TEST OF THE PUMP FLOW 

The required parameters to be measured:

 

- Head (pressure).

- Flow.

 

 

The number of measurements depends on  the following factors

If the operating conditions of the pumping system are constant or vary minimally in time a single measurement or test is enough.
If the system demand varies over time, it is necessary to determine maximum and minimum flow,  the flow of the longest regime. See the Levels of assessment chapter

Typical scheme of a pump installation

Typical scheme of a pump installation

Flow measurement 
 
There are different methods of flow measuring:

- Using installed on the pump stationary flow meters. 

You should be assured that measuring devices have been calibrated. 
This method allows to save time and prevent interrupting in the technological process

 
- Using portable flow meters. 
The most popular types of portable flow meters are ultrasonic flow meters:
Transit time ultrasonic flow meters.
This time difference is a measure  Ultrasonic flow meters measure the difference of the transit time of ultrasonic
pulses propagating in and against flow direction.   for the average velocity of the fluid along the path of the ultrasonic beam.
Ultrasonic flow meter operation

2.    Doppler ultrasonic flowmeters. (Use of the Doppler shift that results from the reflection of an ultrasonic beam off sonically reflective materials, such as solid particles or entrained air bubbles in a flowing fluid, or the turbulence of the fluid itself, if the liquid is clean). This method is less accurate and requires the presence of solid particles or gas bubbles. More often applied for measuring flow of sewage waters.

 
Dopler flow meter operation
For measuring a flow of clean water the flow transit time ultrasonic flow meters are used.

The accuracy of measurements very strongly depends on the right installation of flow meters.

The typical schemes of ultrasonic flow meter sensors installation are shown below.

Typical shems of ultrasonic flow meters installation

The main requirement for providing accurate measurements is the keeping the necessary length of straight pipelines before and after sensors.

The common demands for sensors installation are shown below.

Places for sensors installation of a flow meter
Distances for flow meters installation
Verification of a measured capacity of a pump  
 

When portable flow meters are used, the verification of the measurements should be performed by re-installing the flow meter in an alternate location or using multiple measurement techniques.

If large variations are found, then the measurements shall be considered unreliable.

 

Flow values can also be correlated with pressure and power measurements and pump manufacturer curves.

Pressure measurement. Pump head measurement.
Pump's pressure is the difference between outlet pressure and inlet pressure.
 
The required location of pressure gauges is approximately 2 diameters of straight pipe from inlet/outlet flanges.

For accurate calculation of the pump total head, the velocity and the instrument elevation shall be taken into account. 

Sometimes velocity in a pipe where a gauge is installed can be big enough especially when a pipe with a small diameter is used. In this case, the opinion that the pump has the head which is less than it should be can arise. 

 

Keep in mind that the pump head is the sum of static and velocity head but not only pressure head.

How to calculate pump head if pressure value is known? How pressure and head are connected?

H - head in m

p -  pressure in Pa

g - gravity acceleration (9.81 m/s2)

ρ - density in kg/m3

 

- 1 kg/cm2 = 10.3 mwc
- 1 bar = 10 mwc

Hpump - pump's head in m

pout -  pressure in Pa at pump's outlet or pressure pipeline

pin    -  pressure in Pa at pump's inlet or suction pipeline

g       - gravity acceleration (9.81 m/s2)

ρ       - density in kg/m3

Vout  - fluid velocity in outlet pipe, m/s

Vin    - fluid velocity in inlet pipe, m/s

Zout  - a level of the pressure gauge on outlet pipe relatively common level 

Zin    - a level of the pressure gauge on inlet relatively common level  

 

Velocity head and level of a pressure gauge are negligible usually and it is possible to use the simplified formula.
How many points are necessary to measure to draw H-Q curve?
What duty points are recommended for measuring? The more the better can be the answer. But in the field conditions, this is not possible.
If you have a test report of a pump, to draw the pump curve usually it is enough to measure two points.
  1. The first point is a Shut off head (Q=0) or Shut off test. This point shows the pump head at Q=0. This point is very informative. This point gives information about the real pump condition. Comparing the measured head (pressure) with the curve received at the factory, a user can evaluate the rate of a curve declining due to deterioration. If users have a test report of his pump then it is enough for interpolation of a complete curve starting from Q=0. Pros and cons. All centrifugal pumps have a time limitation of operating at Q=0. Because it can cause overheating of a pump. A valve at a pressure line can be not hermetic enough.
  2. The second point can be somewhere in the operating range. For example, close to BEP. Knowing from the curve from a catalog or from test report try to close the valve so that flow was close to Qbep.
After measuring parameters you can do analyses of a pumping system.