Vacuum Pumps Exhaust Piping

Overview

Engineering reference data for Vacuum Pumps Exhaust Piping in pumps.

Key Formulas

Pump Power

$P = \frac{Q \cdot H \cdot \rho \cdot g}{\eta}$

Hydraulic power / efficiency.

NPSH Available

$NPSH_a = \frac{P_s}{\rho g} + \frac{v_s^2}{2g} - \frac{P_v}{\rho g}$

Net Positive Suction Head available.

Affinity Laws

$Q \propto n, \quad H \propto n^2, \quad P \propto n^3$

Flow, head, power vs speed.

Variables

Symbol	Description	Unit
$P$	Power	W
$Q$	Flow rate	m³/s
$H$	Head	m
$\eta$	Efficiency	—
$n$	Rotational speed	RPM

Example Calculation

The vacuum pump exhaust pipe sizing can be estimated using the principle of equivalent flow capacity through parallel pipes or a larger single pipe.

For the given example:

• Exhaust flow rate: $Q = 1200\ \text{cfm}$
• Required piping length: $L = 60\ \text{ft}$

The maximum length for a 6" pipe carrying $600\ \text{cfm}$ is $L_{\text{max}} \approx 120\ \text{ft}$.

Therefore, using two 6" pipes in parallel provides sufficient capacity: $Q_{\text{total}} = Q_1 + Q_2 = 600\ \text{cfm} + 600\ \text{cfm} = 1200\ \text{cfm}$

Practical Note

The diagram-based approach shown is an approximation method. For critical applications, consult manufacturer performance curves or use detailed fluid dynamic calculations that account for factors like:

• Pipe roughness and material
• Number and type of fittings (elbows, valves)
• Total equivalent length
• Temperature and vacuum level specifics

Interactive Charts

References

• Original Source