What device siphons a liquid into a water stream using the Venturi principle?

The device that siphons a liquid into a water stream using the Venturi principle is the eductor. This device operates by creating a pressure differential through the Venturi effect, where the fluid flow speeds up as it passes through a constricted section of pipe, leading to a drop in pressure. This drop in pressure allows another liquid to be drawn into the flow stream from a separate source, effectively mixing the two fluids.

In firefighting and emergency response scenarios, eductors are commonly used to introduce chemicals or foam concentrates into the water supply, enhancing the effectiveness of water for firefighting operations. The ability to mix a supplementary liquid seamlessly with water increases the overall effectiveness of extinguishing agents.

The other choices serve different functions in a fluid or firefighting context. A metering device is typically used to measure the flow rate of fluids rather than to siphon them. A foam applicator is designed to deliver foam solutions but does not utilize the Venturi principle to draw in other substances. Lastly, a pressure relief valve controls excess pressure in systems but does not assist in mixing or siphoning liquids. Understanding the specific functions and principles of each device is essential for effective operation in various scenarios.