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Float or Modulating Valves for Pool Surge Tanks Modulating or float valves are used in surge tanks or vacuum D.E. filter tanks when the top of the tank is at an elevation above the maximum pool water level. In this type system the water level in the surge/filter tank will rise to the same level as the pool water level when the system is shut down. The walls of the tank must be slightly higher than the pool water level. If this is not the case a tight closing level control valve must be used. Modulating float valves are not tight-closing, in fact, our valves are designed to pass some flow when the ball is in the up or "closed" position, so as not to stop main drain flow entirely. The optimum operating condition for the float controlled valve is between 60% and 70% open. The resistance to flow between these two opening positions establishes the minimum depth required for the center of the main drain line so that the desired flow can be maintained.  If the depth and size of the line are incorrect the proper flow rate will not be attainable.  At full closed,  the valve will flow at approximately 20% of the maximum water velocity. Maximum flow in a suction line is normally 6 feet per second of water velocity. Mer-Made offers two different styles of float valves. The basic float valve is the disc configuration (FV) which can be fitted with an elbow or "T". The elbow directs the flow below the water level to minimize the turbulence and the associated generation of chlorine fumes. The "T" configuration allows the pool to be pumped out via the main drain line. A manual valve must be mounted on the "T" leg which can be closed from the deck (long shaft on the handle) to allow pump suction on the pipe from the main drain.  This configuration requires the use of the XWB modification.

The basic float valve will maintain the water level at about the top of the valve body with little or no adjustability. The pivot arm float valve permits adjustable water level settings by the addition of a pivot arm and bracket. The float ball can be set to the minimum or maximum location shown.

See Technical Information section for values of depth versus flow.  Use the chart to select a value and minimum depth needed to achieve the flow rate for the pool turnover you require.  Note that the depth from the chart is NOT all that is required.  To this depth you must add an estimate of the losses in the main drain line before the valve.  The valve tables are limited to a maximum water velocity of six feet per second.  This velocity will generally give line losses which are much smaller than the losses through the modulating valve.