Centrifugal Pump Volute Design

[Ángel Martin]

From the Author's Engineering Collection - and Available on the ETSII4 Module (ETI4 on the CL library).

This program calculates the geometric dimensions of centrifugal pump Volutes with Circular, Rectangular or Trapezoidal sections - reflecting a given configuration and performance conditions of the pump, as follows:

- Nominal flow thru the impeller, QR
- Impeller outer diameter, D2
- impeller rotating speed in rpm
- Impeller outer width, b2
- impeller blade exit angle, beta2
- impellers’ Pfleiderer’s coefficient, mu
this can also be calculated as function of number of blades, ZR - and internal diameter, D1)
- The friction losses coefficient in the volute, lambda3 (should be zero for circular volutes)

- If a diffuser is installed, the outer diameter of the diffuser, D3
if it has blades, the fluid exit radial speed, V3u
without blades, the friction coefficient in the diffuser, lambda2

- For Circular section volutes, the volute width at the tongue, bc

- For trapezoidal volutes, the volute width at the tongue, bc - and the aperture angle, delta

Once these data are entered the program will prompt for the angle to calculate the outer radius of the volute. This can be repeated for many angles in a loop to further characterize the volute geometry along the interval [0, 360], i.e. from the tongue to the throat. All angles are entered in degrees, and a homogeneous unit system is to be used (SI recommended).

Program Details.

Data Entry requires functions PMTK and ARCLI from the AMC_OS/X Module.

The PPC root-finding “SLV” routine is used for each calculation of the results in rectangular and trapezoidal section volutes. It is included in the ETSII4 module as well. Routines “R”, “T”, “T0” are used to describe the equation to solve, depending on the diffuser type.

The routine “NT” (NewType) allows for different types of volutes (Rectangular, Trapezoidal, or circular), and different design parameters known.


Example.
Calculate the dimensions of the three volutes types (use delta = 15 for trapezoidal) for a centrifugal pump with impeller rotating at 1450 rpm, without a diffuser and with the following configuration:
Qr = 52 l/s
D2 = 350 mm
b2 = bc = 10 mm
beta2 = 30 deg
mu = 0.809
lambdac = 0.04

The solutions are given in the table below;

Code:

Angle (deg)     Rectangular     Trapezoidal     Circular (center)     Circular radius
-------------------------------------------------------------------------------------------------------------
  0 (tongue)    R=0.1750        R=0.1750        a=0.1750             r=0.0000
 90             R=0.3167        R=0.2230        a=0.1924             r=0.0174
180             R=0.8965        R=0.2555        a=0.2000             r=0.0250
270                             R=0.2843        a=0.2060             r=0.0310
360 (throat)                    R=0.3115        a=0.2111             r=0.0361