![]() ![]() The pressure will equalize due to the energy absorption within the pipe. The shock arrestor absorbs the excess pressure from the sudden energy surge. The pre-charge pressure for the arrestor should be set 10% below the flow pressure. Most flow going through a pipe will be between 4 and 8 feet per second which equates to an increase of 260 to 520 psi. The kinetically created pressure reverberates through the pipe by increasing the pipe diameter to the point of relief, and as the pressure wave is reflected and returns, it constricts the pipe. This spike will occur within a millisecond if the water is stopped suddenly. When water flows, every foot per second water flow velocity creates 65 psi of increased pressure over static. As flow stops and static pressure returns to the system, the pre-charged expansion tank is fully engaged to handle the expanded water.Ī shock and surge arrestor accepts water at the quick closing valve to help dissipate the kinetic energy from the suddenly stopped water column. Thermal expansion protection is not needed since the expanded water is leaving the plumbing system. ![]() As water flows, the flow pressure drops below static pressure. For example, if the supply line pressure is 60 psi, the pre-charge within the expansion tank should be set to 60 psi. ![]() The pre-charge pressure is set to equal the cold-water static or no flow condition. An engineer or maintenance person must first determine the application and pressure requirements of the system to determine the pre-charge setting.įor domestic water heating systems, the thermal expansion tank is positioned between the cold-water supply to the building and the water heater. Pre-charge pressure is needed for bladder tanks which are used in HVAC domestic hot water, water well, pressure booster, and shock and surge applications. In this blog, we will discuss why you need to pre-charge, how to decide pre-charge settings, and the maintenance that should be done on this type of tank. Pre-charged diaphragm and bladder tanks are necessary to protect systems from excessive pressure, energy, or water in a variety of scenarios. ![]()
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