AIR VALVE MANUFACTURER BEATS THE WORLD
A South African valve manufacturer has emerged as the only company worldwide capable of developing an air release valve under tight time constraints to solve a pipeline problem specific to the United Arab Emirates.
While several manufacturers had designs theoretically capable of meeting the specifications, only Dynamic Fluid Control (DFC) offered a practical solution that could release air at very high volumes and to open at the correct pressures demanded by the application.
The need for the special valve arose when increased flow requirements were imposed on an existing pipeline near Abu Dhabi, which needed to increase by 60 percent the rate of water flow through a Water Transmission Scheme (WTS) pipeline, without any change in the size of protective surge vessels already installed.
The WTS originally involved the generation of 1500MW of power and transmission of 100-million gallons per day of desalinated water to the city of Abu Dhabi, a distance of 250 kilometres.
One of the biggest water pipeline projects ever undertaken using ductile iron pipes, it became the biggest combined power and desalination plant in the world when transmission was last year increased to 160-million gallons per day, or
25 000 m3/h.
After commissioning at the higher flow, surge vessels installed at the mid-way pump station proved inadequate to prevent the entry of air from the vessels into the pipeline during conditions of pump trip, in spite of the PLC‑controlled solenoid valves fitted to close the air inlets.
This air ingress lowered the pipeline pressure, raising the possibility of the pump motors running away and becoming damaged during start-up.
It also caused column oscillation within the pipeline.
After unsuccessful trials on alternative air valves, the client commissioned Dutch-based WL Delft Hydraulics to perform steady state verifications for different operating conditions and pressure surge analyses, and evaluate normal and emergency operations and the design of appropriate anti-surge devices and measures.
Valve manufacturing companies worldwide were approached for a solution that would allow the expensive surge vessels originally installed to remain in place, based on new vent pipe positions and hydraulic parameters specified by Delft Hydraulics.
These included minimum inflow and maximum outflow capacities under the combined conditions of pump trip and increased flow, and an exact pressure under which any proposed air release valve would need to immediately open.
If all specifications could be met, then the ingress of air into the pipeline would be prevented. All air would be contained within the vessel to meet its intended purpose of acting as a cushion against pipeline surge.
One difficulty lay in the size of the valve’s air orifice.
Normally no larger than 2mm in diameter, it would have to increase more than twenty-five fold to 52mm to meet the Delft Technologies specifications.
A second problem was the float needed to seal the port when the water level within the vessel rose above the valve.
This float would need to fall away promptly at the specified pressure of
3,4 bar, and because of the very large size of the port, it would need to have a mass of around 80kg if it was to fall as soon as that pressure was reached.
DFC was the only valve manufacturer with an existing design, the Vent‑O‑Mat, which could accommodate a float of this very large size. According to product manager Hannes Erasmus, it was Vent-O-Mat’s proven and patented design that made possible