pump types

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Basic Principles and Pump Types

HOW TO ESTABLISH HEAD


How to establish total head

We also need to understand what pressure we need at the tap/appliance for it to work effectively

However, if we are using a pump, there is more information we need to know

• We need to know the height between the water and the outlet (static head)

• We need to know what the friction loss will be

• We need to know the operating pressure at the outlet

Once we add all these together we will know the total head we need the pump to generate


Suction and discharge head

Suction head is what happens before the water arrives in the pump – pumps don’t suck! • Atmospheric pressure pushes water into the

pump to replace a partial vacuum created inside the pump

• Atmospheric pressure reduces with altitude • 33.9 feet at sea level • Lose over 3 feet for every 3,000 feet

elevation Discharge head is what happens after the pump • What’s required to get the water from the

pump to where it’s wanted with the required pressure at the end

Discharge head

Suction head

Pump


Positive suction head

Positive suction head (positive inlet pressure)

• Water freely flows to the suction of the pump

• Positive suction head when coming from a tank is also known as a flooded suction

• Examples are above ground tanks and line boosting from mains


Negative suction

Negative suction (suction lift)

• Water source is below the pump and needs to be raised to supply the pump

• Examples are underground tanks and rivers, dams, etc.


Total Suction Head = Static Suction Head + Suction Friction Head (loss)

• Static Suction Head is the

vertical height from the water to the centre line of the pump

• Suction friction head (loss)

is the head required to overcome the friction in the pipe and fittings on the suction side of the pump

Suction static height

Total suction head


Discharge head

• Static Discharge is the vertical height from the centre line of the pump to the highest discharge point

• Discharge friction head (loss) is the head required to overcome the friction in the pipe and fittings on the discharge side of the pump

• Operating pressure is the pressure required at the end of the pipeline, for example to supply a house, operate sprinklers, etc.

Static discharge lift

Example: If a sprinkler pressure required is 40 PSI, this can be converted into feet: 40 x 2.31 = 92.4 feet of head


Total Dynamic Head

Total Dynamic Head is also known as Total Differential Head

• To select a pump we need to determine the Total Dynamic Head (TDH)

Negative Suction (e.g. underground tank, bore, etc.) applications

• TDH = Total Discharge Head + Total Suction Head

Positive Suction (e.g. above ground tank) applications

• TDH = Total Discharge Head - Total Suction Head


TDH calculations – negative suction

b. Suction line (pipes and fittings)

d. Discharge line losses (pipes and

fittings)

Total Suction head = a + b Total Discharge head = c + d + e

a. Static suction lift

c. Static discharge lift

e. Discharge pressure (if required)

Total dynamic head = Total suction head + Total discharge head


TDH calculations – positive suction*

b. Suction line loss (pipes and fittings)

d. Discharge line losses

(pipes and fittings)

Total Suction head = a–b Total discharge head = c + d + e

c. Static discharge lift

e. Discharge pressure (if required)

a. Positive suction head

Total dynamic head = Total discharge head – Total suction head

*(Flooded suction)


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