Ball valves and gate valves serve the same purpose. They will isolate any section of piping desired.
Pressure ratings differ depending on the manufacturer and what type of system the valve is used for. For example, a ball valve can be used on an oil line, water line, gas line where as a gate valve can be used on all the aforementioned systems as well as steam lines.
On older systems (usually multiple dwelling homes) with many hot, cold, and hot water return risers, I prefer to use a gate valve to isolate the riser when the valves need to be replaced because these gate valves are slowly opened and closed by design. The handle needs to be loosened or tightened instead of a lever type as ball valve is designed. By opening a valve too fast, the water fills the void at great speeds which will then break any weak joint in the system. Think of a car crashing into a tree at sixty miles per hour; this is the result of these quick open and close ball valves.
Gate valves can be serviced. The stem and actual gate can be replaced. Our generation does little to service these valves. We are known to replace them, as it is more profitable to replace a valve and section of pipe as opposed to replacing the guts on these valves. Steam radiator valves are the same thing. Let's replace the valves instead of servicing them.
Ball valves by design can be taken apart on the outlet side of the valve. Though they do not have a specific direction on which end to install where; an experienced plumber can see which side can be loosened for inspection.
Valves can be connected (ordered specifically) to which method of pipe connection is desired. For example, grooved valves, pro-pex, crimp, sweat, ips, compression, flared. The only one that can be silver brazed is the gate valve. The guts can be removed and the connections silver brazed. The ball valve can not based on its design and plastic washers.
Ball valves are the new standard (unwritten) of this generation of plumbers.
New construction projects, I use ball valves except of the water mains coming in from the street. Older buildings, my preference is a gate valve.
Side note: ever wonder why you hear a thud when you close the faucet (single lever) or shower body (single lever type)? It's because they are quick closing. This is why hammer arrestor are mandatory now. They absorb the shock of the quick stopping valves, like your car shocks when you hit a pothole. The older style shower bodies and faucets where/are quick closing. They also aren't pressure balanced which is why you'd have fluctuations in temperature when someone opened up another tap.
Shanghai KS Flow Control Equipments Co.,Ltd is a valve manufacture with more than 30 years of valve manufacturing experience, which set up in 1984,specializing in Ball Valve,Gate Valve, Globe Valve, Check Valve and Butterfly Valve.
Pressure range: Class150-Class2500,PN10-PN420.
Size range: NPS1/2-NPS80.
Operation type: manual, gearbox, chain wheel, pneumatic, electronic, hydraulic-pneumatic etc.
Connection End: flanged, BW, SW, NPT, wafer type, etc.
Materials (casting): WCB, WCC, LCB, LCC, LC1~3, CF8, CF3, CF8M, CF3M, CF8C, CN7M, CA15, C5, WC5, WC6, WC9, etc.
Materials (forging): A105, LF1, LF2, F304, F304L, F316, F316L, F11, F22, F6, F51, F316H, F321, F347, etc.