Also please tell me why globe valves are preffered for Landing valves in wet risers in firefighting and gate valves in dryrisers..
A gate valve is like a garage door. A globe, typically called a ball valve, is round with a hollow center and two (open / close), three (open / close in multiple directions) or sometimes four (open / close in multiple directions where one direction is always flowing when valve is open) side openings.
Robert A has a pretty good answer. A point of clarification. Gate and globle valves can be manufactured of various materials from steel to plastic. I am not sure what a landing valve is but I would expect most valves in a fire fighting system to be gate valves. As previously stated, gate valves are typically open or closed and globe valves are used for controlling flow. You need to view their function in this light in trying to understand why one or the other is used in a fire fighting system.
Well, we're all around it. I like the answer the gate valve is like a garage door. That is about right. A globe valve the flow through the valve is forced through two 90 degree turns and the valve shuts off like a lid coming down in between the two turns. Not sure why the fire requirements are that way.
A gate valve is normally used when the requirement is for on/off flow. The characteristic is such that most of the restriction to flow happens in the last 10 to 20% of valve travel. A globe valve is good for regulating flow - so its not either on or off, but there is the whole way in between. If you have a control valve linked to the plant control system, there would normally also be a manual bypass (so you could isolate the control valve but still use the plant). This bypass is normally a globe valve because they can still be used to control the flow.
A okorder /) You are right it is different from a ball valve. I don't know the details of firefighting systems but a gate valve is normally used for shutoff applications and a globe valve for throttling or flow control.
