Your Questions Answered

Design Engineering and Robert Bosch address some of the pressing issues of the day

Q: The use of lubricated air can be an advantage in some pneumatic systems, but what are some of the issues and how can we ensure the optimum operation of the air system?

A: To help ensure a regular and ongoing pattern of air lubrication, it is generally recommended that a service unit is included as part of any installation.

A service unit is usually comprised of two to three components – the filter, regulator and occasionally the lubricator. It is often the effectiveness of this unit that can have the greatest effect on the overall performance of a system.

To get the best performance from your system there are two key procedures to follow. Firstly, always ensure the system pressure is at least 1bar below the primary operating pressure. Secondly, always maintain the correct level of lubrication in the bowl; failure to do so is a frequent cause of many faults. Lubricators are now available with in-built level detection to notify you when they need refilling.

Systems incorporating air lubrication require just as much attention if they are to continue to operate smoothly. It is important to note that selection of the correct unit is required as it may need adjustment for the right amount of lubrication.

Wherever possible, lubricated air should be piped away from the area to a centralised exhaust filter as it may be a health hazard if piped straight into the atmosphere.

Of course, the best possible action to take is to bear these issues in mind when planning any new system. The layout of components should always be carried out with future maintenance in mind.

If appropriate, it is often a good idea to collect the components together in as few areas as possible. In particular, control cabinets can provide considerable advantages that increase exponentially with the size and complexity of a system. These include clear layout of all control elements, short tubing connections for faster signal processing, easier faultfinding and the minimum number of lines to and from the cabinet.

Q: We are aware that our current pneumatic system has some air leakage. The difficulty we have is in determining the trade-off point between continuing with our current set-up or replacement of the system.

A: During normal operations all pneumatic systems experience some loss of air. In an ideal situation this should be zero. In practice, however, it is more realistic to aim for a wastage figure less than 10%.

Ultimately, leakage of compressed air is a waste of power and a cost to your business.

The most effective way of understanding the amount of wastage in your system is by undertaking a simple test.

Start the compressor, and then allow it to reach system pressure before unloading. Record the time it takes for the compressor to come back on load (cut-in) and the time it takes before unloading (cut-out) occurs again.

The leakage rate of the system can be then be quantified using the following formula:


QL = QC x t/(T + t) m3/minQL = System leakage rate m3/min F.A. (F.A. = free air)QC = Compressor free delivery (m3/min)T = time taken between cut-out and cut-in (leakage time in minutes)t = time taken between cut-in and cut-out (charging time in minutes)}}

By quantifying the level of wastage (above or below the mark of 10%) in your system you are able to then make an informed decision on whether or not replacement is in fact the most appropriate option.