Air leakage surveys provide potential for savings

Stephen Cordingley highlights the potential energy savings that can be gained by reducing leakage in compressed air systems.

Wyko has been involved in managing energy issues as part of overall maintenance strategies for over ten years, including site-wide audits and specialist services.

However, following recent energy price rises a rush of customer enquiries concerning basic provision for energy saving has arrived from manufacturing and processing sites that have not previously considered it a high priority.

In order to help address the basic issues and make a first step towards practical and effective energy saving Wyko is releasing a series of guides, each one dedicated to a different area of energy saving in the production environment.

Stephen Cordingley Wyko Energy Saving Manager is responsible for the implementation of Wyko air leakage surveys and here highlights the potential energy savings that can be gained by reducing leakage in compressed air systems.

"Leakage is the largest single waste of energy associated with compressed air usage, for example, leakage rates exceeding 50% of site consumption are common in our experience".

"Compressed air is obviously generated using electricity, the price of which has virtually doubled recently, and when you consider that on average 10% of industry's total electricity usage is dedicated to air generation, rising to 30% in some sectors, the potential figure for overall wastage is immense".

The first and most obvious step is to survey the area, identifying leaks and listing them, Wyko physically tags individual leaks that occur at fixed positions and attribute a severity to them, allowing an estimate to be made for potential savings.

The wastage estimate can then be offset against the capital cost of fixing the leaks.

Says Cordingley: "In most cases, fixing leaks is a fairly straightforward case of replacing worn fittings, seals, valves, manifolds and air preparation equipment, and/or modifying working practices".

"The cost estimates are useful because they put the savings into perspective, as most remedial work has a pay off period of just a few months".

The severity of leaks is gauged in four levels: light, medium, heavy and severe, corresponding to equivalent leak sizes of 0.5, 1.0, 2.0 and 4.0mm, respectively.

The cost estimate for leaks of these sizes obviously varies greatly based on shift patterns, the cost of electricity and the efficiency of air generation on each site, however, a good rule of thumb based on current costs and two eight hour shifts puts the cost of a light leak at GBP 120 per year, up to a severe leak that will cost anything up to GBP 8000 per year.

Detecting leaks is actually a straightforward matter when you have the right equipment, and you know where to look.

A survey of a medium sized plant by an experienced team can be achieved in around three hours using an ultrasonic detector that is designed for the task.

Good ultrasonic detectors can detect leaks from over 15m away even in noisy plant areas and provide an accurate estimate of the severity of the leak.

Wyko also photographs all the leaks that are detected and lists them, providing a quick visual guide for the maintenance personnel or any contractors that are asked to perform the repairs.

The other obvious advantage of using a contractor such as Wyko is that the engineers who visit to carry out the survey will also provide a list of parts required and an accurate cost estimate.

The cost of repair can therefore be quickly compared with the cost of the leaks.

Because Wyko stocks thousands of pneumatic parts and accessories from major brand name manufacturers, the likelihood is that there will be a direct replacement or equivalent part in stock.

A decision can then quickly be made on what action to take to address the leakage issue.

The first place to look on a survey is pipe work, flanges and fittings, as the air supply ring main is often a prime source of leaks.

Although the detectors are very sensitive at picking up leaks we tend to follow the pipework itself looking for perforations due to corrosion and large leaks that are often found at connection points where screw fittings or flanges are employed.

These leaks are frequently caused by pipe strain due to inadequate supports, inadequate joints or twisting.

Says Cordingley: "If you are unsure about leaks and the validity of a survey, wait until production has stopped and listen to the system before the air compressors are turned off, it is normally very obvious".

"Simple soapy water can also be applied to a leaking area to provide confirmation if it is needed".

The next area to concentrate on is where connections to a usage point are made using snap connectors with flexible hoses.

Sometimes several are used together, forming a manifold arrangement.

Such manifolds can leak due to worn connectors and poorly jointed pipework.

In addition, where flexible hoses are used to make connections between the piping network and usage points, leaks can also be caused by any number of factors including: damage to the hose, due to abrasion by surrounding objects; strain on the joint because the hose is too long or short; deterioration of the hose material, or just by choosing the wrong material, especially where the working environment is an aggressive one.

If a compressed air system uses automatic drain traps, these should be "zero loss" types, and should be checked to determine whether they are functioning correctly.

Filters are present in any pneumatic system and can be the source of quite large leaks.

Potential problem areas are drainage points on the filter bowls, including poorly sealing automatic drains, badly fitted bowls and bowls that have been contaminated by synthetic compressor lubricant.

Light leaks are often found in connections to regulators, lubricators, valve blocks and sensors.

The internal air seals on pneumatic cylinders can also cause large leaks, these again can be easily refurbished and quickly returned to production.

There are other items that are regularly identified in leak surveys that require a change of practice in addition to part replacement or repairs.

Air tools for example consume large quantities of compressed air in operation and are subject to a high wear factor.

In many instances their consumption is exacerbated due to leaks that occur at the hose connection and/or the speed control valve.

Worse still, occasionally air tools are left running, even when not in use.

Cordingley adds: "It is common for us to find the use of various air nozzles to provide a blowing force".

"These nozzles often continue blow when the lines are stopped for breaks and between shifts, this practice in itself will accrue substantial costs".

"The solution is to employ demand valves and shut the air off at the end of each shift or when it is not being used".

"The savings can be huge because air nozzles generally have an aperture that would count as a medium sized leak".

It is fairly simple to install a 3/2 valve to shut off the air, providing a suitable switching signal is in place.

If not, it would be worth considering a proximity switch and timer to shut off the air if no product is present on the line after a predetermined amount of time.

Shutting the air off when the line is not being used can be done manually locally or automatically.

Automating it requires some factory level communication and control of air generation, but is more easily achievable when variable speed compressors and/or some type of air compressor management system is in place.

There are other general practices that should be observed when considering energy saving in compressed air systems and range from reducing generating pressure, most systems will operate at a lower pressure than they are set at, and when leaks have been plugged, less air will need to be generated to run the plant effectively.

Keeping the whole system pressurised during nonproductive hours is also a common practice and very expensive, the facility to isolate items of machinery that require constant pressure or parts of the system that require air at different times should be provided, and generating capacity can be trimmed to suit.

Isolation valves can be operated manually or automatically using simple control devices like time switches or interlocks, or they can be controlled using most plant management systems.

Once an initial survey is complete and any immediate problems have been addressed it is recommended that a survey be carried out at least every 18 months to check the system, and after any major changes to plant layout including adding or changing production lines.

Wyko air leak surveys have been used to identify large savings in many plants across the UK, from SME manufacturing sites to large factories operated by companies such as Boots and Toyota.

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