difference between gate valve and stop cock?

Gate valve:
A circular disc (the gate) which is perpendicular to the flow direction and to the pipe is raised vertically when the spindle is turned. When the gate valve is fully open, there is no restriction to the flow and you can see striaght through from one side of the valve to the other. A Sluice Valve is a bigger version of the same thing used on water mains (4",6" and bigger pipes). A gate valve usually has a hand wheel on the spindle.
Stop Cock:
A circular disc or jumper which is parallel to the flow is raised off its seat when the spindle is turned. Even when this valve is fully open, there is some restriction to the flow because the water has to flow upwards and over the seat before it can pass through the stop cock. You cannot see straight through from one side of the stop cock to the other. A stop cock has the same type of square topped spindle but instead of a crutch wheel has a crutch top - a straight cross piece on top.
Isolation Valve - any valve could be used for isolation but the most common type would be a lever type - which consists of a ball with a hole through it and a spherical seat. The ball is mounted on a spindle attached to a a hand lever - which turns through only 90 degrees from fully open to fully closed.

JD
April 2009

Put each term in turn into Google and select IMAGES

Gate Valve returns 347,000 pictures (a gate is lowered to control the flow)

Isolation Valve 95,800 (isolates part of a system)

Stop Cock 7892,000 (usually isloates a whole system)

Stop Tap 4,390,000 (more socially acceptable version of above)

Peccavi
April 2009