These Woodpecker Pressure Compensating (WPC) Jr. Drippers feature a built in check valve and will maintain a constant flow rate regardless of placement on the line. Typically used with our plastic weight or dripper stake assemblies for hanging basket or bench top container applications. A unique aspect of this dripper is that it won't begin to emit water until it reaches 5 PSI. That makes it great for greenhouses or systems that need to pressurize before the drippers start working. This stops the problem where the first plants in systems get over-watered before the last plants get any water. This dripper has a pressure range from 2 - 50 PSI.