A recent installation at a "Smart House" close to Branson, Missouri used a Sub Drive, the homeowner called an "on demand" system. The multi-million dollar house was all computer controlled, and used a Sub Drive system with a 3 gallon pressure tank. The pump man installed the pump, the plumber installed piping to the house, the electrician wired the system, then the irrigation contractor came in to set up the sprinklers system.
The wellhead was a couple of hundred feet away from the main house and the mechanical room. The Sub Drive controller and 3 gallon tank where installed in the mechanical room. The irrigation contractor teed into the water line out by the wellhead.
Problems were encountered as soon as the irrigation system was turned on. The long distance to the Sub Drive controller, and pressure sensor with a 1 PSI bandwidth, caused the sprinkler system to pulse. The sprinklers would throw 35', then drop to 20', and the process kept repeating itself over and over. The pulsing problem at the sprinklers was similar to the pulsing seen on a standard pump system with a waterlogged tank.
The irrigation contractor had already purchased and installed a CSV at the wellhead, prior to the tee to the irrigation. There was no pressure gauge at the wellhead or on the irrigation system. The system was still pulsing, so the irrigation contractor called technical support at Cycle Stop Valves. Without knowing the pressure settings or being able to see a pressure gauge, the tech at CSV recommended turning the adjustment bolt on the CSV counterclockwise one full turn. The pulsing immediately went away, and the sprinklers began hitting the 35' mark precisely and continuously.
Installing the CSV turned out to be a much better solution than ditching through the yard, and boring a new hole through the house to install the sprinkler line, after the Sub Drive pressure sensor. It was also not an option to put the Sub Drive controller in the vault, as the humid environment would quickly destroy the computerized electronic controller. It was also quickly noticed that the CSV keeps the Sub Drive system from pulsing while small amounts of water are being used in the house. Without the CSV, the Sub Drive pressure sensor was pulsing the pump system 45 times per minute, while a shower or other water use was on. With the CSV, the pressure remains constant, and the pump does not pulse, while a shower or other appliance is being used.
The irrigation contractor was very happy with the CSV retrofit of the Sub Drive system. However, he soon realized that the CSV was doing the "constant pressure" control, and that the Sub Drive itself was no longer being utilized as the main control. Since the CSV is the only "constant pressure" control that is needed, replacing the Sub Drive controller with a standard controller, will eliminate the "harmonics" and "stray voltage" problems to the "smart house" that can be caused by variable speed control of the Sub Drive system.