There are many types of valves on your plumbing, but no matter what they are made of or how they look they do the same job. And that is to allow, restrict or stop the flow of water. In this section we will cover only a few examples.
Spindle type valves all have a spindle as the name suggests that once turned clockwise screws down into the valve pushing down a plunger which restrict and even stop the flow of water, depending how much you turn it in. Having that much control over the flow is why this type if valve is used so widely. They also allow the best rate of flow due to little resistence once fully opened. Types of valve that work this way include taps, radiator valves, lockshield valves, pump valves and gate valves.
Ballofix valves again like the name suggests are controlled by the ball inside the valve. The ball inside the valve has a hole drilled through it, so that when the hole is aligned it will allow water to pass but if it is turned 90 degrees either way the water will stop. The way which the hole points is indicated on top of the valve by the slot or handle (depending which type) used to open or close the valve. The only downside is the fact that restrict the flow even whe fully open. They take up less space than spindle valves so are the choice if space is confined.
Spring loaded valves are closed by the spring inside pushing the seat down until a sufficient force pushes it open. This is how dumball valves/check valves work. In the case of a dumball valve on a gravity circulating system the spring has closed the heating circuit to the flow of the hot water from the boiler (stop circulation around the radiators that would occur naturally by convection). But when the pump is turned on the force of the pump pushes the spring up and opens the heating circuit up. However the spring holding the valve closed also stops back-flow as is the case of the check valve. An example of this is on a combi boiler with an external filling loop. It allows water from the cold mains into the central heating to fill it up but doesn't allow the heating to be pulled back through the valve to contaminate the cold water supply.