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Mer-Made Filter, Inc. · Pumps, Circulation and Flow Control · Surge tank main drain flow control

Modulating float valves

Fiberglass float-actuated modulating valves that balance main drain and gutter flow inside a surge tank.

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← Back to all productsAvailable through FreyTechFacts verified against manufacturer literature 2026-09-26.

Overview

Modulating float valves are installed inside a surge tank on the main drain line. As the tank level rises from increased gutter flow, the float ball closes the valve to balance flow between the gutter and main drain lines. The manufacturer states the valves are not tight-closing: they are engineered to allow 20 to 30 percent of main drain line flow when the ball is in the full-up 'closed' position so main drain flow is never stopped entirely. The valves operate best between 60 and 70 percent open.

Four styles are offered. FV-S and FV-D are standard single- and double-arm valves for gravity-flow applications. FV-S-XWB and FV-D-XWB are inline valves with an extra-weighted ball, used when the main drain is connected to the pump suction. FV-SP and FV-DP are pivot-style valves that hold the water level higher than the centerline of the main drain in gravity applications, and FV-SP-XWB and FV-DP-XWB are the pivot-style equivalents for inline applications.

Construction is corrosion-grade isophthalic polyester fiberglass with stainless steel metallic parts and an 8 in. diameter polyethylene float ball. Flanges conform to standard ANSI 150 lb drill patterns. The valve is offered in 4, 6, 8, 10 and 12 in. sizes; an elbow may be added as an option. The same valve is supplied as standard on Mer-Made surge tanks.

Is this a fit for your facility?

Usually a fit when

  • Gutter (perimeter overflow) pools with a surge tank where main drain flow must be modulated against gutter return.
  • Competition and large pools that rely on continuous surface skimming through gutters.
  • Replacement of an existing float valve in a surge tank, with 4 to 12 in. sizes and ANSI 150 lb flanges.

Look elsewhere when

  • Applications requiring a tight-closing shutoff valve; the manufacturer states these valves intentionally pass flow when closed.

Ideal facilities and conditions: Surge tank main drain flow modulation; Gravity-flow main drain lines; Inline main drain lines connected to pump suction (XWB models); Holding surge tank water level above main drain centerline (pivot models).

Problems it addresses

Key capabilities and benefits

Capabilities

  • Not tight-closing by design: passes 20 to 30 percent of main drain flow when the ball is fully up.
  • Four styles: standard (FV-S/FV-D), inline extra-weighted ball (XWB), pivot (SP/DP) and inline pivot (SP-XWB/DP-XWB), each in single- or double-arm form.
  • Corrosion-grade isophthalic polyester fiberglass body; stainless steel metallic parts; 8 in. polyethylene float ball.
  • Flanges conform to ANSI 150 lb drill patterns; sizes 4, 6, 8, 10 and 12 in.
  • Optional elbow; standard single float arm on the left side looking into the flow.

Operational and buyer benefits

  • Manufacturer states that modulating the main drain line sweeps surface debris quickly to the filters.

Available models and configurations

FV-S / FV-D (standard, drawing T-11478)Single- or double-arm valve for gravity-flow main drain lines.
FV-S-XWB / FV-D-XWB (inline, extra weighted ball, drawing T-11480)For main drain lines connected directly to pump suction.
FV-SP / FV-DP (pivot style, drawing T-11479)Holds water level higher than the main drain centerline in gravity applications.
FV-SP-XWB / FV-DP-XWB (inline pivot, extra weighted ball, drawing T-11481)Pivot-style valve for inline (pump suction) main drain applications.

Technical specifications

Body resinCorrosion grade isophthalic polyesterSource: https://mermade.com/wp-content/uploads/sites/4/2025/06/t-11478-fv-s-or-fv-d-float-valve.pdf
Metallic partsStainless steelSource: https://mermade.com/wp-content/uploads/sites/4/2025/06/t-11478-fv-s-or-fv-d-float-valve.pdf
Float ballPolyethylene, 8 in. diameterSource: https://mermade.com/wp-content/uploads/sites/4/2025/06/t-11478-fv-s-or-fv-d-float-valve.pdf
FlangesStandard ANSI 150 lb drill patternsSource: https://mermade.com/wp-content/uploads/sites/4/2025/06/t-11478-fv-s-or-fv-d-float-valve.pdf
Closed-position flow20-30% of main drain line flow when the valve is closed (brochure); approximately 20% of maximum velocity (product page)Source: https://mermade.com/wp-content/uploads/sites/4/2024/01/mermade-filter-modulating-float-valves.pdf
Optimal operating range60-70% openSource: https://mermade.com/product/modulating-float-valves/
Suction line velocityMaximum water velocity 6 feet per second in suction linesSource: https://mermade.com/product/modulating-float-valves/
ConfigurationsDisc configuration (FV) with elbow or T options; single- or double-armSource: https://mermade.com/product/modulating-float-valves/

Specifications are summarized from manufacturer literature and depend on configuration. Confirm current values with FreyTech before design.

Installation requirements and retrofit considerations

Prerequisites

  • A surge or balance tank with the main drain entering the tank, where the valve can be mounted and the float can travel freely.
  • Selection of gravity (standard/pivot) versus inline XWB style depending on whether the main drain connects to the pump suction.

Retrofit and replacement notes

  • ANSI 150 lb flange pattern in 4 to 12 in. sizes for fitting to existing main drain flanges inside a tank.
  • Dimension drawings T-11478 through T-11481 are available for checking clearance in an existing tank.

Integration with other equipment

No equipment integrations are documented for this product. Coordination happens through the design team.

FreyTech's role: design, installation, commissioning, training, support

Project services

  • Evaluation of fit for your facility
  • Supply, lead time and pricing confirmed on request
  • Installation and support coordination where the product calls for it

Ongoing service and support

  • Parts, consumables and warranty coordination through FreyTech

Brochures, manuals, warranties and specifications

All resources for Modulating float valves · Request documents

Modulating float valves: frequently asked questions

Does the float valve shut off the main drain completely?

No. The manufacturer states the valves are not tight-closing and are engineered to pass 20 to 30 percent of main drain flow when the ball is in the full-up position, so main drain flow is never stopped entirely.

Which style do I need?

Per the manufacturer: FV-S/FV-D for gravity-flow main drains; the XWB (extra weighted ball) inline versions when the main drain is connected to the pump suction; and the pivot (SP/DP) versions when the tank water level must be held above the main drain centerline.

Related products

See the Pumps, Circulation and Flow Control category.

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Next step

Is Modulating float valves right for your facility?

Send us your pool volumes, current equipment, and what is not working. A specialist will review fit honestly and recommend next steps.

Serving commercial aquatic facilities across New York State.

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