This valve configuration is typically used to select between the main hydraulic system and the emergency backup that’s biased in the normally closed port. Its non-interflow design means that its three ports are never open simultaneously. These valves can also be used to extend a large unequal area actuator, where reduced actuation force may be permissible in one direction. Lee spring-biased shuttle valves are available in sizes from 0.187 to 0.500 of an inch.