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PART 15 – RELIABILITY
By John Firth
Don’t we all want a totally reliable layout? It is something we all strive for but as an engineer, I confess to a secret desire for a complex problem now and again to tax the grey matter, but at a time of my own choosing.
This article deals with some of the issues involved in increasing reliability. One way to achieve 100% reliability is never, never, never to allow a visitor to set foot in your layout room. The moment they do, locos will defy gravity by leaping from the track and short circuits will inexplicably appear somewhere in that complex junction that has never given any problems before. Given that it may not be acceptable to exclude visitors, I will look at some of the things that can be done to reduce the effect that they will have on your layout.
It must be emphasised that the following comes into the category of “Do as I say” rather than “Do as I do”. Most of this is what I have learned from bitter experience, and I am still learning.
Reliability - Science or Art?
As with most things these days, a science has developed around reliability. Without going into the subject in great depth, it is probably worth being clear what we mean by reliability. Reliability is (roughly) defined as being the probability that something will perform correctly for a period of time without failure. An engine with an oil leak can be considered “reliable” if it is required to operate for 10 minutes starting at noon each day. Before being operated, it can be topped up with oil and will last for the short time it is required to run. However, such an engine is not necessarily of much use in most situations.
“Availability” is a term which is possibly closer to what we are seeking in modelling. Availability is loosely defined as the proportion of time that something is available to operate. For simplicity, I shall use the term “reliability” as a merger of the technical meanings of reliability and availability.
There are a number of approaches to improving reliability. The first has to be to prevent the failure occurring in the first place. This is not always possible so the second strategy comes into play. This is to make fixing the problem when it occurs a quicker process. This involves making diagnosis of the problem quick and then component repair or replacement as simple as possible. A third option which may not be too practicable in model railroading is having spares to hand. Having a spare loco is a quick fix for a failure but spare track on which to run it is less simple.
It is important that the efforts to improve reliability are targeted and proportionate. After the Second World War, the aviation industry suffered many accidents. Decisions were made to improve reliability by replacing components more frequently. Unfortunately, this did not have the desired result as replacing a component earlier may avoid a possible forthcoming failure, but a faulty new component or faulty workmanship in doing the work led to an increased number of failures – a case of “if it ain’t broke don’t mess with it”!
On your layout, one way to avoid catastrophic failure as a result of a power cut could be solved with a duplicate standby generator to provide power during the cut. However, this solution is expensive and the likelihood of prolonged and frequent power cuts are
thankfully rare. Such action would not be proportionate. A more cost-effective solution may be some standby clockwork locos!
So what can be done to make a layout reliable? The first is carrying out the installation with reliability in mind. Then comes “maintainability” - that is constructing the layout in a way so that the equipment that needs replacement or maintenance can be readily accessed. The final issue is maintenance itself. Recognising how the layout and rolling stock can deteriorate will identify tasks that can bring it back to specification. Maintenance should be carried out to address actual failure modes, not just done for the sake of doing it.
A factor that needs to be taken into account is the environment. For example, whether the layout is portable or fixed makes a difference to the design and maintenance needs. A portable layout can experience problems that affect reliability not encountered on a fixed layout, mostly arising from damage in transit, including twisting. An outdoor layout has very different needs to one indoors in a dry, temperature-controlled room.
So much for the theory, now let us have a look at some things that can be done. Again I must stress that you must be the judge of whether these are worth doing in the case of your layout. This will depend on how important reliable operation is to you.
Track mechanical issues
The benchwork and track support needs to be rigid and unable to warp. If warping is able to take place it can do a number of detrimental things. It can introduce twist into the track. Some twist can be accommodated by the ability of trucks to move relative to one another on a car. A long rigid wheel base of a steam loco may be less able to deal with the twist. It does not take much before a wheel and flange is clear of the rail head and is able to derail.
I have made myself a simple tool for detecting track twist using a block of wood about a car length in length and employing two picture mounting plates.
The block should sit flat on the track . If there is significant twist in the track, the block will only make three points of contact with the track and will rock.
Another problem can be vertical curvature. If the gradient changes too severely, then wheels on a rigid wheel base can become clear of the track and derail. It can also lead to uncoupling which is discussed later.
Track gauge is a key factor. Most modellers nowadays use prefabricated track. Normally, this is kept to gauge by clips on each tie, so the opportunity for track to go out of gauge is limited. On my layout, most of the track much older and is spiked down so there is scope for drifting out of gauge so checking gauge is necessary. This illustrates a point about maintenance. The
April 2019 - ROUNDHOUSE 15