A valveless pulsejet (or pulse jet) is the simplest known jet propulsion device. The second type of pulsejet is known as the valveless pulsejet. Ink jet printers operating on the Piezoelectric transducer principle also use valveless pumping. As with conventional pulsejets, there are two main types of designs&colon; valved and valveless. A valveless oil pump improved the Hudson splash lubrication system. The post horn ("also" post-horn) is a valveless cylindrical brass instrument with a cupped mouthpiece. Micropumps having nozzle-diffuser elements as flow rectification device are commonly known as Valveless Micropumps. Valveless pumping assists in fluid transport in various biomedical and engineering systems. The internal-combustion analog of the pop pop boat engine is the valveless pulse jet. This regenerator may be part of a valveless system, such as a Stirling engine. It was the grandfather of all valveless pulsejets. In 1915 De La Rue launched the Onoto Valveless. Due to a valveless design, Duke engine loses less energy between the power strokes. Valveless pulsejets are low in cost, light weight, powerful and easy to operate.