Technical detail for Locomotives
Whenever possible spirit tanks are placed with water tanks between them and the boiler thus minimising the risk of flare ups. They are not detachable which overcomes the risk of flare up due to meths dripping from the tanks as they are removed or replaced. The design also eliminates the problem of waterlogged burners resulting from spills and splashes from water tanks.
The exhaust beats from the four cylinder designs sound no different to two cylinders and whilst it is accepted that it presents a fascinating design challenge, the additional costs and maintenance raise questions as to their commercial viability. We can produce more power from two cylinders than track adhesion can use. Having witnessed one of our Duchesses hauling an eighteen coach train and a bogie well wagon carrying several kilograms of video camera up a long 1:180 gradient with no signs of distress, we are convinced.
The designs are all worked to a scale of 10mm : 1ft, the working parts are robust and easy to remove for servicing. To achieve this, all working valve gear is between the frames where it is protected from accidental damage. This is usually the slip eccentric type which requires the loco to be moved manually in the required direction of travel, for half a turn of the wheels, to set the valve gear. The accuracy to which this valve gear can be set up, its simplicity and robustness makes it the ideal design for the vast majority of applications. Stephenson's valve gear has been incorporated in several designs. Walshaerts valve gear has many moving pivot points which are subject to wear and can result in significant loss of performance. If modelled to scale it is rather delicate as a functional gear, particularly if the loco receives a knock. By using a hidden, robust slip eccentric system we are able to model the Walshaerts gear more accurately and have it moving in prototypical manner but with no ill effect from long term wear or damage.
Tenders or side tanks in tank locos are fitted with hand pumps. Axle driven feed pumps are fitted as standard and are all tested for valve leakage in excess of 300 psi and for delivery rate at normal working pressure.
Loco axles are sprung, as are buffers and coupling hooks. Tender axles are not sprung as the change in weight from fully loaded to empty is generally too great to accommodate in small springs unless they are very strong, which effectively results in a solid suspension.
Lubrication is by a Roscoe (displacement) lubricator fitted with a blow down tube for removal of condensate and ease of recharging with the loco in steam.
Boilers are all copper, silver soldered and hydraulically tested to 200 psi (16.6 At) before fitting to the loco. Coal firing is an option on suitable locos. All locos have pressure gauges and where appropriate, water level test cocks or sight glasses. Our boilers comply with the Pressure Systems Safety Regulations (2000) for vessels under 2 litres.
All our locos are supplied with our ‘CERTIFICATE OF MANUFACTURE’ which includes details of boiler materials and test pressures. If steam models are to be operated when people other than the owner are present we would advise that the boiler is approved by an independent test authority such as a Model Engineering Society or the Gauge One Model Railway Association. All copper boilers should be retested every two years at 1.5 times working maximum safe pressure.