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Lift Plug Type Valves

Lift Plug Type Valves

Lift Plug Type Valves

(OP)
Hello all,

A collegue told me that Lift Plug valves are, in some processes, good alternatives for ball or gate valves as they are full bore, pressure tight and do not wear whilst being turned. I know it is hard to determine how pressure tight a valve is in all conditions, but these are said to shut off better than gate valves.

Anyone experienced with these lift plug valves or knows in which industries/process they are commonly used? Most website argue their lift plug valves are applicable in all severe circumstances, which I think is not a complete unbiased statement...

Thanks in advance,

Roy

RE: Lift Plug Type Valves

Are you thinking Dart valves as used in mining flotation cells?
They consist of a tapered rubber plug fitted into a rubber lined seat, they usually leak a little but considering they throttle abrasive slurry work very well.
Roy

RE: Lift Plug Type Valves

(OP)
Thanks for your reply Roy. I'm thinking of an isolation valve with the same flow-characteristics as regular plug or ball valves. Their main difference is that lift plug valves are slightly lifted before being turned 90 degrees, in order to avoid friction and high torque within the seat.
If they are applied in froth flotation cells...I don't know.

Roy

RE: Lift Plug Type Valves

I believe you are talking about double eccentric plug valves. The closing element 'plug' is a curved plug segment, closing the full bore opening in shut position. Spindle is positioned sligtly off centre pipeline and off centre circle curve of inner housing wall. This will have a lifting and freeing movement of the segment in the first 2-3 degrees of opening turning, and by 90 degrees the element will give a full open port.

This is similar to what is happening in double eccentric ball valves. Except that here the the closing element is a full bore ball, with seat sealing ring mounted on the ball itself. In full open position the sealing is turned 90 degrees away from main flow, and the ball has both a full port and in addition a flow around the ball against the wall to get grit away.

The eccentric plug valve is a available on the market, althoug not that common, the use mainly restricted by sealing properties and cost. The soft sealings will have good and waterthight properties, when metal poorer.

Mostly other types of quality valves will be selected as 'good enough' and cheaper. The price of the valves will often be above other types of valves.

One segment of use is large valves for waste water with large gate valves or knife-gate valves as competitors.

The plug valve will cost considerably more, but will have (in top quality) a very long standtime.

RE: Lift Plug Type Valves

(OP)
Thanks again for the replies lads. I've done some research myself as well and I think Pennpiper's Orbit valves comes the closest to what my collegue meant.
personnally I think that, looking at the design of those eccentric valves, they don't seal completely close accept for low pressure. Further I think the body may suffer from cavitation problems.
The lift-turn-reseat valve as I guess it's officially named, has full-bore entrance without cavities as in standard ball valves. I think the Orbit also has this feature.
The difference between both is that the lift-plug is taken from the seat horizontally, and the Orbit vertically.
However, I think that the moving part in the Orbit is a bit loss in open position, which might cause damage. Is this correct?

Though I wonder in which applications these Orbits are currently used. They seem better than Eccentrics at high velocity to me.

RE: Lift Plug Type Valves


Hi out there,

Let us take a break before we go further . This is becoming a very interesting discussion!

Please let me throw in some points:

1. If you look at the Orbit construction, the first movement away from the seat when opening is actually the 'horizontal' caused by the eccentric placement of the stem in the ball, then afterwards the uplift caused by the threaded stem starts. The Orbit is in my opinion more a ball than a plug valve,

2. The Camflex is mainly a regulating valve but closes and opens double eccentric. It is clearly not a ball valve and neither in my opinion a plug valve, but rather a disc or globe valve.

3. A 'standard - non orbit' double eccentric ball valve will close and open 'horizontally' without lift.

4. A double eccentric plug valve will consist of a segment of a cone or a complete cone but with full opening.

All these constructions have eccellent sealing properties, drop thight, given that the operating data: pressure in and out, fluid velocity (flow) fluid properties, temperature and viscosity included, and regulating requirement (if any) all are within what the valve is constructed for.

The double eccentric sealing is a sealing with normally far better sealing properties and lifetime than for centric valves of same construction, valid for plug, ball, globe and butterfly and other double eccentric constructions.

Conclusion: Cavitation and general lifetime and economical cost/lifetime considerations can only be evaluated, and advice given, if the exact operational data is given and valvetypes to be compared are given.

I suspect you are into the smaller sizes (4 inch or lower?) rather than the larger (above 24 inch). But what is 'high velocity', pressure and the other fluid and operational details?

Some double eccentric ball valves are constructed for more than normal fluid velocity without cavitation if on/off operation.


 

RE: Lift Plug Type Valves

(OP)
I'm currently not into a specific solution for a system, but more trying to broaden my expertise in different shut-off valves. This means I have no exact operational data to compare the different valves. However, I think this discussion is becoming pretty interesting as well.

I think that the lif-turn-reseat plug valve is very suitable for fluids or gasses containing small, dusty particles which might damage the soft components of valve when the velocity is high or when turning the valve.

It seems that all mentioned options have excluded the seal rubbing during rotation(low torque and damage) and all have the possibility to be actuated. Some points of difference:

-The Camflex indeed seems to be for throttling rather than on/off. I suspect that the complete shut off sealing is only at relatively low pressure, as in dome valves as well.

-The eccentric ball and orbit both leave the seal because the eccentric placement of the stem. What is then the function of the rising stem in the Orbit?

-The eccentric ball and orbit both aren't reseated after opening. I think this might cause abrasion at some points. Compare this to an opened (knife)kate valve suffering abrasion on the seal openings at high velocity. A lift-plug or normal ball valve does not have these small openings.

Conclusion: All mentioned valves can be operated at low torque and do not suffer from friction particles during operation. However, only the lift-plug is reseated after opening, ensuring a longer lasting life.

What are your comments?

RE: Lift Plug Type Valves

(OP)
I've come some further in my lift-plug orientated research, which make me think I can state the following:

All other mentioned valves are driven with low torque.
The eccentric plug and Camflex are designed for throttling.
Orbit and ecct. ball aren't reseated in open position, making seat wear possible.
This makes a lift-plug in OPEN position more equal to a standard metal-to-metal plug or ball valve, but with lower torque.
The lift plug is definetly more complicated to actuate than all other options, though I think to most competative design is an ordinary metal-to-metal ball valve.

As I read in one of the otehr topics(can't recall which one) there is a 'best' valve for every solution. I think this is correct, but I also think that the market shows very low transperenct due to al modified types of valves.

So, you experts, what do you think of my analysis and what would you consider the most suitable market for lift plug isolation valves.

Regards, Roy

RE: Lift Plug Type Valves

Just stumbled accross your thread deep into a Google search for something else ... I'm a valve guy ... albeit Non-Industrial, i.e. Municipal Water & Wastewater and Hydro.  Been around a long time.  I believe what your colleague was likely referring to is the metal to metal conical plug valve more commonly known as the cone valve.  Been around since 1926 as a pump control/check valve for controlling discharge of large pumps used in the water and wastewater industries.  Employs a traveling nut type valve operating mechanism that firsts lifts the conical plug off its seats, then rotates the plug 90 degrees and finally lowers the plug back into the seats.  It's close cousin is the AWWA ball valve both metal to metal seated as well as rubber seated.

Hope this helps!

Feel free to contact me if you have any additional questions.

 

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