What is the difference between hydraulic, mechanical, and overall pump efficiency?

Hydraulic efficiency accounts for fluid friction and direction change losses inside the pump. Mechanical efficiency accounts for friction losses in bearings, mechanical seals, and couplings. Overall efficiency is the product of hydraulic, mechanical, and volumetric efficiencies, representing the ratio of fluid power output to shaft power input.

What is a typical pump efficiency for centrifugal pumps?

Single-stage industrial centrifugal pumps typically exhibit efficiencies between 70% and 88% near their Best Efficiency Point (BEP). Large high-capacity pumps can reach over 90%, while very low-flow or high-viscosity pumps may operate at 40-60% efficiency.

How does volumetric leakage affect pump efficiency?

Volumetric leakage occurs when liquid slips back from the high-pressure discharge side to the low-pressure suction side through wear ring clearances or balancing holes. Volumetric efficiency is the ratio of delivered outlet flow to total impeller flow.

Pump Efficiency Calculation & Application

What is the efficiency of a pump?

How to calculate the efficiency of a pump?

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Section summary
1. Definition of pump efficiency
2. Interactive Pump Efficiency Calculator
3. Hydraulic efficiency calculation
4. Mechanical efficiency calculation
5. Volumetric efficiency calculation
6. Pump overall efficiency & Power Sizing
7. Engineering Rules of Thumb & Safety Factors
8. Pump manufacturers

1. Definition of pump efficiency

Pumps are fitted with an electrical drive that delivers a certain power, but not all of this power is transferred to the fluid; losses occur in every component of the pump, so the total power imparted to the fluid is less than the pump’s input power. The pump efficiency is therefore the ratio between the power actually gained by the fluid and the power supplied at the pump shaft. This same principle underlies process efficiency, which evaluates how effectively a system converts input energy into useful work.

Pumps are fitted with an electrical drive which delivers a certain power, however all this power is not transferred to the fluid, only some of it. There are indeed losses in every components of the pump, which means that the total power input to the fluid is less than the pump power. The efficiency of the pump is then the ratio in between the power actually gained by the fluid and the power supplied at the shaft of the pump.

There are actually 3 efficiencies that can be calculated, all related to different types of energy losses :

Hydraulic efficiency (\(E_h\))
Mechanical efficiency (\(E_m\))
Volumetric efficiency (\(E_v\))

Those 3 efficiencies then combine to constitute the pump overall efficiency (\(E\)).

2. Interactive Pump Efficiency & Power Calculator

⚠️ ENGINEERING NOTICE & EDUCATIONAL DISCLAIMER: This interactive calculator is provided exclusively for preliminary estimation and educational purposes. It is not intended for detailed design or equipment procurement without certified vendor rating. No warranty, expressed or implied, is provided, and no liability is assumed.

Unit System: SI Metric (m³/h, m, bar, kW) US Customary (GPM, ft, psi, HP)

Calculation Mode:

Flow Rate (Q):

Differential Head (H):

Liquid Density (ρ):

Hydraulic Head Loss (H_h):

Internal Leakage Flow (Q_v):

Mechanical Power Loss (P_m):

Motor Efficiency (η_motor %):

Hydraulic Power Delivered to Fluid (\(P_{hyd}\)): -

Hydraulic Efficiency (\(E_h\)): -

Volumetric Efficiency (\(E_v\)): -

Mechanical Efficiency (\(E_m\)): -

Overall Pump Efficiency (\(E\)): -

Required Pump Shaft Power (\(P_{shaft}\)): -

Electrical Input Motor Power (\(P_{elec}\)): -

3. Hydraulic efficiency calculation

The fluid needs to circulate in the pump in order to gain power, as for any fluid flow, the fluid will lose energy when it has to flow against the walls of the pump, change direction, or accelerate. There is an overall energy gain but the flow of the fluid leads to some losses called hydraulic losses. Hydraulic losses can be calculated with the following formula :

\[ E_h = \frac{W}{W + W_h} = \frac{H}{H + H_h} \]

E_h = W/(W+W_h)

With :

\(E_h\) = hydraulic efficiency (-)
\(W\) = the actual specific work given to the fluid by the pump (J/kg)
\(W_h\) = the specific work that was lost by the fluid during pumping (J/kg)
\(H\) = useful total dynamic differential head (m)
\(H_h\) = internal hydraulic head loss (m)

4. Mechanical efficiency calculation

Like every rotating equipment, even the best designed pumps have mechanical losses due to friction and heat at their bearings, shaft, and coupling; therefore, the mechanical efficiency can be calculated using the equation provided in the calculation of pump mechanical efficiency guide.

\[ E_m = \frac{P - P_m}{P} = \frac{P_{shaft} - P_m}{P_{shaft}} \]

E_m = (P-P_m)/P

With :

\(E_m\) = mechanical efficiency (-)
\(P\) or \(P_{shaft}\) = total shaft power (kW)
\(P_m\) = power lost in the mechanical parts of the pump (kW)

5. Volumetric efficiency calculation

Pumps are bringing liquid from the inlet of the pump, to the outlet of the pump, however, as the pressure at the outlet is higher than the inlet, the fluid tends to go back in the reverse direction, leading to "leakages" in the volute of the pump. A little bit of liquid leaks back which means that it needs to be propelled 2 times, it's a loss called volumetric loss. It can be expressed the following way :

\[ E_v = \frac{Q}{Q + Q_v} \]

E_v = Q/(Q+Q_v)

With :

\(E_v\) = volumetric efficiency (-)
\(Q\) = total volumetric flow pumped out (m³/s)
\(Q_v\) = leakage flow back to suction (m³/s)

6. Pump overall efficiency & Power Sizing

The individual efficiencies are rarely considered in isolation in daily operations; pump manufacturers usually provide an overall pump efficiency curve that represents their combination.

\[ E = \frac{P_{\text{output, fluid}}}{P_{\text{input, shaft}}} = E_h \times E_m \times E_v \]

E = P_{output_to_fluid} / P_{input_at_shaft_coupling} = E_h*E_m*E_v

The hydraulic fluid power delivered to the liquid is determined by:

\[ P_{\text{hydraulic}} = \rho \cdot g \cdot Q \cdot H \]

Once the hydraulic power required for an application has been calculated, it must be divided by the pump overall efficiency (\(E\)) to determine the actual shaft power required to drive the pump, and further divided by the electric motor efficiency (\(\eta_{\text{motor}}\)) to select the appropriate motor rating.

💡 Practical Plant Engineering Rules of Thumb & Design Margins

Operating Near BEP: Pumps should ideally operate between 80% and 110% of their Best Efficiency Point (BEP) flow rate. Sustained operation below 50% BEP causes heavy internal recirculation, vibration, shaft deflection, and premature mechanical seal failure.
Motor Sizing Margins: Always size the driving motor with a safety margin above absorbed shaft power to prevent overload during cold startups or high-flow excursions:
- For shaft power < 15 kW (< 20 HP): Add 25% power margin.
- For shaft power 15 to 55 kW (20 to 75 HP): Add 15% power margin.
- For shaft power > 55 kW (> 75 HP): Add 10% power margin.
Viscosity Penalties: Viscous fluids (> 10 cSt) drastically reduce hydraulic efficiency and head while increasing shaft power demand. Apply Hydraulic Institute (HI) viscosity correction factors for heavy oils and polymers.
Typical Efficiency Ranges: Single-stage standard process pumps (ANSI/ISO): 65–85%; Large double-suction water pumps: 80–92%; Multi-stage high-pressure boiler feed pumps: 70–88%; Small low-flow positive displacement pumps: 50–75%.

8. Manufacturers

If you have calculated the pump you need for your application and would need to know the efficiency of actual pumps that could fit your needs, you can contact the pumps GrosClaude : https://www.pompes-grosclaude.com/en/home/

(Note that MyEngineeringTools has no link with this company)