You should be able to shut down n open hose. It controls the pressure and volume available to the tool, same idea as a water tap.

Actually a typical air regulator controls pressure. Volume reduction is just a side effect. Example: An air hose (not open on the end) attached to your compressor will have the pressure your regulator is set at. Like 50 psi for example. Conversely a water fawcet controls only volume. A garden hose attached to your fawcet (not open on the end) will have the system pressure in it at any fawcet setting big or small. In other words if your house water pressure is 60psi then your garden hose will have 60psi in it if it is just laying there not being used with a closed end and the fawcet is open a little or a lot.

several designs. cheap plastic with the knob or metal diaphramn design with the tee handle and jam-nut. The ones we are common with are the cheap ones on low end air compressors with spring and cone shaped seat. when close the cone shape contacts and shuts-off the air. when you open it, it alows a small opening at a time. the shape of the seat, size and design alows the air to be requlated by turning the spring control valve. The cheap plastic ones usually don't work to well like something hangs up when trying to open them up to full pressure.

Best to go to an auto paint/ welding supplier store and buy the good kind, and be done with it. Those el-cheapo's will be nothing but trouble. If you are fairly young, then invest in good equipment and it will last a long time. no use rasslin with the cheap tools.
I have air regulators that are at least 50 years old, and they still work good. When i was starting out in the auto racing game, i borrowed a set of welding guages from a friend. When i took them back, he told me to keep them, so i did. That was back in 1949, and i'm still using them now. I figger they were made back around the early thirties!
And, buy them from a welding shop supplier! Those sets ya buy at the flea market are not very long-lasting, and parts for them might be scarce.