Project: sc090025/R1

 
Flow rates
can be easily measured with modern flow meters which operate on the 
electromagnetic principle. These are extremely accurate (fractions of a percentage deviation 
from true) and generally not particularly expensive at smaller sizes. Most older pumping stations 
do not have this kind of flow meter built in owing to their lack of availability when the site was 
built; more recent installations may have omitted this to save cost and because there is 
generally no requirement to know the quantity of water discharged. As flood defence pumping 
stations generally use independent pipework systems, multiple costs would be involved 
For existing pumping stations where flow meters are not installed, different types of clamp-on 
flow meters are available, which provide an indication of the delivery flow, but from tests carried 
out their accuracy and repeatability may be in question. Experience has shown that delivery 
from older sites is often significantly lower than expected, usually due to impeller damage, but 
without any flow measuring equipment this may have gone unnoticed for years. 
Delivery head
is the simplest of all parameters to measure directly, as a simple drilled and 
tapped hole in the delivery pipe can be made to accommodate a small pressure gauge. This 
can be designed to read static or dynamic head, and will show if there are any unexpected 
restrictions downstream which increase the pumping head. Care must be taken when installing 
this kind of gauge to avoid venturi effects in fast-flowing pipelines. It is possible to obtain a 
completely false reading from a pressure gauge if, for example, the hole is drilled into a bend 
where the rapid change in water direction results in a drop in pressure at one point and an 
increase in pressure on the opposite side of the pipe. This effect does not occur in static water 
flows as it is a dynamic effect only. 
For best results, this kind of tapping should be made in straight sections of pipe where possible, 
and if it is unavoidable to tap into a bend, many gauge tappings should be put in place and their 
readings averaged out. 
Motor speed
can be measured with a simple stroboscopic measuring device, and will yield 
useful information on the likely onset of cavitation within the pump chamber. Motor speed may 
differ from the stated speed on the information plate if, for example, the duty has changed since 
the original installation. An unexpectedly high motor speed may also provide a clue of other 
unseen damage such as impeller breakage.