Control Valve

You have a valve designed for the southern hemisphere.

Probably because a customer wanted it that way, or the process dictates it.

Dear,

Thank you for the comments.

There must be some technical reason's, other than these known ones and I am searching for that.

Rgds.

These valves open while moving downwards and close during upwards movement. These are called reverse acting valves. They are normally spring to close and air to open type. The system pressure works against the closing of the valve. Here valve opening time should be short and is more important than closing time and should be used in such requirements.

Dear,

Thankyou for the comments.

My question is with regards to the valve body not the actuator.

Rgds.

On any normal application, the fluid enters from the bottom of the valve disk against the closing force (force exerted by air). But if reversed, say fluid enters from the top of the disk, the fluid pressure (force) adds to closing force exerted by air. If an application calls for positive closing (besides controlling), may the later is preferred.

Arif,

this is often done to get a better "flow" of the medium. (noise reduction)

The medium expands from one side of the plug to the other side.

In reverse flow there is more space for the mediun to expand, only you need more power to open the valve (bigger actuator), to compensate this you can use a balanced plug.

Hello Arif

Flow over the plug or under the plug in case of Globe valves and Shaft upstream abd downstream incase of Butterfly valves

Over the plug is used to ensure flow assists in valve shutoff. Shaft Upstream must be selected if the actuator is sized for a shutoff pressure lower than maximum upstream pressure,

In addition to the answers already given, you may find good information in the Fisher Control Valve Handbook.

All the best.

Dear,

Thank you for your guidance.

Rgds.

For the answer check out the link:

http://aboutinstrumentation.blogspot.in/2011/11/all-about-control-valves.html