Can someone please help me out with the differences between;
1.a manual gate valve and hydraulically actuated gatevalve
2.needle valves and gate valves.
i will be very thankful if someone could help me out.

Manual gate valve has a handwheel and a hydraulically operated gate valve a hydraulic power cylinder. Some hydraulically operated valves use the water pressure to operate the valve through a series of solenoids. The more common type of hydraulically operated valve is a globe valve. research Cla Val, Singer and Dorot websites.

A needle valve has a slender tapered form so turning the handwheel opens the orifice slowly. A gate valve has a corcular hole with a wedge tha fills the holes. Suggest you research the Crane, Tyco and Hoke websites to see the various types of valves.

You, as well as all others, will get more precise answers if you try to give a bit more details when posting questions.

Actual sizes and pressure classes are some of the more important issues.

Example: If you are here talking about larger sizes (more than 4 inch (100mm) for needle valves, a needle valve in the English language, could also describe a complete different type of valve from the common needle valve: a regulating (for pressure and flow control) valve with most common vaned ring or slotted cylinder, up to 40 inches  (one meter) or more, constructed to avoid cavitation, and  with a wide control span.

(In other languages, for instance German, this type will have a more precise name: 'ringkolbenschieber' translating to 'ring-piston axial (type valve)'.)

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