Pipeline operation is characterised by three frequently occurring and potentially damaging internal conditions: shock due to the velocity and mass of the flow medium, surge due to column separation and re-joining, and vacuum created by pipeline draining or breakage.Even at normal filling rates, a fast approaching flow medium can generate a transient pressure rise (shock) of potentially damaging proportions, unless air is retained in the pipelineto cushion it. Similarly, a pipeline that experiences column separation due to pump stoppage, can be subjected to high pressures when the separate column rejoins.Draining a pipeline poses additional challenges, carrying the potential for the development of negative pressure (vacuum) and associated risk of structural damage.
The locally designed Vent-O-Mat range of valves continues to hold a leading position worldwide as the product of choice to alleviate these three conditions, delivering simultaneous three-way protection in the roles of air-release, vacuum-break and surge moderation. The valves are manufactured at the Benoni works of Dynamic Fluid Control (DFC).
The Vent-O-Mat range comprise two main series, RGX and RBX, the latter targeting sewage and effluent applications in which the transfer of solids and viscous substances tends to jam standard air valves and render them useless.
Virtually maintenance-free, both the RGX and RBX-series valves have been designed around the laws of physics governing air valve and pipeline operation, so that installed valves are characterised by instantaneous reaction to pipeline dynamics, providing protection relevant to the prevailing situation.
DFC claims Vent-O-Mat to be the most cost efficient and cost effective protection currently available on the world market. A major advantage of this product is that protection against destructive surge and water hammer phenomena are independent of mechanical devices, ensuring reaction within milliseconds. Air release through any one of three discharge orifices is effective under all pipeline flow and operating conditions.
To protect against vacuum, these same orifices have diameters equal to the nominal size of the valve to ensure the least possible resistance to the intake of air, and consequently the least possible negative pressure within a draining pipeline. The use of cylindrical floats ensures instantaneous reaction and discourages the Venturi phenomenon.
Vent-O-Mat valves are intended as an integral part of a planned, holistic pipeline protection strategy that should, according to application needs and financial constraints, include surge vessels, check valves, control valves and/or any other equipment needed to alleviate unacceptable surge behaviour.
The RGX and RBX-series valves offer definite financial and technical advantages when incorporated as part of a holistic surge protection strategy. These include the slowing of surge velocities and therefore the magnitudes of surge pressures, and the reduction of oscillation duration caused by a pump trip. In the latter case, the air valve continuously absorbs and dissipates the energies of the surge. There is also potential for reduction in the size and quantity of conventional surge protection devices such as surge vessels.
Protection during initial pipeline filling is automatic at a time when most surge protection devices are not operational.