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The purpose of the SNH Air Intel Check Valve is to permit ahigh flow air intake into the pipe, in order to prevent negative pressure, the resuit of which would be damage to the sealing joints and a risk of the pipe being crushed. It provides a normal flow during pipe draining.
Generally speaking, the choice of the ND of the air inlet check valve is based on an admissible negative pressure in the pipe of 2 metres water column. We then apply a ratio between the air flow in L/s and the cross section of the passage of the air inlet check valve, in dcm2 equal to 1900.
This figure is constant whatever the ND for the air inlet check valve, since it is given by the maximum velocity of air input which is 1900 dcm/s, that is 190m/sec.
We obtain maxi. air input flow rates for a negative pressure of 2m/wc. to :
|CHECK VALVE||DN 80 = 1000 L/s|
|DN 100 = 2000 L/s|
|DN 150 = 3500 L/s|
|DN 200 = 6000 L/s|
|DN 250 = 10000 L/s|
When the negative pressure reaches 3, 4 or 5 m/wc, these flow rates are increased by 30, 60 to 100 %.- the maximum service pressure (see table below).