Control Valve Station Design

[tkdhwjd]

Dear Colleagues,

When the required body size of a control valve is lower than the inlet and outlet line size, inlet reducer and outlet expander are normally provided. Under what circumstances do we use eccentric reducer/expander? Likewise, under what circumstances do we use concentric reducer/expander? If eccentric type is required, under what circumstances do we use bottom flat orientation (or top flat orientation)? Are there any industry standards? Thanks in advance for your help.

 

[JimCasey]

Eccentric reducers (bottom flat) are useful if the valve is presented with 2-phase flow (Gas and a liquid) . It makes sure the liquid-phase does not puddle and accumulate. At some point that would lead to steam hammer in the valve as the flow alternated between liquid and gas flow. That is highly unusual-usually the flow into the valve is single-phase and it becomes 2-phase due to the throttling process (Flashing/Cavitation) but I digress. I can't imagine a case where it would be advantageous to install eccentric reducers flat on top.

One other trick: Insert a valve-length nipple between the upstream reducer and the valve. This is particularly helpful on wafer-style valves because it ensures that there will be room to install or extract the studs. I have seen cases where the reducer was installed against the valve on both sides and the studs hit the reducer before they could be threaded thru the flange.