If you own a pump, you
should be able to evaluate your pump’s performance and ensure that it’s ideal
for the purpose you installed it for. This is done by plotting points on a
graph and drawing a pump characteristic curve. This curve provides insights
into the relationship between the total
head (i.e. how much kinetic energy a pump can generate) and flow rate.
There are 3 key points on
this curve that we often consider (click on them to know more):
Another aspect of the curves
that we consider is what kind of curves they are:
curves: Here, the head is seen to be decreasing at a rapid pace while the flow
is seen to be increasing. This curve type is steep and gives you more control,
which makes it more sought-after. This is because a small change in flow will
result in a sizeable drop in pressure.
curves: Here, the head decreases at a very slow pace as the flow increases. This
type of curve is ideal for sprinkler systems because here, a significant change
in flow is coupled with a small change in head.
curves: In this case, the curve is similar to a normal curve with the exception
of the fact that the head rises and then falls as it nears the shut-off head point. This curve type should be
If you’re recently started learning about centrifugal pumps, you probably aren’t well-acquainted with what the term ‘head’ refers to in this case. So, let’s start with that.
Head is a measure of how
much kinetic energy a pump can generate. If a pump’s discharge is directed
upwards, the head would refer to the
height that the pumped fluid would be able to reach.
Is head the
same as pressure?
No. The pressure isn’t used to measure the energy produced by a pump because it is impacted by gravity. Head,
on the other hand, remains unaffected by the weight of the fluid when it’s
So, what does
‘shut off head’ mean?
Shut off head is the maximum head achievable by water pumps and occurs at zero flow. It consumes minimal power at this point. One clear sign of shut off head is when your pump vibrates more than usual and generates way more noise.
It is not
recommended to operate your pump at zero flow for an extended period of time
You may be wondering why. This is what would happen if you operate your pumps at zero flow for long periods of time:
friction created by the impeller will generate enough heat to boil the water
present in the pump.
will cause the mechanical seal to break and the plastic components of the pump
will damage or melt.
likely to leak into motor windings in residential systems.
a result of high pressure, the pressure switch will shut the pump down, leading
to minimal or no flow.
In simple terms, viscosity
is how thick a liquid is. For instance, water isn’t very viscous, but sludge is. Fluids may also gain/lose viscosity if heat or pressure is applied.
Viscosity is measured in units known as Seconds Say bolt Universal (SSU) and is
measured using a viscometer.
right pump depending on fluid viscosity
The consistency of the fluid you want to pump will determine the kind of pumps you’ll need. This is because thicker fluids cause more resistance when energy is applied. That means that pumps used for water may not be suitable for oil.
There are two options you
can select from once you’ve evaluated the viscosity of the liquid that needs to
Centrifugal pumps: These are ideal for relatively less viscous liquids, for instance, water. While these water pumps don’t necessarily stop functioning in fluids that are slightly more viscous, their efficiency may take a hit. This is because a centrifugal motor isn’t designed to operate in thick liquids. A centrifugal pump is ideal for relatively thin liquids that need to be pumped at high speeds.
Positive displacement pumps: These pumps are specially designed to work effectively in thicker fluids. These fluids are basically liquids which are over 2000 SSU in viscosity. These pumps would be ideal for oil. A positive displacement pump is also suited for fluids that need to be pumped slowly and gently to keep their properties intact. This could include food pastes, paint, etc. that would become runny and unusable if pumped at high speeds.
Vijay Engineering and Machinery Company, one of the best pump dealers in Mumbai, is a one-stop solution for all your pumping needs. We provide incessantly adept assistance at every step; be it providing knowledge & industry tips when it comes to choosing the perfect products from our wide range of Kirloskar pumps or servicing the ones you’ve got running for years. Want to know more about us? Click here to get in touch!