The impact of air on a water and waste water system:
The presence of air in a pipeline and its impact on operations is one of the most misunderstood aspects of the Water & Wastewater industry. Many operational problems are blamed on improper installation of the line but they are really due to failure to de-aerate the line.
Air is always present in a pressurized, operating pipeline. This air comes from three main sources;
- Present air – before a system starts there is air present in the pipe. When a pipe is filled with fluid this air must be eliminated. Most of the air is pushed downstream and released properly, however some air can become trapped at high points in the system.
- Air in water – water consists of about 2% air, during operations air will separate from the water and this too will become trapped at high points.
- Air through mechanical equipment – air is forced in through pumps or drawn in through valves under vacuum conditions.
There are two main impacts of air on a system:
- Air accumulation – pockets of air collecting at high points can lead to a line restriction. They increase headloss, extend pumping cycles and increase energy consumption.
- Increased velocity – Air collecting at high points in the system means fluid is forced through a smaller space so fluid velocity is increased. As the air space grows larger two problems may occur:
- A pressure drop higher than pump capacity can develop and stop all flow
- The air pocket can become dislodged from the high point and is pushed downstream. The causes a huge increase in fluid velocity which is then suddenly stopped by another high point causing a high pressure surge know as a “water slam”. This is the most serious problem related to air accumulating at high points and can cause serious damage to valves, fittings, gaskets and can even break the line.
How to stop the impacts of air in a system:
Historically, engineers have tried using sandpipes to try and expel large amounts of air. Others used ball or gate valves to bleed off air at high points, but it was impossible to predict when a high point in a system may need bleeding. More commonly, open fire hydrants were used in the belief that all of the air will be released. The problem with this method is that hydrants are connected to the side of a pipe, still leaving some air trapped at high points.
Valmatic offer the following features to overcome the problems of air in a pipeline
Efficiency and vacuum control – The main purpose of Valmatic’s air valves is to create pipeline efficiency by continuous removal of air at pipeline highpoints and vacuum protection by admitting large quantities of air upon pump shut down or system failure
Surge Control – Air valves play an important role in pipelines to control or reduce surges. Through computer modeling and transient analysis, it has been shown that air valves play a vital role in avoiding pipeline surges during column separation conditions
Pipeline Surges– To prevent a vacuum from forming, a Surge- Suppression Air Valve or Vacuum Breaker is used to allow air into the pipeline.
- A Surge-Suppression Air Valve consists of a Combination Air Valve fitted with a Regulated-Exhaust Device to allow full airflow into the pipeline, but restrict the airflow out of the pipeline.
- A Vacuum Breaker also allows rapid entry of air into the pipeline, but lessens flow out of the pipeline. When equipped with an Air Release Valve, the Vacuum Breaker will provide controlled release of air through the small Air Release Valve orifice.
- Both of these methods work to decrease surges by temporarily trapping a pocket of air and cushioning the impact of the water columns when they return by regulating the exhaust of the air pocket
Vertical pump column surges – The use of a vertical turbine or deep well pump against an air filled column and closed check valve causes high velocity to develop quickly in the pipeline. This can lead to surges in the pump column. Regulating exhaust of air during start up is the best way to prevent this. A Well Service Air Valve equipped with a Dual Port Throttling Device or a Regulated Exhaust Device vent air from the column at a controlled rate so most of the air escapes just before the check valve opens.
Valmatic have created the Air Valve as a solution to air in water systems…
Automatic Air Valves are available in many different designs to suit the wide range of application problems they are needed to solve. They automatically allow air in and out without the need for an operator and they come in three basic configurations:
Tips and pointers…
- It is critical to choose a valve with the correct size and for it to be fitted at the right location within a system.
- It is recommended that air valves are installed every half a mile on straight horizontal pipelines.
- Valmatic also provides Windows-Based software to help choose the correct size and location of a valve for a system.
The Features and Benefits of choosing Valmatic Air Valves:
- Valmatic have over 40 years experience when it comes to producing air valves, their air valves are developed and based on decades of successful application of air valves in the industry.
- Valmatic Air Release, Air/Vacuum and Combination Air Valves are manufactured in accordance to the rigorous industry requirements.
- Valmatic’s AWWA Air Valves feature 316 stainless steel trim, full size ports, ANSI threaded or flanged connections and stringent testing.
- Valmatic manufactures air valves in a wide range of materials and pressure ratings with many accessories including Regulated-Exhaust Devices, Dual Port Throttling Devices, Isolation Valves, Screened Hoods and Backwash Accessories
NSF/ANSI 61 Certification
- Valmatic Air Valves for water service are NSF/ANSI 61 certified for use in drinking water applications.
Type 316 Stainless Steel Trim
- Valmatic air valves have internal components made from 316 stainless steel as standard. This is the best steel to use to protect from aggressive waters and hydrogen sulfide exposure in wastewater application.
- Floats are unconditionally guaranteed for the life of the valve from corrosion, collapse or leakage.
- A damaged or off-center float will prevent a valve from sealing tight
- The high air and water velocities in air valves can cause unguided floats to violently strike the sides of the valve body
- Val-Matic floats are guided; four inch and larger valves feature double guides (top and bottom).
- Guiding assures that the float approaches the center of the seat every time to provide a positive drop tight seal
Self Cleaning Float Guides
- Valmatic floats are guided by hexagonal float stems
- These pass through round stainless steel bushings which prevents debris build up and self cleans the bushings.
- All Valmatic valves have a resilient seat or orifice button that is compatible with a 316 stainless steel float or seat for drip tight sealing.
- Valmatic elastomers are specially formulated for water and wastewater service and have been NSF/ANSI 61 certified
- Air Release Valves have a synthetic sealing button mounted to the float linkage mechanism
- The seats contain raised sealing beads and/or a unique flex edge that provide positive shutoff
Full Size Flow Area
- Val-Matic Air/Vacuum and Combination Air Valves are equipped with full and equal size inlets and outlets in accordance with AWWA C512.
- All Combination Air Valves with float guides in the outlet have expanded flow areas around the guide spokes to provide full flow area through the valve
MGA Controls Ltd have an exclusive partnership with Valmatic Co. Valmatic are known for their valuable experience and success in manufacturing and supplying a wide range of Air Valves to many applications within the industry. MGA Controls Ltd are fully trained on the Valmatic product range and we believe their range of Air Valves to be the superior Air Valves in the market today. For enquiries or more information, please contact our technical team on +44 (0) 8444 501123, or visit our Valmatic website pages.