Continuing enquiry has prompted Irrigation NZ to issue this update on checking irrigation pumps and systems following the September 4, M7.1 earthquake in Canterbury
Your assistance in spreading the word is much appreciated
Irrigation New Zealand (INZ) continues to advise caution where irrigation managers are looking to start up bore pumps in groundwater zones affected by the earthquake.
INZ’s primary recommendation is to have the system checked by an electrician and have a pumping specialist conduct the first start.
INZ advises contacting your insurance agent for advice on any limitations on risk cover.
However, if this is not practical within your operational time frame then things to consider are set out below:
- The pump curve from the Operation and Maintenance Manual supplied with your irrigation system will give you a guide to the pump performance (flow rate and pressure head, speed and kilowatts).
- We recommend discharging the first flush of potentially silty water at the well head to open air and not down the mainline.
- However, the rising column may have lost prime due to leakage of the foot check valve in the submersible. The rapid re-filling of the rising column with water with no back pressure on start up is a risk.
- The nature of the motor control system will determine the ability to limit pump speed. Borehole pumps must be run up to at least 30Hz immediately, which is important for the bearings. Speed and motor load are sometimes displayed on electronic pump drives.
- Pumps can be started against either a fully closed or 90% closed valve to control the rate of column filling. Even a small valve opening will allow rapid discharge of air while on large pumps a fully shut valve may be hard to open if it is not fitted with a gear drive.
- The critical factor is to ensure you slowly start opening then adjusting the valve opening % within 15 seconds to control the rate of air discharge to fill the rising column.
- Once the column is full, set a greater speed sufficient to allow a flow rate adequate to visually identify a “good flow” at the well head discharge. This visual estimate may be needed if water is not passed through a meter at the open discharge. Flow over the motor is important for cooling.
- Note: A start against a closed valve will produce the maximum head. Running the pump with no back pressure risks cavitation if the pump runs to the far right of the curve. Neither situation should be allowed to continue for greater than 10-15 seconds. Both situations should have been considered when the pump was selected and tested at the original commissioning period.
- Monitor the discharge water closely for sediment content and do not leave it running unattended.
- There is a risk that running the pump to full performance too soon will draw in unnecessary levels of silt. Running sediment, even fine silt, through pumps for any length of time will potentially cause damage.
- Most bore pumps checked to date have produced clear water within a few minutes. If the water does not start to clear then it is possible the well will need redeveloping by a professional well driller.
If you have any concerns about this process then seek assistance.
More information re pump start up and checking irrigation systems can be found on the IrrigationNZ website www.irrigationnz.co.nz
Further comment:
Stephen McNally 04 4717146
Ian McIndoe 03 9646521
Irrigation NZ is a national body representing all irrigation interests in a unified voice to promote excellence in irrigation development and efficient water management based on the principles of responsible and sustainable water management throughout NZ.