Lug / Wafer Type Butterfly Valves

[Itayabla]

Hi,

I was wondering if you can help me; what exactly is the difference between the lug and wafer type butterfly valves and when are these specified? I can't seem to find a clear definition of each.

Thanks in advance.

 

[gerhardl]

As seen from Scandinavia we have the same problem of definitions, both in the Scandinavian and the English language as you have.

- One of the reasons is the misuse and mixup of the meaning of the words 'flange' and 'wafer' and 'lug' in specifications and different context. Most often you have to add some extra wording or explanation to be sure of what you are talking about.

There are three different main types of centric BFL valves housing form with this short building length in my opinion:

1. Wafer: To be mounted between flanges, without any flange on the valve itself of any type or ears with threads for bolts.

Note: could be supplied with a set (Normally two or four) 'ears' as open holes with a minimum af material, larger than bolt diameter to help facilitate placement when mounting and dismounting.

Theese ears are sometimes given the name half-lug (type valves), a mixup in my opinion as they have nothing to do with type 2. The mixup is not less as half-lug often is misabbreviated to 'lug'.

2. Lugged (with threaded holes) centric valves. Also called full lug or mono-flange. A lugged type will have threaded holes for normally all bolts. The mixup comes as the mono-flange valve could also have a 'brim' with unthreaded holes, and as full-lug often are shortened to lug, or used to describe unthreaded holes.

3. U-profile flange. With two flanges, one on each side with open holes. Limitation as the flanges normally will have a too limited space between flanges for anything but bolts entered from outside through both flanges and nut mounted on opposite side of pipeline flange.

This type is often misused to offer or use a cheaper valve if a description craves a 'flanged valve' without further additions - but meant to describe the longer building length (as forinstance often given in double-eccentric valves) with flanges so far apart that a separate set of bolts can be used for both flanges. Bolts entered from valveside of valve flanges and out, if needed.

If this can help sort out the common mixup, I would be happy!

 

[itascot]

Wafer valves are "held in place" between two flanges, a lugged valve is bolted onto line flanges through threaded holes in lugs (can be between two flanges, or end of line).
A flanged valve is assembled on to line through nuts & bolts, valve flanges have through holes, not threaded (can also be end of line, however this is fairly uncommon).
Hope this can assist.
Ciao,

 

[rmw]

I think lug valves come in threaded and through hole versions.

I had to choose between wafer and lugged with through holes recently and I couldn't see the value of having a "thread protector" between the flanges, so I chose the wafer.

With the wafer, the OD of the valve is more critical because the OD of the wafer is what locates the valve between the flanges, while with a lug valve, the holes do the alignment.

We have another application where the threaded lug is used so that it can serve as an end of line valve if the line on the other side of the valve is taken down, so we deal with both.

rmw

 

[Scotsinst]

In the refining and O&G production industry, exposed bolts can expand and be a leakage risk during a fire.
A wafer type is therefore only installed in flammable service if protected by rigid fire insulation.
Lug type valves are used in end of pipeline service.
Lug types can be threaded or with the threads drilled out. The advantage of drilling out the threads is ease of installation/removal (removing galvanized bolts and re-installing can cause galling which requires re-cutting the thread). Installing a single through-bolt is easier.
The area near the shaft typically will have two threaded holes on either side at 0° and 180° for machine bolts.
Wafer are cheaper than lug.
Double flanged butterly valves available in triple offset designs are the same price as lug and easier to install/remove but have longer face-to-face dimension.