for install advice. I probably would have missed the horizontal installation.

 

[GeoSmith]

The triple offset is bad for abrasize medium because they are made of metal only, without plastics in the valves. Espeically seal and seat surface. But, I am not sure which metal is more resistant to the corrosive and abrasize fluid?

 

[GeoSmith]

JImcasey,

I don't understand the last trick that you mentioned? How to put the 1" thick plate in front of the valve. What is the meaning of vane? Why it can extend the life of the valve? Thanks in advance.

 

[rmw]

He used the term vane, while others might use the term disc. He is advocating putting the 1" piece of platae right in front of the disc upstream and in the same plane as the disc so that it acts as a deflector causing abrasive particles to flow around the disc which is in the wake of the deflector plate.

Interesting idea.

rmw

 

[JimCasey]

I would be so much better able to describe stuff if I could post images to this forum....My wife says I can't even speak without a pencil in my hand.

Thanks for clarifying what I had said, rmw.

Still Foxtrap could be a LOT more explicit about his application. Process ladings, chunk size, pressures, temperatures, flowrates. Whether he needs on-off or modulating control. The biggest difference between whether he needs a $400 rubber seated butterfly valve or a $10000 ceramic ball valve is about 150 degrees in his process conditions.

Pinch valves can be useful for chunky slurries, knife-gate valves can be great for stringy slurries, but where one works the other would likely be awful.

 

[Foxtrap]

Hello,

I do apologize for being quite vague in my application description but that is mostly due to the fact I was unequipped to ask the questions I needed to know from the client before finding a valve to recommend.

I was looking for help in the recommendation but also an idea of what are the factors involved specifying a valve. What is a pinch valve?

Foxtrap

PS: "Her" application...

 

[jsummerfield]

Use a lugged valve not a wafer for flammable service like sour gas. In the event of fire the expanding through-bolts permit the sour gas to feed the fire.

John

 

[JimCasey]

A pinch valve uses a reinforced elastomer tube (like a radiator hose). The actuator squeezes on both sides of the tube, to "Pinch" it shut. Sometimes there is no actuator, just a pressure chamber around the tube.The tube is molded "squashed" and pressurized open by the process. When you pressurize the chamber to something greater than the process, and the pressure squeezes the tube closed. The tube will form around chunks in the process and seal. Obviously limited by the properties and chemical compatibility of the elastomer with the process fluid (Significant variety available), and it takes a relatively high actuator force due to the large unbalanced areas. See "Red Valve" for info on Pinch valves.