blow-off valve sizing1

8/13/2019 Blow-Off Valve Sizing1

http://slidepdf.com/reader/full/blow-off-valve-sizing1 1/14

Design Rationale:1.) Blow-off assembly is used to flush out accumulated sediments at low spots and dead-ends of

pipelines and for draining pipelines for repairs, maintenance, and inspection.2.)

Design Data:Cd = unitless Coefficient of DischargeDT = - hr Recommended Discharge TimeVD = - m/s Recommended Discharge Velocity

(AWWA M51 Chapter 4)L = m Length PipeD = m Diameter of Pipe

Elev. 1 = m Low Level Point of the WaterlineElev. 2 = m High Level Point of the Waterline

H = m Pressure Head at the Outlet(Assumed to be Half of the Dif ference in Pipe Elevation)

g = m/s Acceleration due to Gravity

Solving for the Volume to be DrainedV = A x LV = xV = m³ Volume of Water to be Drained

Solving for Diameter of the Blow Off DT = hrs or secs Assumed Discharge Time

V

DT

Q = m³/s Discharge Rate

Solving for the Area of Blow Off using Torricelli's Theorem

Q = Cd x A x (2g x H) ½

Cd x (2g x H) ½

A = m²

Solving for the Diameter of Blow Off π x d ²

4 x A ½

d = m use d = mm

0.62 4

0.03

8.3

9.81

A =4

d =π

45.91

0.3 0.6

10151.8

2.54 10152583

3 10800

Q =

0.24

A =Q

29.31

0.2 200



PROJECT :DESCRIPTION :DATE :DESIGNED BY : CHECKED BY :

EngineeringDevelopment Corp. ofthe Philippines

blow-off valve sizing1

Documents