Fluid Mechanics Solutions

ANTI SEARCH OPTION.

 

Modern Valve technology has produced air valves with an anti-surge mechanism. Basically the objective is to restrict the flow of air out of the pipeline enabling the remaining air volume to act as a cushion when the flow reversal causes the water columns to rejoin thereby dampening the pressure rise.

One such valve is the Vent-O-Mat series. The air is admitted and exhausted through a large orifice. When the pressure at the valve exceeds a "switching value", a float with a smaller orifice covers the normal outflow orifice to restrict the rate of air escaping from the pipeline. The remaining air is released through the smaller orifice in time.

It is essential to size the valves correctly in order for the anti-shock mechanisme to function. For example, if the valve selected is too large, the admitted air volume can be completely exhausted through the the normal sized discharge orifice without a pressure build up to the "switching value" during flow reversal. As a result, the rejoining water column may create a high transient pressure as no air cushion has been formed.

The switching point in the folloing table is the pressure in the pipe at wihich the valve switches or activates the anti-shock mechanism. It is the pressure difference between the pressure in the pipe and the atmospheric pressure.

 

 

 

 

Vent-O-Mat  Inflow Orifice  Large Orifice     Anti-Shock        Switching Point      Switching Point             

 Type             diameter(mm)          (mm)          (mm)                  (kPa)                      (m)                         

 

025RBXRGX         25                        25               4                     3.0                        0.305                   

050RBXRGX         50                        50               9                     3.5                        0.357                   

080RBXRGX         80                        80              14                    4.25                      0.433                     

100RBXRGX        100                      100             17                    4.5                        0.459                    

150RBXRGX        150                      150             25                    5.1                        0.520                    

200RBXRGX        200                      200             34                    6.1                        0.622                   

                    

VACUUM RELIEF (AIR INTAKE) PIPELINE DRAINING: View Animation.

 

Upon pump stop, the discharge check valve closes. Sewage/effluent drains from the sewage air valve and the pump's vertical column. The negative differential created by the draining liquid causes atmospheric air to push the "Anti-Surge" Float down, opening the Large Orifice and allows air to displace the draining liquid to prevent potentialy damaging internal negative pressure*.
The hollow smooth side float design, discourages the adherence of solids and viscous substances which, therefore tend to withdraw from the valve into the pipeline when draining occurs, for this reason NO FLUSHING CONNECTIONS ARE NECESSARY

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VENTING (PUMP START UP) View Animation.

 

Air/gas is forced through the "Anti-Surge" Orifice resulting in the deceleration of the approaching liquid column due to the resistance of rising air pressure in the valve.
This dampens transients when the sewage air valve closes and the liquid column opens the discharge check valve.

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 PIPELINE FULLY CHARGED View Animation.

 

Sewage/effluent has entered the valve chamber and buoyed the floats to close both the "Anti-Surge" orifice and the small orifice. The design's compression/volume relationship prevents the media from ever exceeding the maximum surge level indicated in diagram 3. The resultant sewage/effluent free area protects against the fouling of the orifice seals by solids or high viscous substances - for this reason NO FLUSHING CONNECTIONS ARE NECESSARY.

 

 

 PRESSURIZED AIR/GAS RELEASE PUMP OPERATING View Animation.

The volume of disentrained air/gas increases in the valve and displaces the sewage/effluent level to the lower, normal operating level (small orifice control float buoyancy level ) Any additional lowering of the sewage/effluent level, as would occur when more air/gas enters the valve, will result in the control float dropping away from the small orifice through which pressurized air/gas is then being discharged to atmosphere. The control float will close the small orifice when sufficient air/gas has been released to restore the sewage/effluent level to the normal operating level. The considerable sewage/effluent free are obviates the possibility of leaks that could otherwise be caused by solids entering the sealing areas - for this reason NO FLUSHING CONNECTIONS ARE NECESSARY

*Note: A differential pressure of less than 0.05 bar (0.7 psi) across the large orifice is required to open the valve fully under vacuum conditions.