Hot water system and valve

A gravity operated valve comprising:

• (a) a valve casing comprised of lower and upper sections secured together detachably, the lower section having an inlet fluid passage and the upper section having an outlet fluid passage and a vertically elongated communication passage communicating the outlet passage with the inlet passage,
• (b) a valve seat ring secured removably between the lower and upper valve casing sections and having an upwardly facing annular valve seat facing said communication passage,
• (c) a hollow vertically elongated cylinder secured to said valve seat ring outwardly of the annular valve seat and extending vertically upward into said communication passage, the cylinder having a cylinder wall having an outer diameter substantially smaller than the diameter of the communication passage, the cylinder having a closed top and an open bottom communicating with the valve seat ring opening, the cylinder wall having an opening therethrough adjacent the valve seat ring,
• (d) a weighted piston slidably fitted within said cylinder for vertical movement therein, said piston defining an upper cavity within said cylinder above said piston, said piston having a valve face on the bottom thereof for sealingly fitting on the upwardly facing valve seat on the valve seat ring when the fluid pressures at said inlet passage and said outlet passage are in substantial equilibrium, said piston being free to rise off said valve seat toward the closed top of said cylinder when the fluid pressure at said inlet passage is greater than the fluid pressure at said outlet passage, and
• (e) a flow limiting passage communicating the communication passage in the upper valve casing section with said upper cavity in the cylinder for dampening the speed of movement of the piston in the cylinder.