Adjustable pool safety valve

A vacuum safety valve for a pool, said pool having a vacuum pump and a drain line said drain line having a first and second end, said first end of said drain line being connected to said pool and said second end of said drain line being connected to said vacuum pump, said vacuum safety valve being connected to said drain line between said first and second ends of said drain line by way of a stub, said valve releasing air into said drain line to cause said pump to lose prime when the vacuum level in said drain line exceeds a predetermined level, comprising:

• (a) a housing having an exterior and an interior, said interior of said housing containing a channel,
• (b) a vacuum port in said housing passing from the exterior of said housing to a first point in said channel, said drain line being connected to said vacuum port by way of said stub and said drain line being further connected through said stub and vacuum port to said first point in said channel by way of said vacuum port,
• (c) a vent port in said housing passing from the exterior of said housing to a second point in said channel to connect said channel to the atmosphere external to said housing at said vent port,
• (d) a releasable blocking means located in said channel between said first and second points to block the flow of air through said channel from said vent port to said vacuum port, said releasable blocking means normally being in a blocking position in said channel, wherein said releasable blocking means includes:
• (i) a spring having a first and a second end and a longitudinal axis running from said first to said second end of said spring, said spring being located within said channel in said housing with the first end of said spring resting against and being supported by said housing,
• (ii) a piston located within and in slidable contact with said channel in said housing to prevent air flow past said piston where it contacts said channel, said piston having a first and a second end on opposite sides of said piston, and a central axis running between said first second end, said piston being capable of moving in the direction of said central axis in said channel and positioned with said second end of said piston in contact with said first end of said spring, and said piston having a hole passing through it from it's first to it's second end to control the amount of air passing through said piston,
• (iii) a plunger being located in said cavity within said housing, said plunger having a first and second end on opposite sides of the plunger with said first end of said plunger being in contact with said second end of said piston without covering the hole in said piston, said first end of said plunger being cone shaped and said plunger having a central axis extending through said first and second ends of said plunger and passing through the apex of said cone, said plunger moving in said channel in the direction of its central axis,
• (iv) an end cap having a first and a second end on opposite sides of said end cap and said end cap being connected to said housing to said channel at its second end, said end cap having a hole through it from its first to its second end, said hole forming said vent port connecting the atmosphere to said channel, and
• (v) a first “O”-ring mounted in said end cap at its first end, and about said hole in said end caps, said first “O”-ring being exposed to said channel and facing said cone shaped second end of said plunger, said cone shaped end being pressed into engagement with said first “O”-ring by said spring to block the flow of air through said channel, and said plunger being pulled back from engagement with said first “O”-ring to release the block to the flow of air through said channel.
• (e) means for releasing said releasable blocking means to permit air to flow from said vent port through said channel to said vacuum port when the vacuum level in said vacuum port exceeds said predetermined level, and
• (f) means for setting at the pool site said predetermined vacuum level at which said releasable blocking means is released to accommodate the different vacuum levels encountered at different pool sites.