During our relay pumping/LDH seminar last May in Shelby County, Alabama, we came across an interesting use of a 5" jumbo wye and a 5" double-clappered siamese. The use of the two appliances occurred during the relay pumping drill where 2,200-ft of 5-inch hose was deployed in an effort to practice adding pumpers to a long hose lay. There were no in-line relay valves available for use so one group of folks decided to use a jumbo wye, a siamese, and a short length of length of 5-inch LDH to create their own "in-line" set-up to allow a 1500 gpm pumper to be added to the middle of the long hose lay.
The idea worked just fine and the pumper was able to increase supply pressure and output to the operation without interrupting water flow. You have heard us say this many times, if you use LDH then it is important to have plenty of adaptors and plenty of appliances so that most any water supply matter can be addressed in little time.