Clamont
Mechanical
- Dec 10, 2012
- 40
I was recently given the calculation for emergency venting as per NFPA 30 using a "manhole with long bolts" 22.7.3.2.1 (2) as per the below.
CFH = 1,667*Cf*A*√(Pt-Pa)
Where;
Cf = Flow coefficient of valve (set at 0.5)
A = Area of open manhole or area of manhole lift
Pt = Absolute pressure inside the tank (inH2O)
Pa = Absolute pressure outside of the tank (inH2O)
My questions is as per below;
1) Is this calculation correct and where can I verify it?
2) How do you determine the pressure when the manhole cover is in the fully open position as required by NFPA 30 22.7.3.10 (2). I can easily calculate the opening pressure however do not know how to calculate the pressure when fully open assuming I had a predetermined length of bolt.
I look forward to replies.
CFH = 1,667*Cf*A*√(Pt-Pa)
Where;
Cf = Flow coefficient of valve (set at 0.5)
A = Area of open manhole or area of manhole lift
Pt = Absolute pressure inside the tank (inH2O)
Pa = Absolute pressure outside of the tank (inH2O)
My questions is as per below;
1) Is this calculation correct and where can I verify it?
2) How do you determine the pressure when the manhole cover is in the fully open position as required by NFPA 30 22.7.3.10 (2). I can easily calculate the opening pressure however do not know how to calculate the pressure when fully open assuming I had a predetermined length of bolt.
I look forward to replies.
