PRESSURE VESSEL CALCULATION
Discharge : 4.5 L/s
Head : 65 m
Flow / Pump = 270 L/min (4.5 L/s)
Pressure = 6.5 Bar (65 m)
Pressure Vessel, Vt = 16.5x Qmax (Pmax x Pmin)
Ax (P x Pprec)
Where,
Vt = Total Volume of Tank in Litres
Qmax = Average flow of Pump in L/min 270 L/min
Pmax = Maximum Absolute Cut-off Pressure 6.5 Bar
Pmin = Minimum cut-in Pressure 2.5 Bar
A = No. of Pumps (2) x No. of starts per hour (10) 20
P = Pmax- Pmin+ 1 Bar 5.0 Bar
Pprec = Pmin-0.1 2.4 Bar
Absolute Tank pre-load pressure (should be less than Pmin)
Vt = 16.5x 270 x 6.5x 2.5
20 x 5x 2.4
= 301.64 L
Approximately, Vt = 302 L
Hence, Proposed Standard Size 1 No. of 300 L Pressure Vessel.
Life Line Trading Technical Submittal 2022
NPSH AVAILABLE CALCULATION
Discharge : 4.5 L/s
Head available : 65 m
The available NPSH can be calculated by use of the following formula:
hsv = hpsa + hss - hfs - hvpa
Where:
hsv = Available Net Positive Suction Head in feet of liquid.
hpsa = Suction surface pressure, in feet of liquid on the surface of the liquid from which the
Pump takes its suction. This will be the atmospheric pressure, in the case of an open
Tank or vented tank = 33.96 ft
hss = Static suction head, in feet of liquid. (Positive if the liquid level is above the
Pump, Negative if the liquid level is below the pump) = +2.9 m (+9.51 ft)
hfs = Friction head loss, in feet of liquid, between the liquid surface in the suction tank and
the suction flange of the pump.
hvpa = Vapor pressure of the liquid, at the pumping temperature, in feet of liquid= 1.61 ft
at 32.2o Celsius
CALCULATIONS: -
hfs = Friction head loss, in feet of liquid, between the liquid surface in the suction tank
and the suction flange of the pump including fittings.
Total pipe length from the foot valve to the suction port= 6m
Considered 40% for the fittings; then = 6x 40% = 2.4 m
Therefore, Total length = 8.4 m
Friction loss when 4.5 L/s flow through 3” uPVC pressure pipe
Friction loss in 1000 m = 12 m
Friction loss for 8.4 m = 12x8.4/1000 = 0.10 m
Total head loss in pipe = 0.10 = 0.32 ft
So, hsv = hpsa + hss - hfs - hvpa
= 33.96 + (+9.51) – 0.10- 1.61
= 41.76 ft = 12.72 m
NPSH required = 1.95 m (From the Performance curve)
NPSH available = 12.72 m
12.72 m > 1.95 m
So, NPSH available > NPSH required
Result:
The available suction head is more than required suction pressure, The NPSH margin value
is positive.
Life Line Trading Technical Submittal 2022
