These are the tried-and-true workhorses for measuring flow in a pipe. Think of a fixed-orifice flowmeter like putting your thumb over a garden hose: the water has to squeeze through a smaller opening, which makes the pressure drop right after the pinch. This meter simply measures that pressure difference—the bigger the drop, the faster the fluid is flowing. Because there are no moving parts to break, they’re super reliable, simple to install (usually just an orifice plate bolted between pipe flanges), and they can handle almost any liquid, gas, or steam you throw at them. They’re a cost-effective, dependable solution, though you should remember they cause a small, permanent pressure loss in your line.