What causes a rapid closing down of hot water valve and convulsive knocking when turning hot water on in an outdoor shower?

Answer 1

Water Hammer is best described as the result of instant decrease of volume through the piping system. For instance: If you have a pipe and valve in the fully open position then the pressure is being quickly released through the valve and very little pressure is put on the pipe system. The water however is traveling through the pipe system at a high velocity to get to the open valve. If that valve is suddenly closed then the pressure within the piping system remains the same but the velocity goes from high to zero instantly. The resulting decrease in velocity will sometimes cause the hammer effect within the pipes. It is just like having a box on the seat of your car when you are traveling down the freeway. When you are going very fast the box remains in place and is not a nuisance. If you gradually slow down the car the box remains in place and no problems are noted. If however, you stop suddenly, then the box continues to move in a forward direction and hits the dash with a thud. If your pipes are securely in place within the walls there is usually little or no hammer under normal conditions. if the pressures within the system are high or the pipes are not very secure within the walls and floors of the house, then the water hammer condition can occur. a simple HAMMER ARRESTOR installed in the correct position or even an EXPANSION TANK placed at the hot water heater is a very in-expensive and reasonable solution. This is much less expensive than removing the drywall at the piping path and re-securing the pipes along the entire path. Soldering or special tools and skills may be required depending on the type of piping that you have. Your local home improvement store may have everything that you need. Assistance from a plumber may also be required. However, both of these solutions are reasonable for an experienced home owner to do in a couple of hours. Hope this helps! Terry