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Vent-O-Mat RGXII - Air Release Valves

The Vent-O-Mat Series RGXII "Anti-Surge" sewage air release and vacuum break valve, is an evolution of market feedback and the incorporation of the already proven Vent-O-Mat technology which itself resulted from years of extensive research. The valve unlike many others is not just an adaption of an air valve to handle sewage, but the result of over 30 years of dealing with sewage and seeing what works and adapting it to the needs of the end user.


The original “Anti-Shock” & “Anti-Surge” air release and vacuum break valves for water, sewage, and effluent pipelines.

Vent-O-Mat Advantages & Key Features

  • High capacity air discharge during pipeline filling
  • High volume air intake for vacuum break purposes, both during draining of water pipelines and/or column separations
  • Independent third-party tested
  • Controlled pressurized air discharge releases air when pipelines are fully-charged
  • Surge relief prevents pipeline bursts during pump trip & rapid pipeline filling
  • More compact & shorter to accommodate existing installations and retrofits
  • Designed for low head sealing as well where line pressures are generally lower than normal

Available Configurations

  • Standard – 4 functions
  • Biased
  • Flanged/Threaded Outlet


Size Range

  • 2" (50mm) to 8" (200mm)


  • -40degF to 176degF

Max. Operating Pressure

  • Up to 145psi (10bar)

Min. Operating Pressure

  • 2.9psi

End Connection

  • MNPT, Flanged/Studded ASME B-16.5

Flange Drilling

  • ANSI 150#

Body Material

  • Fusion Bonded Epoxy powder coated Ductile Iron or Stainless Steel 304L or 316L

Top Cover

  • Stainless Steel 304L

Float Material

  • High Density Polyethylene (solid)

O-Rings and Nozzle Seat

  • EPDM

Available Configurations

  • Standard – 4 functions
  • Biased
  • Vacuum-Break Only
  • Vent Only
  • Flanged Threaded Outlet

Surge and Waterhammer Protection

Surge Protection - Initial Filling

The RGXII is always biased in the "Anti-Surge" mode meaning all air release is controlled through the “Anti-Surge” Orifice which is aerodynamically engineered to throttle air discharge when liquid approach velocity would otherwise become too great and induce an unacceptable pressure rise. The air throttling action increases resistance to the flow of the approaching liquid which consequently decelerates to a velocity which reduces the pressure rise when the valve closes (see operation of valve on page ). Vent-O-Mat series RGXII is an essential precaution for pipeline priming.

Surge Protection - Pump Trip Conditions

In instances where a pipeline experiences liquid column separation due to pump stoppage, high shock pressures can be generated when the separated liquid column rejoins.

The Vent-O-Mat series RGXII takes in air through the unobstructed large orifice when liquid column separation occurs, but controls the discharge of air/gas through the "Anti-Surge" Orifice as the separated column commences to rejoin. The rejoining impact velocity is thereby considerably reduced to alleviate high surge pressures in the system (see operation of valve on page ).

Other surge control measures may, dependant on pipeline profile, diameter and operating conditions, be needed to provide the primary surge alleviation function with the Vent-O-Mat sewage air-valves forming an integral and valuable addition in a combined strategy for further reducing surge pressures. The benefit of the "Anti-Surge" Orifice can be readily demonstrated by suitable surge modelling software.

Surge Protection - Pipeline Operating

The operation of valves and similar flow control devices can cause high-pressure transients in an operating pipeline.

The unique, single chamber design of the Vent-O-Mat series RGXII valve enables a pocket of air to be trapped in the valve chamber. Automatic operation of the small orifice control float regulates the volume of air entrapped.

The volume maintained in the valve will provide a cushioning benefit to the pipeline for short duration transient pressure "spikes". This effect can be modelled by the design engineer using suitable surge software


1. Prior to the ingress of liquid into the valve chamber, as when the pipeline is being filled, valves shall vent through the”Anti-Surge” orifice at all times.

2. Valves shall be tested and not exhibit leaks or weeping of liquid past the large orifice seal at operating pressures of 0.2 bar (2.9 psi) to 1.5 x valve rated working pressure.

3. When the pipeline is fully charged valves shall respond to the presence of air/gas by discharging it through the small orifice at the pressures within the specified design range, and shall remain leak tight in the absence of air.

4. Valves shall react immediately to pipeline drainage or liquid column separation by the full opening of the large orifice so as to allow unobstructed air intake at the lowest possible negative internal pipeline pressure.

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Product code

Vent-O-Mat RGXII - Air Release Valves

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