- 1. VENTING OF A FILLING PIPELINE:
- 2. SURGE ALLEVIATION – PIPELINE PRESSURIZED:
- 3. PRESSURIZED AIR RELEASE FROM A FULL PIPELINE:
- VENTING OF A FILLING PIPELINE (SUB CRITICAL WATER APPROACH VELOCITY)
- VENTING OF A FILLING PIPELINE (EXCESSIVE WATER APPROACH VELOCITY)
- PRESSURIZED AIR RELEASE FROM A FULL PIPELINE
- VACUUM RELIEF (AIR INTAKE) OF A DRAINING PIPELINE
The operation of a kinetic air release valve is such that fast approaching water is almost instantaneously halted by the valve’s closure without the shock cushioning benefit of any retained air in the pipeline. Consequently a transient pressure rise or shock of potentially damaging proportions can be generated in a pipeline system, even at normal filling rates.
In addition to venting through the Large Orifice (1) when water approach velocities are sub critical, the Vent-O- Mat series RBX air release valves feature an automatic Anti Shock Orifice (8) device that serves to decelerate water approaching at excessive speed, thereby limiting pressure rise to a maximum of 2 x rated working pressure of the valve.
In instances where a pipeline experiences water column separation due to pump stoppage, high shock pressures can be generated when the separated water column rejoins.
The Vent -O- Mat series RBX takes in air through the unobstructed large orifice when water column separation occurs, but controls the discharge of air through the ‘Anti Shock’ Orifice as the separated column commences to rejoin. The rejoining impact velocity is thereby sufficiently reduced to prevent an unacceptably high surge pressure in the system. In the same way the series RBX valve prevents high surge pressures resulting from liquid oscillation in a pipeline.
Effective discharge by the valve of pressurized air depends on the existence of a ‘CRITICAL RELATIONSHIP’ between the area of the Small Orifice (7) and the mass of Control Float (4), i.e., the mass of the float must be greater than the force created by the working pressure acting on the orifice area. If the float is relatively too light or the orifice area relatively too great, the float will be held against the orifice, even when not buoyed,and air discharge will not be effected.
To ensure that the correct ‘CRITICAL RELATIONSHIP’ exists the requisite ‘DROP TEST’ described under TEST SPECIFICATION on page 17 must be applied to any air release valve which is intended for discharge of pressurized air.
Air enters Orifice (3), travels through the annular space between the cylindrical floats (4), (5), and (6) and the valve Chamber Barrel (2) and discharges from the Large Orifice (1) into atmosphere.
In reaction to increased air flow, Float (6) closes Large Orifice (1) and air is forced through the Anti Shock Orifice (8) resulting in deceleration of the approaching water due to the resistance of rising air pressure in the valve.
Attention is drawn to Pre Note 1 and 2 on page 1
Subsequent to the filling of a pipeline, liquid enters the valve Barrel Chamber (2) and the Floats (4), (5) and (6) are buoyed so that the Large Orifice (1) is closed by Float (6), the valve will then become internally pressurized. A minimal working pressure of < 0. 5 bar (7. 3 psi) acting on the relatively large area of the Orifice(1)will lock Float(6)into the closed position across the Large Orifice(3).
Disentrained air rises through the liquid and accumulates in the valve chamber, when the volume of air is sufficient to displace the liquid, Float (4) will no longer be buoyant and will gravitate downwards thereby opening the Small Orifice (7) and allowing accumulated air to be discharged into atmosphere, as air is discharged the liquid raises Float(4)and re-seals the Small Orifice(7)and prevents escape of liquid.
Specific attention is drawn to pre note 3 on page 1.
Simultaneous drainage of liquid from Valve Chamber (2) causes Floats (4), (5) and (6) to gravitate downwards onto the Baffle Plate (9), thereby allowing atmospheric air through the valve to rapidly displace drainingliquid in the pipeline and prevent potentially damaging internal negative pressure.