Centrifugal pump Calculations
Formulas & Calculations
How to Calculate...
- Head Calculation
- Hydraulic power calculation
- Pump Shaft Power
- Electrical Power
- Specific Speed
- Centrifugal Pump Calculations Energy loss in discharge valve throttling
- NPSHa - Net Positive Suction Head Available
- Head ↔ Pressure
- Volumetric flow ↔ Mass flow
- Break Power Calculation
Formulas
Head
Head is net work done for unit weight of water.
H = Head ; Unit - Meter
P = Water Pressure ; Unit - kPa, psi
Γ = Specific weight of Fluid ; Unit - kN/m³
V = Water Velocity ; Unit - m/s
g = Gravitional force ; Unit = m/s² Value = 9.8m/s²
Z = Elevation to be lift
Horizontal pump - Datum is a horizontal plane from center line of shaft
Vertical pump - Datum is horizontal plane of impeller eye.
See calculations
Pump Capacity ( Volume flow rate of pump)
Capacity is the amount of water pumped per unit time.
Capacity Q = A V
A = Area of pipe
V = Volume flow rate
See calculations
Hydraulic power calculation
⍴ = densityGravitional force of fluid ; Unit = kg/m³
g = Gravitional force ; Unit = m/s² Value = 9.8m/s²
H = Total Head = Hd - Hs; Unit = m
Hd = Discharge head
Hs = Suction head
Q = Discharge flow ; Unit = m³/hour
See calculations
Pump Shaft Power
ηpump = Pump efficiency
Maximum shaft power
Mmax = É‘1 ⍴ g H Q / η0
See calculations
Electrical Power
ηmotor = Motor efficiency
See calculations
Pump Efficiency
WP = Water Power; Unit - kW
BP = Break Power [Shaft power - Power input to the pump shaft] ; Unit - kW
See calculations
Specific speed
Pump performance derivation by Pump speed, Design capacity and head.
N = pump speed; Unit - RPM
P = Pressure, PSI
Q – Volumetric flow rate,
P = Power, kW
Q = pump design capacity
H = Head ; Unit - RPM
Pumps have similar performance and speed regardless of their sizes.
See calculations
NPSHa - Net Positive Suction Head Available
BP = Barometric Pressure [meter of water]
VPw = Vapour pressure of water; Unit = m.
(H1)s = Head loss due to pipe friction in the suction line; Unit = m.
(M1)s = Minor losses in suction line; Unit = m.
VHs = Velocity head in suction line; Unit = m.
SL = suction line side lift; Unit = m.
DD = drawdown; Unit = m.
h= elevation above sea level; Unit = m.
K1, K2 = Unit constants
BP in m of water if h in meter
K1 = 10.33 and K2 = 5.55 * 10⁻⁸
BP in m of water if h in ft
K1 = 33.89 and K2 = 1.69 * 10⁻⁸
Head ↔ Pressure
P = Pressure, PSI
SG – Specific gravity
Volumetric flow ↔ Mass flow
Q – Volumetric flow rate,
M – Mass flow rate
SG - Specific gravity
Motor input current ↔ Power
Seal box pressure
System Head Calculation
Hs = SL+ DL + DD + Hi + Mi + H0 + VH
Hs = System head, m
SL = Suction side lift, m
DL = Discharge side lift, m
DL = Eu - Ep
Eu = Elevation of the point of delivery
Ep = Elevation of pump
DD = Water source drawdown, m
Hi = Head loss due to pipe friction, m
Mi = Minor losses through fittings, m
H0 = Operating head, m
VH = Velocity head, m
VH = Q2 / KD4
Q = Flow, m3/hr
D = Discharge pipe dia, m
k = Constant [ 435.7 ]