VARIANT AIR RELEASE AND VACUUM BREAK VALVES FOR WATER
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.
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.
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
|VALVE SIZE||INTAKE AT 3.5m∆P|
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|
|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
|SIZE||MODEL NUMBER||PRESSURE RATING||HEIGHT||DIAMETER|
|25mm Screwed||025LX16||1600KPA||325 mm||95mm|
|25mm Screwed||025LX25||2500KPA||325 mm||95mm|
250mm and 300mm available on request
- 4 – 75 Degrees Celcius.
Standard factory tests:
- Hydrostatic – 1.5 times working pressure.
- Automatic orifice operation.
- Low pressure sealing – 20kpa.
- Screwed Valves: Male BSP
- Flanged Valves: SANS 1123 studded
Triple acting three stage
BODY : 16 Stainless steel
AUTOMATIC FLOAT : High Density polyethylene
KINETIC FLOAT : High Density polyethylene
ANTI SHOCK FLOAT : High Density polyethylene
AUTOMATIC SEAL : EPDM
KINETIC SEAL AND O RINGS : Nitrile
SPACERS, STUDS, NUTS AND BOLTS : 304/316 Stainless steel
FOR AIR VALVE CHAMBERS ON PIPELINES 300MM AND SMALLER
- An equal tee must be installed in the main pipeline. This creates a chamber below the air valve and ensures that air travelling along the pipeline is effectively trapped prior to discharge.
- A flange with riser pipe is bolted onto the vertical leg of the equal tee. The riser could be either flanged or screwed to suit the isolating valve. It is advisable that the riser is long enough to ensure that the air valve is above ground level.
- A suitable isolation valve must be installed below the air valve so that the air valve can be serviced -Subject to the clients preference and pressures the valve may be screwed or flanged. Resilient seal gate valves, gate valves ,but or full bore ball valves are all acceptable.
- The valve should be located in a chamber large enough to allow maintenance staff access.
- Two breather pipes having at least the same diameter as the air valve must be provided.
- The chamber must have ample drainage so that it can’t be flooded.
Variant Air valves
Operation and maintenance manual
- The valve must be installed in the vertical position
- It is preferable that a suitable isolating valve be installed under the air valve so that the air valve can be serviced
- The air valve must be installed on a suitable air accumulator tee to trap the air bubbles during pressurized operation
- The air valve chamber should include adequate vents for venting and draining of the pipeline
- If the air valve is not installed above ground level, a sump pump and / or suitable drainage must be incorporated into the valve chamber
Start up and operation
- Ensure that the isolating valves on all the air valves are open before filling commences.
- On filling the air will be vented from the air valve through the large orifice. Once water reaches the air valve the large orifice will close and any further air in the pipeline will be discharged through the automatic orifice
- If the pipeline is filled too quickly or a pump trip occurs, the air valve will switch to anti shock mode, restricting the outflow of air and creating an air cushion to minimize transient pressures.
- Should the pipeline drain the air valve will open fully allowing unobstructed air flow into the pipeline.
Valve leaks under pressure
- Close off the isolating valve and open the valve by loosening the tie rod nuts
- Please note that when the isolating valve is closed the pipeline has no vacuum protection
- Inspect the large o ‘ring for damage and ensure the valve is free of any dirt. Replace O ring if required
- Check the automatic orifice and seal for wear and replace if necessary
- Re assemble valve ensuring that the gaskets are intact
- Cross tighten the nuts, ensuring that the valve pulls up evenly
- Open isolating valve