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Rainwater Tank Pump Systems, top ups and switching devices Print E-mail

Nearly every rainwater harvesting system in Australia has some kind of pump. A pumping system can be installed on a rainwater tank to increase the water pressure to be used for garden watering or inside the house for the toilet, washing machine, or whole of house. Some water appliances will not work unless there is pressure produced by the pump. The pump can be installed outside (surface pump) or inside (submersible pump) the rainwater tank (See Table 1 for benefits of each system).

Pumping Systems to comply with HB230-2008, Chapter 6


Table 1 : Benefits of Pumping Systems

Characteristic

External Pump

In-tank Pump

Performance

Correctly installed will provide consistent performance.  Long or poorly installed suction lines  can cause problems

Correctly installed will provide consistent performance

Noise

Horizontal Multistage design pumps are extremely quiet but lower cost jet pumps can be noisy

Water in tank will minimise noise

Electrical cabling

Can be an issue for children and animals

Less accessible if installed correctly.

Weather protection

Needs to be protected from sun and rain

No protection required for the pump but may need protection for external controller (from sun and rain).

Maintenance

Easier to maintain

Need to pull pump out of tank to maintain

Cost

Usually lower cost

Can be higher cost


Water Security – Mains Switching Devices and Top-up Systems

A pumping system can be used for garden watering and general outside use through a standard garden tap. If the pumping system is required for water use to inside the house (toilets, washing machine or whole of house), and mains water is available, then an automatic tank connection device is recommended to ensure that the appliances will work even when the rainwater tank has run out of water.

There are two types of automatic tank connection devices:

1) Mains Switching System (either electronic or hydraulic),

An Automatic Mains Switching System  will change to mains water supply when there is no water in the rainwater tank. It will revert from the mains water supply back to rainwater when it rains and the tank has water.


Diagram 1 – Mains switching system for inside house supply

2) Top-up system.

A Tank top-up device will always keep a certain level of water in the rainwater tank so the pumping system is always in operation.

These two systems are shown in Diagram 2. The Characteristics of these systems are summarised in Table 2.

Tank connection devices to comply with HB230-2008, Chapter 5.11


Diagram 2 – Top up system for inside house supply

 


 

 

Table 2 – Characteristics of Mains Back-up Systems

Characteristic

Auto Mains Switching System

(AMSS)

Tank Top-up

(TTU)

Comments

Electronic

Hydraulic

Requires a pump to provide water

No

No

Yes

When the pump does not work an AMSS auto switches to mains. A TTU does not.

Requires electric power to provide water

No

No

Yes

When there is no electricity an AMSS auto switches to mains. A TTU does not.

Requires electronic switches to operate

Yes

Not for mains /rainwater switching function but usually  requires an electronic controller to operate pump

Not for rainwater filling of tank but usually  requires an electronic controller to operate pump

A TTU and hydraulic AMSS use mechanical devices only for switching of tank filling but the pump does require a controller – usually electronic.

Requires Mains water flow

Yes

Normally full mains flow and pressure

Yes Dependent on system whether full flow and pressure

No

Reliant on pump to provide flow and pressure

Some hydraulic AMSS use pressure reducing devices that can reduce flow and pressure.

 


 

Problem Trouble-shooting

It is important that the operation of the pumping system is understood in order to maintain the system and fix problems. If there is a problem with the pumping system then refer to the Operations Manual of the pump and/or mains back-up system.

Independent research from Professor PJ Coombes has identified some critical fine tuning issues for efficient pump operation. We need to understand flow rates for water efficient appliances are 4-8 litres/minute, mains water supplies water at 40-80 litres/minute, a rainwater pump at about 20 litres/minute. Firstly the tap to the toilet is often turned right down by plumbers to reduce mains water pressure. This causes the pump to cycle, or switch on and off lots of times, which is inefficient. When operating on rainwater open the tap supplying the toilet cistern right up. Secondly, calibrate the pressure settings of the pump to household flow rates, a plumber can show you how to do this. Lastly and most importantly, small water leaks in the system, eg a slightly leaking toilet, will also cause the pump to cycle and become much more expensive to run. Efficient pump operation requires all leaks to be fixed. 

The table below provide generic troubleshooting, which may or may not apply to a specific model or brand of system:


Table 3 – Trouble shooting guide for pump systems

Problem

Root Cause

Possible Solution

Pump is turning on and off repeatedly

The pump will turn on when the pressure in the discharge piping is low. It will turn off when it has pumped the pressure high. The pressure in the household piping can only go down if there is a tap open or a leak in the system

Check all taps for leaks. Check all toilets that there is no slow leak into the bowl. Check washing machine by turning off water isolation tap. Repair leaks if necessary. If leak cannot be found contact a plumber to investigate leak that may not be visible.

Pump continually operates

The pump will operate continually if there is a tap open or a severe leak. If this is not the case then the pump controller may be faulty.

Check for open tap and leaks in system from toilet and pipework. Contact a plumber if there is a leak. If no leak is detected, contact the pump manufacturer, repairer, or retailer.

Pump doesn’t operate when rainwater in tank

The pump should operate when a tap is opened or a toilet is flushed. There could be electrical supply problems to the pump or even pump failure.

Turn the pump off and then on at the power point.

a) If the pump does not start, test power point by using another appliance. If other appliance doesn’t operate, check circuit breaker at switchboard. Reset circuit breaker and test appliance again. If circuit breaker trips again contact electrician. If pump is causing circuit breaker to trip contact pump manufacturer or retailer.

b) If the pump starts but doesn’t continue the problem maybe with the switching device. Contact the pump manufacturer, repairer, or retailer.

No water to tap or toilets or washing machine

Tank top-up systems rely fully on the pump to deliver water to toilets and/or washing machine. Systems that have electronic or hydraulic switching to mains water should deliver water at all times even when there is no rainwater in tank.

Check pump operation and power supply by following procedure in section above.

Clean all filters and strainers to ensure there are no blockages.

Contact the pump manufacturer, repairer or retailer.

Low flow to tap or toilet or washing machine

There could be blockages in the system that is restricting flow.

It is possible that the pumping system or mains switching system supply is designed for low flow.

Clean all filters and strainers to ensure there are no blockages.

If the flow is still not acceptable contact the pump manufacturer, repairer, or retailer.


Suction Pipe Trouble-shooting

Experience has shown that suction lines cause problems with pumping systems.

The most common cause of suction related system problems is air leaks on suction pipework.  All threads should be sealed with thread tape correctly. (This may involve up to 10 wraps of tape around each thread).

Since tanks, pumps and homes can move over time due to seasonal changes, the use of flexible pipework between all components, especially on the suction can alleviate stress placed on them.

Refer to the diagram below for assistance in overcoming problems caused by suction lines (Diagram 3).

Diagram 3.1 – Long Suction Pipework : Suction pipework that passes under pathways or travels long distances can cause priming problems with pump. Priming problems is caused by air becoming trapped in the pipe and preventing the pump from working.  It is ideal to keep the suction pipework as short as possible. Some pump manufacturers suggest installing a filter or strainer  to protect the pump – check to see if the brand or model involved needs a strainer and where this should be installed.


 

Diagram 3.2 – Elbows in Suction Pipework : It is better to reduce the number of elbows in the suction pipework where possible. It is best to have no elbows but where necessary have as few as possible. Try to prevent having an elbow directly onto the inlet of the pump. This can cause suction and noise issues with the pump.


 

Note Y Strainer not required for all models

Diagram 3.3 – Flexible Suction Pipework : It is important to keep the suction pipework short and straight as possible, with a filter or strainer.  If the flexible suction pipework needs to be looped ensure the loop goes downwards. This will prevent air from being trapped in the high point.


Note Y Strainer not required for all models

 


Maintenance

It is important to check operation of the pumping system regularly by listening for the day-to-day operation of the pump. Unusual noise or no noise needs to be investigated. Clean all strainers and filters every 6 months.

A good quality pump and switching device should provide trouble free service for up to 10 years. Members of the RHAA use the Australian Standard, HB230, for pumps and rainwater harvesting system components.


This material has been prepared as a result of discussions with the NSW Department of Planning although RHAA is solely responsible for the material. The RHAA provides these as general principles with no implied liability for the advice. In all circumstances you should rely on your own sources for advice that will meet your specific needs. 

 

 

Last Updated on Friday, 22 April 2016 09:31
 
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