Water Pressure

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# Water Pressure - PowerPoint PPT Presentation

Water Pressure. Water Pressure. Measured in pounds per square inch (psi) Pressure expressed in units of feet of water where 1 psi = 2.31 feet of water Desirable Within most homes- approx. 40 psi. Friction Loss (head loss). Friction Loss (head loss)

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### Water Pressure

Water Pressure
• Measured in pounds per square inch (psi)
• Pressure expressed in units of feet of water where 1 psi = 2.31 feet of water
• Desirable
• Within most homes- approx. 40 psi
• After loss, still need to be able to provide at least 40 psi (92.4 feet)

Actual Pressure = Static Pressure – head loss

(all expressed in psi)

Static Pressure =

(elevation of H20 level – elevation of water at outlet point)

2.31 ft/psi

Static Pressure Example:

Determine the static pressure of a water tank sitting on your property that is 100 feet in the air and the base is at an elevation 2500 ft.

Static Pressure =

(elevation of H20 level – elevation of water at outlet point)

2.31 ft/psi

Static Pressure Example:

Determine the static pressure of a water tank sitting on your property that is 100 feet in the air and the base is at an elevation 2500 ft.

Static Pressure =

(elevation of H20 level – elevation of water at outlet point)

2.31 ft/psi

Static Pressure =2600 ft – 2500 ft = 43.3 psi

2.31 ft/psi

Greenville Example:

Determine the static pressure (psi) of water for a storage tank in Greenville at an elevation of 2409 feet above the water-discharge elevation point of 2231 feet.

Greenville Example:

Determine the static pressure (psi) of water for a storage tank in Greenville at an elevation of 2409 feet above the water-discharge elevation point of 2231 feet.

Static Pressure =

(elevation of H20 level – elevation of water at outlet point)

2.31 ft/psi

= (2409 – 2231) / 2.31 = 77.06 psi

Greenville Example:

Static Pressure: 77.06 psi

**However, friction, or head losses, reduce the static pressure.

**Hazen-Williams

- calculate head loss due to friction in straight pipe

Hazen-Williams formula

Hf = (10.44)(L)(Q1.85)

(C1.85)(d4.8655)

Hf = head loss due to friction, feet

L = length of pipe, feet

Q = flowrate of water through the pipe, gpm

C = Hazen-Williams coefficient (on table)

d = diameter of the pipe, inches

Hazen-Williams formula

“Q” - Design Basis for Water Consumption Document

“C” – Hazen-Williams coefficient; non-dimensional

number that relates to the roughness of the pipe

(See Specific Roughness and H-W Constants for Various Materials)

Pipe Systems
• Most made of ductile iron (d.i.) or cast iron
• 8 inches in diameter or greater
• New, clean ductile iron pipe has a C = 130
• Over time, chemical reactions affect the roughness of the pipe.
• C = 100 (existing pipe networks)
Greenville Example (cont.)

Determine the head loss for a water distribution system

that is a straight line from the Greenvillle water tower to a structure 4 miles away. The piping system is made with newly installed 8-inch ductile pipe. The flow rate has been determined to be 100 gallons per minute (gpm).

Hf = (10.44)(L)(Q1.85) =

(C1.85)(d4.8655)

Greenville Example (cont.)

Determine the head loss for a water distribution system

that is a straight line from the Greenvillle water tower to a structure 4 miles away. The piping system is made with newly installed 8-inch ductile pipe. The flow rate has been determined to be 100 gallons per minute (gpm).

Hf = (10.44)(L)(Q1.85) = (10.44)(4●5238)(1001.85) =

(C1.85)(d4.8655) (1001.85)(84.8655)

Greenville Example (cont.)

Determine the head loss for a water distribution system

that is a straight line from the Greenvillle water tower to a structure 4 miles away. The piping system is made with newly installed 8-inch ductile pipe. The flow rate has been determined to be 100 gallons per minute (gpm).

Hf = (10.44)(4●5238)(1001.85) = 8.9 ft.

(1001.85)(84.8655)

= 8.9 ft of head loss because of the resistance to flow

Greenville Example (cont.)

Now determine the actual pressure at the entrance to the structure.

Actual Pressure = Static Pressure – head loss

(all expressed in psi)

Greenville Example (cont.)

Now determine the actual pressure at the entrance to the structure.

Actual Pressure = Static Pressure – head loss

(all expressed in psi)

= 77.06 psi – 8.9 ft (1psi/2.31 ft)

= 77.06 psi- 3.85 psi

= 73.21 psi