How to Control the Pump

7/23/2019 How to Control the Pump

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Basic Hydraulic Principles

PUMP CONTROLS




How to control the pump

The pump be controlled manual/automatically – need to know

• Water requirements of animals, people, etc.• Consumption pattern, for example at a hotel

What works best?

• Pressure switch• Pressure tanks• Anti-cycling control• Constant pressure




Pressure switch

This is how a pressure switch works•

Pump will start when the cut-inpressure is reached, for example a tap isopened and the pressure drops

• Pump will stop when the cut-outpressure is reached, for example all taps

are closed and there is no flow thepressure will build up in the system andturn pump off

• If there is a small flow this system willcycle (turn on/off until flow stops orincrease to be higher than cut out)

• No dry running protection• Requires a draw off tank (pressure tank)

Cut In

Cut Out




Pressure tanks come in different sizes and they are used for draw off• When you open a tap, instead of the pump turning on straight away the tank has

water under pressure and will release this into the system• When the tank is empty the pump will turn on• Pressure tanks are used for evaporative coolers as they draw a small amount of water.• If there is no tank and there is an evaporative cooler, the pump will cycle

Pressure tanks

Free standing60 – 450 litres

Pipe mount8 – 18 litre

Air charge

Water

Inlet

Air valve




Pump off

Draw offsupplying smalldemands

Pump on

All pump outputservicingdemand

Pump on

Demand reducing,tank being rechargedready to stop

Pressure tanks

Pump-on and pump-off routines are shown here




Anti-cycling control – operation

Controls the operation of the pump by:• Starting on falling pressure

(adjustable option)• Stops on flow – approximately 1.5 lpm• Dry run protection with manual or

automatic restart•

Small tank can be added• Operation follows pump curve so pressure

may change with flow rate depending onpump curve

• Minimum flow for a Pressure• Manager is 1 lpm




Anti-cycling control – good and bad

Advantages• Keeps pump in operation down to

min flow• Protects the pump in the event the

water supply fails• Incorporates internal NRV

Disadvantages • No draw-off as standard• Pressure drop at higher flows




Constant pressure (VFD)

Variable speed control reduces speed as demand• Saves power up to 50 % in low flow• Constant pressure, so no fluctuations as taps open and close

– gives the consumer the best comfort while consuming water• Adjustable pressure• Higher initial capital cost• Dry run protection (pump will turn off if there is no water)




Pressure during operation

•

• A = Operation with Pressure Manager (anti-cycling system – impression of constantpressure, but in reality to protect against cycling). Pressure will drop when you openmore taps

• B = Operation with traditional tank and pressure switch and tank (variable pressure)• C = True constant pressure , via a variable speed drive

C

The graph below shows the pressure fluctuation during operation

of the three different ways to control a pump over time




Example – pump selection

Select a pump for duty of 60 l/min at 31.6 m anti-cycling

Pump selected:CMB3-55




Example – pump selection

Constant pressure VFD for duty of 60 l/min at 31.6 m

Pump selected:CME3-3




Review of basic pump selection

What is required for successful pump selection:

1. Pump selection starts by determining the volume (flow rate)required

• Output of various outlets, showers, sprinklers, etc.

• Water requirements of animals, people, etc.

• Consumption pattern, for example at a hotel

2. Calculate the amount of energy the pump must impart to thewater (total head)

• Elevation (vertical height) from source to point of discharge

•

Losses in pipes and fittings• Operating pressure required at point of use

3. Power supply available

4. How will the pump be controlled – manual/automatically




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How to Control the Pump