| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 100 === The function of a pressure balance valve is to protect the user of shower from scald or temperature surge. Transient temperature variation normally happens in ordinary houses with single loop plumbing system. When the shower is in use and another valve in the same loop, such as toilet, washing machine, or basin faucets is opened, cold water pressure will drop instantly, while hot water pressure remains the same. As a result, hot water will surpass cold water, and the shower user will feel the temperature surge. Sometimes it will cause serious problem of scald.
Pressure balance valve is designed for preventing this problem. It is made of a floating piston moving horizontally in a fixed frame with openings in both sides of hot water and cold water. The motion of the piston is determined by the pressure difference between hot water and cold water. With the adjustment in flow area, a new equilibrium state can be reached.
The flow characteristic of the pressure balance valve is investigated in this paper. A test stand was established to measure the flow rates of hot water and cold water as the pressure on one side was adjusted while that on the other side remained the same. The motion of the floating piston was also observed to find the final equilibrium position as pressure was changing. It was found that there is an overshooting in the adjustment of the flow area. As the cold water pressure is reduced, the valve will overact such that cold water would surpass hot water, and the resulting temperature is lower than the expected value.
The flow in the whole plumbing system as well as inside the pressure balance valve was also developed in this paper to investigate the flow variations of the system. It was found that the leakage inside the pressure balance valve plays an important role in determining the final equilibrium flow rates. That is, hot or cold water will pass through the gap between the floating piston and its frame during the process of balancing, and result excessive or insufficient flow compensation. These all affect the temperature we expect to have. This study aims to probe into the existence of the pressure balance valve.
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