Variant combination air release and vacuum break valves protect pipelines from damaging vacuum conditions while ensuring that the system maintains design efficiency. The integral anti-shock feature provides protection against the damaging effects of uncontrolled filling and pump stoppages.


  • High capacity air discharge
  • High capacity air intake
  • Pressurized air release
  • Surge alleviation


  • Optimum flow characteristics
  • Low pressure sealing
  • Compact design
  • No dissimilar metal corrosion

Operation of Variant Air Valves

Large orifice air discharge

During initial filling the pipeline is filled with air. As water is introduced into the pipeline, the air flows naturally towards the highest points along the pipeline. Air valves, positioned at these high points, allow air to pass freely through the large orifice to atmosphere.

Vacuum break

During scouring or when a pipeline ruptures, it is imperative that the pipeline is protected from damaging negative pressures. Variant air valves provide a full bore, unimpeded flow path that maximises the valve’s air intake capacity. The rapid inflow of air effectively prevents damaging vacuum conditions.

Pressurized air release

During normal operating conditions, air accumulates in the air valves, located at the high points along the pipeline. Once sufficient air has collected in the valve, the automatic float drops, opening the automatic orifice and allowing the air to escape to atmosphere.

Surge protection

Should pump stoppages cause water column separation within the pipeline, air is admitted rapidly through the air valve’s large orifice to protect the pipeline. As the water column returns, this air is then gradually discharged through the air valve’s anti-shock orifice. By restricting the discharge through the anti-shock orifice, sufficient air is retained in the pipeline to create a temporary surge accumulator. In instances where pipelines are filled too quickly, the anti-shock mechanism is blown shut by the excessive air flow. Air is now only released through the anti-shock orifice in a controlled manner, creating an air cushion in the pipeline. This air cushion slows down the approaching water column and absorbs any potential surges.

Air Valve Selection and Technical Specifications


The overriding criteria for air valve sizing is the intake requirement under vacuum conditions. To protect the pipeline and joints, it is necessary to limit the system negative pressure to 3.5m vacuum by admitting sufficient air into the pipeline as it empties. One needs to consider the pipeline diameter, gradient, rupture percentage and scour valve size when calculating the required flow rate. Once the required intake flow rates have been calculated, the appropriate air valve can be selected.

Although the air valve size is determined by the air flow required under the vacuum conditions, the flow rate (switching rate) at which the anti-shock mechanism is activated, needs to be considered to ensure that your pipeline will be adequately protected.

Intake flow rates at 3 .5 meters vacuum

25mm  58 l/s
50mm  215 l/s
 80mm   573 l/s
 100mm   792 l/s
 150mm  2053 l/s
 200mm  3361 l/s

Orifice sizes and switching rates

 SIZE mm 25mm LX 50mm LX 80mm LX 100mm LX  150mm LX 200mm LX
Anti Shock orifice 4 9 14 17 25 34
Inlet 25 50 80 100 150 200
Outlet 25 50 80 100 150 200
Switching Flow L/S 12 30 119 161 447 632

The LT can be supplied with a range of switching rates for each size.

Model LX Specifications

25mm Screwed 025LX16 1600KPA 325 mm 95mm
25mm Screwed 025LX25 2500KPA 325 mm 95mm
25mm Flanged 025LX16 1600KPA 260mm 115mm
25mm Flanged 025LX25 2500KPA 260mm 115mm
25mm Flanged 025LX40 4000KPA 320mm 115mm
50mm Screwed 050LX16 1600KPA 335mm 120mm
50mm Screwed 050LX25 2500KPA 335mm 120mm
50mm Flanged 050LX16 1600KPA 255mm 165mm
50mm Flanged 050LX25 2500KPA 255mm 165mm
50mm Flanged 050LX40 4000KPA 296mm 165mm
80mm Flanged 080LX16 1600KPA 330mm 200mm
80mm Flanged 080LX25 2500KPA 330mm 200mm
80mm Flanged 080LX40 4000KPA 380mm 200mm
100mm Flanged 100LX16 1600KPA 330mm 235mm
100mm Flanged 100LX25 2500KPA 330mm 235mm
100mm Flanged 100LX40 4000KPA 385mm 235mm
150mm Flanged 150LX16 1600KPA 440mm 285mm
150mm Flanged 150LX25 2500KPA 440mm 300mm
150mm Flanged 150LX40 4000KPA 520mm 300mm
150mm Flanged 150LX40 4000KPA 520mm 300mm
200mm Flanged 200LX16 1600KPA 510mm 340mm
200mm Flanged 200LX25 2500KPA 510mm 360mm
200mm Flanged 200LX40 4000KPA 595mm 375mm

250mm and 300mm available on request

Working temperatures

  • 4 – 75 Degrees Celcius.

Standard factory tests:

  • Hydrostatic – 1.5 times working pressure.
  • Automatic orifice operation.
  • Low pressure sealing – 20kpa.

End connections:

  • Screwed Valves: Male BSP
  • Flanged Valves: SANS 1123 studded



Triple acting three stage

Material specification

BODY : 304/316 Stainless steel
AUTOMATIC FLOAT : High Density polyethylene
KINETIC FLOAT : High Density polyethylene
ANTI SHOCK FLOAT : High Density polyethylene
SPACERS, STUDS, NUTS AND BOLTS : 304/316 Stainless steel

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