Since the introduction of water meters for commercial use at the end of the 19th century, it has been necessary to remove them from service periodically. The meters are then checked, and a decision is taken as to whether it is possible to use them for a further period, or whether they should be cleaned and/or rehabilitated before undergoing another verification process and being reintroduced into the field for a further specified period.
Meters were frequently removed from service, especially at the beginning of the last century, and were repaired piece by piece by skilled mechanics. As the meters at that time were constructed of metal (mostly brass/bronze) and as the water quality then was not as good as it is today, a thorough cleaning was indeed necessary. Very often methods of mechanical cleaning by means of brushes were used, and after the repair the meters were calibrated on a small calibration rig. Average repair cycle times could be up to 1.5 man hours per meter.
In the 1960s plastic meter inserts were introduced. They offered the advantage of lower production costs, and were also more resistant to scaling and accumulation of deposits on the inner parts. This development led to a more cost-effective maintenance scheme for water meters. The use of new materials meant that the re-verification time of a water meter could technically be extended, but national metrology regulations prevented this in many cases. Nowadays meter refurbishment is professionally done in large numbers using modern techniques and cleaning fluids to clean internals in an effective and efficient way. Calibration is also done in large numbers, reducing the total cycle time (repair and calibration/verification) to approximately 9 man minutes per meter!
TECHNICAL PROCESS ASPECTS OF REFURBISHMENT
The process outlined in Figure 1 describes the steps undertaken by a private water meter refurbishment shop, which refurbishes water meters in large numbers – a practice that has proved to be highly efficient. It is therefore recommended that there should be at least 250 meters per batch, to optimise the sequential process steps and reduce the change-over time of process equipment.
After the incoming meters have been registered there is a selection process, depending on the requirements of the customer. Some customers ask as a first step that the meters be verified in the condition in which they come from the network. Others have a company policy which requires all meters to be refurbished, irrespective of their condition at the time they are temporarily removed from service. This is also the stage at which old meters, which will not be repaired, are taken out of the process.
CLEANING METER PARTS
Meters are then sorted and temporarily stocked, in order to be able to run batches of at least 250 identical meters. After dismounting, the metal parts are separated from the plastic parts and adjustment plugs are removed. The metal parts, usually the meter body and the head, are cleaned in industrial washing machines, using phosphoric acid solution at 30-40ºC. The next stages involve neutralising the acid in an alkaline solution and rinsing once or twice in clean water. After the metal parts are dried they are checked for remaining deposits and worn coatings. Meter parts that need additional mechanical cleaning are treated in a shot blasting or grit blasting machine.
The plastic parts are separated in large subassemblies or parts, depending on the design of the meter. They are then also cleaned, using a combination of mild acid solution and ultrasonic techniques. A combination of both low and high frequency ultrasonics provides the most efficient removal of deposits and particles found in water meters.
In designing the cleaning process, it is important that the integrity of the parts is protected at all times. Ultrasonic technology is able to reduce the cleaning time by as much as 90% when compared to conventional methods. This is accomplished by enhancing the effect of the chemical cleaning agents, and the physical removal of particles from surfaces in contact with the cleaning liquid. One important advantage of the use of ultrasonic techniques is its ability to clean the complex inner parts of the water meter, like the register, without damaging them.
After cleaning and rinsing the inner parts are dried and visually inspected for wear and damages. Worn or damaged parts are replaced and if possible the roller-register is set back to zero. The metal parts are coated if necessary and dried.
Meters are then re-assembled using new gaskets and/or ‘O’-rings and pre-adjusted at known settings. Before entering the calibration stage the meters are tested for water tightness according to specifications.
ECONOMIC AND MANAGERIAL ASPECTS
The cost of refurbishment and re-verification of water meters is always compared to the cost of buying new meters. When refurbishment costs reach 60-70% of the cost of a new meter, many meter owners (in most cases water supply companies) decide to replace old meters with new stock. The old meters, separated into metal and plastic components, are sold for scrap.
The costs involved in refurbishing a water meter can roughly be divided into the following categories:
- Handling costs (energy costs, write-off for depreciation of equipment).
- Cleaning costs (goods consumed, energy costs, write-off for depreciation of equipment).
- Labour (man hour, wages).
- General costs (rental costs of the building, management fees, taxes etc.).
It is impossible to give an example of the breakdown of refurbishment costs per meter, as the different components vary in different countries and with different companies.
Historically, the water supply companies in western Europe often had their own water meter repair shop. Today, with the drive to focus on their core business, utilities are trying to move non-core activities – including water meter repair – outside their company boundaries. This has given rise to the establishment of many privately-owned water meter refurbishment shops which offer these services at competitive prices.
In general, water supply companies dispose of their water meter repair shops when they expect to receive one or more of the following benefits:
- Lower costs, because the private meter refurbishment shop can operate refurbishment processes more cheaply than the water supply company. Refurbishment is the core business of the private water meter refurbishment shops, and they enjoy scale advantages by refurbishing large numbers of meters in more effective series.
- Accounting advantages – by shifting resources off the balance sheet, the water supply company can report a better return on assets.
- Reducing the high costs of employee termination. If a water utility is prepared to enter into a long term contract, it is possible to negotiate the re-employment of qualified meter refurbishment personnel at the private water meter refurbishment shop.
Figure 2: Average repair and calibration time for a domestic water meter
There are also disadvantages to using the services of private water meter refurbishment companies:
- When long-term contracts are entered into – either to reduce the risk of irregularities in the supply of refurbished meters or to arrange for the re- employment of water meter refurbishment personnel who might otherwise be made redundant – a water supply company will be prevented from searching the market for competitive suppliers.
- The availability of sufficient stock for water meter replacement programmes relies heavily on a predictable flow of refurbished meters at the required quality level. Water supply companies may feel they are better able to control this if the refurbishment is done internally.
- With the move of skilled staff to private refurbishment shops, the expertise involved in the refurbishment and calibration of water meters will leave the water supply company.
A lot of factors influence the cost price for refurbishment of water meters. From a technical and economical point of view, meter refurbishment can best be done in large series of identical meters, to minimise changes in the refurbishment process and to reduce the time taken for refurbishment and calibration (man-minutes). When the work is done by specialised water meter refurbishment companies, utilities can concentrate on their core business, while knowing exactly what the cost of the refurbishment of their water meters will be. Designing an efficient process flow, and working with an acceptable volume of meters, allows the private water meter refurbishment company to function successfully in a market-driven environment, with the ultimate aim of being recognised as a reliable partner for the water supply company.