Apart from the construction and manner of operation of the closure member, are there any other differences between gate valves and needle valves?  Manual or actuated... or any other distinguishing feature asides?The key difference is called "linearity".  For a needle valve, the flow vs. valve opening is nearly linear (e.g., if the valve is 30% open then it will pass about 30% of it's maximum flow). 
The linearity of a gate valve is nearly non-existant.  A gate valve will pass 100% of maximum flow at about 25% open.  At 10% open it will pass about 5% of maximum.  A plot of flow vs. percent open (for a given set of pressures and temperatures) is sharply non-linear.  If you ever try to throttle with a gate valve you'll see that the quiver in the valve position will give you a wildly varying mass flow rate.
I've never seen a case where a gate valve had a legitimate place in any measurement application.

MORE NEWS