As we all know from physics lessons and, in some cases unfortunate personal experience, water expands when it freezes. When this expansion takes place in an open body of water the results are usually fairly picturesque and provide all kinds of photo opportunities for the budding David Bailey's among us.
However, when water turns to ice and expands in confined environments the effect can be devastating, causing massive damage to any component or vessel left in a primed state.
Unfortunately, when this damage occurs within an irrigation system the effects are often unnoticed until well into the spring when the system, is 'needed'. It is, therefore, essential that due concern is taken in late autumn to purge those areas of the system that are most at risk from frost damage.
In recent years talk of global warming and climate change, combined with what have generally been milder winters than we are used to, have resulted in more and more people in lower lying or coastal regions deciding it is not worth spending time or money on draining down irrigation systems.
However, as last winter proved, we only need one or two days or nights of severely low temperatures to cause horrendous damage to systems not correctly drained down.
In the spring of 2009 our service department attended a record number of sites to repair frost damaged pipe work, valves and pumps. In some cases, clients were lucky and only had to repair exposed pipe lines, whilst others were less fortunate and had to replace whole pump units that had been damaged beyond repair. The cost of these repairs running, in certain cases, into thousands of pounds.
To avoid this unnessesary cost, simply ensure that the system is drained down to a point where any remaining water has room to expand without causing damage to components.
Key areas to attend to are pumping stations, boxed valve assemblies, above ground or 'side suction assemblies' and rising main feeds to the storage tank.
If a system has been installed correctly there should be multiple drain down opportunities available, including pump drain off points, mains pipe purge valves, rising main drain cock and various hose points. All of these should be opened fully to minimise any risk of trapped water.
There are certain areas to watch out for, one being that butyl lined tanks should not be emptied to less than two thirds full. This is because the butyl can dry out or be exposed to frosts, both of which will shorten the life of the product.
On bowling greens many systems now have submersible pumps installed within the storage tanks. If you empty the tank you must also remove the pump to protect it from the elements.
Another handy tip is to ensure that any rising main is purged completely by making sure that the ball cock valve assembly is hanging free, allowing any water trapped by vacuum to be discharged through the drain cock.
Pump stations should be dealt with great caution and care, particularly those with variable speed drive units installed, or complex pump drive panels.
Whilst it is important that the pumps are drained of water, it is equally important that the expensive drive units are not just turned off for the winter. These drive units generally house multiple transformers, circuit boards and electronic components and, when powered down, create perfect conditions for the formation of condensation. This condensation can sit on the boards and cause short circuits come spring time.
It is therefore always advisable (unless recommended alternatively by the manufacturer) to leave drive panels powered up for the winter. The heat from internal transformers will normally be sufficient to prevent condensation.
If you are leaving panels powered up, be absolutely certain that pumps cannot be driven in drained down mode. Some panels have a built in default to go to run mode following a power cut. This must be overridden to prevent huge repair costs.
On the control system front, it is generally agreed that disconnection of the field wires from the control panel is a good way of protecting the unit from short circuits or power surges. However, if this process is carried out, be absolutely certain to physically remove the cables from the unit entirely. The reason for this is that power surge can arc across from bare cables onto adjacent circuit boards and damage components.
Obviously, I would recommend that you employ the services of experienced engineers to carry out system winterisation. Not only does this save you time and aggravation, but it also makes someone accountable should any frost damage occur.
A full engineer drain down should also include a thorough inspection of components and a quick station test to confirm all automatics are operational, thereby identifying any items requiring attention and allowing rectification works to be carried out whilst the system is not used.
However, if you choose to carry out the works in house, never underestimate the potential risk when working in a pump house or on the system generally.
Please remember - you have water under very high pressure and high voltage electricity in close proximity, either or both of which can kill or cause severe injury if not respected.