Gate valve, wedge 2

[rocio74]

Hello all,

I would like to know if exist some rule in the selection of the wedge type (solid, flexible, parallel slide, double disc, etc) of the gate valve.

In the valve specifications that I have, the solid wedge is used for all diameters in 150# and for diameters lesser than 2" for 300# to 2500#; from 300# until 900# the flexible wedge is used for diameters bigger than 2"; for 1500# and 2500#, the parallel slide or double disc is used for diameters bigger than 2".

Currently, I have to select the wedge type for the gate valve of 48" in 150# and 300#. I would like to know if I can select solid wedge for 150# and flexible wedge for 300#



Thanks in advance,

Rocio

 

[gerhardl]

All valve selections, in my opinion, starts with a complete description of application, full fluid description with flow, pressure, temperature , operation mode and cyclus, certifications, material requirement,etc, etc..

Secondly: within theese parameters: what is available commercially, to what deliverytime, price, operational cost including maintenance and life expectancy at local conditions. Survey to include (idealistically) all valve constructions suitable. (Why wedge valves only?)

Third: selection for each single (group?) of valves, idealistically again best value cost over required lifetime.

Reason: the market and product construction changes. True values ten or fifteen years ago need not necessarily be true today.

Apart from this a 'rule of tumbs' and experience over time has its value, but if this is refitting or valves for a new project I would try to 'open up' for market and product input before deciding or setting up 'locked' data sheets.

 

[rocio74]

I understand what you are saying but, in my job, I have to prepare the valve specifications before to make an offer request to the suppliers. Therefore, I need a criterion to select valves which it can be based on experience, other projects, etc.
The data that I normally have for preparing the specifications are: fluid/service type, pressure, temperature.

As I commented previously, I have to select the wedge type for the gate valve of 48" in 150# and 300# for the services: vapor, water and condensate. Maximum pressure 25 bara and maximum temperature 220ºC.



On the other hand, what is the difference between solid wedge and flexible wedge? what is better? is it only an economical question?




Thank you very much for your help,

Rocio

 

[gerhardl]

Hi,

I suggest that you use the forums search function (bar on top of forum page) to view previous threads, which will give you some input.

For instance below link, where Jim Casey corrects and supplement me on details more regarding your practical use.

http://www.eng-tips.com/viewthread.cfm?qid=179684

Using search words flexible wedge and wedge will lead you to some other threads

 

[rocio74]

Thank you very much Gerhardl, I will use the linf for my purpose.


Bye,
Rocio

 

[reverman]

Most manufactures have standardized on flex wedge for most valves over 2" regardless of pressure class.


If I was writing a spec today I would just specify flex wedge for all valves over 2", possibly with an exception for 3 and 4" class 150 valves those can be solid or flex. (wedges 2" and under are too small to make an effective flex design)

 

[rocio74]

Thank you for the aclaration,

Regards,
Rocio

 

[franen]

In my experience is more frequent solid wedge for low pressure also for big size velves, you can find also flex wedge, instead parallel or double disc are unusual.. For this kind of valves is better to foresee a relief device for overpressure in the body neck, especially for vapour/steam applications
Bye
Francesca