Flow Velocity & Friction Loss

Flow Velocity Charts
Schedule 120
Schedule 40
Schedule 80
SDR 21
SDR 26
SDR 41

Friction Loss

Friction loss through PVC and CPVC pipe is most commonly obtained by the use of the Hazen- Williams equations as expressed below for water:

f = .2083 Flow Velocity Formula

where:

f = friction head of feet of water per 100' for the specific pipe size and I.D.
C = a constant for internal pipe roughness. 150 is the commonly accepted value for PVC and CPVC pipe.
G = flow rate of gallons per minute (U.S. gallons).
di = inside diameter of pipe in inches.

Compared to other materials on construction for pipe, thermo-plastic pipe smoothness remains relatively constant throughout its service life.

Water Velocities
Velocities for water in feet per second at different GPM's and pipe inside diameters can be calculated as follows:

  G
V = .3208 A

 

Where:

V = velocity in feet per second
G = gallons per minute
A = inside cross sectional area in square inches

NOTE: GF Harvel does not recommend flow velocities in excess of five feet per second for closed-end systems, particularly in pipe sizes 6" and larger. Contact GF Harvel tech services for additional information.

Thrust Blocking
In addition to limiting velocities to 5'/sec., especially with larger diameters (6" and above), consideration should be given to stresses induced with intermittent pump operation, quick opening valves and back flow in elevated discharge lines. Use of bypass piping with electrically actuated time cycle valves or variable speed pumps and check valves on the discharge side are suggested with the higher GPM rates. Thrust blocking should be considered for directional changes and pump operations in buried lines 10" and above, particularly where fabricated fittings are utilized. Above grade installations 10" and above should have equivalent bracing to simulate thrust blocking at directional changes and for intermittent pump operations. Thrust blocking of directional changes and time cycle valves are also recommended for large diameter drain lines in installations such as large swimming pools and tanks. Use of appropriate pump vibration dampers are also recommended.

Pipe Size Inches Socket Depth (In.) THRUST IN POUNDS FROM STATIC INTERNAL PRESSURE Joint Resistance To Thrust 90° Ell Safety Factor
For Plug, Cap Tee & 60° Ell For 22 1/2° Ell For 45° Ell For 90° Ell
6 6 7,170 2,800 5,480 10,140 37,464 3.7
8 6 11,240 4,380 8,590 15,890 48,774 3.1
10 8 16,280 6,350 12,440 23,020 81,054 3.5
12 8 23,040 8,990 17,600 32,580 102,141 3.1
14 9 26,610 10,380 20,330 37,630 115,752 3.1
16 10 34,910 13,620 26,670 49,360 150,798 3.1
18 12 44,290 17,270 33,840 62,630 203,577 3.3
20 12 43,410 16,540 32,400 59,970 226,194 3.8
24 14 61,040 23,810 46,640 86,310 316,500 3.7

 

Socket depths are from ASTM D 2672 for belied end PVC pipe. Working pressures utilized for the tabulation above are for Sch 80 2"- 18" sizes and SDR 160 psi for 20" and 24" sizes.

The calculation for thrusts due to static internal pressure is:

Thrust = ( (Av I.D.)2 π) (working pressure) (x)
  4  

 

x = 1.0 for tees, 60° ells, plugs and caps, .390 for 22½° bends, .764 for 45° ells, 1.414 for 90° ells

Joint Resistance to Thrust= (O.D.) (π) (socket depth) (300 psi) 300 psi = Min cement shear strength with good field cementing technique.

FRICTION LOSS THROUGH FITTINGS

Friction loss through fittings is expressed in equivalent feet of the same pipe size and schedule for the system flow rate. Schedule 40 head loss per 100' values are usually used for other wall thicknesses and standard iron pipe size O.D.'s.

Average Friction Loss for PVC and CPVC Fittings in Equivalent Feet of Straight Run Pipe

Item

1/2

3/4

1

1 1/4

1 1/2

2

2 1/2

3

4

6

8

10

12

14

16

18

20

24

Tee Run 1.0 1.4 1.7 2.3 2.7 4.0 4.9 6.1 7.9 12.3 14.0 17.5 20.0 25.0 27.0 32.0 35.0 42.0
Tee Branch 3.8 4.9 6.0 7.3 8.4 12.0 14.7 16.4 22.0 32.7 49.0 57.0 67.0 78.0 88.0 107.0 118.0 137.0
90° Ell 1.5 2.0 2.5 3.8 4.0 5.7 6.9 7.9 11.4 16.7 21.0 26.0 32.0 37.0 43.0 53.0 58.0 67.0
45° Ell .8 1.1 1.4 1.8 2.1 2.6 3.1 4.0 5.1 8.0 10.6 13.5 15.5 18.0 20.0 23.0 25.0 30.0

 

Values 10"-24": Approximate values from Nomograph.

Pressure Drop in Valves and Strainers

Pressure drop calculations can be made for valves and strainers for different fluids, flow rates, and sizes using the CV values and the following equation:

P = (G)2 (specific gravity liquid)
  (CV Factor)2
where:
P = Pressure drop in PSI; feet of water = PSI
.4332
G = Gallons per minute
CV = Gallons per minute per 1 PSI presure drop

CV Factors GPM

Item 1/4 3/8 1/2 3/4 1 1 1/4 1 1/2 2 2 1/2 3 4
True Union Ball Valve 1.0 8.0 8.0 15.0 29.0 75.0 90.0 140.0 330.0 480.0 600.0
Single Entry Ball Valve 1.0 8.0 8.0 16.0 29.0 75.0 90.0 140.0 330.0 480.0 600.0
OIC Ball Valve - - 8.0 15.0 29.0 75.0 90.0 140.0 - - -
True Check Ball Valve 1.0 3.0 4.6 10.0 28.0 45.0 55.0 90.0 225.0 324.0 345.0
Y-Check Valve - - 5.0 6.0 12.5 40.0 40.0 65.0 130.0 160.0 250.0
3-Way Flanged Ball Valve - - 5.0 10.0 16.0 - 45.0 55.0 - 200.0 350.0
Needle Valve Full Open 5.0 7.5 8.0 - - - - - - - -
Angle Valve 1.0 - 5.0 10.0 16.0 - 45.0 70.0 - - -
Y-Strainer (clean screen) - - 3.8 6.6 8.4 20.0 25.0 35.0 60.0 60.0 95.0
Simplex Basket Strainer (clean screen) - - 6.0 9.5 29.0 - 40.0 55.0 - 125.0 155.0
Duplex Basket Strainer (clean screen) - - 5.0 6.0 7.0 - 28.0 35.0 - 80.0 100.0